THE EFFECT OF LAND USE ON SOL FERTILIN

AND PHOSPHORUS DYNAMICS IN

SUB-ALPINEGRASSLAND SOLS OF GANSU, CHINA

A Thesis

Submitted to the College of Graduate Studies and Research

in Partial FuWent of the Requirements

for the

Degree of Doctor of Philosophy

in the

Department of Soi1 Science

University of Saskatchewan

Saskatoon

Q Copyright Ronggui Wu, 2001. AU rights reserved. National Librafy Bibliothèque nationale 1+1 of,,, du Canada Acquisiüons and Acquisitions et Bibliographii Services services bibliographiques 395 Weiiington Street 395. rue Weltingbwi ôttmum ON K1A ON4 OltawaON KlAûN4 Canada Canada

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University of Saskatchewan

Saskatoon, Saskatchewan

Canada STN SA8 This study, conducted on subalpine grasslands in Gansu, China, deais with the impacts of land use on soi1 fertility, P dynamics, soil erosion, and above ground vegetation. Land uses include three magnitudes of pasture degradation, Iightly (LDGP), moderately (MDGP), and heavily degraded pasture (KDGP), and cultivated fields varying 1 to 50 years of cultivation. Soil saniples were collected hm18 sites at seven locations, fiom either Chernozemic or Castanozemic (Chestnut) soils lying between 2,600 to 3,000 m above sea level (ASL). The objectives of this study were 1) to determine if there is any soi1 degradation as indicated by soil fertility declines and soil erosion; 2) to understand soi1 P dynamics under different land uses; and 3) to determine if pasture degradation can be evaluated by plant cover, plant species changes, and soi1 erosion.

To determine if there were any influences of pasture degradation and cultivation on soil FertiIity and soi1 erosion, rnacro-organic nuîrients, total N, P, K, CEC, pH and EC were analyzed. The activity of ')'CS was detemilned to estimate soi1 emsion as well.

In HDGP, soi1 CEC, total C and total N dropped by 18%, 33%, and 28%, respectively, on a regional decompared to LDGP. Furthemore, cultivating grasslands significantly decreased soi1 CEC, organic C and total N by 21%, 59% and 52%, respectively, fier 30 to 50 years' cultivation. Soil pH also significantly increased with longer cultivation. With soil degradation, soil EC increased in previously saline soils, but decreased in non-saline soil. Cultivation aiso increased the proportion of water-soluble Na fiom 7% in LDGP to 22% of total soluble cations after 41 years' cultivation at Tianzhu-AB. Soil erosion and mineralization of orgaaic matter were responsible for lower soi1 CEC, organic C, total N, and soil macr~rganicmatter. The concentration of I3'cs was significantiy reduced when Pasture was heavily degraded, or was put into crop production. More than half of 13'cs aftinty in soii was lost with 30 to 50 y=' cuItimion compared to LDGP. Topography and climatic dEerences had a Qreat influence on soi1 erosioa Pasture degradation, cultivation and erosion also caused changes in soil P dynamics. Phosphocus fiactionation showed that more labile P was found in LDGP compared to HDGP. Cultivation and fertilization significantly raised labile P and Ca-Pi Ievels. Mineraiization of organic P, incorporation of sub-soi1 by tiHage following erosion, and fertilization were major sources of topsoil Ca-Pi in cultivated fields. In general, Fe- and Al-associated Pi was higher after pasture was cultivated. Soi1 organic P, especially the moderately labile fraction extracted by NaOH, declined with pasture degradation and cultivation.

Once pasture became heavil y degraded, changes in plant species composition and plant cover were observed. A 99% plant cover was found in LDGP, while the Iowest plant cover of 62% was observai in HDGP. The plant palatability index (PI) was develaped in this study based on numbers of individual plants inside of the quadrat and their assigneci numerical values. Results showed that the PI decreased fiom 205 in LDGP to 173 in MDGP, and then to 151 in HDGP, implying that the abundance of more palatable plants may decrease with pasture degradation, while plants with lower forage due tended to increase.

Research results were applied to the whole area between 2,600 to 3,000 m ASL in Gansu based on area estimation and land use patterns. Grassland was the major land use, accounting for 85% of the total. Cultivated land occupied onIy 3.5% of the totai, but the latter was vital to local fmers for food and feed production. Lands between 2,600 to 3,000 m ASL had a great potential for soil degradation. About haIf of the 1.9 million ha grassland had been either moderately or heavily degraded, resulting in 22.7 and 1.8 million tons of C and N losses, respectively. ~otential1.yavailable P loss reached 25.8 thousand tons on grassland. Cultivating 80,000 ha of grasdands resulted in 3.8 million tons of C, 0.3 1 million tons of N and 11.6 thousand tons of P losses in the region.

Based on the results from this thesis, severai recommendations such as grazing capadty control and proper management of cultivated fields were made to prevent soi1 fiom hherfertiiity deciine and degradation 1 would like to express rny sincere appreciation and gratitude to Dr. Holm Tiessen, my supervisor, for his guidance, vduable criticism, support and encouragement throughout the course of this study. My gratitude is also extended to dl my advisory committee members: Drs. Y. Bai, E. da Jong, R G. Kachanoski, T. Roberts, K. C. 1. Van Rees for their constructive comments, The author would also like to thank Dr. Bao Lin, my co-supervisor fiom China, Dr. R E. Redmann, my former cornmittee member, for their constructive criticisms and advice. Special thanks go to Dr. E. de Jong and Dr. T. Robens for their corrections on my written English. Particular thanks are also &en to Dr. R. P. Voroney fiom the Department of Land Resource Science, University of Guelph, as the extemal examiner of this thesis for his valuable comments and suggestions. 1 also appreciated the following individuals whose contribution made this study successfit: Dr. D.J. Pennock for bis help on statistical analyses; Ms. J. Moir, Mr. B. Goetz, Ms. T. Redl for their technical assistance in sarnple analyses; Mr. H. C. de Gooijer and Mr. G. Sulewski for their help on map scanning and printing; Professors Zhizhong Cao and Xindai Mo fiom Gansu Agricultural University, Professor Zihe Zhang fiom Gansu Grassland Research Institute, Professors Tianwen Guo and Long Li from Gansu Academy of Agricultural Sciences for their great heIp with site selection, collecting soi1 samples, identiQing plant species, and providing local information. The tnendship of fellow graduate students, staff, and faculty of the Department of Soil Science, University of Saskatchewan, over the past four years was appreciated. Thanks also go to the Soil and Fertilizer Institute, Chinese Academy of Agrkultural Sciences, Potash and Phosphate institute (PPI)/Potash and Phosphate Institute ofCanada (PPIC) for their great support and for providing me with study leave. Financial support fiom PPVPPIC through the course of this study is greatly appreciated. FinalIy, 1 wouId like to tiiank my wife, Yonghong Bi, and my son, Di Wu, for their support and encouragement during the completion of this study. TABLE OF CONTENTS

PERMISSION TO USE ...... i .. ABSTRACT ...... ri ACKNOWJXDGEMENTS ...... iv TABLE OF CONTENTS ...... v LIST OF TABLES ...... ix ... LISTOF FIGURES ...... xi11 1. INTRODUCTION ...... 1 2. LITERATUREREVJEW ...... 5 2.1 Soi1 degradation ...... 5 2.1.1 General review ...... -...... 5 2.1.2 Factors affecting soi1 degradation ...... 6 2.1.2.1 Soilerosion ...... 6 2.1.2.2 Soi1 fertility decline ...... 7 2.1.2.3 Soi1 salinuation ...... 8 2.1.2.4 Imbalance between nutrient removal and replenishment . 8 2.1.2.5 Population pressure ...... 8 2.1.3 Estimating soii degradation ...... 9 2.1.3.1 Soilerosion ...... 9 2.1.3.2 Evaluating soi1 qualit. and productivity ...... 10 2.2 Grassland degradation ...... 10 2.2.1 Degradation and plant species ...... 11 2.2.2 Main reasons for grassland degradation ...... --...... 12 2.2.2.1 Overgrazing ...... 12 2.2.2.2 Overexploitation of native plants ...... 12 2.2.2.3 Rodent and insect effects ...... 13 2.2.2.4 Population pressure and social inhience ...... 13 2.2.2.5 Poticychange ...... 14 2.2.2.6 Others ...... 14 2.3 Nutrient dynamics in grarsland soii ...... 15 2.4 Phosphorus in soi1 ...... 16 2.4.1 Soi1 phosphorus forms ...... 16 2.4.1.1 GeochemicalP ...... 17 2.4.1.2 Biological P ...... 18 2.4.2 Phosphorus transformations in soi1 ...... 20 2.4.2.1 inorganic P transformation ...... 21 2.4.2.2 Organic P transformation...... 21 2.4.3 Determination of soii phosphorus ...... 22 2.4.4 Factors affacting soii P dynarnics ...... 25 3. MATERIALS AND METBODS ......

3.1 Site selection and sampting ...... 27 3.1.1 Sarnpling on a local de...... 27 3.1.2 Sarnpling on a regional de...... --.- ...... 29 3 -2 Vegetation sampling ...... 30 3.3 Collecting information about the location ...... 32 3.4 Soilanalyses...... 32 3.5 Estimating land use areas in the research region ...... 36 3 -6 Statistical analysis ...... 36

4. LAND USE PATTERNS IN GANSU ...... 38

4.1 Basic information on Gansu ...... 38 4.2 Land use panems in the research locations ...... 48 4.2. 1 Zhangye Prefecture ...... 48 4.2.1.1 SunanCounty ...... 48 4.2.1.1.1 Luchang ...... 50

4.2.1.1.2 Huangcheng ...... - ...--- 51 4.2.1.2 Shandan County ...... -...... 52 4.2.2 Tianzhu Autonomous County ...... - ...... 53 4.2.3 Gannan Prefecture ...... 56 4.2.3.1 Xiahe County ...... 57 4.2.3.2 Hezuo City ...... 58 4.3 Summary ...... 59 5. RESULTS AM) DISCUSSION ...... 62 5.1 Effect of land use pattern on soi1 fertility ...... 62

5.1.1 Resuits tiom local sale sampling ...... -... 62 5.1.1.1 Tiarubu-A/B ...... 62 5.1.1.2 Tianzhu-C ...... 76

5.1.1.3 Shandan-A ...... -- ...... 79 5.1.1.4 Shandan-B ...... 84 5.1.2 Results fiom regional sale sampling ...... 88 5.1.3 ConcIusions ...... 92 5.2 Effect of land use patterns on soi1 P dynamics ...... 94 5.2.I Results fiom local desampling ...... 94 5.2.1.1 Tianzhu-NB ...... 94 5.2.1.2 Shandan-A ...... 98 5.2. L -3 Shandan-B ...... 100 5.2.2 Results from regional sale sampiiig ...... 103 5.2.3 Conclusions ...... 106 5.3 Effct of land use patterns on soii erosion ...... 108 5.3.1 Results fiom local scale sampiiuig ...... 108 5.3.1.1 Tianzhu-A/B...... 108 5.3.1.2 Tianzhu-C ...... 111 5.3.1.3 Shandan-A ...... 114 5.3.1.4 Shandan-B ...... 115 5.3.2 Results from regional scale samphg ...... 116

5.3.3 Conclusions ...... - ...... 118 5.4 Variation of plant species composition among degraded pastures ...... 120 5.4.1 Plant species ...... 120 5.4.2 Plant cover ...... 124 5.4.3 Plant pitiatab&y ...... 124 5.4.4 Reiatiomhip between soil nutrieas and above ground vegetation 125 5.5 Extrapidg research results ...... 127 5.6 Summary and conclusion ...... 130 REFERENCES ...... 138 APPENDICES ...... 156 1. Specific information on local sale sampüng ...... 156 A. Location one: Tianzhu Grassland Station ...... 157 Site-one: Tianzhu-A ...... 158 Site two: Tianzhu-B ...... 159 Site three: Tianzhu-C ...... 160 B. Location two: Shandan Horse Stud Station...... 162 Site one: Shandan-A ...... 163 Site two: Shandan-B ...... 166 II . Quadrat sampling and specific information (regional sampling) ...... 169 Ni . Pnncipai persons intervieweci dunng three trips to Gansu ...... 187 N . Estimation on soi1 nutrient losses and gains ...... 189 A TOC loss at Tianzhu-B ...... 189 B . Fertilizer contribution to total P at Tianzhu-B ...... 189 C . Fertilizer contribution to total P at Shandan-A ...... 190 D . Fertilizer contniution to total P at Shandan-B ...... 191 E . Estimation on sources of Ca-Pi at Tianzhu-B ...... 192 . . V . Plant palatability ...... 194 LIST OF TABLES

Table

Incidence of dEerent types of soi1 degradation ...... Information on nurnber of soi1 sarnples in each site ...... Crop response to sa~initymeasured as EC (d~m*' at 25"~)...... The grassland area of the largest IO provinces in China ......

Mean seasonal temperature (OC) in the main regions in Gansu ...... Annuai precipitation and evaporation in dEerent locations of Gansu ...... Land use patterns in Gansu province ...... Relationship between altitude and grassJsoil types ...... Dominant crops and their yields dong elevation gradients ...... Land use patterns in Zhangye Prefecture ...... Land use patterns in Sunan County ...... The climatic data between 2, 500 to 3,000 ASL in Sunan County ...... Basic idonnation on Huangcheng Sheep Stud Station ...... Land use patterns in Shandan Horse Stud Station ...... Pasture and cultivated land in individuai sub-stations ...... Elevation and ciimatic data in individuai sub-stations ...... Land use patterns in Wuwei Prefechrre ...... Land use patterns in Tianzhu County ...... The ciiitic information on Tianzhu County ...... Land use patterns in Gannan Prefecture ...... Land use patterns in Xahe County...... The ciimatic information on Xiahe County ...... Land use pattems in Henio City ...... The climatic information on Hemo City ...... Land use patterns in theprefectures of Gansu (1,000 ha) ...... Land use patterns in individuai counties (1, 000 ha) ...... Estimation of degradeci pasture in firent locations (1, 000 ha) ...... Land use pattern in individual sites of Tianzhu, Gansu ...... Table Page 5.2. Pasture degradation and plant coverldensity in Tianzhu ...... 63 5.3. Chernicd properties in MDGP-A and Ml3GP.B. Tianzhu.A/B ...... 63 5.4. Soi1 physical and chernical properties in dEerent horizons. TianzhuNB ... 64 5.5. Variation of soi1 variables in different transects, Tianzhu-A/B ...... 64 5.6. Soil physical propenies in Tianzhu-NB ...... 65 5.7. Descriptive statistics for soi1 variables in Tianzhu-NB- ...... 66 5.8. Descriptive statistics of soil variables after sine transformation, Tianzhu-Ah3 ...... 68 Land use patterns and soi1 pH in Tianzhu-AIB ...... 70 Land use patterns and soi1 ECî,values in Tianzhu-Ah3 ...... 71 Composition of water-soluble cations in Tianzhu-Ali3 ...... 71 The impacts of land use on soii CEC and NtL(Cl-extracted cations in Tianzhu-A/B ...... 72 Land use patterns and total roi1 nutrients (g kg") in Tianzhu-A/B ...... 74 Land use patterns and macro-organic nutrïents (g kg-') in Tianzhu-AB ...... 75 Descriptive statistics of selected variables in TianzhuX ...... 77 Land use patterns and soi1 chemical properties in TianzhuC...... 77 Land use patterns and macro-organic nutrients in TianzhwC ...... 78 Basic information on degraded pasture in Shandan-A ...... 80 Physicai properties of tested soils in Shandan-A ...... 80 Land use patterns and soil chernical properties, Shandan- A ...... 81 Land use patterns and individual WC1-extracted cdons, Shandan-A ...... 82 Land use patterns and individual water-soluble cations, Shandan-A ...... 82 E&ct of land use on macrwrganic numents (g kget), Shandan-A ...... 83 Cornparison between speciai samples and Cult-6, Shandan- A ...... 83

Basic uiformation on tested soiis in Shandan-B ...... dan.. 84 Land use patterns and soil chemicai properties in Shandan-B ...... 85 Land use patterns and ml-extracted cations, Shandan-B ...... 86 Land use patterns and water-soluble cations, Shmdan-B ...... 86 Land use patterns and water-soluble anion compositions ...... 87 Table page 5.30. The relationship between land use and soi1 SAR and ESP. Shandan-B ...... 87 5.31. The impact of land use on macm-organic nutrients (g kga'). Shandan-B ...... 88 5.32. Land use patterns and soi1 chernical properties on regional scale ...... 89 5.33. Efféct of land use on TOC. TN. and TP on regional scale ...... 90

5.34. The impact of land use on macro-organic nutrients. regional sale ...... 90 5.35. Mean of selected variables fiom pasture soils in different locations ...... 91 5.36. Paired sample statistics tkom 18 sites of degraded pastures ...... 92 5.37. Land use patterns and soi1 Pi fiactions (mg kg-') in Tianzhu-AIB ...... 94 5.38. Land use patterns and soi1 Poûactions (mg kgm')in Tianzhu-AB ...... 96 5.39. The proportion (%) of Pofiactions with land use in Tianzhu-AB ...... 96 5.40. The proportion (%) of Pi in total extracted (P, +Po) in Tianzhu-Ml ...... 98 5.4 1 . Land use patterns and soi1 Pifiactions (mg kg-') in Shandan-A ...... 99 5.42. Land use patterns and soi1 Po fractions (mg kg*') in Shandan-A ...... 99 5.43. Land use patterns and Po fiactions (%) in Shandan-A ...... 100 5.44. Land use patterns and soi1 Pi fiactions (mg kg-') in Shandan-B ...... 101 5.45. Land use patterns and soi1 Pofractions (mg kg") in Shandan-B ...... 102 5.46. The proportions of Po(%) dected by land use in Shandan-B ...... IO2 5.47. Climate and soi1 chemicai propenies at the two Shandan sites ...... 103 5.48. Land use patterns and soi1 Pi fractions (mg kg") on regionai scaie ...... 103 5.49. Land use patterns and soi1 Po fractions (mg kg*') on regional sale ...... 105 5.50. The proportions of Po fractions (%) on regional scaie ...... IO5

5.51. The radioactivity of 137 CS and soi1 erosion rate in Tianzhu-AIB ...... 109 5.52. CorreIation between ')'CS (kBq m-') and soi1 properties Tiamhu-A/B ...... 110 5.53. Soi1 erosion in different dope positions, TianzhwC ...... 112 5.54. Revised soi1 erosion rates in ditrerent slope positions, Tianzhu-C ...... 113

5.55. Land use patterns and '''CS radioactivity in hand dan-A ...... 114 5.56. Land use patterns and "'CS radioactivity in Shank-B...... L15 5.57. Impact of land use on '37~sradioactivity on regional scaie ...... 117 5.58. Correlation between I3'Cs (Bq kg1) and soi1 chernical properties ...... 117 5.59. The efféct of cdtivation length on soiI erosion at two locations ...... 118 Table Page 5.60. Plants observed in the research regions ...... 121 5.61. Proportion of Ne-forms in different degraded pastures (%) ...... 123 5.62. Statistical analyses on ground cover (%). regional scaie ...... 124 5.63. Grass paiatability and its assigned numerical value ...... 125 5.64. Statistical analyses on plant palatability ...... 125 5.65. The proportion of forbs + shnibs in difFerent quadrats (%) ...... 126 5.66. Soi1 fertility changes in forb- and shrub-dominated Pasture ...... 126 5.67. Soi1 fertility changes with occurrence of Achnatherum inebrians ...... 127 5.68. The estimated areas between 2. 600 to 3. 000 m ASL in diffeernt regions of Gansu ...... 128 The areas of degraded pasture and cultivated lands in 2. 600 . 3. 000 m ASL in Gansu ...... 128 Estimation on losses of soii nutrients over the research region (tons) ...... 129 Degraded pasture classification used in this study ...... 156 Basic information at research sites on local scale ...... 156 Some unusual sample points in Tianzhu-C ...... 162 Some special sample points in Shandan-A ...... 166 Some special sample points in Shandan-B ...... 168 Principal persons inte~ewedduring thetrips to Gansu ...... 187 Phosphorus fiactions (mg kg") in roi1 profüe of Tianzhu-AIB ...... 192 The balance of Ca-Pi (mg kg-') &er 16 years' cultivation of MDGP ...... 193 LIST OF FIGüRES Figure page 2.1. The P cycle. showing inputs. losses and major transformations in the soi1 environment ...... 20 Soif P fiactionation chart ...... 24 Distribution of sampling locations in Gansu province ...... 28 A 50 cm x 50 cm quadrat used in this study ...... 29 A satellite view of Gansu Province. China ...... 39 Prefecture-level administrative units in Gansu province ...... 40 Correspondhg locations of Table 5.3 in the province ...... 42 Soi1 map of Gansu Province. China ...... 43 Frequency distribution of water-soluble cations fiom MDGP. Tianzhu-AfB ...... 69 Frequency distribution after a sime transformation of water-soluble cations from MDGP, Tianzhu-A/B ...... 69 The niationship between soii CEC and ciay content in Tianzhu-A/B ...... 73 The relationship between soi1 TOC and CEC in Tianzhu-AJB ...... 73 The relationship between soil TOC and cultivation years in Tianzhu ...... 79 Relative proportions of extracted P (Pi + Po)in Tianzhu-AIB ...... 97 The relationship between sand content and "'CS radioactivity ...... Ill The relationship between 13%s adioactivity and cultivation yean ...... 114 Box-plot of 137Cs radioactivity in Shandan-B ...... 116 The quadrat î?om LDGP in HGD, Tianzhu County ...... 120 Chernozemic soi1 profüe in Tianzhu, Gansu province ...... 158 Field layout and transect arrangement in Tianzhu-A ...... 159 Field layout and transect arrangement in Tianxhu-B ...... 160

Field layaut and transect arrangement in Tianzhu-C ...... - . 161 Soi1 profüe of Chernozem in Shandan-A ...... 163 Field layout and transect arrangement in Shandan-A ...... 165 Soil pmfiie of Chestnut soii in ShPndm-B ...... 167 Field layout and transect arrangement in Sùandan-B ...... 167 Rapid increases in the world's population demand the production of ever increasing quantities of food, fiber and fiiel from the land. To meet this need vast tracts of land are being fmed more intensively, and large areas of grasslands are being overgrazed and degraded. Additiondy, new and ofien marginal land is being brought into production. Land must be wetiilly managed if its productivity is to be maintained or increased. If it is not well managed, or if it is used in a way that is beyond its potentid, soi1 degradation will inevitably occur. Soil degradation is one of the most crucial problems today. It might be defined as: a reduction of the current andor tùture capacity of soil to produce, in terms of quantity, quality, gdsor se~ces@regne, 1987; Higgins, 1988). Acton and Gregorich (1 995) stated that soi1 degradation refers to the general process by which soil declines in quaiity and is thus made less fit for a specific purpose, such as crop production. Soil degradation can be both quantitative: loss of soi1 due to erosion, mass rnovement and solution, or qualitative: decline in fertility, reduction of plant nutrients, structural changes, changes in aeratiodmoisture content, change in trace elements, sdts, aikaiine compounds, pollution with some chernical compound, change in soi1 dora or fauna (Barrow, 199 1). Soil degradation can be a natural phenomenon or anthropogenic. Soil fertility and soii erosion are very important indicators of soil degradation. Soil fertility is the ability of the soii to supply the nutrients essential for plant growth (Troeh and Thumpson, 1993). Thus, nitrogen 0,phosphocus (P), ' cation exchange capacity (CEC), individual cations such as calcium (Ca), magnesium (Mg), potassium (K), and sodium (Na), are often quanaed to evaiuate soi1 fertility dechne or soil degradation. Soil organic carbon (C) and pH are other important indicators of soil fedity since changes in soil C concentration and pH value will &ect nutrient supply, buffer capacity, and nutrient availability. Soii erosion is the removal of soii materiai by water or wind at rates in excess of soil formation (Barrow, 1991). Troeh and Thompson (1993) stated that erosion is a powerfùl process in part because of its persistence. It occurs naturaily as geologic erosion that nobody is liiely to stop, but it also occurs as human-caused acceIerated erosion that people may make it even worse. Soi1 fertility decline and soil erosion are intenelated with soii degradation. The land areas subject to soil degradation and soil fertility decline are growing as more grassland is misused, or cultivated, and less crop residues are retumed to the mil, or less plant cover becomes available for protection and improvement of soil. Soi1 degradation is an international issue; every country in the world has been putting a considerable effort towards adapting a suitable strategy to control it. The research on this topic is relatively sparse in China, especiaily for grassland soils being cultivated in the nonhwestem regions. China has a total area of 960 million ha, but arable land accounts for only 13.5% of the totaI (NA, 1999). Several decades ago the Chinese governrnent adopted a policy of self-sufficiency in the production of food and fiber. To achieve this, China must provide enough food and fiber for over 1.2 billion people with 130 million ha arable area (NA, 1999). This is a great challenge for the Chinese govemment because about 22% of the world's population is located in China, and must be fed with only 7% of the world's arable land. To produce more food on limited arable land, Chinese fmers have been adopting intensive farming practices. Multi-crop systems have been used for centuries. These Parming practices have had a positive effect on elinating food shonages in China. However, in some areas, especially in areas where animal husbandry and crop agriculture are both practiced, fmers/herdsmen have exploited their native grassland for short-tenn income. Crops such as oats, rapeseed, alpine-barley, etc., have been cultivated in order to meet the need for the ever-increasing population, ignoring the negative effects on soi1 quality and soi1 fertility caused by incorrect or unsuitable soil management. Presently there is no reference to indicate if soi1 physical and chernical properties have deteriorated or soil fertility declined &er cultivation of Chinese grassIands. These kinds of data needed to evaiuate grassland soi1 degradation and soil erosion are not available in these areas. Therefore, there is a need to study soi1 quality and grassiand degradation in China A national grassland wey indicated that naturai grassland areas in China accounted for about 393 million ha (Liao and Jia, 1996), of which 33 1 million ha was believed usable, making up 41% of the nation's totd land area (Liu et al., 1994a) and covering a stretch of more than 3,000 km from northeast to southwest. The main types of rangeland are temperate steppe, alpine meadow and temperate desert, which account for about 23.2%, 16.6% and 14.3% of the total grassland area, respectively (Liu et al., 1994a). In the northwest region, there are about 120 million ha naturai grassland, of which about 18.6 million ha are in Gansu province (Liu, 1997). With the adaptation of reasonable management practices in some grassland areas, both animai and forage production have been increased in the last several decades. However, some problems still exist. With ever-increasing population pressure, more grasslands have been cultivated, and more animais have to be grazed in relatively small areas, resulting in serious grassland degradation. In the past, scientific research on grasslands in China had been mainly focused on rangeland resources (Zhu, 1993; Liu et al., i994a; Han et ai., 1994; Wei and Liu, 1994). forage and livestock (Li et ai., 1994a), piant communities in rangeland (Shen et al., 1994; Nan et ai., 1994; Niy 1994; Li et ai., i994b), nutrients status of different gras species (Zhang et ai., 1996), forage plant germplasm (Wu, 1994; Jiang 1994; Bai et ai., 1994; Liu et ai., 1994b), and introduced grasses (Yan et al., 199 1; Guo, 1996). Almost al1 of the grassland researchers are fiom organizations such as Grassland Institutions, or Animal Husbandry Sections, and soi1 scientists and soi1 fertility experts are generally not involved in such research. As a result, soil fertility reduction and soil degradation, desertification and salinization of the grassland soils have not been well documented (Uiang, 1993). No systematic research on causes of soil fertility decline and grassland degradation has been reported, Phosphorus, as one of the main nutrients in soi1 fertility and gras production, has played an important role in maintaking soi1 fertility and improving grassland ecosystems. But, iittle research on changes in soi1 P and its interaction with grassland ecosystems fiom lightly degraded to heavily degraded Pasture, and to cultivated grassland soils has been reported. Therefore it is worthwhile to do some studies on this nearly virgin 6eld ofresearch in China The objectives of the present research were: 1) to determine if there is any mil degradation as indicated by soi1 fertility declines and soi1 erosion in selected areas of Gansu province; 2) to understand soii P dynamics under différent land use patterns; 3) to determine if pastute degradation can be evaluated by plant cover, plant species changes, soii nutrient changes and soi1 erosion in sub-alpine grassland; and 4) to extrapolate the results to regions with similar ecology and land use in Gansu province. 2.1 Soil degradation 2.1.1 Generai review Soil degradation is not a new phenomenon, nor is concern about it a recent development (Roberts, 1989). Greek and Roman writers commented on soil erosion, deforestation, and other problems, and environmentai concem was incorporated into Confùcianism in China (Barrow, 1991). Soil degradation implies a regression from a higher to a lower state (UNEP and FAO, 1983); a detenoration in productive capability. It is not necessarily continuous, and may take place between penods of ecological stability or equilibnurn. Soils are formed over very Iong periods of tirne, but if their environmentai balance is changed, for example, by the removai of vegetation cover, the delicate balance is upset, thus a process of deterioration or degradation may begin. La1 and Stewart (1990) indicated that soil degradation is a cornplex phenomenon. It is driven by strong interaction arnong socioeconomic and biophysical factors. [t is tùeled by increasing population, fiagile economy, and dismal fmpolicies. Once the degradative processes are set in motion they have a snowball effect. It was estimated that total histone soil losses might be more than the whole area now under cultivation in the world (FAO, 1984). During the 1980s, about 5 million ha of cultivated area was lost every year through soil degradation, and by the end of year 1999 the projected loss is one third of the cultivated land in the world (FAO, 1984). About 182.7 million ha (19% of the tord land ara) land has ben affecteci by water erosion or degradation in China (Liu, 1997). The provinces with largest eroded areas were Sichuan with 24.9 million ha, Imer Mongolia with 18.6 million ha and Gansu with 17.2 million ha. Among 45.4 miilion ha land in Gansu, approximately 38% is considered as eroded. The reason for such large areas of eroded land is Iikely due to incorrect land use (Soil Survey Office of Gansu Province (SSO), 1993). Desertification is another phenornenon of mil degradation. In China deserts and desertified lands totaled about 168.9 million ha, making up 17.6% of the whole land area (Gao et al., 2000a). Desertification spreads at the rate of 246,000 ha annuaiiy. Since 1949, about 670,000 ha arable lands, 2.4 million ha pasture and 6.4 million ha forests andor bushes have been desertified. OvergraPng and over-cuhivation (cultivating grassland) are iduential factors for soi1 desertification. in dry and semi-dry areas of northern China, for example, desertification caused by overpzbg, over-cultivation, or improper rnining accounted for 30%, 27% and 34%, respectively (Zhu and Cui, 1996). Because of desertification in northem China, severe sandstoms occurred fiequently, especially in spring (Gao et al., 2000b). [t was estimateci that the totai loss caused by wind/sand disasters amounted to 54 büiion RMB (local currency) each year in China, making up 16% of the total loss in the world. It was also recorded that more than 10 occurrences of sandstonns were encountered in spring of 2000 in northem China (Gao et ai., 2000~).The main sources (80%) of sands were fiom lnner Mongoiia where pasture degradation and desertification were severe. In some regions, many of the agricultural practices were designed to achieve short- tem yield goals, but ignored the negative impact on ecological systems. This is more cornmon in northwestern China where grazing and crop production are prevailing. For instance, cultivation of grassland mils promoted crop production in the first few years, but on the other hand; it greatly disrupted the baiance of organic constituents in the soi1 and local ecosystem, causing soi1 erosion and degradation.

2.1.2 Factors affecting soi1 degradation

Severai inter-related factors affect soi1 degradation. The major causes of soi1 degradation include 1) soil erosion, 2) soil fertility decline, 3) mil salinity, 4) imbalance between nutrient removal and replenishrnent, and 5) population pressure.

2.12 1 Soil erosion Among different sail degradation processes, water and wind erosion are thought to be major causes for soii degradation (Table 2.1). Table 2.1. Incidence of different types of soi1 degradation. Global Asia Degradation type (1o6 ha) (%) (106 ha) (%) Water erosion 1,094 55.7 440 58.9 Wmd erosion 548 27.9 222 29.7 Fertility decline 135 6.8 14 1.9

ûihers 16 0.8 2 0.3 Total 1,965 100 747 100 Source: OIdeman, 1993.

Vegetation or sail cover plays a vital role in dinishing soi1 erosion and degradation. At a given rainfàil or wind speed, if land is wvered with hi* density of vegetation, the possibility of soil erosion will be reduced considerably because vegetation can intercept or dirninish rain force or wind force on soil. It is reported that vegetation cover also Uifluences the effect of sun and wind on the soi1 surface and this in turn affects its erodibility (UNEP and FAO, 1983). Soi1 structure and soil depth also affect soii erodibility. if soi1 structure has broken dom and disappeared, and soil depth is shallow, sol erosion may be greater compared to the mils with good structure and greater depth. Topography and the degree of land slope have very strong influences on amount of erosion by water. UNEP and FA0 (1983) reported that soi1 losses fiom steep slopes are much greater than fiom gentle slopes. The Iength of a fidd and dope is also important, the Ionger the slope, the more severe the erosion.

2.1.2.2 Soi1 tèrtiiity deche Soi fertiüty and soi1 erosion are interreiated. if soil erosion is severe, a very low mil fertility will result since most available piant nutrients are stored in topsoil and infertile subsoil is brought to the dace and incorporateci with A horizon. Soil pH is also negatively affected by soi1 degradation and erosion; acid soi1 will become more acid (Hartemink, 1998) and neutral or aIkahe soil wül become more alkaline (Donnaar and Willms, 1998). Once soil fertility declines, plant cover becomes sparse, causing even more severe soil erosion. As show in Table 2.1, soi1 fertility decline contributed about 7% to soi1 degradation in the world.

2.1.2.3 Soil saiinization Saline soils in Gansu, China, are characterized by signifiant accumulation of gypsum and magnesium carbonate (Ghassemi et al., 1995). In saline soi1 the high concentration of soluble salts makes it harder for plants to absorb water from the soi1 solution. if soil solution becomes too concentrated, plants become sparse, or only sait- tolerant plants cm grow. Poor soi1 properties always acwmpany soi1 saiinity. if soils are severely salinized, ground cover reduces considerably, thuq soil degradation and erosion may occur.

2.1.2.4 Imbaiance between nutrient removal and replenishment In some regions such as Gansu and ber Mongolia, nutrients added to the fields are much Iower than crop removd (including grain and/or stalks). As a result, plant nutrients have been depleted and soi1 resistance to erosion or degradation will be weakened. The imbalance between nutrient removai and replenishrnent in grassiands has been existing for a long time. In generai, most of the grassland has not received any fenilizers, thus, some nutrients, especially P, are being depleted due to their removal with diary products tiom whete animais are grazed. Consequently, soil degradation may occur if this Unbaiance situation is not eIiminated.

2.1.2.5 Population pressure With increases in population, more and more food and fiber have to be provided to maintain basic living standards. Zhu and Cui (1996) reported that the population increase was 3.1% annually in the area where grazing was integrated with agriculture in northwestem China. The population density increased fiom 10-15 in 1949 to 40-60 people per km2 in the 1980s. remfting in a great pressure on the limited resources of northwestern China. Increasing population requires that more and more food be produced fiom the limitai arable land in China. Sorne of the marginal lands have been cultivated, causing a serious problem with soil erosion and desertification (Yang, 1993). if fmers are lacking knowledge, and do not know how to manage their land correctly, cultivated fields will be degraded rapidly.

2.1.3 Estimating soil degradation 2.1.3.1 Soil erosion To quanti@ soi1 erosion in the landscape, field expeiments shodd be conducted if one wants to find out the absolute arnount of soi1 erosion caused by water andior wind. If the objective of measuring soil erosion is only for comparison between eroded and un- eroded or Iess eroded fields, the radioactive fallout isotope I3'cs may be used as a tracer to estimate soil loss and gain (Rogwski and Tamura, 1965; Ritchie et al., 1974; Mitcbetl et ai., 1980; de Jong et al., 1982, 1983, 1994; de Jong and Martz, 1989; Ritchie and McHenry, 1990; Froehlich et ai., 1993; Kachanoski, 1993; Quine and Walling, L993; VandenBygaart et al., 1998). Because soil degradation is related to soi1 erosion and mil fertility decline, it can be evaluated through 137~sradioactivity detemination and roi1 analysis of pasture or cuitivated mil. Estimates of 13?cs losses or gains are usuaily calculated by cornparhg levels at the time of sampling with baseline estimates Eom fallout data, hom '%s Ievels in nearby un-eroded sites, or fkom previous measurements at the sarne sites. The main advantage of this method is that it permits the investigation of rates and patterns of erosion integrated over the since giobai failout of 13?cs commenceci in the 1950s and 1960s (Froehlich et ai., 1993). Since most other existing estimates of erosion rates represent only short observation penods, data obtahed fiom 137~srneasurement pmvide a means of validating these results over longer tirne des. The 13%s distribution in soi1 is iduenced by land management or land use. For example, VandenBygaarî et al. (1998) reported that the lJ7cs distribution in agricultural soil is mainly unifom in the plough layer, indicating the depth of tillage as the tilled layer becomes homogenized due to annual ploughing. However, the I3%s in forest soils is rnainly distributed in top layer, showing a negative exponential tünction with depth below 10 cm. The distribution in the top 10 cm or so is influenceci, at least partially by the soil organic matter decomposition cycle, and biopedoturbation trom agents such as earthworms.

2.1.3.2 Evaluating soil quality and productivity To investigate the impact of soil degradation on soil quality and productivity, the indicators of soi1 quality and productivity should be dearly identified. These indicators are generally regardeci as the following (Acton and Gregorich, 1995; Harris et al., 1996; Doran and Parkin, 1996). Soi1 physical properties including soil texture, bulk density, infiltration, etc. Chernical properties including total organic C, P and N, soil pH, electrical conductivity (EC), CEC, etc. Bioiogical properties includig number, type, and fiction of soil microbes and invertebrates, specific respiratory activity, enzyme activity, etc. Crop/plant attributes including plant vigor, ground cover, rooting pattern, etc. Water quality including surface water and ground water quality. Air quality such as solid particles suspended in the air.

2.2 Grassland degradation Dong and Liu (1992) reported that there was about 3.3 billion ha grassland being affecteci by desertification in the whole world, or 73% of the grassiand in the totai. In China, one-third of 393 million ha grasslands have been degraded (Li 1991) and 21% of the degraded Pasture were seriously degraded (Liu et al., 1994a). Li (1991) also pointed out that approxjmate 30% of the totai grassland had been adverseiy affècted by rodents and insects. in the üansitional areas of crop production and animal husbandry about 86 million ha of grassland has been impacted by desertification (Long, et al., 1994). Grass production has been reduced by 3040% in the recent two decades (Li, 1992). There are about 286 million ha pasture in northern China, with a very high degradation rate of about 1.3 million ha per year (Xu, 1990). For example, the usable pasture in the Inner Mongolia Autonomous Region is around 63.6 million ha, however, about 38.7 million ha (60°h of the total) pasture has been degraded (Gao et al., 2000b). Furthemore, in Hulunbeier and Xilingele, once two very productive pasture bases, the degraded pasture accounted for 23% and 41% of the total grassland, respectively. Zhang (1995) pointed out that grassland degradation results in a decline of production and ecologicaI fùnction of grassland ecological systems due to structural degradation. Such degradation leads not ody to decline of gras and animal production in pasture, but also to detenoration of our living envîronments. Soi1 physical and chemical properties such as tiIth (Guan et al., 1997), infiltration rate (Barrow, 1991). soi1 organic matter, total N and P (Guan et al., 1997). and biochemical activity (Long, et al., 1994; Zhao et ai., 1997) were also affected when grassland was degraded.

2.2.1 Degradation and plant species Plant species may be changed if grassland degradation occurs. For example, in nonnal dry Pasture (steppe) of Wengniute, ber MogoIia, the dominant species are Slip burgeana (bunge neeldlegrass) and Cfeistogeneschinenris (Chinese cleistogenes). Stipa hngeana was replaced by Artemisia firai& and Thymiis mongolicus (Mongolian thym) afler pasture was iightly degraded. Convoh~lusL, (bindweed) appeared when pasture degraded moderately, whereas Thynnrs mongolicus and Stellera chamaejasme dominated in heaviiy degraded pasture (Sun, 1989; Xiu, 1996). in desert Pasture AgriophylIum menarium was the only species found where once Digitma ischenttlm and Ariemisia (sagebrush) dominated normal pasture (Sun, 1989). This is consistent with the work by Nie and Yu (1993). in degraded sub-alpine meadow more valuable plants such as EIymus nutans, Elytnus sibiriçus and Roegneria nutans became sparse or disappeared, whereas Iess valuable species such as Anemone gaim. Euphorbia. Gentiana algiah and Stellera chamaejasme became dominant (Qü et al., 1993). Aneurolepidium chineme, for example, decreased when grassland had been degraded. Concomitant with plant species changes, gras production decreased tiom 1,040 kg ha", on dry weight basis, in normai desert pasture to about 420 kg ha-' in heavily degraded pasture (Sun, 1989). Xu (1990) indicated that the number of perennial gras species decreased fiom 21 in no& pasture to seven in heavily degraded pasture, whereas the number of annuai or biennial species of weeds increased fiom three to eight. Plant cover and gras height decreased by 36% and 56%, respectively. Compared to the 1950s. plant cover was reduced by 30 to 50% in Alashansuoqi of Inner Mongolia due to grassland degradation and desertification (Xu, 1990).

2.2.2 Main reasons for grassland degradation

2.2.2.1 Overgrazing tt is reponed that rational grass utilization in ~rasslandshould be maintained at about 50% of grass production, whkh results in a vigorous growth of gras and a good production of animal husbandry (Zhang, 1995). However, about 80% of the gras hm been grazed each year in China At such a grazing intensity it is diicult for gras to be restored to its normal development. Xu (1990) reported that the optimal stocking rate was 42.15 million sheep units in Inner Mongolia, however, the actual rate was 56 million, 33% more. Overgrazing sornetimes caused soi1 compaction and reduced infiltration or loosenïng of the soi1 surface, which increased the possibility of erosion (Barrow, 19911, and lead to declinhg grass production (She and Sun, 1995). When pasture was overgrazed, unpalatable and spiny or difticult-to-gmze plants tended to survive and more palatable plants decreased.

2.2.2.2 Overexploitation of native plants In some areas of China, iicorice root (G&cyrrhiza uralemkfisch). and other native species vduable in medicine are rernoved fiom the soi1 to supplement farm income, without consideration of its negative effect on grassland ecoIogy. in consequence, grassIand degradation occurred due to covering by infertiie sub-soi1 or sands fiom digging roots. Yang (1993) reported that about 0.5 m3 soi1 was dug out to get 0.5 kg of licorice root. As a result, 26 mZof pasture wodd be niuied. The colIection of gras residues for fuel before spring was another reason for grassland degradation (Yang et af., 1995). After gras residues were removed from the pasture, the replenishment of organic matter was reduced to some extent.

2.2.2.3 Rodent and insect effects Myospalax bailey and Ochotona curzoniae are the main rodents that negatively effect grassland production. Wan and Wang (1990) reported that there were 84 small soil hills dug by the Myospdax bailey in 100 rnz of gmsland, resulting in 1.416 m2 ha" of the land destroyed. It was assumed thone Myospalax bailey ate about 264 g of grass daily. This would remove 47.5 kg grass during their half-year's activity. Other researchers also reported that rodents contributed significantly to degradation of grasslands (Sun, 1989; Xu, 1990; Tang, 1992; Zhu, 1993; Chen 1994). Rodents' burrowing activities resulted in soil deposits on the soi1 surface in which successionai plant communities began to develop during periods of low rodent populations. However, these were soon destroyed as rodent populations again increased. Thus, rodents not only played a part in degradiig grasslands, but aIso in interferhg with plant regeneration. Grass caterpiilars are ais0 hanntùl to grass growth, causing psdegradation. Wan and Wang (1990) pointed out tfiat in an area in which caterpillars were active about 917 kg ha" fiesh grass was lm due to caterpilar activities (based on [O0 caterpüiars eating 1.53 g pidaity, 1 m2 having 100 caterpülan and the caterpillars being active 60 days a year).

2.2.2.4 Population pressure and social influence Ideaily, 950 million peopte can be supported with the resources avaihble in China (Zhang, 1999, however the population now exceeds 1.2 billion and this is pIacing great demands on the existing arable land. As a rdt, marw land has been exploited, and some of the native grassland has ken put into crops. Regdations on the use of grassland have not been fuily implemented in some areas in China. For example, according to regdations on grassland, the number and kinds of grazing animals raised are dependent upon grass types and griuing capacity. Many herdsmen ignore this policy. They assume grassland, the property of the me, can be used freely without any ecological concern. Consequently, more and more animals have been put on the lirnited grasdands. Degradation is evident under these circumstances.

2.2.2.5 Policy change Dunng the past four decades a significant deterioration of native grassland ecosystems has taken place in northem China due to a shift fiom nomadic grazing systems to sedentary, cultivated agriculture (Suhayda et al., 1997). This policy Ied to grassland degradation in vast areas, especially during the 1950s and the 1960s. To produce more food, some of the grasslands were converted into crop fields, resulting in shrinkage of pasture areas. As a consequence, grazing pasture was put in a high risk of degradation.

2.2.2.6 Others Tourism and other recreation activities have brought considerable extra income to local farmers and herdsmen, however, these activities also create great potential for grassland degradation. In some areas, ground cover of plants decreased drarnaticaily due to tounsm activities in sumrner (personal observation). Military maneuvers were another cause of grassland degradation. FolIowing military activity, some of bombig pits were left uncovered, causing reduction of ~rass production for years (Zhang, 1998). Farmerdherdsmen in some areas use alkaiÏ earth tiom pasture soi1 to seal their roofs once a year to protect against caùi during summer. This practice destroys 85 ha of pasture each year around Anda city with ody 56,000 households (Yang et al., 1995). Systematic study of the interaction of C, N, P and suIfirr (S) transformations provides a vaiuable means of understanding the structure and functioning of the ecosystem (Stewart, 1984). For ecosystem studies in China, the published papers have focused mainly on southern and centra1 croplands, rather than on grasslands (Takahashi et al., 1988). Grassland soils are noted for their high leveis of organic matter and high structural stability. However, agricultural management practices infiuence the amount of organic matter present in these soils. When the native grasstand has been cultivated, reduction of organic matter and deterioration of soil structure in these soils have been observed. Soi1 nutrient changes caused by grazing ador cuitivation of grasslands have been reponed by severai researchers (Tiessen et al., 1983; EIliott, 1986; Bauer et al., 1987; Aguilar et al., 1988; Cambardella and Eliiott, 1993, 1994). Most of these publications deal with soi1 otganic C WorN. Changes in soi1 organic C have been discussed most. Anderson (1995) indicated that C concentrations in surface horizon of Canadian prairie mils have deciined markedly with dtivation, &en by more than 50%. Tiessen (1982) pointed out that organic matter losses due to cultivation reduced the P fertility of many Saskatchewan mils, and resulted in a detenoration of soi1 structure and fertility, which might have si@cant future economic impacts. Cambardella and EUiott (1993) stated that cuitivation destroyed the macro-aggregate structure of grassiand soib with a concomitant reduction in soil organic C and N. Mer fiactionating soii organic P in native grasdand, Sumann et al. (1998) indicated that onhophosphate monoesters were the major chernieal ~o~~oundsin their sampies. They accounted for 32 to 71% of the organic P in the extracts, whereas diester-P accounted for only 7 to 40% of organic P. This is consistent with ranges reponed for uncultivated soils by Tate and Newman (1982), Hawkes et al. (1984), and Condron et al. (1990). The higher proportion of monoester-P was related to the low temperature in the region To quant@ sui1 organic C and N losses, severd conceptual models have been developed (Parton et al., 1987, 1988; Cambardella and Elliott, 1992). However, the models' ability to predict soil organic matter levels is iimited by their sensitivity to several factors for which data are difficult or impossible to obtain. After systematicaily studying the changes in organic and inorganic P composition of two grassland soils, Tiessen et al. (1983) stated that labile P fiactions were greatly reduced during cultivation, indicating a signiscant reduction in available P and P fertility of cultivated soils. This reduction in P fertiiity was closely tied to soi1 organic matter losses.

2.4 Phosphorus in soil

Phosphorus is considered to be one of the most ecologicaIly important elements, and piays an essential role in the life processes of ail life foms because of the role it plays in many important biomolecules such as DNA (deoxyribonucleic acid), phospholipids, and ATP (adenosine triphosphate) (OYHalloran, 1986; Mullen, 1998). The cycle of P is controlled initially by soi1 parent material and subsequently by soil properties resulting from pedogenesis (Roberts et ai., 1989). Walker and Adams (1958) revealed that total P content of grassland soils was closely related to P content of the parent materials. Aguilar et ai. (1988) aiso indicated that variable total-P contents were observed dong toposequences, which reflected changes in parent matenais and redistribution of sediients.

2.4.1 Soi1 phosphorus forms Different forms of soil P are interrelateci and associated with biologicai and geochemical processes (Beck and Elsenbeer, 1999). Biological processes are more dynarnic than geochernical processes, Cross and Schlesinger (1995) operationally defined soi1 P as two forms, geochemicai and biological. They suggested that geochernical P included ail inorganic fractions, and that biologicd P encompassed ail organic hctions. mer researchers used the terms of primary mineral, secondary minerai, labiie, soluble, organic, and occluded P (Smeck, 1985; Sanyal and De Datta, 1991). 2.4.1.1 Geochemicai P Geochemical P is composed of 1) primary mineral P, 2) secondary minerai P, and 3) labile inorganic P pi),including that in mil solution. Primary mineral P exists in soi1 rninerals before their weathering. The foms of primary mimrals which contain P are quite variable, due to the ability of phosphate to isomorphically substitute for silicate in many crystal structures (Lindsay and Vlek, t 977). The secondary mineral P is sorbed on the surfaces, precipitated with iron (Fe) and aluminum (Al) hydroxides and carbonate (Smeck, 1985), reacted with Ca by labile P during soiI weathering / formation process. The Ca phosphate (Ca-P) mineraI forms can contain varying arnounts of carbonate, fluoride, sulfide, hydroxide and a number of cations (Lindsay and Vtek, 1977; Tiessen, 1991; Tiessen and Stewart, 1994). These compounds are sparingly sotubk in water, and cm only be removed fiom the soi1 using acid extractions (Chang and Jackson, 1957; Williams and Waiker, 19694 1969b). Cross and Schiesinger (1995) pointed out that in ecosystems with Young, sIightIy weathered soils, most of the P should be in forms of primary minerais, such as hydroxyl- apatite. in ecosystems with a moderated weathering regime, most of the P shouId be found in organic compounds or adsorbed to cIay minerais. in ecosystems with highly weathered soils, most of the P should be in the non-labile, occluded, or stable organic forms. As early as the 1950s. Chg and Jackson (1957) classified secondary minerai inorganic P as Ca+, Fe phosphate (Fe-P), Al phosphate (ALP), and reductant solbble (Rs-P) or occluded phosphates. The occluded P is cdled Rs-P because strong reducing agents are required to dissolve the coating materials and release the occluded P. In highly weathered acid soils, Ai-P, Fe-P and Rs-P are dominant. Neutral and slightly acid soils usuaiiy contain aii four P Wons in comparable arnounts. Alkaline and calcareous soils contain mostIy Ca-P (Sa.and MikkeIsen, 1986). According to Smeck (1985), labile Pi is isotopically extractable or anion resin- extractable P which can be deteminecl by the methods of OIsen and Sommers (1982). However, 'liessen and Moir (1993) broadly defined labile Pi as released dhs weathenng or added fiom fertiiiition. These foms of P, which are thought to consist of Pi adsorbed on surfaces of more crystalline P compounds, sesquioxides, or carbonates. were extracted with resin and bicarbonate. Soi1 solution P is in the form of H$oJJand HPO~*.These forms of P are readily available to plants. in general, labile P is thought to be readily available to microbial and vegetation cornmunities in the short term because it rapidly desorbs fiom the surface of soil particles. Non-labile P is considered to be tightly bound to soil particles, and unavailable to plants (Cross and Schiesinger, 1995). Phosphorus in both primary and secondary minerals is regarded as non-labile Pi.

2.4.1.2 Biological P Biological forms of soil P are an imponant source of available P for plants. Kowever, the rates and pathways of P through soi1 organic matter are poorly understood when compared to the physicaichernical aspects of the P cycle in the soil. It is reported that biological P represents about 20-60% of total P in most mineral mils (Tiessen and Stewart, 1994). Dalal (1977) indicated that soil organic P (Po) couid be in a wider range between 4% and 95%. It is believed that most organic P compounds are esters of orthophosphoric acid and inositol phosphates (Tisdale et al., 1993). Phospholipids, and nucleic acids have been identified (Barrow, 1961). The approximate proportion of these compounds in total Po is as foliows (Tisdale et al., 1993): inositol phosphate 10-50% Phosp hotipids 1-5% Nucleic acids 0.2-2.5% Therefore, on the average, only about 50% of Pa compounds in mils have been chemically identified. Most of the inositol phosphates in soiis are products of microbial activity and the decomposition of plant residues. The group of monoester-P comprises mainly inositol phosphates. They have a high stability against microbial and enzymatic attack due to their high charge density and by precipitation as AI-, Fe-, and Ca-salts of low solubility (Anderson, 1980). The diester-P fiaction, which contains nucleic acids, phospholipids, and other cornpounds, is a more labile soil Po fiaction (Sumann et al., 1998). Nucleic acids such as RNA and DNA, representing only a smdl portion of Po in soils, are believed to break down much faster than monoester-P (Anderson, 1980). Phosphoiipids are insoluble in water, but are readiiy utilized and synthesued by soil microorganisms. Of the phospholipids detected in soii, the phosphoglyce~desappear to be the dominant fonn, and they appear to break dom rather quicldy in soi1 (Dalai, 1977, Anderson, 1980). in recent decades, several researchers have operationally defined biological P as labile and non-labile Po forms (Hedley et al., 1982; Tiessen and Stewart, 1994; Samadi and Gilkes, 1998; Fan et al., 1999; Maroko et ai., 1999; Sui et al., 1999), indicating that labile Po refers to that that was extracted by biwbonate, while non-labiie Po is the rest of organic P in the soil. Biological P dynamics in the soil have been discussed by several researchers. Tiessen (1991) pointed out that not only the amount of Pochanged under altivation, but also the types of compounds. Condron et ai. (1990) found that phosphodiesters and teichoic acid were entirely eliminated fiom Canadian soils upon nihivation. ïhese esters are relatively labile in soil since they are less strongiy adsorbed than monoesters, and under conditions of reduced organic inputs and accelerated mineralization only monoesters remain in the soi1 in appreciable quantities. A soil development sequence in New Zealand on tussock grasslands showed that diester P, probably originating fiom microorganisms, comprised the most important source for available Pi under soi1 and chmatic conditions favoring rnineralization (Tate and Newman, 1982). The availability of soi1 Po to plants and microorganisms is controiled by the rate of Pi release by mineralition, rather than the amounts of Po present. According to the definition of bioIogical P (Cross and Schlesinger, IWS), microbiai biomass P is also under biotogical category. However, microbial biomass P has special roles in Po turnover in the soil. The amount of soil biomass P is around 1 I- 67 kg ha-', about 1-3% of totaI wii P. This portion of Po represents the actively cycling pool of Po in the soi1 environment and is part of the labile, or readily available Po. Through this pool, the active mineralkation and immobihtion of P in soii occurs. Concentrations of 5 to 75 mg biomass P kg" soii are common (Mden, 1998). Brookes et al. (1984), however, observed that the biomass P fiaction ranged fiom 1.4 to 3.5% of total Po in arable soiis to more îhan 20% in some grassland and forest soils in Great Britain. neP cycle is schematicaIIy iliustrated in Figure 2.1. Biomars P is abject to incorporation into humic substances and mineralization and Unmobilization reactions. The turnover or cycling of hebiomass contributes significantly to the labile P, pool.

Figure 2.1. The P cycle, showing inputs, losses and major transformations in the soiI environment (Wdbridge et ai., 1991).

2.4.2 Phosphonts transformations in soi1

In most nanual ecosystems, geochemical processes may determine the long-term distribution of P in soils, but in the short te- biologicd processes i&ence P distribution because rnost of the bio-avaiIabIe P is derived fiom the cychg of soii organic matter (Smeck, 1985; Waibndge et al., 1991; Cross and Schlesinger, 1995). Soi1 P transformations are UifIuenced by soi1 type, cihatic conditions, and nianagement practices (Zhang and MacKenPe, 1997). The source of al1 P in soil is tiom primary apatites and addition of fertilizers. As a consequence of weathering, soluble P is released, and it may be lost through erosion and leaching, be utiiiued by plants and microbes, enter the labile pool, or be transformeci into secondary P minerals.

2-4-21 inorganic P transformation In generd two transformations of Pi are involved in P cycling, adsorption and precipitation. Adsorption refers to P accumulation on surfaces of soi1 components (Sanyai and De Datta, 1991). It lads to net accumulation at an interface. either chemicaily, or physicaily retained; whereas precipitation is the process that causes an accumulation of a substance to form a new bulk-soiid phase. Adsorption mechanisms prevail at low P concentrations, in generai, while precipitation is prevailing at higher P concentrations in soil. In neutral and alkaline soils, various forms of Ca-P are the stable minerals that govern P concentration in soi1 solutions. In acid soils, P adsorption is generally attributed to hydrous oxides of Fe and Al. Soi1 development greatly affects P transformations in soil. Cross and Schlesinger (1995) reported that the pool of primary phosphate declines as soil deveioped. On the contrary, the secondary P fiaction such as Ca-P in weakly weathered or aikaii mils and Fe-P, or Al-P in highly weathered soils increases as P becomes geochemically adsorbed lfixed to the Caca or Fe and Ai oxides.

2.4.2.2 Organic P transformation The initiai source of soii Po is plant and animai residues, which are degraded by microorganisms to produce other organic compounds and release Pi. Mineralimtion of Po can provide considerable amounts of P for plant growth. The effect of organic matter decomposition on P availability has been reported by several researchers (Walker and Syers, 1976; Tiessen et ai., 1983; Tate, 1984; Sanyai and De Datta, 199 1). Tate (1984) pointeci out that Po was an important source for crop production. More than one half of the average P removed fiom Engiish arable soils in cereal crops came fiom organic fomby mineraiization. The C/P ratio of decomposing organic residues regulates the immobiiiition and mineralkation of P. if the CR ratio is pater than 300, net immobiliition of Pi occurs; if the C/P ratio is Iess than 200, net mineraiization occurs, which turns non-available P into bio-available P form (Tisdale et al., 1993). However, White (1981) reported that the balance between net mineraiization and immobilition depends on the C/P ratio of the substrate actually being decomposed, rather than on the ratio for soii organic matter or plant residues in general. This cntical C/P ratio was calculated to fall in the range of 50 to 70, Aithough Po mineraiization depends primarily on the activity of soi1 micrwrganisms, invertebrates, especially earthwonns, have an important regdatory tùnction in this process as well (Tate, 1984). Surface casting earthworms, for example, can increase the short-tenn availability of P in plant residues 2- or 3-fold through the release of (maidy) Pi tiom plant materiai by physicai disniption; this is especially important in soils of low P status (Manseli et ai., 198 1).

2.4.3 Detennination of soi1 phosphorus To investigate the effect of land use on soil P dynamics, the ideal is to identiS, and quanti@ individuai P compounds in soil. However, it is almost impossible to identifi individual P compounds because P in the soil is so complex. The Oisen-P method, commonly used for determinhg P availability in neuual or calweous soils, has not been reiiable for predicting labile P in sorne soils without also evaiuating organic P contributions (Yang and Jacobsen, 1990). One of the methods of studying soil Po is to fiadonate it according to its stabiiity in given chernical reactants. Numerous techniques have been developed for the extraction and determination of soi1 Po (Hance and Anderson, 1962; Donnaar, 1964; WiUiams et al., 1970; Daial, 1977; Anderson, 1980). Bowman and Cole (1978a) used sodium bicarbonate (NaHC03) and sodium hydroxide (NaOH) to obtain different Po fractions. The NaHCa-extracted Po was considered as highly IabiIe P, whereas NaOH- extracted Powas moderateiy labide. In tropical mils, NaOH-exüacted P is an important source for plants, thus, this fiaction of P is sometirnes called labile P (Friesen et al., 1997). Chauhan et al. (1981) found that NaOH-extractable Po could act as a source for rnicrobial uptake in situations where there was a Iow amount of available P in the soil. Bowman and Cole (1978b) split the NaOH extract into acid-soluble fulvic acids and insoluble humic acids, and considered the hlvic acid P, which may in part be derived fiom recently added organic materiais and plant litter (Grindel and Zyrin, 1965), to be fairly labile while the humic P was considered to be quite resistant to decomposition. Fractionation of Pi into various forms was developed by Chang and Jackson (1957), and subsequently modified by Williams et al, (1967) and Jiang and Gu (1989). However, Powas not included in their procedures. Since traditional methods have faileâ to predict availability in grasslands, severaI researchers have attempted to develop procedures to fiadonate soi1 P in order to give a better interpretation of P pools or relative labitity of P forms. Sequential P fiactionation (Figure 2.2) distinguishing labile, moderately labile and more stable foms among inorganic and organic P was proposed by Hedley et al. (1982), and modified by Tiessen et al. (1984). Recently, numerous researchers have been using this method to classify soi1 P according to its hnctions through the extractants that remove P from soil in a sequentid fiactionation scheme (Tiessen, 1991; Tiessen and Moir, 1993; Cross and Schlesinger, 1995; Agbenin and Tiessen, 1995; Samadi and Gilkes, 1999; Fan et al., 1999; Maroko et al., 1999; Sui et al., 1999; Daroub et ai., 2000). Since the soi1 samples in this study were collected f?om sub-alpine graçslands in a temperate zone, similar to Saskatchewan where the procedure was developed, the sequential P fiactionation procedure descnied in Figure 2.2 should be ideal to charaCteriZe P dynamics in these soils. In the P Wonation procedure (Figure 2.2) six hctions are grouped as: Resin P: anion exchange resin (in the HCO,~ form) Nnilates plant mots by removing the dissolved P fiom the soil solution via surtace adsorption (Kuo, 1996). It can maintain a constant solution pH, and does not dissolve Ca-phosphate. Tiessen and Moir (1993) stated that resin extracts did not chemically mo* the soi1 solution. In contrast several researchers (Sibbesen, 1978; van Raij et al., 1986) indicated that, in highly weathered mil, resin in the HCO,- form codd increase the pH to a high leve1 that enhances P extractability. However, the soiI samples fkom temperate zones are weakly weathered, so HC03 form resin should be an ideal extract to evaluate soi1 P availability. Resin-extractable P is considered to be the most bioIogically available to the plants (Sibbesen, 1977).

Resin P,

Labile P, and Po

Rcsimie Ewaa fa 16 hr in 30 mi O. 1 MNaW amtrifi Pdentially labile PJP, Digest. &iemnne Pi;Recipitate Oh4 and detemillie P,

Evtra~for 16 hr in 30 ml 1.0 M HCI. caimk Ca-~ssoc. Ca-~ssocu1tedPi Pt rmieResidlK? - Ad10 ml cutc. HCI boilina 20 min. Add amhx 5 mi wnc. HCl P Pools Digest, detemPne Pt;Recipitate Oh4 and &termine P, PRO

Carrpieteiy digest wvith 5 ml Ca.&SOS and Conc HiOz Residual P

Figure 2.2. Soi1 P fiadonation chart (Tiessen and Moir, 1993).

Bicarbonate-P: the amount of P extracted by 0.5 M NaHC03 (Olsen et al., 1954) der min-extraction is not comparable to the widely used bicarbonate extraction because of resin-extracted P has already been removed. Thus bio-available forms of Pi include both resin- and bicahonate-extractable Pi (bicarb-Pi)(Tiessen, 1991; Agbenin and Tiessen, 1995). Cross and Schlesinger (1995) defined soi1 P as consisting of labile form and refiactory fonn. The labile or bio-available form P is the sum of resin P, bi&-Pi and bicarb-P, while refractory form or unavailable P refers to al1 of the other fiactions estimated with Hedley's method- Cross and Schlesinger's (1995) definition did not distinguish moderate and stable P ûactions. Ai. Fe-Associated Pi: soi1 Pi extracted with 0.1 M NaOH is held on inted daces in soi1 aggregates (Yang and Jacobsen, 1990). It is chemisorbed on Ai and Fe oxides (Ryden et al., 1977). This Pi fiaction has relatively tow availabiiity to plants, and is caüed moderately labile P (Daroub et al., 2000). However it is a potential source for plants. In generai, this fiaction of P is more important in tropical compared to northern soils. Ca-associateci Pi: soil Pi extfacîed by 1.0 M hydrochloric acid (HCI) is defined as Ca-associated P (Tiessen and Moir, 1993). It is non-labile P (Kuo, 1996). From the analyses of Ai-/Fe- and Ca-associateci P, the stages of soil development may be explained (Srneck, 1985). Hot HCl extracted P: soil P extracted with hot concentrated HC1 is considered not available to plants or microbes. The chernical form of this fiaction is poorly understood. However this fiaction serves as a P pool that may be transfonned to an available form by physical, chemical or biological processes. riliedein et al. (2000) indicated that this fiaction of P included acid hydrolysable Po and occiuded P in crystalIine Fe oxides. Residual P: after the above five extractions, the soi1 residue is digested for measuring total P with concentrated sulfiiric acid + hydrogen peroxide &SO,+ 40,). This fraction may contain both inorganic and organic P that is very resistant to decomposition. It is noticeable that the chernicd compounds in hot HCl and residual fiactions are not defined with this P tiactionation procedure. However, each of the six fiactions represents a pool of rapid-, moderate-, or slow-cyciing P in mil. Phosphocus tiactionation is therefore usehl to interpret P dynamics in diierent land uses.

2.4.4 Factors affecting soil P dynamics Soii P dynamics are affecteci by several factors, includiig soil pH, redox potential (Eh), organic matter concentration, temperature, etc. These factors are well documented (Tisdaie et al., 1993; Miller and Gardiner, 1998; Brady and Weil, 1999). Besides these common hctors, ciimate, land use and time also influence P dynamics in the mil. Sumarm et al. (1998) did not fùid any signifïcant conelation (P *.OS) between soi1 Po and the contents of organic C, total N, Caca, exchangeable Ca, Mg, and Y clay content, pH, bulk density, CEC, and base saturation. Consequently, they believe that climate is the primary determinant for soi1 P, composition in the Great Plains. Use of soii for grassland, arable crops, fallow or reafforestation influenced the contents of NaHCOyextracted P. The means of bicarbonate-extractable P followed the order grassland > arable > fdlow or reafforestation (Leinweber et ai., 1999). This indicates that a permanent gras cover results in e~chmentof this rather labile fraction of P that includes P in organic and inorganic forms. Greater mean contents of the most labile forms of P (resin-P) tend to occur in arable soils, and more residuai (stable) P in the soils under fdlow or reafforestation (Leinweber et ai., 1999). Syers and Walker (1969) used a chronosequence of soils developed on wind-blown sands, to study the changes in soi1 P with time in New Zeaiand. They found the amount of total P in the soi1 profile decreased with increasing time of development. The decrease in total P was attributed to the free draining nature of the sandy soils, which would allow considerable leaching to occur over the pedological time scale under consideration. As discussed previously, climate and land use have effects on soi1 P dynamics. But few of publications have been well documented to study P dynamics in different land use. Therefore, it is worthwhile to conduct these researches on diierent land uses in China. 3. MATERLUS AND METHODS

3.1 Site selection and sampling A total of seven locations were selected within a range between 2,600 m to 3,000 m above sea level (ASL) in Gansu province, China. These seven locations are Luchang, Shandan Horse Stud Station (SHSS),Huangcheng, Tianzhu Grassiand Station (TGS), Garijia, Sangke, and Nayi (fiom northwest to southeast, illustrateci in Figure 3.1). The detaileâ information about these seven locations is given in Chapter 4. Two kinds of land use patterns were selected to determine their effect on soi1 fertility, P dynarnics, and soi1 erosion. One was grazed pasture with different degrees of degradation, and the other was cropped fields, with variations in years of cultivation. For the purpose of this study the pasture degradation was broadly classified in three categories based on ground cover and plant density: 1) Lightly degraded Pasture (LDGP), 2) Moderately degraded pasture (MDGP),and 3) Heavily degraded pasture (HDGP).

3.1.1 SarnpEng on a local scale Local scale in this study refers to a particular site in one location. A total of five sites in two locations were selected for local scde sampling in August of 1997, three (Tianzhu-& Tianzhu-B, and Tianzhu-C) were in TGS, and two (Shandan-A and Shandan-B) were in SHSS, Gansu province. Soil samples were taken along transats. The specific transect layout and detailed information on the sites are given in Appendix 1. About 34 to 62 soi1 samples were taken dong one transect at each site using a 4 cm diameter probe. The exact number of soii sarnples and uansect Iength depended upon landform and location. The sampling interval along a uansect was constant. In general, two transects were employed in most of the samphg sites. Soil sample size was approximately 500400 g (wet), representing a composite eom two to three cores randoudy sampled within a 50 cm diameter at the sampiiing point. The samphg depth was O - 15 cm in Tianzhu-AIB, O - 20 cm in Tianzhu-C, and O - 28 cm in SHSS for both grasslands and cultivated fields, which represents the plough layer in the sites afkr grassland was put into cropland. The distance between two transects, and the interval between two sampling points dong the same transat were varied depending on field size. A separate sample fiom B andlor C horizon was also taken if it was available at the two locations.

Map of the P.R. China

Figure 3.1. Disuibution of sampling locations in Gansu province (de1: 10,200,000)+ Locations: 1 = Luchang, 2 = Shandan Horse Stud Station (SHSS), 3 = Huangcheng, 4 = Tianzhu Grassiand Station (TGS), 5 = Ganjia, 6 = Sangke, 7 = Nayi. 3.1.2 Sampling on a regionai scale To extrapolate the research resultç to large areas with a similar ecoIogy and land use, more soi1 sampIes were coltected fiom 18 sites in seven Iocations of Gansu province in JuIy of 1999 at an altitude range ktween 2,600 m to 3,000 m ASL, wbere both grazing and arable farming were important local practices. Soi1 samples from grassland were collected inside of the quadrat (Figure 3.2).

Figure 3.2. A 50 cm x 50 cm qoadrat used in this study.

The procedures of sampling con be descnbed as the follows: 1) contacthg Local technicians to select two to three different classes of degraded pastures at each site; 2) randomly pIacing the quadrat in correspondhg Pasture, estimahg pht cover, identifying plant species, and counting numbers of individual plants hide of the quadrat; and 3) taking a soi1 sample inside of the quadrat. To obtain a representative soi1 sample, 4 to 5 soi1 cores were randomly coiiected to a depth of 15 cm after removing the quadrat (the same probe was usai as local scale sampling). The cores were thoroughiy mixed to obtain a composite soi1 sample to represent soi1 status in correspondhg degrrided pashire. If cultivated fields existed ndy,two to three separate samples were tdcen fÎom these fieIds as well (quadrat was not used), and the year of fvst cultivatioa was recorcied. The detailed information on sites sampled by quadrats is presented in Appendix Ii. The number of soii samples taken from transects and quadrats in each site is presented in Table 3.1.

3.2 Vegetation sarnpling For each degraded Pasture class (lightly, moderately and heavily degraded) at each site of seven locations, the number of plant species, individual plant numbers, and ground cover classes were estimated using the quadrat method (Muelter-Dombois and Ellenberg 1974). A 50 cm by 50 cm quadrat was made with a wire (Figure 3.2). Inside the quadrat, 10x 10 cm intersections were made, giving 25 smd squares and making it easier to count the numbers of the individual plant species. Plant species were identified with the help of Professor Xintai Mo fiom the Grassiand Department of Gansu Agricultural University. To determine if there are any similarities of plants between degraded pastures, the similarity coefficient or index of similarity (1s) (Mueller-Dombois and Ellenberg, 1974) of plant communities is caiculated based on the equation (Index J =JACCARD):

where c = the number of common species, a = the number of species unique to the first category, and, b = the nurnber unique to the second category.

The palatability index (PI) of plants in pastue is calculated as:

where n = the number of individual species found in the quadrat, 4 = the number of plants of speciesj found in the quadrat, and = values of palatability for speciesj (this wül be disçussed in Section 5.4.3). Table 3.1. information on numbers of soi1 samples in each site.

County/city Location Sitet # of # # of total Transects Quadratr samples fiom fields Sunan Luchang LC Huangc heng HC 1 2 1 3 HC2 3 1 4 HC4 2 2 HC5 2 2 4 Shandan SHSS SDA 2 108 SDB 2 107 SD11/15 2 9 II SD19 3 4 7

SD4 2 2 4 Tianzhu TGS TZA 3 103 TZB 2 70 TZC 1 40 (TZA+B) NNG HGD Xiahe Ganjia GJI GJ3 GJ4 Sangke SK 3 1 4 Hmo Nayi NY 2. 2 Total 23 10 42 3 3 502 + LC = Luchang @eer Stud Station), SmCounty. HC 1 = Site one in Huangciieng Sheep Station, ...... SDA = Site A in Shandan Horse Stud Station (SHSS), ...... SD 11 = Section-I of sub-Station one, SHSS, .- TZA = Site A in TiduGrassland Station (TGS), ...... NNG = Nanniguo ViiIage, Tianzhu County. HGD = Honggeda village, Timzbu County. GJI = Site-1 in Gaajia Township, Xiahe County. SK = Sangke Township, Xiahe County. NY = NayiTownship, Hemocity. 3.3 CoUecting information about the location The foUowing background information was gathered at each location if available: Precipitation, evaporation, annual mean temperature, accumulated degree days (20°C, and 3 IOOC), kost tiee period, plantfcrop grow duration, etc. Cultivation history, rotation, femlization and other field management were recorded for cultivated Wds. Number of animals grazed in the region, and other factors impacting Pasture degradation. SoiVgeographic information such as soi1 type, position of the site, etc.

To obtain the above information, the special trips to Gansu were made, two in 1997 and one in 1999. Professor Zhe Zhang, Director of Gansu Grassland Research Institute, Professor Zhizhong Cao, Head of Grassland Department, Gansu Agricultural University, and Professor Tianwen Guo, Director of Soil and Fertilizer Institute, Gansu Academy of Agricultural Sciences provided basic infonnation on grassland resources, land use and soil classification in Gansu. They also made good suggestions on site selection. At each location, personnel fiom agricultural and animal husbandry sections were inte~ewed. Most fhndamental information was obtained fiom county statistics and county reports on land resources. Personal contacts were also important to get new data. The detailed sources of information on individual locations are provided in Chapter 4, and Appendii 1 and U. The detailed contacts and key persons interviewed are listed in Appendix m.

3.4 Soil analyses Soii fertiIity and soii erosion can be used as indicators for waluating soi1 degradation. Different ecological conditions and diierent grassland soil management should result in variation in soil feMlity and other soil properties. The detailed anaIyses were therefore focused on: 1) Soil physical and chemid pmperties related to land use patterns, 2) SoÏl P dynamics, and 3) Soit 137-Cesiurn (13'cs) radioactMty. Soil bulk densitv was determined at the depth of 10 to 15 cm unuig a 100 an3 Cutting Ring (5.05 cm in diameter), and weighed on oven-dry buis based on the method outlined by Nanjing Soii institute (1978). Macro-oraanic fiaction, organic N and P in macro-organic matter play a vital role in providing plant nutrients der mineraiiion, or as a nutnent pool, particularly for Pasture soiIs. Therefore, macro-organic matter was separated fiom soi1 by using a 300- mesh (50 p) sieve. Total N, P and C in macro-organic matter were anaiyzed for topsoil samples only. Soil DH was measured in a 2: 1 water to soii suspension following 30 min shaking in an end-to-end shaker at 36 rpm using a PHM82 STANDARD pH meter. Electrical conductivity was determined in a water extract fiom the same sample used to measure soi1 pH using a CDMS3 Conductivity meter (Rhoades, 1996). Table 3.2 presents a reference for soi1 salinity measured by EC. Because the soi1 samples in this study were analyzed at a waterhil ratio of 2:I (ECZ:~),an approxirnate one-fourth of values measured with saturated paste (or one half of the value with 1: I suspension) may be used for the same crop response categories. Soil EC in regional scde samp1es was analyzed in China with a soiYwater ratio of 5: 1.

Table 3.1. Crop response to saiinity measured as EC (dS m.' at 25°C). Sanirated extract ' 1: 1 Suspension S Crop response ' 0-2 0-1 .O Almost negiigible effects 2-4 1.1-2.0 Yields of very sensitive crops restricted 4-8 2.1-4.0 Yields of most crops restricted 8- 16 4.1-8.0 Oniy tolerant crops yield satisfactorily > 16 >8.0 Oniy very tolerant crops yield satisfactorily

Bemein(l975). For clay loarn soii (Henry et al., 1987).

Water-soluble cations such as Ca, Mg, K, and Na were dirdy determined on the same (EC) extracts by atomic absorption spectrophotometer (Wright and Stuczynski 1996). If ECZ:, nom a partidar site (Idde oniy) was over 1.0 dS rn-', indicating the yields of smsitive crops are rehcted. individual anions nich as HCW, c%" and Cl- were also determined. Carbonate and bicarbonate were determined by etectronic titration (Regional Safilaboratory, 1954) whde chioride (Cl) was determined by a colorimetric methcd (Bower and Wdcox, 1965), using a Technicon Auto Analyzer. Exchan~eable cations were detennined with 1.0 M N&Cl extraction (1:4 soiVsolution ratio) and measured by atomic absorption according to the procedure outlined by Sumner and Miller (1996). Soii CEC was calculated by summation of exchangeable Ca, Mg, K, and Na. Bio-available K was extracted with 1.0 M m0Ac(only for regional sampling), and measured by atomic absorption (China National Standard Bureau, 1987). Soi1 total C and ooanic C were analyzed by using LECO CO-12 Carbon Analyzer. Inorganic C was calculated as the difference between total and organic C (LECO,1987). Totd N and P were measured by colorimetric analysis using a Technicon Auto- analyzer U after digestion with HzS04 - Hz@ acwrding to the method described by Thomas et al. (1967). Phosohoms fiactionation: both inorganic and organic P were fiactionated according to the procedure outlined in Figure 2.2. The P fiactions are extracted sequentiaiiy by anion exchange min, followed by 0.5 M NafiCa, O. 1 M NaOH, 1.0 M HCI and concentrated Hot-HC1. Inorganic P in different fiactions was determined fiom the extracted solution, whereas total P (Pt) was determined after digestion with ammonium persulphate. Organic P was calculated as the difference between Pt and Pi, fiom extracts of OSM NaHC03, O. 1 M NaOH, and 1.0 M Hot-HC1. Organic f was not determined in the solutions extracted by tesin and 1 .O M Hot-HCI due to negligible amounts of organic P in these soldons (Yang and Jacobsen, 1990). nie isotope '% ftom selected mil amples was andyzed by hi& efficiemy gamma specmiscopy method (de Jong a al., 1982; Kachamski et al., 1992). Soi1 "'CS activity was calcuIated based on foiiowing estimation:

Total [17csfor any hduse pattern in ash site wucalwlated as: '"cS = D x '37(3rB where 137 CS = total 13'cs in a specific land use paaem (Bq d), D = depth of sampling in the site (m), IJ7cs= the specific adivity of I3'cs in individuai mple at sarnpling depth (Bq kg-?. B = bulk density at sarnpling depth for a specific land use pattern (MQmA3).

huai erosion rate (kg m2) on cultivated land cm be estimated f?om the following equation developed by Kachanoski (1993):

w here E = the annual erosion rate (kg m-3, M = the specific soi1 rnass of the plough layer in which the 137Cs is distributed (kg m"), R = the ratio of the I3'cs concentration in the eroding sediment to that in the plough layer, T" = total mass of (Bq m2)present in the soil &er n yean of erosion,

T, = total mus of '"?CS (Bq m2)present in the soil of uneroded land use. and n = number of cultivation years.

Soi1 losses in pasture wils was calculated based on the following equation (de Jong and Kachanoski, 1988):

where Er = erosion rate expressed as percent of topsoil loss per year, 137 Ch = speeifc achvity of I3'cs in uneroded pasture (Bqm*'), 137 Cî. = spdcactivity of '17cs 7Cs emded pasture (kBq m-'), and n = number of years since 13'cs fallout (40 years was used in this study). When calculatiig soil erosion rate in cultivated fields with equation 3-4, it was assumed that pasture adjacent to the cuitivated land was an uneroded land use. Thus, To in equation 3-4 might change tiom one site to another. The LDGP of Tianzhu-A, HDGP of Tianzhu-C, LDGP of Shandan-A, and MDGP of Shandan-B were used as T, for estimating soi1 losses in their correspondiig sites. Because a steep dope was encountered in Tianzhu-C, a large underestimation might be resulted if HDGP was taken as a baseline (To).Therefore, a revised soil erosion rate was calculated using the la sampling spot (relatively uneroded) as T, as well. To estimate the impact of soi1 erosion on TOC and Ca-Pi in Cult-16 of Tianztiu-B, it was assumed that Cultu-16 was initially cultivated ody when pasture was moderately degraded (MDGP)because MDGP was adjacent to Cult- 16. Selected samples fiom individud degraded pasture and cdtivated fields were analyzed for their particle size using the pipette method (Gee and Bauder, 1986). Soi1 samples (10.0 g) were pretreated with 25 ml of 1.0 M HCI to remove carbonates and then 50 ml of Hz02 was added to rernove organic matter.

3.5 Estirnating land use areas in the research region To extrapolate the results to al1 the areas in Gansu province with a similar ecological condition and land use, the representative areas between 2,600 to 3,000 rn elevarion of the whole province, as weii as individual counties where the research was conducted, were determined using a planimeter. A total of 19 landform maps (1:250,000) from China National Mapping Department (1990, 199I), with IO0 m interval contour lines on them, were used to make an estimation of the area. Basic iand uses and relative population density cm be observed on the maps, which also provided ttndamental information on land use patterns and for site selection.

3 -6 Statistical analysis AU of the statistical analyses were done using SPSS software version 10.0. AU data tiom individual variables were tested for normal disuiution using techniques tiom expIoratory data analysis descrii by Van Kessel et al. (1993). The normal dimiution is symmetric, and has a skewness value of zero, A dimiution with a significant positive skewness has a long right tail. A distribution with a significant negative skewness has a long Ieft tail. As a rough guide, a skewness value more than twice the standard error is taken to indicate a depamire fiom symmetry. if data were nonnally distributed, parametric analysis was used. The diierences between land use patterns were assessed using Tukey's honest significant difference (HSD) test (Lilienfein et al., 2000). The multiple analyses were conducted if a particular determination was significantly different between land use patterns at 0.05 level. Some cases used 0.10, or 0.20 probability levels as indicated in the thesis.

If the data were not normaiiy distributed even afier data transformation, a nonparametric dysiswas used. Thus, the ciifferences between land uses were assessed using Kniskai-Wallis test. if significant differences were observed for a given determination between land use patterns, a multiple cornparisun test for ranked data was used to assess the nature of the differences between different land use patterns (Siegel and Castellan, 1988) at the a = 0.05 level. The probability of O. 10 or 0.20 were used in some cases (Van Kessel et al., 1993; Pennock et al., 1995; Jowkin and Schoenau, 1998) as indicated in the thesis. Pearson correlation coeBcients for difTerent measurements were also tested using SPSS when appropriate. Pararnetric variabtes are summarized in tabIes by their means, while nonparametric data are displayed in tables as medians. 4. LAND USE PATTERNS iN GANSU

There are about 392.8 million ha ofgrassland in China, making up 41% of the total land (Liao and fia, 1996). Of the total grassland, 330.9 million ha are usable, accounting for 84% of the total. Grassland acreages for the larges 10 provinces in China are presented in Table 4.1. Gansu province ranks sixth, making up 4.9% of the total usabte grasslattd in China.

Table 4- 1. The grassland area of the Iargest 10 provinces in China. Provincdregion Total grassland Usable grassland (106 ha) (%) (1o6 ha) (%) Total in China 392.8 100 330.9 IO0 Tibet 82.1 20.9 70.8 2 1.4

Xinjiang 57.3 14.6 48.0 14.5 Qinghai 36.4 9.3 31-5 9.5 Sichuan Gansu 17.9 4.6 16.1 4.9 Yunnan 15.3 3.9 11.9 3.6 Guangxi 8.7 2.2 6.5 2.0 Heilongjiang 7.5 1.9 6.1 i -8 Hunan Total (10 provinces) 332.9 84.8 279.8 78.1 Source: Liao and lia, 19%.

4.1 Basic infiormation on Gansu Gansu is a long narrow province, located in northwest China between the Inner Mongoiian Autonomous Region in the north and Qùighai in the south. Xinjiang Autonomous Region borders Gansu to the west and Niaand Shaanxi are to the east. A satellite view of tbe province is show in Figure 4.1.

Gansu province has a population of about 25 million and administratively includes five dies (Lanzhou, Baiyin, Jinchang, Jiayuguan and Tianshui) directly under provincial administration, seven prefectures (Jiuquan, Zhangye, Wuwei, Dingxi, Pingliang, Qingyang and Longnan) and two autonomous regions (Linxia and Gannan) (Figure 4.2).

Figure 4.2. Prefecture-leveI administrative units in Gansu province (de1 : 10,000,000).

In general, dry, continental clirnatic features are typical in the province. However, the types of climate varied 6om one location to another. For example, subtropical humid climate in the east changes to a warm temperate, and then to a dry climate in the West (SSO, 1993). CoId, humid, montane ciimate is characteristic for the Qilian Mountains. Mean seasonal temperatures with the province are Listed in Table 4.2 (SSO, 1993). Whters are coid and summers are warm or hot. Temperatures shift greatly from day to night as well as tiom season to season in the central and western parts of the province. The maximum temperature difference between the day and the night may reach 26 - 32

OC in the Hexi Corridor, whereas it is even higher in Gannan (about 30 - 35 OC). In general the rainfall is very low, erratic and for most parts peaks in late June, July and August. The annual precipitation ranges fiom about 36 mm in the desert region in the nonhwest to 800 mm or more in the south (Table 4.3). The locations presented in Table 4.3 within the province are illustrated in Figure 4.3.

Table 4.2. Mean seasonal temperatures ("C) in the main regions in Gansu. Location Winter Spring Summer Autumn Hexi Corridor -7 - -11 6 - 12 17 - 25 6-9 Qilian Mountains < -12 0.2 - 5 11 - 16 0.5 - 4 Gannan -8 - -10 2-4 10 - 13 1-3 Longnan >O 11 - 16 21 - 25 10 - 15 Source: SSO, 1993.

Table 4.3. Annuai precipitation and evaporation in different locations of Gansu. Location Elevation (m) Precipitation (mm) Evaporation (mm)

Dunhuang 1,150 36 1,703 Jiuquan 1,520 83 1,028 Sunan 3,050 234 856 Zhangye 1,500 120 959 Shandan 1,800 190 1,036 Wuwei 1,580 163 985 Tianzhu (Wushaoling) 2,980 416 76 1 Lanzhou 1,500 330 720 Xiahe 3,100 437 619 Hezuo 3,000 577 586 Tianshui 1,400 558 724 Kangxiaa 1,200 85 1 56 1 Source: SSO, 1993. Figure 4.3. Corresponding locations ofTable 4.3 in the province. (scale 1 :10,000,000). 1 = Dunhuang, 2 = Jiuquan, 3 = Sunan, 4 = Zhangye, 5 = Shandan, 6 = Wuwei, 7 = Tianzhu, 8 = Lanzhou, 9 = Xiahe, 10 = Hemo, 1 1 = Tianshui, 12 = Kang'tian.

The province has about 45.4 diion ha of land (SSO, 1993). Of this, 70% is in the mountain and high plateau region, 26% in the Gobi and 3% in the plain. Desert mils (# 12, 13, and 14 on roll map in Figure 4.4) and young mils or Entixils (# 15, 16, 17. 18, 19, and 20) are dominant in the province, makhg up 26% and 21% of the total land. respectively. Chemozem (# 7), Castanom (# 8) and dark loessial soiis (# 9) accwnt for 8%- Figure 4.4 shows that there are 37 poil types in Gansu province according to the Chinese mil classification (SSO, 1993).

Grassland is the major land use in the province, as it accounts for about 39.4% of the total (Table 4.4).

Table 4.4. Land use patterns in Gansu province.

Land use Area ( 1o6 ha) I(%) Grassiand 17.9 39.4 Cultivated 5.1 11.2 Forestry 4.2 9-3 Housing/road/industry 0.7 1.5 Watershed 0.6 1.3 Hardly usedlother 16.9 3 7.2 Total 45.4 1O0 Source: Gansu Animal Husbandry Bureau, 199 1.

Grasslands of economic importance to animal husbandry in Gansu can be classified into four major foms (Longworth and Williamson, 1993):

Desert arasshnd: This kind of grassland is distributed dong the southern side of the Hexi Comdor, and it covers an area of approximately 6.7 million ha. Goats, camels and sheep are the dominant animals of economic importance in this Pasture. The major gras species on the low and Bat grasslands are Achraathencm splendens and Phragmites aclanr. Form il arassiand: This particular form of grassland is scattered throughout the province and is predominantly located in agicultural areas. h totai, the Fonn II grassland has an area of about 5.5 diion ha The dominant native species on the alpine and cold grasslands are Stippurpurea and Agropyron cristatum. Real meadow arassiand: This fonn of grassland is found mainiy in Gannan Tibetan Autonomous Mechire and dong the Qilian Mountains. There is about 4 million ha of this type of grassland. The principal native species of grasses fumd on this grassland are Kobrda genus and Cyperaceue gems. Sods studied Ui tbis thesis were maùily fiom this type of grassland. Bush and msprassland: This fom of grassland is mainiy located in the mountainous region of Longnan Prefecture, and covers a total area of 0.8 million ha.

[t was estimated in 1990 that about 4.6 miliion ha of the avaiiable pastureland was degraded (Longworth and Williamson, 1993). Out of this, 2 million ha was considered as heavily degraded, 1.3 miliion ha was moderately degraded and another I .3 miliion ha was lightiy degraded. Local fmers usuaily divide their grasslands into three categones: springlwinter, sumrner, and fall pasture. The grassiands below 3,000 m ASL are sometimes used for fenced pasture andor crop cultivation (spring/winter pastwe), while grasslands at 3,000 -3,200 nt ASL are used as open range for feeding animals in the faii (fall pasture), and pasture between 3,200- 3,800 m ASL are caüed summer pasture. Another specid feature in Gansu is the Hexi Corridor (SSO, 1993) where the Qinghai - Tibet, Loess, and inner Mongolia Plateaus meet. The Corridor is a narrow, 1,200 km passage. AU of the sol samples for the local scale sampling were collected fiom the north dope of the Qiiian Moumains dong the Comdor. The local grassland-desert ecosystem comprises three sub-systems: mountains, oases and deserts, with the last one as a dominant component (Ren and Zhu, 1995). In generai, the Comdor region is ecologically fiagiie. Degradation of dtivated land and pasture are very severe under high and increasing population density. One can distinguish a series of aititudinal vegetation belts on the north slope of the QiIian Mountains dong the border between Qinghai and Gansu provinces (Table 4.5). It is evident that vegetation and soi1 type are changing with eIevation in the agriculturd systems @oth crop production and grazing are practiced), a mark& infiuence of elevation on crop can be seen. For example, fiom the HuazangP, capitd of Tianzhu County at about 2,000 m elevation, the twrain climbs to above 3,000 m within 50 km. Cropping and yield patterns dong tfüs gradient are illustrated in Table 4.6. Spring wheat dominates the cuitivated fields at about 2,000 m elevation, and the yield of wheat is the highest at this elevation. Grazing animais are not very common below 2,000 m elevation in this panicular location. Table 4.5. Relationship between altitude and grasdsoil types. Altitude (m) Grass Aand Vegetation t Soi1 type:

1,500 Oases ST, BA, TF, CS, HB,KF Solonchak (28)

1,500-2,000 Sandy grave1 deserts SG, AC, CK, HS Sierozem (1 I) 2,000-2,300 Dry montane steppe SB, SBr, AS, AD, DF, EE Sierozem (1 1) 2,300-2,500 Shnib steppe SA, SP, RN, EN, AC, AS Castanozem (8) 2,500-3,200 Forest meadow PC, SPr, PF, KB, HI', PA Chemozem (7) 3,200-3,500 High montane meadow KP, CH, GA, M,RC, RO Subalpine Meadow soil (33) 3,500-4,000 Alpine meadow PV, KC, PS, KH, CKa, GA Alpine meadow

>4,000 Snow belts SD, AL, HY Alpine fiozen

Sources: Walter and Box, 1983; SSO, 1993. f ST = Schoenoplectus tabemaemoritarii, BA = Bolboschoems @nisis, TP = Triglochin pahstre, CS = Carex spp., HI3 = Halostachys belangerima, KF = Kalidium foliatum, SG = SI@ glareosa, AC = Artemisia capillaris, CK = Caragana korshimkii, HS = Hedjsarum scoparium, SB = Stipbungecnia, SBr = Stip brevifolia, AS = Agropyron spp.., AD = Aneurolepiditim dasystachys. DF = Dasiphorafhiticosa, EE = Ephed-a equiseiina, SA = Stipa aliena, SP = Stippurpurea, RN = Roegneria mttans, EN = Elynius nutans, AC = Agropyron cris~aîtrrn, AS = Achnaihemm splrndens, PC = Picea crcll~s~~olia, SPr = Sabina prezewalskii, PF = Potentillafntticosa, KB = Kobresia bellmdii, HT = Helictotrichon tibetictim, PA= Pwanmta, KP = Kobresia p~gnraea, CH = Carex heterostachya, GA = Gentiama al'&, RC = Rhod&ndon cquitatum, RA = Rhodderuùon anthopogounides, RO = Rhoddendron oreodoxa, PV = Polygomm vtvipancm, KC = Kobresia capiIIifolia, PS = Polygomm sphaeruriachyirm, KH = Kobresia humilis, CKa= Carex kansuems, SD = Sarrssurea, AL = Arenaria L., Hy = Hytotelephium H. $ Chinese soi1 ~Iassificationsystem (soil # in Figure 4.4). Table 4.6. Dominant crops and their yields dong elevation gradients. Elevation (m) Dominant crops Yields of cereals (kg ha -') 2,000 Spring wheat 2,400-3,200 2,300 Spring wheat, potato, rapeseed 2,200-2,800 2,600 Pure oats, rapeseed, spring wheat 1,800-2,500 2,800 Barley, oatq rapeseed 1,500-2.300 3,000 Alpine barley, oats, rapeseed 900- 1,500 Source: Xu, et al., 1997; 1999.

At about 2,300 m ASL, the yield of spring wheat is around 2,200 to 2,800 kg ha', lower than that at the elevation of 2,000 m. At about 2,600 m ASL, grassland is extensively used for grazing, and some lands are also used for cropping depending on rainfall. At about 2,800 m ASL, cereal and oil crops cm be planted, including pure oats, bariey (not alpine barley), and rapeseed. These crops are still green in the late growing stage in mid August and are sometimes cut for forage. The fie of individuai potatoes is smailer than that at the tower position, but bigger compared to that at the higher elevation. At 2,850-2,900 m ASL, the first snow may come in mid September. Alpine barley, oats, rapeseed and potatoes can be planted around this elevation, with an expected yield of 1,500 to 2,250 kg grain of bartey per ha, Harvesting tirne for barley is around the 20th of August, and the 10th of September for oats. However, at 3,000 m ASL, the grain yield of barley and oats are 600 to 800 kg ha-' lower than those at 2,800 m ASL. Snow even occurs in lune, and the 6rst snow usudiy falls around the 10th of September. It is very hard to harvest potatoes without any protection practice at this elevation. It is very clear that crop miety, crop yield, and harvesting date are greatly dependent on elevation, which govems sunshine hours, accumuiated degree days, fiost- fiee penod, etc. W~nthis region average yields drop rapidly with increashg elevation. 4.2 Land use patterns in the research locations

4.2.1 Zhangye Prefecture Zhangye, or otherwise called Golden Zhangye, is one of the seven Prefares of Gansu (Figure 4.2). Seven counties are under its administration. Sunan and Shandan are two representative pasture counties, therefore research sites were selected in these two counties. The general information about Zhangye Prefecture is presented in Table 4.7.

Table 4.7. Land use patterns in Zhangye Prefecture. Land use Area ( 1,000 ha) (%) Grassland 2,550 60.9 Cultivated 3 10 7.4 Forestry 200 4.8 Hardly used Iothers 1,130 26.9 Total 4,190 1O0 Source: Chai, 1988.

4.2.1.1 Sunan County Sunan is a narrow county in the Prefecture, ranging tiom N37"28' to 39'49, and fiom E97"20' to 102O13' (AM-Sunan, 1987). Altitudes range between 1,400 and 5,560 m, thus, most of Sunan is extremely mountainous. Population is about 35,800 in the whole county, of which 67% are involveci in agriculture. A survey conducted in June of 1998 indicated that a total of 692,000 animals are being grazed. The raising of sheep, and to a lesser extent of goats, is the dominant rural activity (BAH-Sunan, 1999). Over 90% of the sheep are Gansu Alpine Fine Wools. Other information about the land use pattem is given in Table 4.8- Mountain and hiUy areas account for 89.7% and hiiiy plain for 10.3% of the area. This means there is Little land available for cropping or for improved pastures. The officiais ftom the Bureau of Animai Husbandry (BAH) addressed two major pasture degradation problems, one is overgrazhg, and the other is severe drought during recent years. Under this circumstance, excessive numbers of dshave been putting great pressure on the natural ecosystem.

Table 4.8. Land use patterns in Sunan County. Category 1,000 ha % Grassland 1,370 57.2 In which Springiwintw 53.8 Summer/fall 46.2 Bushes for grazing 54 2.3 Cultivated field 6.1 0.3 Spare bushes t 246 10.3 Forestry 86 3.6 Watershed 8.6 0.4 Housinglroads 2.5 0.1 Industry 4.7 0.2 Hardly used land 612 25.6 Total 2,389 100 Sources: AAH-Sunan, 1987; BAH-Sunan, 1999. t ifground cover is more than 30%, it is not used for grazing.

The BAH has adapted four basic strategies to overcome the problems of pasture degradation: 1) educating herdsmen on the impacts of animais on pasture, 2) controlling growth rates of animais, 3) increasùig the productMty per mimai, and 4) rationai pasture use. The area between 2,600 and 3,000 m ASL is esthted to be 167,700 ha, and about 85% of this area is considered as grazing land* In the region, ground cover is around 50- 65%. ksh gras production is approismately I,WO-1,300 kg ha-' (Wen, 1999). Temperature and precipitation Vary a great deai fiom year to year and &om place to place depending upon altitude, etc. The annual average rainfalI record4 by the Meteorological Station at Hongwan (county capital) fluctuated greatly. The bwest recording was 175 mm in 1968 while the highest was 41 1 mm in 1979 (Longworth and Williamson, 1993). The climatic data between 2,500 to 3,000 m ASL are presented in Table 4.9.

Table 4.9. The cimatic data between 2,500 to 3,000 ASL in Sunan County.

Annual temperature 1.5 OC January temperature -12.S°C July temperature 13S°C Precipitation 325 mm Evaporation 1,650 mm Source: AAH-Sunan, 1987.

Chernozemic soil is found mainly on plains and gentle dopes facing north, or partly facing north at altitudes of 2,700 to 3,000 m. The parent materiais are colluvial or aeolian deposits. Total area of this soi1 is about 110,500 ha (4.6% of total land). Castanozemic soil (Chesmut) accounts for approximately 280,000 ha, making up of 11.7% of the total land. The Chernozem and Chestnut soi1 dorninate cultivated fields (AAH-Sunan, 198 7).

4.2.1.1.1 Luc hang Luchang, called the Deer Stud Station, is located in 16 km nonhwest of the county capital. It was established in 1958. The total land area of the station is around 7,320 ha, 47% of which are Pasture. More than half of the pamre is reported degraded; about 25% of this is considered as heady degraded (An, 1999). Because the station is rnainly used for deer breeding and dercoiiecting, the cultivated land is small; only about 27 ha is cropped. The chteat the station is dry; the average annual precipitation is only 253 mm while evaporation is hi& with 1,820 mm per year. Annual mean temperature ranges fiom O to 3 OC (AAH, Sunan, 1987). 4.2.1.1.2 Huangcheng Huangcheng Sheep Stud Station was set up in 1950. It is located about 285 km southeast of Hongwan, capital of Sunan County. Although this station is administrated under Sunan County, it is regarded as one of the seven locations because it is far away fiom the county capital. Land area in Huangcheng district totais 397,000 ha, making up about 16.6% of the whole Sunan County. The basic ùifomation on Huangcheng Sheep Stud Station is describeci in Table 4.10. The original pasture in the station was around 22,500 ha in the 1950s, however the area decreased considerably, partly due to misuse of the pasture and some of the pasture being cultivated. Oniy about 13,200 ha are left, of which 10,000 ha are usable for grazhg animais. Fresh grass production dropped by 32.5%, from 4,000 kg ha" in 1960s to 2,700 kg ha*' in 1989 because of degradation (ST-Huangcheng, 1996).

Table 4.10. Basic information on Huangcheng Sheep Stud Station. Category Datalinformation Altitude 2,620 m Total area 25,000 ha Pasture 13,200 ha HDGP 2,000 ha MDGP 4,000 ha LDGP 7,200 ha Cultivated 1,000 ha Soil type Light Chestnut Parent materid Aeolian deposit Annual precipitation 362 mm AnnuaI evaporation 1,112 mm

Annual temperature 2.7 OC Source: ST-Huangcheng, 1996. 4.2.1.2 Shandan County Shandan Horse Stud Station, located about 54 km south of the capital of Shandan County, can be traced back to Han-Wu-Di era, about 2,000 years ago. However it was not weU managed unti1 1949 when it was taken over by the Chinese Amy. The area managed by the station ranges between N37'12.5' to X021', and E10093' to 101°29.5', totaling 219,300 ha. The land use pattern of the station can be described as in Table 4.1 1.

Table 4.1 1. Land use patterns in Shandan Horse Stud Station. Land use Area (1,000 ha) (%) Pasture 79.7 36.3 Bushes for grazing 45.9 20.9 Cultivated 25.0 11.4 Forestry 46.7 21.3 Watershed 0.5 0.2 Housing/roads 1.4 0.7 Hardly usedothers 20.1 9.2 Total 219.3 100 Source: Shandan Horse Stud Station. 1985,

The grassland managed by individual sub-stations varies greatly. Most of the grassland in the Station is managed by the 1' and the 2d sub-stations (Table 4.12).

Table 4.12. Pasture and cultivated land in individual sub-stations. Sub-station Pasture (ha) .t % Cultivated (ha) YO First 53,250 42.4 5,330 21.3 Second 40,990 32.6 9,200 36.8 Third 24,100 19.2 5,900 23.6 Fourth 7,220 5.8 4,590 18.3 Total 125,560 IO0 25,020 100 Source: Shandan Horse Stud Station, 1985. f Includiig bushes for grazing. Since more than 75% of the pasaire is located in the 1' and the 2* sub-station, soi1 sampIes were taken mainly hmthese two wb-stations; a few samples were collected f?om the 4' Sub-Station. Gened chtic data For individual sub-stations is presented in Table 4.13.

Table 4.13. EIevation and chticdata in individuai sub-stations. Sub-station First Second Third Fourth EIevation (m) 2,900 2,640 2,60 t 2,5 10

Mean annual T (OC) -0.5 0.2 1.6 2.4 Annual precipitation (mm) 380-420 3 56 362 253 kmual evaporation (mm) t ,200 1,702 NAT 2,000 l 1O°C degree days NA 1067 1186 NA Source: Shandan Horse Stud Station, 1985. + Not available.

4.2.2 Tianzhu Autonomous County Tianzhu, a Tibetan Autonomous County, is located about 100 km north of Lanzhou, the capital of Gansu province. It is one of the five counties administrated by Wuwei Prefecture. The iand use of Wuwei Prefecture is given in Table 4.14.

Table 4.14. Land use patterns in Wuwei Prefecture. Land use 1,000 ha (%) Grassiand 2,870 68.3 Cultivateci [and 3 10 7.4 Forestry 250 6.0 Clthers 770 18.3 Total 4,200 100 Source: AHS-Wuwei 1982.

TiuCounty has 192 villages in 22 townships, ranging &om E102"001 to E103"40', and N36"301to N37°55'. The altitude Vanes between 2,040 to 4,878 rn (BAH- Tianzhu, 1998a). Of the 229,900 people in the county, 87.5% are in the agiculturai and animal husbandry sectors. Therefore, most people in the county are involved in agriculture. There are large areas of agricultural land around the county capital, but the eastem parts of the county are high rnountain pastures. During the late fifiies and early sixries, large areas of the Pasture were brought into crop production. However the climatic conditions were not suitable for crop production, causing severe soi1 erosion and degradation. Increasing grazing pressure on the remaining pastures has intensified the erosion problem. Total number of the reached 648,000 in 1998. About 77% of them are sheep, and haif of those are fine-wool sheep. Overgrazing is one of the main causes for grassland degradation. For example, the number of animais increased fiom 62,500 in 1982 to 80,100 in 1998 in Songshantan Township only (BAH-Tianzhu, 1998a). The sheep unit in this township dropped to 0.56 ha. The land use pattern of Tianzhu County is characterized in Table 4.15. The clirnatic features of the county are shown in Table 4.16.

Table 4.15. Land use patterns in Tianzhu County. Land Area ( 1,000 ha) % Pasture area 39 1.4 54.7 Natural 362 Serni-fenced 22.3 Fenced 4.5 Pianted 2.6 Gran'ng bush 114.2 16.0 Cropland 24.5 3 -4 Forestry 157.3 22.2 Others 27.5 3.8 Totai 714.9 1O0 Source: AHS-Wuwei, 1982; Cao, 1999. Table 4.16. The climatic information on Tianzhu County.

Mean annual temperature -0.2 to - 1.3OC Annuai precipitation 260 - 630 IIIIII Annual evaporation 1,600-1,700 mm Source: BAH-Tianzhu, 1W8a.

There are about 182,870 ha of spring and winter pasture with an average production of 3,750 kg ha-', and 205,330 ha surnmer and autumn pasture with an average production of 3,150 kg ha-' (Cao, 1999). Five pasture types are classified in this county: nodgrassland, hilly meadow pasture, sparse meadow pasture, bush meadow pasture, and alpine meadow pasture. In a normal year, fiesh grass production in the whole county averages about 3,400 kg ha-' (BAH-Tianrhu, 1998b). A total of 142,000 ha of pasture are considered degraded in the county, accounting for 36% of its total (Cao, 1999). The major characteristics of degraded pasture in Songshantan (a typical township with heavily degraded pamre), for example, are as follows @AH-Tianzhu, 1998b, Cao, 1999):

Tail ~rassspecies evoived to short one; and low quality grasses replaced high quality grasses. For example, the less us& gras Arremisiafigtuh replaced the dominant native species, Srip ûungeana, which is a high value forage gras for animal production. Grasses became sparse, plant cover reduced by 11% and grass height shorted by 41% compared to the 1950s (Songshantan-Tianzhu, 1999). Grass producbon (fiah) declincd by 43%, from 2,100 kg haw1in the late 1950s to 1,200 kg ha-' in the 1990s. (Zhang, 1998). Desertification, salinization, poisonous gras species and the effect of rodent and insects became more and more severe with degraded pasture. Gannan is another important base for gming animals. A total of seven counties and one city are under Gannan Prefecture. Soi1 samples were coilected from Xiahe County and Hezuo City, respectively. Hezuo city was admhistrated by Xiahe County, but it is independent now. General land use patterns in Gannan Prefecture are shown in Table 4.17.

Table 4.17. Land use patterns in Gannan Prefecture. Land use Area (1,000 ha) (%) Grassiand 2,723 70.3 Forestry 884 22.8 Cultivated 121 3.1 Housingkoads 24 0.6 Watershed 20 0.5 Others 103 2.7 Total 3,875 1O0 Source; AM-Gannan, L988.

In Gannan Prefecture, there are about 3.87 million ha of total land. Grassland and cultivated land account for about 70% and 3% ofits total area, respectively. In May or June, the families move with their tents to the summer Pasture area located 10 to 12 km hmthe winter base. The flockdherds graze on allocated areas of the hi11 rangeland. In November, the bers return to the village with their flockdherds where the animais gaze on winter pastues close to the village. On an average, each fàmily has 28 cattle (mainiy yak) and 67 sheep. Milk, butter and cheese dong with alpine barley fom the mainstay of the Tibetan farmers. Yaks are used for transportation, food, milk and hides. The miik is essential to the Tibetan diet and is used for butter, cheese and dnnking. 4.2.3.1 Xiahe County Xiahe County ranges between N34'33' to 3593', E10t044' to 103°25', Qinghai province neighbors in the West. There are about 502,580 ha grassiand in the county, of which 492,500 ha are used as pasture for 450,600 anirnals (BAH-Xiahe, 1999). Three kinds of pasture dominate the county, narnely, alpine, sub-alpine and gras meadow. Generd land use patterns in Xiahe County are presented in Table 4.18.

Table 4.18. Land use patterns in Xiahe County. Land use Area (1,000 ha) t (%) Grassiand 667 76.8 Forestry 142 16.3 Cultivated 37.2 4.3 Housing/roads 5.7 O.7 Watershed 2.6 0.3 ûthers 14.5 1.7 Total 869 1O0 Source: ARO-Gannan, 1988. + Data include those fiom seven townships that are under Hemo's administration now.

A total of 216,000 ha (43% of the total) pasture is considered as degraded, including 117,300 ha (23%) affected by insects and rodent animals (SR-Xiahe, 1999). In normai years, fresh grau production in native pasture h around 3,290 kg ha". while HDGP and MDGP produce less than 1,500 kg ha-', half of the production compared to that in the 1980s. If fenced for rotational grazing, Le., to prevent degradation, the fresh grass yield could reach as high as 5,190 kg ha', or increase by 57.8% (BAH -Xiahe, 1999). The practices used to prevent pasture fiom degradation include rodent and gasshopper control and fenced grazing. For example, alpine rodent-rabbits (Ochotona curzoniae) were controiied by using C-Bacillus botulinus. China Fen-Shu (Myospdax fontmieri) was controlled by traps. The climatic information about Xiahe County is presented in TabIe 4.1 9. Table 4.19. The climatic information on Xiahe County. Climatic feature Data Annual mean temperature 2.5 "C January mean temperature -9.1 "C July mean temperature 12.9 "C Frost fiee days 32 Annual precipitation 437 mm Annual evaporation 1305 mm Source: GRSO-Gannan, 1985.

4.2.3.2 Hem0 City Hemo became independent tiom Xiahe County a few years ago. Thus, the information about the Henio is relatively sparse. The brief land use patterns for the area surrounding Hezuo are presented in Table 4.20.

Table 4.20. Land use patterns in Hemo City.i Land use Area (1,000ha) (%) Grassland 164.3 69.1 Forestry 46.8 19.7 Cultivated 16.3 6.9 Housing/roads 2.3 1 .O Watershed 0.8 0.3 Others 7.1 3 .O Total 237.6 100 Source: Regionalkation Office-Xiahe, 1985. f Data are from the seven townships, which were under Xiahe's administration before Hemo became officially independent in 1998.

The total area of the Nayi Township (NY)where soi1 samples were taken is around 30,860 ha. Grassiana and cultivated land are 21,400 and 6,100 ha, making up 69?!and 20% of its totai, respectively (GRSO-Gannan, 1985). About 4@!4 of the grassland is considered as MDGPIHDGP in Nayi (Wang, 1999). The Meteorological Station at 2,936 m elevation and E102"54', N35O gives the following data (Table 4.21):

Table 4.21. The climatic information on Hezuo City. Climatic feature Range

Evaporation 1,233 mm hua1mean temperature 1.5- 2.0°C January mean temperature -10.6"C July mean temperature 12.7"C Source: GRSO-Gannan, 1985

4.3 Summary Grassiand was the main land use in the three prefecnires where this study was conducted, and accounted for about 66% of the area. Cultivated land was relatively srnall in acreage, making up only about 6%, but it is very important to local fmers because farmers have to rely upon these cultivated land to produce foods andfor Forage. Other land uses include forestry, watershed, housing, roads, industry, hardly used land, etc., making up about 28% (Table 4.22).

Table 4.22. Land use patterns in three prefectures of Gansu (1,000 ha). Location Total Grassland Cultivated Others Zhangye 4,190 2,550 3 10 1,330 Wuwei 4,200 2,870 3 10 1,020 Gannan 3,875 2,723 121 103 1 Grand total 12,265 8,143 74 1 3,381 (%) IO0 66-4 6.0 27.6

For the four counties sampled in this study, the total grassiand accounts for about 64% of their total land uses (Table 4.23). It is well representatnre of land use in the three prefectures (Table 4.22). However, the proportion of cultivated land dropped to 3.5% because the research counties are located at higher elevations, which are not tàvorable for crop production. Land used for housing, roads and industry is oniy 0.6% of its total area. Hardly used land makes up a considerable part in the category of other land use patterns. For example, it accounts for about 25.6% in Sunan (Table 4.81, and 9.2% in Shandan Horse Stud Station (Table 4.1 1).

Table 4.23. Land use patterns in individual counties (1,000 ha). County Total Grassiand Cultivated Forestry Housing/roads ûthers Sunan 2,389 1,370 6.1 86 7.2 920 S handan t 505 329 89 45 6 3 6 Tianzhu 715 506 24.5 157 5.6 22 Xiahe: 869 667 37.2 142 5.7 17 Grand totd 4,478 2,872 157 430 25 995 (%) 1O0 64.1 3.5 9.6 0.6 27.2 + Shandan County, not Shandan Horse Stud Station. $ Including seven townships that are under administration of Hezuo City.

The areas of degraded pasture were estimated by research techniciansheads at the research locations visited in 1999. A total of 693,400 ha grassland in the seven research locations were categorized for degradation status. Since the area of MDGP was estimated dong with HDGP in Tianzhu and Nayi of Hezuo, the HDGP and MDGP were merged as one category in Table 4.24, About haif of the 693,400 ha of pasture was lightly degraded, and another half was either heavily or moderately degraded. Table 4.24. Estimation of degraded Pasture in different locations (1,000 ha). HDGP Location Total % LDGP % Source? IMDGP Luchang 3.5 2.6 74 0.9 26 An, y. Huangc heng 1O 4.5 45 5.5 55 Wang, J. SHSS 79.7 40.9 51 38.8 49 Tang, C., & S. Wang Tianzhuz 39 1 142 36 249 64 Zhang, Z., & C. Xu Ganjia, Xiahe 7 1.8 56.8 79 15 21 Ma, L. Sangke, Xiahe 1 16 9 1 78 25 22 Yin, H. Nayi, Henio 2 1.4 8.5 40 12.9 60 Wang, S. To ta1 693 346 50 347 50

f Full name of the persons can be found in Table Ad. * Whole county. 5. RESULTS AND DISCUSSION

5.1 Eff- of land use patterns on soi1 fertility One of the objectives of this study was to determine if soil degradation was related to soi1 fenility and soi1 erosion on different land use patterns of selected regions. Few such studies have ben systematically conducted in grassland soils in China. In this section, different land use pattems such as LDGP, MDGP, HDGP and crop fields with various cultivation length were examined at both local and regionaI sales. Local scale in this study referred to a particular site in one location. Soil samples at the local scale were taken dong transects. The impacts of land use pattern on soil fertility were evaluated based on the specific site with local ecological conditions. Regional scale results compa.the seven locations, where soil samples were collecteci fiom quadrats and nearby cultivated fields.

5.1.1 Results fiom bcal scaie sarnpiing 5.1.1.1 Tianzhu-Ail3 Three sites, Tianzhu-A, Tianzhu-B and Tianzhu-C, were selected around Tianzhu Grassland Station. Land use pattems at individual sites are Qiven in Table 5.1.

Table 5.1. Land use patterns in individual sites of Tianzhu, Gansu.

C Land use LDGP MDGP HDGP Cult-ût Cult-I6 Cult-41 CuIt-48

+ Cropped field with number representing number of years of cultivation.

Tianzhu-A is about 0.5 km southwest of Tianzhu-B, while Tianzhu-C is approximately 3.4 km southeast of Tianzhu-A There are three land use patterns in Tianzhu-A, three in Tianzhu-B, and two in Tianzhu-C (Table 5.1). Since no ecologicaI and climatic differences existed between Tianzhu-A and Tianzhu-B, the results and discussion eom these two sites were presented together. It is evident that differences for plant cover and plant density fiom MDGP were not very large between Tianzhu-A and Tianzhu-B (Table 5.2). No significant differences in soi1 fertility were found between these two MDGPs, excepting total P (Table 5.3). Therefore, these two land use patterns were merged as one as well.

Table 5.2. Pasture degradation and plant coveddensity in Tianzhu. Site Land use Plant cover (%) Plant densityt NDSS

Tianzhu-A MDGP 100 250 8 Tianzhu-B MDGP 1O0 275 9

+ Numben of plants per quadrat (0.25 m2). :Numbers of plant spefies inside ofthe quadrat (0.25 m2).

Table 5.3. Chernical propehes in MDGP-A and MDGP-B,Tianzhu-NB. Soi1 variables MDGP-A MDGP-B Significance at 0.05 levei

PH 7.46 7-44 NS? ECLi (dS mm') 0.54 0.52 NS CEC (cmol kgm') 40.4 39.0 NS TOC (g kg*') S 82.2 78.0 NS Total N (g kg") 7.6 7.3 NS Total P (g kgT') 0.79 0.86 Yes Total K (g kg-') 15.2 15.4 NS

+ Not significantly different at 0.05 probability level according to T-test. f Total organic C

Soil samples were taken to 15 cm depth, which represents the plough layer. The B horizon thickness ranged fiom 25 to 50 cm, and the depth of the C horizon ranged hm 85 cm to 1 IO cm. Soil fertiiity as indicated by CEC, TOC and Total N dectined with depth, but pH increased with depth (Table 5.4). Soi1 texture of the site was a silt-clay loam according to texture classification (Brady, 1990), containing a high proportion of silt particles. The percentages of silt and clay particles dedined with depth, whereas a reverse trend was found with sand content (Table 5.4). Soi1 parent materiais are alluvial and wind-blown (SSO, 1993).

Table 5.4. Soil physical and chernical properties in Merent horizons, Tianzhu-NB. CEC TOC Total N Total P Sand Silt Clay Horizon pH (moi kg-') (g kg*') (g kg-') (g kgmL) (%) (% (%) At 7.4 39.3 84.5 7.5 0.76 3.6 69.1 27.3 B 7.9 30.8 41.9 3.2 0.78 14.9 60.6 24-5 C 8.6 22.8 7.9 0.6 0.55 33.6 52.2 14.3 t Refers to LDGP.

The transects in Tianzhu-A and Tianzhu-B are fiom southeast to northwest (Appendix-1). The dopes of the study fields are gentle, about 5% in Tianzhu-A and 3% in Tianzhu-B, both are fiom the south down to the north. There are no significant differences in soil pH, CEC, and TOC between the transects in Tianzhu-A and Tianzhu- B (Table 5.9, indicating there is no significant dope effect on soi1 FeniIity in this site. Therefore, the results presented at this combined site only dealt with land use impact on soi1 variables.

Table 5.5. Variation of soil variables in different transects, Tianzhu-A/B.

Transect PH CEC TOC PH CEC TOC

t Values in the same column foiiowed by the same letter are not signiIicantly different at 0.05 probability Ievel according to Tukey's HSD (Tianzhu-A) or T (Tianzhu-B) test. Soil bulk density in LDGP and Cult-8 are lower than other land uses (Table 5.6). Clay content deceased significantly fiom 27% in LDGP to 20% in Cult-41, whiIe sand content increased by 5%, fiom 4% to 9%. Sïlt content remained almost unchangeci.

Table 5.6. Soil physical properties in Tianziiu-AlB. Land use Bulk density (Mg m-') Sand (%) Silt (%) Clay (%) LDGP 0.68 bf 3.6 c 69.1 a 27.3 a MDGP 0.78 a 3.7 c 68.8 a 27.5 a

+ Values in the same colurnn foiiowed by the same letter are not significantly different at 0.05 probability level according to Tukey's HSD test.

To get a reliable conclusion fiom statistic analyses, ail of the data (except bulk density and particle size) were tested for their normal distributions. The descriptive statistics for the soi1 variables are presented in Table 5.7. Table 5.7 indicate that eight of 11 land use-related variables show their ratios of skewness to their wrresponding standard errors are less than 2, or around 2, displaying an approximate normal frequency distribution. These variables are CEC (except Cult-a), TOC, totai N (TN), total P (TP), total K (TK), macrosrganic C (except Cult-8). macro- organic N, and macrwrganic P. Of the three remaining variables (pH, EC and WSC), two show either a very high positive skew (Cuit-8 in EC, for example), or negative skew (Cult-41 in pH). A logarithmic transformation of these &ta failed to approximate a normal distribution in al1 land use pattems. However, a sine transformation made WSC of ail land use patterns follow a no4distribution (Table 5.8). But some land use pattern in soi1 pH and EC are still not normaiiy distriiuted. Table 5.7. Descriptive statistics for soil variables in Tianzhu-AB. Variables Land use Mean Skewness SES? C.V.% RSSES PH LDGP MDGP cuit-8 Cdt-16 Cult-41 EC*:i(dS m*') LDGP MDGP Cult-8 Cult- 16 Cult-4 1 WSC~(cmolkg+') LDGP MDGP C~lt-8 Cult- 16 Cult-4 1 CEC(cmol kg-') LDGP MDGP Cult-8 Cult- 16 Cult-4 1 TOC (g kg*') LDGP MDGP Cdt-8 Cdt- 16 Cult-4 1

f Standard error of skewaess. Ratio of skewness to its standard error. 7 Water-soluble cations. Table 5.7. Descriptive statistics for soi1 variables in Tianztiu-A/E3 (cont'd). Variables Land use Mean Skewness SESt C.V.% RSSEf Total N (g kg-') LDGP 7.49 -1.28 0.59 10.3 -2.2 MDGP 7.46 0.04 0.38 5.9 O. 1 Cult-8 6.22 -1.20 0.50 8.6 -2.4 Cdt-16 5.04 0.57 0.69 12.2 0.8 Cult-41 3.80 0.3 t 0.5 1 6.0 0.6 Total P (g kg') LDGP 0.76 0.29 0.64 4.3 0.5 MDGP 0.82 0.03 0.38 8.0 O. 1 Cuit-8 0.78 -1.13 0.50 2.8 -2.3 Cdt- 16 0.90 -0.02 0.69 4.6 0.0 Cult-41 0.92 1.O8 0.5 1 7.7 2.1 Total K (g kg") LDGP 15.13 0.59 O. 85 4.4 0.7 MDGP 15.3 1 0.36 0.44 2.1 0.8 Cdt-8 Cult- 16 Cult-4 1 Macro-organic LDGP c (g kg'') MDGP Cult-8 C~lt-16 Cult-41 Macroiirganic LDGP 1.26 0.50 O. 54 19.0 0.9 N (g kg-') MDGP 1.32 -0.10 0.29 23.1 -0.3 Cdt-8 0.72 0.88 0.37 18.0 2.4

f Standard error of skewness. $ Ratio of skewness to its standard error- Table 57. Descriptive statistics for soi1 variables in Tianzhu-A/B (cont'd). Variables Land use Mean Skewness SES? C.V.% RSSE: Macro-organic LDGP 0.078 0.89 0.54 35.9 1.7 P (i3 kg-') MDGP 0.084 0.62 0.29 29.8 2.1 Cuit-8 0.059 0.56 0.37 18.6 1.5 Cdt- 16 0.071 4.22 0.60 19.7 -0.4 Cdt-4 1 0.089 0.54 0.45 29.2 1.2

-f Standard error of skewness. $ Ratio of skewness to its standard mot,

Table 5.8. Descriptive statistics of soi1 variables after sine transformation, Tianzhu-AlB. Variables Land use Mean Skewness SES? C.V.% RSSE:

PH LDGP MDGP Cult-8 Cdt- 16 Cuit-4 1

EC 1:l (dS me') LDGP MDGP Cult-8 Cult- 16 Cult-4 1 WSC (cm01 kg-') LDGP MDGP Cult-8 Cult- 16 Cult-4 1

-- t Standard error of skewness. Ratio of skewness to its standard error. Figure 5.1 and 5.2 illustrate the fiequency distribution before and after data transformations for water-soluble cations fiom the land use patterns of MDGP in Tianzhu-AB. It shows that a long tail (high positive skew) is observed before data transformation (Figure 5. l), but it tum an approximate normal distribution after the data are transformed (Figure 5.2).

Water-soluble cations (mol kg*') Figure 5.1. Frequency distribution of water-soluble cations fiom MDGP,Tianzhu-A/B.

Water-soluble cations

Figure 5.2. Frequency distribution after a sine transformation of water- soluble cations fiom MDGP,Tianzhu-NB. According to above statistics analyses, soil pH and soi1 EC are compared using nonparametric analyses, while the remaining determinations are discussed using parametric method. Soil DHis significantly impacted by land use patterns (Table 5.9). The effects of land use patterns on soi1 pH values are compared using Kmskal-Wallis test. It is found that when native pasture is brought into crop production, soil pH significantly increases &er eight years' cultivation. Increasing years of cultivation cause fùrther pH rise. This cm be explaineci by topsoil 105s by erosion with cultivation, so that subsoils with high pH (Table 5.4) are brought up and mixed with the plough layer.

Table 5.9. Land use partems and soii pH in Tianzhu-AlB.

-. Number of - -

LDGP 18 7.4 7.4 ct 3 9 MDGP 70 7.5 7.5 c 48

t Values in the same column followed by the same letter are not significant1y dierent at 0.05 probability lwel according to Kniskal-Wallis test. $ Sample TZB 1- 12 was missing during shipment.

Soil EC is shown in Table 5.10, The EC decreased when pasture was put into crop production. Compared to LDGP, EC dropped by 6%, 16% and 20% on average for 8, 16 and 41 years' cultivation, respectively (Table S. IO). Soi1 EC of cultivated land was significantly lower than that of either LDGP or MDGP. The variance of EC from

MDGP was significantly higher than that fiom LDGP (F = 3.46, > Fo.05)' indicating Pasture degradation may develop the patchiness of hi@ diinity

Generally speaking in dis study, soiIs are considered salinized if EC2:l is over 1.0 dS m-'. Plant growth on those soils is usually retarded. However, soii EC in LDGP and MDGP is around 0.5 dS m", and soluble Ca and Mg are dominant cations (?able S. 1 1). Therefore, the relatively higher soluble cations in Pasture soils benefit plant growth, particuiarly the greater percentage of K.

Table 5.10. Land use patterns and soi1 EC2,ivalues in Tianzhu-A/B.

- -- -- Mean Land use Mean Rank Median (dS m.') % LDGP 0.50 1O0 105 0.51 a+ MDGP 0.53 1 06 117 0.53 a

+ Values in the same colurnn followed by the same letter are not sigdcantly diierent at 0.05 probabiiity level according to ffiskal-Wallis test.

Table 5.1 1. Composition of water-soluble cations in Tianzhu-AB.

Land use (mol kg-') LDGP 1.17 af 67.9 a 21.0 a 3.9 a 7.2 b MDGP 1.20 a 66.6 a 20.2 a 3.5 a 9.7 b

- -~ ~ ~ -~ ~~~ ~~- t Values in the same column followed by the sarne letter are not significantly dierent at 0.05 probabiiity level according to Tukey's HSD test.

As show in Table 5.1 1, the proportion of soluble Na increases Erom 7% in LDGP to 22% der 41 years' cultivation (Cult-41). High concentrations of soIuble Na are usually associated with poor soii structure and poor petmability, resulting in low plant production and causing soi1 erosion and degradation. -&y -&y is defined as "the sum of total of the exchangeable cations that a soi1 can absorb (Brady and Weil, 1999). The summation of ml- extracteci Ca, Mg, K and Na was used in this study because none of the soiis were acid. Table 5.12 presents the CEC and individual cations in different land use patterns. As discussed praiously, parametric statistic analyses are conducted for assessing the impacts of land use patterns on soi1 CEC using Tukey's procedure for multiple comparisons of means at a 0.05 level of significance (Cambardella and Elliott, 1994; Steel et al., 1997).

Table 5.12. The impacts of land use on soi1 CEC and WC1-extracted cations in Tianzhu- AlB.

Land use CEC (cmol kg*') Ca (%) M!3 (%) K (%) Na (%) LDGP 39.3 a? 83.0 a 14.7 a 1.8 a 0.5 b MDGP 39.8 a 83.0 a 14.3 a 2.0 a 0.7 b Cult-8 37.1 b 83.6 a 14.7 a 1.2 b 1.0 ab Cult-16 35.0 c 82.3 a 13.6 a t.8 a 1.1 a Cuit4 1 31.7 d 80.3 a 14.2 a 2.2 a 1.3 a

+ Values in the same colurnn followed by the same letter are not sigruficantly differem at 0.05 probability lwel according to Tukey's HSD test.

Table 5.12 indicates that thme is no significant difference of CEC between LDGP and MDGP, however, soi1 CEC significantly decreased with cultivation iength. It is also noted that cultivation of pasture resulted in a signiticant increase of soil exchangeable Na. Soil CEC is highly correlated with soil clay content (Figure 5.3) and soi1 total organic C (Figure 5.4). Soil ciay content (r = 0.97**) is more closely related to CEC, compared to TOC (r = 0.90**). Clay content is also significantly correlated with TOC (r = O.go**). Soil total oraanic C. total N. P and K are major pools For supplying plant nutrients, particulariy for N and P in pasture soiIs. Soil organic matter possesses geat capacity to absorb cations. Soi1 organic C decmes with pascure degradation and cultivation. The more years' cuitivation, the Iess TOC remains. Total organic C fiom MDGP dropped by 5% (p = 0.20) compareci to LDGP (Table 5-13). Li (1998) similarty indicated that overgrazing for 40 years in Lynnrs chkltsls pasture resulted in a 12.4% C decline. If pasture was converted into crop fields, TOC declined sharply. For instance, TOC decreased about 55% afler 41 years' cultivation in

1O 20 25 30 Clay content (%)

Figure 5.3. The relationship between soi1 CEC and clay content in Tianzhu-A/B.

O 20 40 60 80 100 120 Soi1 organic C (g kg-')

Figure 5.4. The reiationship between soi1 TOC and CEC in Tianzùu-NB. soils, Lilienfein et al. (2000) also found that conventionai tillage was 28% higher in total P than native savannah soils due to regular fertiüzation. Data in Table 5.13 also showed that total K did not change within shorter period cuItivation, compared to pasture soils. However, longer cultivation raised total K to a higher level. This was probably due to animal wastes that were applied in earlier years. Mvare defined in this study as C, N and P obtained fiom the sand-sized (0.05 to 2 mm) tiaction of organic matter. The organic matter in this fraction prhuily comprises plants debris, recognized by its cellular structure, but may also contain fungal hyphae, spores, seeds, charcoal, and animal remains (Gregorich and Ellert, 1993). Therefore, macro-organic nutrients are easily decomposed by rnicroorganisms to release nutrients for plants. Table 5.14 presents the influences of land use on macro-organic nutrients in Tianzhu-AlB.

Table 5.14. Land use patterns and macro-organic nutrients (g kg-') in Tianzhu-AIB. Land use Macrosrganic C Macro-organic N C/N Macro-organic P LDGP 20.3 ai 1.26 a 16.1 a 0.079 ab MDGP 18.9 a 1.32 a 14.3 b 0.084 ab Cuit-8 9.2 b 0.72 b 12.8 c 0.059 c Cuit- 16 8.4 b 0.66 bc 12.7 c 0.072 bc Cult-4 1 7.1 b 0.52 c 13.7 c 0.088 a t Values in the same column followed by the same letter are not significantly different at 0.05 probability level according to Tukey's HSD test.

Cultivated fields usually contain 1.0 to 3.0 g kg" of macro-mganic matter, but grassland mils with relatively slow decomposition rates contain considerably more (30 to 100 g kg-') (Gregorich and Ellert, 1993). Table 5.14 shows maao-organic C in Tiaazhu-A/B ranges fiom 18.9 to 20.3 g C kg" in Pasture, and 7.1 to 9.2 g C kg-' in cultivated fields. If organic C is converted to organic matter by multiplyiag a factor of 1.724 (Nanjing Soi1 Institute, 1978), pasture contains about 32.6 to 35.0 g kg-' of macro- organic matter, which fds in the range reported by Gregorich and Ellert (1993). Although MDGP showed a slight drop in rnacro-organic C, compared to LDGP, no significant decrease was observed, However, macro-organic C in pasture was significantly higher than that in cultivated fields. The influences of land use on macro-organic N are almost the same as on macro- organic C, except significant decease in Cuit41 when compared to Cult-8. Soil macro- C/N ratio decreased significantIy when pasture was degraded. Cultivation fiinher narrowed this C/N ratio considerably. This could be attributed to higher amount of plant residue in pasture soils. Soil macro-organic P also declines when pasture is cultivated, except that fiom Cult-4 1.

5.1.1.2 Tianzhu-C The landfonn in Tianzhu-C was different fiom those in Tianzhu-A and Tianzhu-B. A larger and steeper dope (37%) was sampled in this site. Therefore, the results are separately presented in this study. A total of 40 soi1 samples were collected dong a transect. The est four at the top slope and Iast two samples at the very bottom were HDGP, the remaining 34 samples were divided into three groups such as shoulders, midslopes and footslopes. Shaulders included soi1 samples fiom TZC 1-5 to TZC 1-1 6, midslopes fiom TZC 1-17 to TZC 1-27, and footslopes fiom TZC 1-28 to TZC 1-38 (Appendix-I). Al1 of the data fiom Tianzhu-C are normally distributed (partly listeci in Table 5-19, and parametric statistical analyses are used. Table 5.16 shows the impacts of pasture and slope position on soil fertility in Tianzhu-C. Compared to HDGP,soil pH increases significantly in the cultivated fields, regardless of dope positions. Shoulders are more erodible, resulting in a slight higher pH value than other dope positions. The lowest pH value is found in footslopes. Soil EC did not show any diffetences between three siope positions, and HDGP was not significantly different hmthe others. nie CEC in HDGP averaged 29.4 cm01 kgm', about 1.6, 2.6, and 2.7 cm01 kg*' higher than that in footslopes, shoulders, and midslopes, respectively. Among three cultivated siope positions, the footslopes had a sisnificantly higher CEC than the other two positions. Table 5.15. Descriptive statistics of selected variables in Tianzhu-C. Variable Land use Mean Skewness SESt C.V.% RSSES PH HDGP 7.72 1.23 0.85 2.2 1.5 Shoulder 8.01 1.16 0.64 1.9 I.8 Midslope 7.96 1.60 0.66 1.O 2.4 Fwtslope 7.93 1.13 0.66 0.4 1.7 ECt:i(dS m-') HDGP 0.4 1 0.51 0.85 11.3 O. 1 ShouIder 0.39 1.25 0.64 19.3 2.0 Midslope 0.35 0.34 0.66 10.9 O. 5 Footslope 0.38 0.85 0.66 9.3 1.3 t Standard error of skewness; $ Ratio of skewness to its standard error.

Table 5.16. Land use and soi1 chernical properties in Tianzhu-C. Soi1 variables Unit HDGP ShouIder Middope Footslope PH 7.72 bt 8.01 a 7.96 a 7.92 a C.V.(%) 2.2 1.9 1.O 0.4

Eck1 dS m-' 0.41 a 0.39 a 0.35 a 0.38 a C.V.(%) 11.2 19.3 10.9 9.5 CEC mol kg-' 29.4 a 26.8 c 26.7 c 27.8 b C.V.(%) 3.3 2.4 2.3 2. I TOC B kg-' 36.8 a 22.0 b 21.5 b 25.2 b C.V.(%) 11.8 26.0 14.5 9.5 TN 3 kg-' 3.51 a 2.19 c 2.48 bc 2.83 b C.V.(%) 19.9 7.2 9.0 7.0 CN 10.5 a 10.0 a 8.7 a 8.9 a TP s ML 0.79 b 0.68 c 0.78 b 0.93 a C.V.(%) 12.4 16.5 9.6 7.8 TK S kg-' 16.5 ab 15.3 c 16.0 bc 16.9 a C. V.(%) 2.8 2.5 4.3 2.1 t Values in the same row foiiowed by the same letter are not si@cantiy different at 0.05 probability level according to Tukey's HSD test. Soil total organic C demonstrated the same trend as soi1 CEC. It was 37 g kg-' in the HDGP,or 46% higher than the footdopes. Aithough total N in HDGP at Tianzhu-C was much lower than that in Tianzhu-AIB due to soil erosion, the highest total N concentration was observed in HDGP compared to cultivated fields, indicating cultivation caused significant loss of soil N. Total N concentration also changed with slope positions. Shoulders are significantly lower in total N than the footslopes, while midslopes lie in between. Soil total P increased significantly fiom shoulders to footslopes. This is most likely due to soi1 eroded Erom shoulders and deposited on footslopes. Soil total K showed the same trend as total P. The highest concentration was found in footslopes. Land use and slope positions also anected soi1 nutrients in the macro-organic fractions of mil. Table 5.17 shows HDGP is high in both macro-organic C and N, significantly higher than the midslopes and shoulders, but is similar to the levels found in footslopes. Along the cultivated dope, rnacrosrganic C and N are the highest in footslopes, and the lowest in shoulders. Soil C/N ratio is not significantly afTected by land use and dope positions. The highest macro-organic P is observed in footslopes, it is even higher than that in KDGP. Soi1 deposition and P fertilization might be responsible for the higher amount of macro-organic P in footslopes.

Table 5.17. Land use patterns and maawrganic nuuients (g kg") in Tiaruhu-C. Land use Macro-organic C Macrosrganic N C/N Macro-organic P HDGP 7.27 at 0.49 a 14.8 a 0.043 b Shoulders 2.37 c 0.17 c 13.9 a 0.032 b Midslopes 4.11 bc 0.29 bc 14.2 a 0.051 b Footslopes 5.60 ab 0.42 ab 13.3 a 0.075 a

f Values in the same colurnn foiiowed by the same Ietter are not significantly different at 0.05 probability Ievel according to Tukey's HSD test.

To determine the effect of cultivatioa time on TOC, aII data fiom Tianzhu-A43 and Tianzhu-C were analyzed. Figure 5.5 shows within the tested Iength (48 years), soil TOC declines relatively rapid at the beginning years, and levels off with the increase of cultivation Iength (MDGP as 0.1 year).

I O 10 20 30 40 50 60 l Cultivauon years in Tianzhu

Figure 5 S. The relationship between soi1 TOC and cultivation years in Tianzhu.

5.1.1.3 Shandan-A There are two sites in Shandan Horse Stud Station, Shandan-A and Shandan-B. These sites are about 10.3 km apart. Shandan-A is located at 3,040 m ASL. whereas Shandan-8 is 200 m lower than Shandan-A. Precipitation in Shandan-A (400 mm annuaiiy) is higher than that in Shandan-B (356 mm). In Siundan-A, three levels of degraded pasture were observed along a transect, niunely, LDGP, MDGP and HDGP. Detailed information on field layout and soi1 profile is presented in Appendix-1. As shown in Table S. 18, LDGP has the highest plant cover and plant density. As in Tianzhu-A/B (Table 5.61, soiI bulk density was similar for al1 degraded pastures, but dtivation increased bulk density by 0.1 Mg m-3 in Shandan-A (Table 5.19). The difference between pasture and cultivated fields was probably due to heavier fm machines used in the Shandan Stud Station and lower soiI TOC. No obvious dierences in particle size fiactions were observed. Table 5.18. Basic information on degraded pasture in Shandan-A. Pasture Plant cover (%) Plant densityi. NDSS LDGP 100 217 7 MDGP 95 205 7 HDGP 60 187 6 t Number of plants per 0.25 m2. $ Number of plant species inside of the quadrat (0.25 ml).

Table 5.19. Physical properties of tested soils in Shandan-A. Land use Bulk density (Mg m-') Sand (%) Silt (%) Clay (%) LDGP 0.72 b+ 3 a 70 a 27 a MDGP 0.74 b 3 a 69 a 28 a HDGP 0.74 b 5 a 69 a 26 a Cult-6 0.82 a 3 a 70 a 27 a B horizon 9 71 20 + Values in the same coiumn followed by the same letter are not significantly different at 0.05 probability level according to Tukey's HSD test.

Data in Table 5.20 indicate that soi1 pH significantly increases when LDGP becomes HDGP. Cultivation increases soi1 pH by 0.15 units, and pH of Cuit-6 is significantly higher than al1 three degraded pastures. Soi1 EC does not change very much, excepting HDGP that is higher than the others. HDGP also has the highest C.V., indicating large variations among the samples. The F test confimts the variance of EC fiom HDGP is statisticaily higher than that fiom MDGP or. LDGP, suggesting HDGP has a hi@ risk to develop patchiness with higher saiinity. The same trends are found for soi1 CEC, OC, total N and total P, Le., there are no significant differences between the three different classes of degraded pastures. However, six years' cultivation causes a marked difference for CEC, TOC, total N and total P. The largest variability for al1 of the determinations is found in HDGP,reflecting the patchiness of this pasture cover. About 0.083 g kg" soi1 P was contributed &om the application of P fenilber basai on the estimation in Appendix IV-C. The actual total P difference between LDGP and

Cult-6 was (0.74465) 4-09g P kg-L. The si@~cant increase of totd P in Cdt-6 WU therefore attributed to fertilizers. Since no organic fertilizers (animal wastes) were applied on this site, the estimation of the fertilizer contribution to total P built-up in the soil was very close to soil determinations.

Table 5.20. Land use patterns and soi1 chernical properties, Shandan-A. Soi1 variable Unit LDGP MDGP HDGP Cuit-6

C.V.(%) ECz:i dS m" C.V.(%) CEC cmoi kg-' C.V.(%) TOC g kg-' C.V.(%) TN S kg-' C.V.(%) C/N TP g kg-' C.V.(%) TK g kg-' C.V.(%)

t Values in the same row followed by the same letter are not significantly different at 0.05 probabiiity level according to Tukey's HSD test.

Although soil TOC and total N were not signiftcantly affected by land use, soil C/N ratio declined considerably when pasture was heavily degraded. Six years' cultivation rdted in a same CM ratio as HDGP. The influence of land use on ml-extracteci cations and water-soluble cations are shown in Table 5.21 and Table 5.22, respectively. ExchangeabIe Ca and Mg did not show any significant differences, but proportion of Na increased when pasture was cultivated. The exchangeable K was significantiy higher in HDGP than other land uses. There are no definite trends observed fiom LDGP to HDGP, and then to Cult-6 for proportion of water-soluble Ca, Mg, K and Na concentrations, indicating short-term cultivation did not result in significant differences of water-soluble cations.

Table 5.21. Land use patterns and individuai NKCI-extracted cations, Shandan-A. Land use Total (cm01 kg-') Ca (%) Mg (%) K (%) Na (%) LDGP 37.1 at 83.8 a 14.4 a 1.4 b 0.3 b MDGP 37.0 a 83.7 a 14.4 a 1.5 b 0.3 b HDGP 36.9 a 82.6 a 14.6 a 2.4 a 0.4 ab Cult-6 35.4 b 85.5 a 13.1 a 1.0 b 0.5 a

+ Values in the same column followed by the same letter are not significantly different at 0.05 probability level accordiig to Tukey's HSD test.

Table 5.22. Land use patterns and individuai water-solubte cations, Shandan-A. Land use Total (cmol kg*') Ca (%) Mg (%) K (%) Na (%) LDGP 1.3 ab+ 63.3 a 23.3 a 2.4 b 11.0a MDGP I .2 ab 67.0 a 20.6 a 2.6 b 9.7 a HDGP 1.6 a 60.6 a 22.0 a 4.4 a 13.0 a Cultd 0.9 b 67.7 a 18.9 a 1.2 b 12.2 a + VaIues in the same column followed by the same Ietter are not significantly dEerent at 0.05 probabiiity level according to Tukey's HSD test.

Soi1 nutrients in macro-organic fiactions play a vital roie in supplying plant nutrients, especially for N and P. Data in Table 5.23 show that macro-organic C, N and P dropped significantly when pasture was cuitivated, whereas pasture degradation did not cause large differences for macro-organic C, N and P. However, after pasture was heavily degraded or cultivated, a narrower soit C/Nratio was observed. Both of the two transects crossed a strip where the top 10 to 12 cm of soiis were removed in 1976 to build a wall for fencing animals (Appendk-l). A total of 11 sp&d soi1 samples were taken from the strip, and another two soi1 samples were coliected fiom the top of the wall cded waii-samples (Table 5.24). No significant differences were observed between special sampIes and LDGP, except a significant C Ioss in the special samples (Table 5.24). Compared to Cuit-6, the special samples resulted in lower pH and higher totai N. Higher amount of totai P was obtained in Cult-6, reflecting the contribution of P fertilizer addition, but no significant differences for EC, CEC, TOC, total N and total K. This means, to some extent that six years' cuitivation was equivalent to the loss of top 10 to 12 cm soil.

Table 5.23. Efféct of land use on macro-organic nutnents (g kg"), Shandan-A. Land use Macro-organic C Macrosrganic N CM Macro-organic P LDGP 1 1.97 at 0.74 a 16.2 a 0.046 ab MDGP i 1.58 a 0.74 a 15.6 ab 0.049 a HDGP 11.54 a 0.77 a 14.9 b 0.057 a Cult-4 5.52 b 0.38 b 14.5 b 0.039 b + Values in the same column followed by the same letter are not significantly different at 0.05 probability level according to Tukey's HSD test.

Table 5.24. Cornparison between special samples and Cult-6, Shandan-A. Soi1 variables Unit Cdt-6 Special samples LDGP Wd-samples PH 7.73 at 7.64 b 7.58 b 6.94 c ECz I dSm-l 0.4b 0.46 b 0.45 b 1.89 a CEC mol kg-' 36.4 b 36.7 b 38. I b 45.7 a TOC g kg-' 47.6 c 51.9 c 59.5 b 105.0 a Total N gicg-' 4.66~ 5.23 bc 5.48 b 8.75 a Total P g kg" 0.74 a 0.67 b 0.65 b 0.75 a Total K S kg-' 15.5 a 15.3 a 15.3 a 14.1 b f Values in the same row followed by the sarne letter are not significantly different at 0.05 probability level according to Tukey's HSD test.

The most noticeable is higher TOC in the wall-samples, indicating topsoil is high in TOC. Soi1 pH and totai K are significantly lower in the wall-samples than those in the nearby fields. The lower total K in the wall samples is probably due to higher organic matter in the topsoil, while dmost al1 of K is in mineral hctions, not in organic matter. The totd P concentration in the wall is significantly higher than that in special samples and LDGP, but shows no diflérence with Cultd. Higher arnount of total P in the wdi indicates P accumulated in the topsoil during the course of soi1 development.

5.1.1.4 Shandan-B In Shandan-B, only rnoderarely degraded pasture was found for cornparison with cultivated fields. The pasture had 80% ground cover, six plant species and 70 individuai plants pn 0.25 m2. Along two transects, three différent crop fields were crossed (Appendix-9. These fields had been cultivated for one, 13 and 29 years, respectively. Basic infonnation on the soi1 physical properties is presented in Table 5.25.

Table 5.25. Basic information on tested soils in Shandan-B. Land use Bulk density (Mg m-3) Sand (%) Silt (%) Clay (%) MDGP 0.99 at 2 a 74 a 24 a Cult-l 0.94 a 3 a 73 a 24 a CuIt- 13 1.01 a 3 a 74 a 23 a Cult-29 0.94 a 2 a 74 a 23 a B horizon 2 71 27

t Values in the same column followed by the same letter are not significantiy différent at 0.05 probabiiity level according to Tukey's HSD test.

Bulk density is dmost the same among these four land use patterns. Because clay content in B horizon is about the same as in A horizon, topsoil erosion and cultivation had no impacts on the sand fraction in this site. This dfiers from the results at Tianzhu- AB, while a considerable increase in the sand fiaction was found afler pasture was cultivated because of high fiaction of sand in subsoil in Tianzhu-M. The influences of land use on mil fertility in Shandan-B are presented in Table 5.26. Soil pH values in a11 hur land uses are al1 around 8. Soil EC is much higher than those in Shandan-A, Tianzhu-AB, and T'du-C. Soil EC hmMDGP, Cult-13 and Cult-29 are relatively higher tbfiom the newly cultivated Cult-1. Land of MDGP, with EC vahe of I .95 dS III-', is regardd as moderately salinized soil, whereas Cult-13 and Cult-29, with EC values over 2.0 dS cm-', are broadly classified as severely saiinized (Henry et ai., 1987).

Table 5.26. Land use patterns and soi1 chemicai properties in Shandan-B. Soi1 variable Unit MDGP Cuit- 1 Cult- 13 Cult-29

PH 8.01 a? 8.02 a 8.05 a 7.96 b C.V.(%) 0.7 1.5 1.1 1 .O EC2:r dS m-' 1.95 b 0.76 c 2.61 a 2.35 ab C.V.(%) 30.0 35.6 33.9 36.3 CEC mol kg-' 32.5 a 31.1 b 32.8 a 30.8 b C.V.(%) 6.3 4.8 6.9 10.2 TOC g kg-' 32.7 a 32.8 a 30.2 b 28.5 b C.V.(%) 6.2 6.4 7.5 6.8 TN 8 kg'' 3.39 a 3.51 a 3.11 b 3.06 b C.V.(%) 3.5 7.0 4.9 3.2 C/N 9.6 a 9.3 a 9.7 a 9.3 a TP 8 kg" 0.80 b 0.80 b 0.88 a 0.89 a C.V.(%) 3.0 3.1 3.9 5.2 TK S kg*' 16.5 a 16.6 a 16.3 b 16.7 a C.V.(%) 0.9 1.4 2.6 1.9

------f Values in the same row followed by the same letter are not significantly different at 0.05 probability level according to Tukey's HSD test.

Since the climate is retatively dry in this site and salinity is relatively high, the relationship between land use and soi1 fertiIity might be masked by these parameters. Nevertheles, some of the previously observed trends were confirmed. There are no dear trends for soi1 CEC changes. However, Cult-29 is significantly lower in CEC than that in MDGP and Cult-13. Soil arec C and N followed the same trends, no signifiant differences are found between native pasture and the newly cultivated field. However, increasing cultivation years significantly reduced soi1 organic C and total N. Soil total P concentration increased when pasture was cultivated for a longer time. The estimation in Appendix IV-D clearly showed that the significant increase of 0.08 g P kg-' total P in Cult-13 was from addition of P fertilizer and rapeseed meals. Calcium is the dominant cation, followed by Mg, Na and K (Table 5.27). Land use of Cult-13 has a lower proportion of Ca and K, but higher proportion of Na, compared to MDGP. No ciear trends of effect of cultivation on individual proportion of WCI- extracteci cations are obsewed at Shandan-B.

Table 5.27. Land use patterns and NHsCl-extracted cations. Shandan-B. Land use Total (mol kg-') Ca (%) Mg (%) K (%) Na (%) MDGP 32.5 a? 64.4 b 26.8 ab 2.3 b 6.5 b Cult- l 31.2 b 71.1 a 22.6 c 3.0 a 3.3 c Cult- 13 32.8 a 62.2 c 28.5 a 1.9 c 7.4 a Cult-29 30.8 b 66.0 b 25.8 b 2.2 b 6.0 b + Values in the same column followed by the same letter are not significantly different at 0.05 probability level according to Tukey's HSD test.

Table 5.28 indicates that Na is the dominant water-soluble cation in al1 of four land use patterns. It is also noticeable that water-soluble cations in Cult-1 were significantly lower than in the other land uses. Further cultivation significantly increased water- soluble cations. The highest absolute amount of water-soluble Na was found in Cult-13 (3.1 cm01 kgs1),which is sienificantly higher than that in MDGP (2.3 cm01 kgeL).

Table 5.28. Land use patterns and water-soluble cations, Shandan-B. Land use Total (cmol kg-') Ca (%) ~g (%) K (%) Na (%) MDGP Cult- 1 1.6 c 29.0 a 18.0 c 3.4 a 49.6 b

t Values in the same column foiiowed by the same letter are not significantly different at 0.05 probability level according to Tukey's HSD test. The compositions of water-soluble anions are presented in Table 5.29. It indicates that sulfate (~04~3and C1' are main anions in this site. Therefore, the dominant water- soluble salt is sodium sulfate (Na2SOs) since Na is more tha. 50% in cation composition and ~04"is over 50% in anion composition.

Table 5.29. Land use patterns and water-soluble anion compositions.

cm01 kg1 % cm01 kg-' % cm01 kg*' %

Cult- 1 0.60 a 38.2 0.47 c 29-9 0.50~ 3 1.8 Cult- 13 0.55 ab 9.7 1.70 a 29-9 3.43 a 60.4

) Sulfate was calculated by the difïerence of total exchangeable cations and (HcO3-+Cl-). Values in the same column followed by the same letter are not signficantly different at 0.05 probability level according to Tukey's HSD test.

Once Pasture was converted into crop fields, exchangeable sodium percentage (ESP) increased in 13 years' cultivation (Table 5.30). However, ESP did not change with 29 years' cultivation. Since sodium adsorption ratio (SM) in al1 land use patterns is below 13, pH value is less than 8.5, but ECklis higher than 2 dS cm-'. these land use patterns faIl into saline soil accordiig to Brady (1990).

Table 5.30. The relationship between land use and soil SAR and ESP, Shandan-B. Land use PH EC21 (dS mm') SAR ESP (%) MDGP 8.01 af 1.95 b 2.5 ab 6.5 b

Cult-29 7.96 b 2.35 ab 2.3 b 5.9 b ? Values in the sarne column foliowed by the same letter are not significantly cliffereut at 0.05 probability level according to Tukey's HSD test. Macro-organic C was the lowest in Cult-29, indicating longer cultivation decreased both TOC (Table 5.26) and labile organic C (Table 5.31). Macro-organic N and P remained unchanged, except higher amount of macrwrganic P in Cult-29. Soil macro- C/N declined significantly when pasture was cultivated. This came to the same conclusion as that in Tianzhu-A/B and Shandan-A

Table 5.3 1, The impact of land use on macrosrganic nutrients (g kg-'). Shandan-B. Land use Macro-organic C Macro-organic N CM Macro-organic P MDGP 5.18 a? 0.34 a 15.2 ab 0.070 b Cuit- l 5.19 a 0.33 a 15.7 a 0.078 b Cult-13 4.48 ab 0.30 a 14.9 b 0.092 b Cult-29 4.31 b 0.3 1 a 13.9 c 0.13 a t Values in the same column foliowed by the same letter are not significantly difrent at 0.05 probability level according to Tukey's HSD test.

in general, the impacts of land use patterns on soi1 Fertility are not as obvious in Shandan-B as in Tianzhu-A/B and Shandan-A. This is probably due to higher salinity, drier climate, and same particle ûactions in plough layer &er cultivation, which obscured soii fertiiity changes during cultivation.

5.1 -3 Results fiom regional scaie sampling A total of 72 soil samples were analyzed on regional scale. Among those samples, 39 were fiom different classes of degraded pastures and 33 were hmcultivated fields. To compare the impacts of land use patterns on soil fertility, and to make it possible to compare the results with those on locai scaies, six land use categories are distinguished: LDGP: lightly degraded pasture, MDGP: moderately degraded pasture, HDGP: heavily degraded pasture, Cl-10: crop fields with cuitivation length between 1 and 10 years, Cl 1-30: crop fields with cuitivation length between 11 and 30 years, C3 1-50: crop fields with cultivation length between 3 1 and 50 years. Table 5.32 shows the impacts of land use patterns on soi1 chemical properties. In general, C.Vs. obtained f?om measurements on regionai scaie are larger than those tiom local scale. This is logicai due to variations in both ecological parameters and soi1 types between the locations. However, clear trends in the relationship between land use patterns and soi1 fertility were found.

Table 5.32. Land use patterns and soi1 chernical properties on regional scale. # of Soi1 pH ECw CEC Land use sarnplest C.V.(%) dS mm' C.V.(%) cm01 kg*' C.V.(%) LDGP 11 7.6 b$ 4 0.17 b 17 29.0 a 20 MDGP HDGP 17 7.8 ab 4 0.27 b 97 24.0 ab 26 CI-IO 13 7.9 ab 2 0.33 b 57 23.7ab 28

f No soil samples were taken lÏom the quadrats of LDGP and MDGP in Tianzhu- A/B because soi1 samples were already collected in 1997. The quadrats at these two sites were used only for identifjing and counting the number of plant species. Therefore, a total of 39 soi1 sarnpies were statistically analyzed tiom the quadrats. However, al1 of the quadrats were used for data analyses when evaluating the gras degradation on plant species composition in Section 5.4. Values in the sarne column foliowed by the same letter are not significantly dEerent at 0.05 probability level accordiig to Tukey's HSD test.

Soi1 pH increased when pasture had been cultivated for more than 30 years (Table 5.32). However, no significant differences were obtained for three levels of degraded pasture. The largest C.V. was found in EC, similar to results at the iocal scale. When pasture was converted to crop fields, soil EC increased, wbile soil CEC declined. The Wuence of land use on soi1 TOC and TN is not staîistically significant between different classes of degraded pasture due to large C.V. in TOC and TN, aithough TOC and TN in HDGP are 33% and 2% lower than those in LDGP (TabIe 5.33). However, significant merences between LDGP and crop fields with over 10 years' cultivation are found. No significant differences in total P are observed between different land uses.

Table 5.33. Effect of land use on TOC, TN, and TP on regional scale. Soi1 TOC Soi1 TN CM Soi1 ïP Land use (g kg*') C.V.(%) (g kg*') C.V.(%) (g kg-') C.V.(%) -- LDGP 60.8 a? 47 5.8 a 3 5 10.2 a 0.76 a 8 MDGP 44.0 ab 5 8 4.9 ab 42 8.9 a 0.75 a 16 HDGP 40.9 ab 73 4.2 ab 47 9.4 a 0.76 a 12 Cl-10 42.5 ab 33 4.4 ab 23 9.4 a 0.85 a 18 C11-30 27.8 b 29 3.2 b 28 8.7 a 0.84 a 11 C3 1-50 24.7 b 29 2.8 b 3 1 8.8 a 0.79 a 18

7 Values in the same column foiiowed by the same Iener are not significantly different at 0.05 probability level according to Tukey's HSD test.

Chernical properties in macro-organic fractions of soi1 on regional scaie are given in Table 5.34. Both macro-organic C and N declined when Pasture was cultivated. Macrosrganic P concentration in LDGP is significantly higher than that in C3 1-50. Other land use patterns do not show any si@cant differences in Macro-organic P.

Table 5.34. The impact of land use on macrosrganic nutrients, regional scale. Macro-organic C Macro-organic N CM Macro-organic P Land use (8 kg") C.V.(%) (g kg-') C.V.(%) (g kg") C.V.(%) LDGP 13.3 at 69 0.90 a 77 14.8 ab 0.069 a 68 MDGP 9.5ab 99 0.59 ab 106 16.1 a 0.042 ab 93 HDGP 6.7 abc 64 0.48 ab 69 14.0 b 0.045 ab 71

-- -- Values in the same column foiiowed by the same letter are not significantly different at 0.05 probabiiity level according to Tukey's HSD test. Because large variations of soil variables exist among locations (Table 5.39, most of soi1 fertility-related parameters are not significantly different between degradeci pastures when compared across al1 sites (Table 5.22 to Table 5.24). if soi1 variables are analyzed using paired sampie statistics, significant differences in most of soil variables are obtained between LDGP and HDGP, or between MDGP and HDGP (Table 5.36). However, no statisticai differences are found between LDGP and MDGP.

Table 5.35. Mean of selected variables from pasnire soils in different locations. TOC CEC TN TP Location PH s M' moi kg-' S kg" S kg" Luchg 8.0 a+ 21.6 b 16.8 b 2.5 b 0.71 bc Huangcheng 7.4 bc 78.4 a 27.2 ab 6.9 a 0.78 b SHSS 7.9 a 32.9 b 24.7 ab 4.2 ab 0.78 b TGS 7.6 ab 78.1 a 33.0 a 6.9 a 0.76 bc

Nayi 7.1 c 36.6 ab 20.7 ab 3.5 b 0.95 a i. Values in the same column followed by the same letter are not significantly different at 0.05 probabiiity level according to Tukey's HSD test. Table 5.36. Paired sample statistics fiom 18 sites of degraded pastures. CEC TOC TN TP MC) MN? MPt Pair PH mol kg" g kg-' g kg-' g kg-' g kg-' g kg-' g kg-' LDGP- 7.5 3 1.9 76.2 6.9 0.75 16.7 0.091 1. 18 MDGP 7.6 28.8 58.9 6.4 0.74 17.4 0.070 0.84 (4 pairs) NSS NS NS NS NS NS NS NS

LDGP- 7.5 29.9 1 6.1 0.75 ' 14.1 0.069 0.91 HDGP 7.6 26.7 54.7 5.4 0.77 9.4 0.062 0.70 (9WW SDq SD SD SD NS SD NS SD MDGP- 7-6 25.1 45.5 5.0 0.75 10.0 0.044 0.62 HDGP 7.7 24.7 35.1 4.3 0.75 6.2 0.037 0.44 (10 pain) SD NS SD SD NS SD NS NS

+ MC, MN, and MF = macro-organic C, N and P, respectively $ Not significantly different at 0.05 level accordhg to T test. 7 Significantly different at 0.05 leveI accordmg to T test.

5.1.3 Conclusions

The results tiom local scde sampling allow the following conclusions: Significant effects of land use on soi1 fenility parameters at five sites were observed. Soil pH increased when pasture became degraded, especiaily when it was cultivated. Forty-one years' cdtivation increased pH value by 0.5 units in Tianzhu-A/B. About 0.15 unit increases were observed in Shandan-A with six years' cultivaiion. Soil CEC declined significantly when pasnue was converted into crop fields. No signifiant differences were found among different degrees of pasture degradation. Results fiom the Tianzhu site showed that mil CEC dropped fiom 39 cm01 kg" h LDGP to 37, 35 and 32 cm01 kg-' with eight, 16 and 41 years' cuhivation in Tianzhu-AB, respectively. This represented a 19% of CEC decline with 41 years' cultivation. Coarser soi1 and loss of soil organic C by erosion andior rnineralization were responsible for lower CEC in cultivated fields. 3) Soil organic C declined insignificantly when pasture was degraded. However, once pasture was put into crop production, mil organic C dropped sharply. The longer the cultivation, the lower soil organic C. Within 48 years' cultivation soi1 organic C changed following a negative power fùnction, indicating organic C decreased strongly at the beginning of cultivation years, and leveled off with increasing of cultivation time. Results in Tianzhu-AIB, for example, indicated that about one-fourth of 84.5 g TOC kg" was lost within 8 years' cultivation. Another one-fourth of organic C loss would take about another 30 years. Soi1 total N followed the same trends as soil organic C influenced by land use patterns. Soil C/N ratio became narrower when pasture was degraded or cultivated. 4) Soil totaI P remained almost unchanged between different degraded pastures, but addition of P fertilizers either increased total P significantly. 5) Labile macrosrganic C, N and P were significantly reduced when Pasture was cultivated. This trend was not seen at the footslopes in Tianzhu-C and in Shandan- B where special ecological parameters (mil deposition in Tianzitu-C, soi1 saiinity in Shandan-B) were found. 6) Because drier climate and soi1 salinity were encountered in Shandan-B, the relationship between soil fertility and land use patterns was not as obvious as that in Tianzhu and Shandan-A.

Results fiom both local and regional desshowed the same trend for soil fertility changes as the results of land use. Soil TOC and total N declined significantly when pasture was heavily degraded when paired sarnples were analyzed. However, on the average, the magnitudes of land use impacts on soi1 fertility were weakened ,on the regionai scaie compared to those fiom Iocai debecause large C.V. was found on regionai de. 5.2 Effects of land use patterns on soi1 P dynamics As in section 5.1, the influences of land use on soil P dynamics are discussed at both local and regional des.

5.2.1 Results hmlocal seale sampling Every second sample dong the five transects in the two locations was analyzed. ln some cases, dl sarnples dong the whole transect were examined for detailed study.

5.2.1.1 Tianzhu-A, Results tiom Tianzhu-A and Tidu-B are discussed together as these two sites are close to each other. A total of six Pi hctions in Tianzhu-A/' are presented in Table 5.37.

Table 5.37. Land use patterns and soil Pi fractions (mg kg") in Tianzhu-AIB. Land use LDGP MDGP Cdt-8 Cult-16 Cult-41 Resin-P (1) 23.6 bi 20.5 b 19.5 b 24.6 b 42.0 a Bicarb-Pi (2) 20.5 b 18.1 b 20.3 b 22.2 b 33.9 a

(1) + (2) 44.1 b 38.6 b 39.8 b 46.8 b 75.9 a NaOH-Pi 15.1 b 15.2 b 15.1 b 18.6 b 28.9 a DHCLPi $ 140.4 c 163.3 c 160.7 c 281.21 371.3 a HHC1-Pi $ 96.1 a 104.6 a 97.4 a 108.7 a 102.7a Sum-Pi fi 295.7 c 321.7 c 313.0 c 455.8 b 578.9 a Residual-P 72.1 a 73.2 a 70.7 a 66.0 ab 58.9 b

-- - t Values in the same row followed by the same Ietter are not significantly different at 0.05 probabiiity level according to Tukey's HSD test. $ DHCI: Diluted HCl(l.O M), HHCI: Hot HC1 (wncentrated HCI), the same abbreviations are used hereinafter. 7 Sum of Pi fiactions (resin-, bicarb-, NaOH-, DHCI- and HHCI-Pi).

Data in the Tabk 5.37 indicate that LDGP is slightly bigher in bio-available P (resin-P and bicatbPi), although not staàstically significant, compared to MDGP. Cultivation length affects amounts of bio-available P. Both resin-P and bicarb-Pi increase with longer cultivation time, but did not reach the 0.05 statistical significance level within 16 years. However, bio-available P fiom Cult-41 is significantly higher than those fiom Cult-8, Cult-16, and pasture. The increased resin-P and bicxb-Pi resulted with longer cultivation time is probably due to addition of P fertiiizers. As shown in Table 5.37, Pi extracted by 0.M NaOH increased with longer cultivation the (Cult-41). Lilienfein et al. (2000) also pointed out that Iabile inorganic

P extracted by NaOH increased in fertilized system. . Higher amounts of FefAI- associated Pi (the NaOH-Pi fiaction in Table 5.37) in cultivated fields are probably due to mineralization of Po. Calcium-associated Pi increased significantly with cultivation years tiom Cult-8 to Cult-16 and then to Cult-41. Short-term cultivation did not result in an increase of &Pi, compared to LDGP and MDGP. According to the estimation on Appendix IV-E, the most likely sources of higher Ca-Pi in CuIt-16 were 1) mineralition of Po either tiom organic matter or fiom animal wastes, 2) incorporation of subsoil and 3) addition of P fwtilizer. Mineralization of organic matter and animal wastes contributed about 45% to the total increase of Ca-Pi (similar to TOC lost as estimated by mineralization in Appendix IV-A). Incorporation of subsoil and addition of P fertilizer contribute about 3 1% and 24% to &Pi, respectively. The arnount of HHCI-Pi is not significantly af3ected by pasture degradation and cultivation. The sum of total emcted Pi increases with cultivation length, but no significant difference is obtained when LDGP becomes MDGP (Table 5.37). The influence of land use patterns on soi1 Po is shown in Table 5.38. The bicarb- P, which has been shown to be relatively labile and actively cyciing in studies on temperate soils (Tiessen et ai., 1992), declines significantly when pasture is cultivated (Cult-16 and Cult-41). The soil Po tiaction extracted with NaOH was reduced significantly hmLDGP to Cult-8 and was nearly halved in Cuit-41, indicating a considerable amount of soil organic P was mineralized during cultivation. The more stable fraction of Po extracted by HHCL also showed a decline with pasture degradation or cultivation years, dthough short period cultivation (Cult-8 and Cultl6) was not statisticalIy dierent from pasture. The sum of Po decreased significantIy tiom pasture to crop fields that had been cultivated for 16 years or more. About 80% and 64% of the original Po remained after 16 and 41 years' cultivation, respectively. Phosphonis maintaineci in the organic pools may be better pmtecteâ fiom loss through fixation than P flowing through inorganic pools such as cultivated lands.

Table 5.38. Land use pattern and soü P. fractions (mg kg-') in Tianzhu-AIB. Sum-Pot Land use Bicarb-Po NaOH-Po HHCI-Po (mg kg*') (%) LDGP 14.7 bS 174.6 a 141.2 a 330.5 a 1O0 MDGP 17.5 a 172.1 a 135.8 a 325.4 a 98

t Sum of three Po fiactions (biwb-, NaOH- and HHCl-Po). Values in the same column foUowed by the same letter are not significantly dEerent at 0.05 probability level according to Tukey's HSD test.

Although HHCI-extracted Po declined with cultivation length in absolute amount, it increased as a percentage of sum-Po with cultivation years (Table 5.39). This indicates that Po becomes relative more stable, rather than becoming more labile der the Pasture is cropped.

Table 5.39. The proportion (%) of Po fiactions with land use in Tianzhu-AB. Land use Bicarb-Po NaOH-Po HHC1-Po LDGP 4.4 a? 52.8 a 42.7 c MDGP 5.4 a 52.9 a 41.7 c Cult-8 4.3 a 47.9 bc 47.8 ab Cult-16 4.3 a 45.0 c 50.7 a Cult-4 1 4.7 a 44.4 c 50.8 a

+ Values in the same coIumn foUowed by the same letter are not si@cantIy different at 0.05 probability level according to Tukey's HSD test.

Figure 5.6 shows the relative proportion of total P extracted by diEerent extractants- Labile-P in this study refers to sum of those hctions extracted by resin and NaHC03. Labile-P represents about 7-10% of the total extracted P. which is much higher than the 4-5% in tropical soils reponed by Lilienfein et al. (2000). In relative terms NaOH- and HHCl-extracted P declines with Pasture degradation and cultivation time, while the opposite trend was found for DHCI-extracted P. The residual Fiaction also declined, suggesting that this fraction of P may contain a considerable arnount of organic P which declines after long-term cultivation.

Valun in hcsomc row fallawuf by iheumlcaa3111 mx. stgnifiwni. diffcltnt a 0.05 level (Tuke's HSD tat)

Figure 5.6. Relative proportions of extracted P (Pi + Po)in Tianzhu-AlB.

The relative amounts of different forms of P in the soi1 may refiect the stage of soi1 weathering or development (Smeck, 1985). in this mdy, higher proportions of NaOH- extracteci P from LDGP and MDGP do not indicate that Pasture degradation results in more Fa-associated Pi and more weathering because the dominant proportion of this fiaction is in organic form (Table 5.40). The inorganic form of NaOH-extracted P accounts for onIy 8% in LDGP, but 24% in Cult-41, indicating Poaccumulated in FM- Pi and Ca-Pi forms in Cdt-41. Table 5.40. The proportion (%) of Pi in total extracted (Pi +Po) in Tianzhu-AB. Land use NaHC03-Pi NaOH-Pi HHC1-Pi LGDP 58 ct 8 c 40 b MDGP 51 d 8 c 44 ab Cuit-8 61 c 9 bc 40 b Cult-16 66 b 14 b 45 ab Cult-4 1 77 a 24 a 49 a

f' Values in the sarne column followed by the same letter are not significantly different at 0.05 probability level according to Tukey's HSD test.

A significantly higher proportion of NaHCOs-extracted Pi was observed in cultivated land (Table 5.40), indicating this extractant can only be used if Po does not contribute to plant nutrition when bio-availability of P is predicted. The relative arnounts of Pi extracted by NaOH and HHCl were also higher in Cult-41 than those in degraded pasture. Soi1 organic C is highiy correlated with bicarbP, (Pearson r = 0.72**, n = 171, significant at 0.01 level) and NaOH-Po (r = 0.83**), while HHCI-Po is less well correlated with organic C (r = 0,40*, significant at 0.05 level). Macrosrganic C is considered as labile C, it is also highly correlated with bicarb-Po (r = 0.60**) and NaOH- Po (r = 0.63**), but not with HHCl-Po (r = 0.14). This may indicate that NaOH-Po is also a labile fiaction.

5.2.1.2 Shandan-A Data in Table 5.41 show that pasture degradation does not significantly affect Pi fiactions at this site. However, cuitivation with fertilizer added does increase the labile Pi fiactions. Sùnilar results were reported by Lilienfein et al. (2000) for Brazilian soils. Zhang and MacKenzie (1997) ahfound that fertilization rates significantly influenced d soil P fiactions, especidy bicarbPi. By using path analysis, Beck and Sanchez (1994) indicated that Pi extracted by NaOH was a major sink for applied P in fertiliid soi1 while Po was a major source of labile P in unfertilized soi1 during 18 years of crop production in Peru. Results fiom this study revealed that the major@ of added P was transfonned to the Ca-associated form (DHCl-Pi), whereas Pi extracted by NaOH and HHCl were not affécted by addition of fertilizers. The lack of agreement with Beck and Sanchez's (1994) study is because they worked with a tropical mil, whereas the soils in this study are temperate Chernozemic soils.

Table 5.41. Land use patterns and soii Pi Wons (mg kg-') in Shandan-A. Land use Resin-P Bicxb-P; NaOH-Pi DHCI-Pi HHCI-P; Sum-Pi LDGP 10.6 bt 12.6 b 9.4 a 73.8b 101.4a 207.8b MDGP 10.9 b 12.0 b 10.0 a 83.6 b 100.3 a 216.8 b HDGP L0.3 b 10.2 b 9.7 a 65.7 b 98.7 a 194.6 b Cult-6 16.8 a 16.2 a 10.4 a 118. I a 108.7 a 270.3 a

t Values in the same coiumn followed by the same letter are not significantiy dierent at 0.05 probability level according to Tukey's HSD test.

The impact of land use on Po -ions is shown in Table 5.42. Resuits indicate that absolute amounts of P, Fractions are not significantly influenceci by land use patterns. except that Po extracted by HHCI fiom Cult-6 is significantly higher than that fiom uncdtivated soils (LDGP).

Table 5.42. Land use patterns and suil Pona*ions (mg kge') in Shandan-A Sum-Po Land use Bicarb-Po NaOH-Po HHCEP, (mg kg-') ("/O) LDGP 8.4 a? 133.4 a 133.7 b 275.5 a 1O0 MDGP 9.8 a 137.3a 154.4ab 301.4a 109 HDGP 8.7 a 136.1a I45.8ab 290.5a IO5 Cdt-6 8.2 a 123.8 a I63.1a 295.1a 107

t Values in the same column folIowed by the same letter are not sigdicantly different at 0.05 probability level according to Tukey's HSD test. In generai, P, tlactions varied little between the four land use patterns at this site. Hedley et al. (1982) indicated that a long-term rotation of wheat-wheat-fallow reduced Pt by 29%. Of the PLlost, 22% came from extractable Po and 52% tiom stable forms. It is Iikely that cuItivation fength at Shandan-A is not long enough to result in a significant change in Po. The relative proportions of Po fiactions did not show any significant differences (p = 0.05) between land use pattern (Table 5.43). However, if the data were tested at 0.10 probability level the important NaOH-extracted Po significantly dropped by 6% when pasture had been cultivated for 6 years. More stable forrns of Po increased by 7% (p = 0.10) for their proportion. This is reasonable since more organic Po (associated with organic matter) is mineraiized when pasture becomes degraded or put into crop production. Thus, a relative higher amount of stable Po remains.

Table 5.43. Land use patterns and Po fiactions (%) in Shandan-A Land use Bicarb-Po NaOH-Po HHCI-Po LDGP 3.0 a? 48.3 a a$ 48.6 a b MDGP 3.2 a 45.5 a ab 51.3 a ab HDGP 3.0 a 46.9 a ab 50.2 a ab Cult-6 2.8 a 41.9a b 55.4 a a

------+ Values in the same column foliowed by the same letter are not significantly different at 0.05 probability level accordiig to Tukey's HSD test. $ Values in the same column followed by the same bold letter are not sigruficantly different at 0.10 Level according to Tukey's HSD test.

6.2.1.3 Shandan-B in Shandan-B, four land use pattems were sampled. Data in Table 5.44 reveal that Cult-1 does not have any significant influences on Pi fractions, compared to MDGP- However, increasing culcivation length increases the bio-available Pi tiactions (resin-Pi and bicd-Pi). As indicated in the section 5.2.1.1, the higher amounts of bio-available Pi, as weIl as more stable Pi, are attributed to application of P fertilizers and organic matter mineralktion in pasture soils, most of the P entering plants is supplied fiom the slow recycling of plant residue P through microbial processes in the soil (Tate, 1984). In fertilized crop fields, the P cycle is more open since P is removed in products and supplemented from fertilizers. Thw, the mineralization process in cultivated fields is stronger than in closed ecosysterns, resulting in a higher proportion of bio-available Pi, In the Shandan-B site, intermediate cultivation length (Cuit-13) is not significantly different from longer cultivation (Cult-29) for any of the Pi fractions. This is consistent with the tindings from shorter cultivation (CuIt-8 and Cult- 16) at Tianzhu-AlB.

Table 5.44. Land use patterns and soi1 Pi fiactions (mg kg*') in Shandan-B. Land use Resin-P Bk&-Pi NaOH-Pi DHC1-Pi HHCI-Pi Sum-Pi MDGP 5.3 bt 8.2 b 4.4 b 294.8b 104.7a 417.4b Cult- 1 7.5 b 7.9 b 4.9 b 264.5 b 108.9 a 393.7 b Cult-13 20 a 20.3 a 9.1 a 361.0a 112.8a 523.2a Cult-29 21 a 24.0 a 9.7 a 371.8 a 104.2 a 530.7 a

+ Values in the same column followed by the same letter are not significantly diierent at 0.05 probability level according to Tukey's HSD test.

The soil Po fiactions are dependent upon mineralization of organic matter. Generally speaking, the longer the cuitivation length, the more organic matter is mineralized. It is evident that NaOH- and HHCI-extracted Po declines when MDGP is used for longer crop production (TabIe 5.45). However, bicarb-Po has no dear trends with the four land uses in this site. The sum of Po t?actions is also higher in MDGP, compared to the Cuit-13 and Cult-29. Organic P reduction averaged about 0.6% per year in Shandan-B, whereas a 1% reduction per year was observed in Tianzhu-A,, suggesting stronger mindition adormore soii erosion in Tianzhu-AlB. The relative proportions of three extracteci Po fonns at Shandan-B differs 6om those in Tianzhu-AB (Table 5-39), at Shandan-B there are few differences between the four land use patterns (Table 5.46). This may be explained the rapeseed meaI that has been applied to supplement P removed by crops for years in this site, some of the mineralized Po may come fiom the tapeseed meai. Furthemore, soil saiinity in this site is quite high (Table 5.30), the higher water-soluble cations probably also mask the general change patterns of Po fractions.

Table 5.45. Land use patterns and soi1 Po fractions (mg kg-') in Shandan-B. Sum-Po Land use Bicarb-Po NaOH-Po HHCI-Po (mg kg-') (%)

P MDGP 4.9 at 51.2ab 151.0 a 207. l a 100 Cult- 1 5.2 a 62.2 a 148.4 ab 215.7 a 104

- - + Values in the same column followed by the same letter are not significantly different at 0.05 probability level accordiig to Tukey's HSD test.

Table 5.46. The proportions of Po (%) affected by land use in Shandan-B. Land use Bicarb-Po NaOH-Po HHCI-Po MDGP 2.4 bt 24.9 a 72.7 a Cult-1 2.4 b 28.8 a 68.8 a Cult- 13 3.2 a 29.3 a 67.6 a Cuit-29 2.9 ab 26.9 a 70.3 a

t Values in the same column foliowed by the sarne letter are not significantly different at 0.05 probability lwel according to Tukey's HSD test.

Tate and Newman (1982) indicated that climate and ciimate-dependent differences in the composition of soi1 Po might play an important role in mineralization rates since temperature and water supply are the governing factors controlling microbial activity (Paul and Clark, 1996). This can be seen in the sum of Po hctions in two different sites of Shandan. Taking MDGP as an example, nim-Po is 301 mg kg-' in Shandan-A (Table 5-42), while it is 207 mg kgm' in Shandan-B (Table 5.45). On average, lower temperature and higher precipitation are found in Shandan-A, compared to Shandan-B (Table 5.47). Therefore, more organic C bas accumulated in Shandan-k The TOC and total N in Shandan-B are only about 55% and 59% of those in Shandan-A, respectively. Table 5.47. Climate and soi1 chernical properties at the two Shandan sites. MDGP Shandan-A (a) Shandan-8 (b) bla (%) Annuai temperature (OC) -0.5 0.2 Annuai precipitation (mm) 400 3 56 89 TOC (g kg-') 59.2 32.7 55 (g kg-') 5.7 3 -39 59 Sm-Po 30 1 207 69

5.2.2 Results fiom regionai scaie sampling As discussed in Section 5.1.2, pastures on regional gale are categorized as LDGP, MDGP, and HDGP. Cultivated fields are grouped as C 1- 10, C 11-30, and C3 1-50, representing crop fields with cultivation length from i to 10, 11 to 30, and 3 1 to 50 years, respectively. Results tiom regionai sale (Table 5.48) are quite similar to those fiom local scale sampling. tt is found that cultivateci fields are significantly higher or slightly higher in resin-P, bicarb-Pi, DHCLPi, and Sum-Pi than Pasture soils. No significant differences in NaOH-Pi, HHCI-Pi and residual-P are observed among land uses.

Table 5.48. Land use patterns and soi1 Pi fractions (mg kg") on regional scale. Land use LDGP MDGP HDGP Cl-10 C11-30 C31-50 Resin-P (1) 14.3 bf 10.7 b 8.8 b 42.1 a 21.2ab 27.7ab Bicarb-Pi (2) 12.5 b 9.7 b 9.7 b 28.8 a 27.6ab 25.5ab

(1) + (2) 26.8 b 20.4 b 18.5 b 70.9 a 48.8 ab 53.2 ab NaOH-Pi 17.0a 14.Ia 14.0 a 18.0 a 12.0 a 21.4 a DHCI-Pi 196.6 b 201.2 b 219.1 b 240.4 ab 385.0 a 299.0 ab HHCI-Pi 110.1 a 110.2 a 110.2 a 119.9 a 115.6 a 115.3 a Sum-Pi 350-4 b 345.8 b 361.9 b 449.0 ab 561.3 a 488.9 ab Residuai-P 72.7 a 75.1 a 76.1 a 80.1 a 74.4 a 76.6 a

t Vahes in the same row foiiowed by the same letter are not significantly different at 0.05 probability Ievel according to Tukey's HSD test. There are no statistical differences in resin-P when pasture becomes degraded, but with increasing degradation bio-available Pi (resin-P and biwb-Pi) shows a downward trend. For cultivated lands, a considerably higher amount of resin-P was obtained in short-term cultivation fields (Cl-IO). The resin-P value ranges fiom an average of 42 mg kg" in a short-term cultivation soil (Cl-IO) to 28 mg kg" in the soils corn long-term cultivated fields (C3 1-50). The higher resin-P in Cl-IO may be contributed hm1) the fast rnineralization of organic matter, and 2) higher rates of P fertilizers used in recent Y-. Bicarb-Pi der removing resin-P does not Vary significantly among different degraded pastues or among cultivation years, however, the amounts of this fiaction in cultivated lands are slightly or significantly higher than those in pasture soils. This reflects probabiy organic matter turnover accelerated by cultivation besides available P added fiom P fertilizers. The absolute amount of Fe- and Al-associated Pi extracted by NaOH is not significantly affected by land use patterns, but the Ca-associated Pi is increased when pasture is cultivated. This suggests that most applied P, as well as mineralized P, is transfomed to Ca-associated Pi, a secondary P form, reflecting chemical changes during soil degradation. The amounts of more stable form of HHCI-extracted Pi are constant regardles of land use patterns and fertiliition histories. The impacts of land use patterns on organic forms of P are shown in Table 5.49. Bio-available Po does not change significantly between land uses. The amount of potentially available NaOH-extracted Po is reduced considerably, especially when pasture has been used as crop land for a longer time (C3 1-50). Only about one-third 'of this fiaction is left when soil has been cropped for 30 to 50 years. The stable form of HHCkextracted Po is not significantly influenced by land use patterns. For the surn of Po fractions, there are no statistical differences among land use patterns, despite about a one-third reduction in sum-Po by more than 10 years' cultivation. Along with 35% of organic P decline in more than 10 years' cultivation, TOC and total N were reduced by 54% and 45% (calculated fiom Table 5.33), respectively, with more than IO years' cuitivation. Table 5.49. Land use patterns and soi1 Po fiactions (mg kg") on regionai sale. Sum-Po Land use Biwb-Po NaOH-Po HHCI-Po (mg kg-') (%) LDGP 9.0 ai 155.9 a 151.6 a 316.5 a 100 MDGP 8.6 a 143.4 ab 156.7 a 308.7 a 98 HDGP 7.2 a 140.4 ab 150.7 a 298.3 a 94 Cl-IO 6.8 a 105.6 abc 163.6 a 276.0 a 87 Cl 1-30 5.7 a 67.6 bc 133.1 a 206.4 a 65 C3 1-50 7.7 a 55.9 c 143.0 a 206.6 a 65 + Values in the same column followed by the same lener are not significantly dEerent at 0.05 probability level according to Tukey's HSD test.

Table 5.50 shows that there are no significant differences in proportion of bicarb- Po in al1 six land use patterns. However, Po extracted by NaOH, a potentially available form of P, decreases with cultivation length. After more than 30 years' cultivation the proportion of NaOH-Po is almost half of that in Pasture. Compared to LDGP, the proportion of more stable HHCI-Po increases significantly with longer cultivation time.

Table 5.50. The proportions of Po fractions (%) on regional scale. Land use Bicarb-Po NaOH-Po HHCI-Po LDGP 2.8 at 49.3 a 47.9 b MDGP 2.8 a 46.5 a 50.8 b HDGP 2.4 a 47.1 a 50.5 b Cl-10 2.5 a 38.3 ab 59.3 ab Cl 1-30 2.8 a 32.8 b 64.5 ab C3 1-50 3.7 a 27.1 b 69.2 a

t Values in the same column foliowed by the same lener are not significantiy different at 0.05 probability level according to Tukey's HSD test. 5.2.3 Conclusions in summary, in relatively ündisturbed ecosystems such as pasture soil, the labile P (both resin-P, bicarb-Pi and bicarb-Po) fiaction is srnaIl and the P cycle is relatively closed. Most of the P entering plants is supplied fiom the slow recycling of plant residue P through microbial processes in the soil. When comparing different degraded pasture, however, the amount of labile Pi (resin-P + bicarb-Pi) tends to be higher in LDGP than MDGP or HDGP. The slightly higher amounts of labile Pi in LûGP is probably due to higher amount of organic C, which supports a high biological activity, in tum accelerating organic C turnover, resuiting in an increase the proportion of labile Pi in the short tenn. in disturbed ecosystems such as cultivated fields, the P cycle is more open because agricultural products are removed, and losses of P otlen occur fiom soi1 erosion. Consequently, fertilizer P is added to compensate for these losses, as well as to raise plant production above natural levels, resulting in a fast turnover rate of organic matter and high level of both resin-P and bichei. Results obtained fiom both local and regional scale sampling indicated that labile Pi in cultivated fields was significantly higher than that in grassland. Mineralization of organic P and application of P fertiiizers are responsible for this. inorganic P extracted by O. 1 M NaOH increased with cultivation in the local sale samples, but no conclusive evidence was found in regional scale samples. In the temperate ecosystem, where this study was conducted, Ca-associated Pi dominates the different fiactions. This fiaction of Pi increases as soils become degraded especially when pasture is cultivated. Bad on the estimation of the contribution of incorporation of subsoil by tillage, fertilization, and mineralization of Po to Ca-Pi, it was found that mineralization of organic P was a major source of the increase in Ca-Pi in cultivation fields. The more stabte fonns of HHC1-extracteci Pi were not affecteci by any land use. Bicarb- dedined significantly with cultivation at Tianzhu-AB. Moderately labile Po extracted by NaOH decreased sharply when pasture was put into crop production. The more stable tiaction of P, extracted by HHCl also showed a tendency to decline with pasture degradation or cultivation years, ahhough short period cultivation (less than 16 years in Tianzhu-A/') was not statisticaüy dierent fiom pasture. The proportion of Po fractions behaved differently than the absolute arnounts, especiafly for more stable fraction. In genera1, the more stable fiaction of Po declined with cultivation in the absolute arnount, however, it was increased in its proportion when pasture was cuitivated. This indicates that cultivation caused the more labile fiaction of Po to be mineralized. What remaind was the more stable Po fiaction in the soil. 5.3 Effect of land use patterns on soit erosion Soi1 erosion is a major environmental concem around the worid. This kind of research is relatively undeveloped in China, particularly in northwestem regions such as Gansu and Qinghai. The reiationship beniveen soil erosion and soi1 fertility in different land use patterns is rarely documented. Therefore, it was considered worthwhile to do some research in this area. In this study, soi1 samples were collected fiom seven locations in Gansu province. On a local scale, soi1 samples were taken dong transects, while the quadrats method was used on regionaf sale. On the local scale sampiing, every second sample in one transect was anaiyzed for specific radioactivity of Incs using the method of de Jong et a1.(1982). For land uses with less than six samples, for example, LDGP in Tianzhu-A and HDGP in Tianzhu-C, ail of the samples in the uansect were anaiyzed. Properties of radioactive L37~sthat make it unique as a tracer for studying soil erosion are: strongly sorbeci, evenly distributed on a regionai scale, and known deposition time. ïhere are no naturai sources of "'CS (Ritchie and McHenry, 1990). The I3'cs is produceci during nuclear fusion. Thus, its presence in the environment is due to atmosphere H-bomb testing or release fiom nuclear reactors (Wise, 1980). Total ')'CS activity for any land use in each site was calnilated based on equation 3-3. SoiI erosion rates were estimated based on equation 3-4 and 3-5. At each site the amount of IS7csin the LDGP was used as the fàitout baseline for the assessrnent of other Iand use patterns. if the LDGP did not exist in the site, MDGP or HDGP was used as the baseline instead. The radioactive decay constant for I3'cs is 0.023 y8 (Kachanoski and de long, 1984; Wang et al., I991). Since al1 the soi1 samples in a location were taken at the same time and were counted within weeks of each other, radioactive decay of I3'cs is not considered.

5.3.1 Resuits fiom Iocal scale sampiing

5.3.1. I Tianzhu-A/B A signrf~cantdedine of '37~sradioactivity was found when Pasture was cultivateci (Table 5.51). It was assumed that 13'cs radioactivity in LDGP was 100% (as the badine). The losses of "'CS in MDGP were about 22% by weight and 12% per square meter. The iuge differences in ')%s radioactivity ùetween weight and per square meter were due to higher bulk density in MDGP.

Table 5.5 1. The radioactivity of 137 Cs and soil erosion rate in Tianzhu-AIB.

"'CS activity '"CS activity Erosion rate + Land use (Bq kg-') (%) (Bq m-3 (1 (kg m-'yfl) (% w') LDGP 26.0 a$ 100 2.66 a 100 - - MDGP 20.4 a 78 2.35 a 88 0.37 Cuit-8 10.9 b 42 1.10 b 4 1 9.5 Cult- 16 8.9 b 34 0.93 b 35 6.5 Cuit-4 2 8.0 b 3 1 0.87 b 33 2.7

t Equation 3-4 was used for left column and equation 3-5 for right colurnn. $ Values in the sarne column followed by the same letter are not significantly diierent at 0.05 probability level according to Tukey's HSD test. 7 During the course of 40 years' erosion.

The losses o~'~~cshmcultivated fields were even higher. Less than half of the 137Cs was observed in Cult-8, and one-third in Cult-16 and Cuit-41. Although large differences between LDGP and MDGP in 13'Cs activity were observed, they were not statistical signifiant. It is notable that the highest annual erosion rate is observed in the early of cultivation years, for instance, in Cult-8 with 9.5 kg m". It is reduced to 2.7 kg m" with 4 1 years' cultivation. The correlations between I3'cs losses and soil properties were conducted. The resuhs of the comlation analyses (Table 5.52) showed that the ment 13%s load decreases generally with increasing inorganic C, pH and exchangeable Na (negative correlation coefficient), and positively correlated with other soil properties. Among these variables macro-organic C and mamrganic N showed the highest positive correlation with I3'cs. It mggesteci tbat more labile numents in macrwrganic forms were eroded away in the topsoil. Mle 5.52. Correlation between "'CS (Bq rn-') and dlpmpetties, Tianrhu-AIB.

Variables Unit # of soi1 sarnples Pearson (r) f

PH 3 6 4-68** ECt,r wsc CEC TOC Inorg-c Ex-Caf Ex-Mgf EX-KS EX-NG Total-N Total-P Total-K Macrosrganic C Macro-organic N Macro-organic P Sand fiaction

t Data with "*" refer to correlation is significant at the 0.05 IeveF Data with "**" refer to correlation is significant at the 0.01 level. iWK1-extracted Ca, Mg, K, or Na.

The relation between soi1 particle size and I3'cs radioactivity was analyzed by regession analysis (Figure 5.7). In this study, sand content was significantly and negatively correiated with "'CS activity (r = 4.75). It can be eaimated by following equation:

y = 6-47x-0~93 w here y = I3%s activny (ki3q m-')* x = sand content (%). Sand (%) I

Figure 5.7. The relationship between sand content and I3'cs radioactivity.

A similar negative power equation, with a similar coefficient of determination (r = -0.77). is obtained with "Ys activity when 137~sis expressed as Bq kg-':

y = 25..?7~-~~* where y = 'Tsactivity (~qkg-'), x = sand content (%). Soi[ becomes coarser derbeing degraded by erosion since fine particles are moved away by wind or water. Results corn this study confirmed that sand content of eroded soi1 increased if the subsoil was high in sand fraction. Chen (1994) also reported that fine particles (

5.3.1 -2 Tianzhu-C Soi1 samples dong the transect in Tianzhu-C are classified as shoulder, midsiopes and footslopes (Appendix 1). When radioactivity of I3'cs is averaged by slope position, a dehite '"CS pattern is found (Table 5.53). The shoulder slope sites are areas of 13%s loss (with 0.62 kE3q m-2), but footslope sites are areas of "'CS relative accumulation (with 0.92 Bqm*2). This is consistent with the results by de hget a1.(1983). However, this does not indicate that no soi1 erosion occwred in footslopes. Only about 64% of 137~sactivity (kBq IXI-~) present in HDGP is found in footslopes. It is noticeable that HDGP is significantly higher in "'CS than the rea of slope positions, even for footslopes where 13'cs is relatively accwnulated when compared to shoulders.

Table 5.53. Soil erosion in different slope positions, Tianzhu-C.

'"Cs activity '"CS activity Erosion rate +

HDGP 12.0 a$ 100 1.44 a 1O0 - S houlder 5.8 b 48 0.62 b 43 2.7 Midslope 6.4 ab 53 0.69 b 48 2.4 Footslope 8.5 ab 7 1 0.92 ab 64 1.5

t For comparison, it was assumed that HDGP was uneroded in this site, erosion rates were estimated within 40 years. Values in the same colurnn followed by the same letter are not significantly different at 0.05 probability Ievel according to Tukey's HSD test.

Based on equation (34, annual soi1 erosion rate on shoulders was estimated to 2.7 kg m.', while midslopes was lower with 2.4 kg m-2 (Table 5.53). This means about 15 cm of topsoil was eroded away in shoulder, and 13 cm in midslopes over 40 years. On footslopes, both erosion and deposition are occurring simultanmusly by tillage and Ml- wash. Thus, the estimated soi1 erosion rates are lower thau in shoulders and midslopes. For comparison in this site, the above estimation assumed that no erosion occurred in HDGP. However, HDGP in this site also suffered severe erosion. There was one spot (la sample dong the transeet, Appendix-9 where erosion rate was relativeiy lower when compared to Tianzhu-AlB. The 13'cs activity was 2.52 kBq rn", or 21 Bq kg-', which is quite similar to that in uneroded LûGP at Tianzhu-AB. Taking this spot as a baseline of "'CS activity, it generates the revised erosion estirnates in Tabk 5.54. Tabte 5.54. Reidsoil erosion rates in diffierent dope positions, Tianzhu-C. 13'cs activity "'CS activity Erosion rate +

HDGP 12.0 a$ 5 7 1.44 a 57 1.1 Shoulder 5.8 b 28 0.62 b 25 4.5

!The 13?csactivity of 2 1 Bq kg" and 2.52 Bqm" wae used as the basdine. f Values in the same column foilowed by the same letter are not significantly diierent at 0.05 probability IeveI according to Tukey's HSD test.

It is evident that HDGP in Tianzhu-C has been also heavily eroded. About 57% of "'>CS activity was found in HDGP based on revised data. Wind erosion and soii movernent by tiIlage implements could be responshle for the lower '"CS levels on the shoulders than midslopes (de Jong et al., 1983). It is ahfound that variation in HDGP is very large due to steep slope (about 30%) encountered betwm the 2nd and 4'" sampling points. The slope of 4U point was even steeper. in surnmary, '37~svaried significantly between HMjP and cultivateci fields. The amount of 13'cs in shoulder is [ower than tht in mid- and foot-siopes. Because the slope in Tianzhu-C is steep (averaged slope 37%), soil loss is greater than in Tianzhu- A/B.arnounting about 4.5 kg poil m-* in shoulda and 4.2 kg mm2in the midslopes annually, with a total amount of 1,800 ton soil lm-' removed in shoulder and 1,700 tons of soi1 in midslopes during the course of over 40 years' cultivation. Taking three sites of Tianzhu as a whole, 13'>cslasses are strongly correlated with cultivation years der analyzing 53 soi1 amples (Figure 5.8). A negative power funnion relationship between Incs concentration and years of cultivation is obsewed. As for otganic C, U7~sactivity is reduced sharply at the beginning of the cultivation penod, and Ieveled off with increasing cultivation the. Y ears of cultivation

Figure 5.8. The relationship betwem '"CS radioactivity and cultivation years.

5.3.1.3 Shandan-A Four land use patterns were selected for cornparing soi1 erosion as affected by land management at Shandan-A Table 5.55 lias I3'cs changes afier Pasture has been degraded and cultivated. Statistically, there are no significant soi1 losses among four land use patterns, although '37~sactivities hmHDGP and short-tenn cultivation (Cult- 6) are lower than that fiom LDGP and MDGP.

Table 5.55. Land use patterns and '37~sradioactMty in Shandan-A

137~~activity IJ7csactivity Erosion rate +

LDGP 9.9 as 100 2.00 a 100 - - MDGP 11.3 a 114 2.33 a 118 HDGP 8.7 a 88 1.81 a 91 0.2

f For comparison, LDGP was used as the baseline ofLT%sactivity. Values in the same column followed by the same Ietter are not significantly dierent at 0.05 probability ldaccordhg to Tukey's HSD test. ïhe "'CS activity is the highest in MDGP, aithough soi1 chernicd pmperties mch as TOC, totai N, soi1 pH, etc. did not show any significant differences between LDGP and MDGP (Table 5.20). The reason for such a high value in MDGP requires hrther investigation.

5.3.1.4 Shandan-B Annual precipitation in Shandan-B is around 356 mm, lower than that in Shandan- A (400 mm). Thus, soi1 erosion in this site should not be as severe as in Shandan-A. As show in Table 5.56, 137Cs in MDGP is 2.53 kBq m", which is higher than that in MDGP of Shandan-A (2.33 kSq m-'). However, long-terni cultivation does increase soi1 erosion. Taking '"CS activity in MDGP as a badine in order to compare cultivation impacts on soi1 erosion, the relative 13'cs concentrations fiom Cuit-1, Cuh-13 and Cult- 29 are only 65%, 85% and 74%, respectively. The significantly lower I3'cs adiwty tkom Cult-1, compareci to MDGP, is not likely due to mil erosion because it was sampled only several months afler Pasture was broken. Possibiy, the plough layer had not yet been thoroughly mixed by tillage, causing large variations of tested vaiue between soi1 samples, especially for '3'~sdetermination (Figure 5.9).

Table 5.56. Land use patterns and 13'cs radioatintty in Shandan-B.

'"CS activitv Erosion rate t

MDGP 9.1 100 2.53 a 100 - Cuit- i 6.3 b 69 1.65 b 65 83.2 Cult- 13 7.6 ab 84 2.16 ab 85 3.1 Cult-29 7.1 ab 77 1.86 ab 74 2.5 t For cornparison, MDGP was used as the baseüne of '"CS activity. $ Values in the same column foliowed by the same letter are not significantly dierent at 0.05 probability level accordhg to Tukey's HSD test. Figure 5.9. Box-plot of ')'CS radioactivity in Shandan-B.

5.3.2 Results fiom regional scale sampling

As in previous sections, land use was grouped into six patterns. No bulk density was measured. Thus, 13?3 radioactivity was calculated based on weight exclusively in this section. Activities of i37~sdecline simcantiy from an average of 20.2 Bq kg" in LDGP to 10.0 Bq kg-' in HDGP, and then to 4.7 Bq kg-' in crop fields with more than 30 years' cultivation (Table 5.57). Short-term cultivation Cl-IO and Cl 1-30 had a similar % concentration as HDGP. A nlatively srnail variation in concentration of I3'Cs activity among sites and locations is found for W.This indicates that the amaunt of '%s deposition fiom nuclea. test in the 1950s and the 1960s bas not been changed very much as long as soi1 erosion remains minimum. However, large van'ations were observai when Pasture became degradeci regardless of the magnitude of degradation, reflecting variability among sites and locations. Table 5.57. Impact of land use on '"CS radioactivity on regional scale.

Land use "'CS (Bq kg-') C.V. (%) Relative (%) LDGP 20.2 ai 3 8 100 MDGP 15.9 ab 70 79 HDGP 10.0 bc 60 49 Cl-10 8.9 bc 54 44 C 11-30 7.5 bc 43 37 C3 1-50 4.7 c 43 23

+ Values in the same column foUowed by the sarne letter are not significantly different at 0.05 probability level according to Tukey7sHSD test.

Correlation analysis (n = 63) indicates that '37~sconcentration is highly and positively correlated with soil macroiirganic C (r = 0.81**), soil total N (r = 0.76**), and soil organic C (r = 0.71**), but negatively correlated with soil pH values (r = -OB**) (Table 5.58). This is consistent with Migsf?om local scale (Table 5.52).

Table 5.58. Correlation between (Bq kg-') and soi1 chernical propenier. Variables Unit # of soi1 samples Pearson (r) +

PH (2:i) 63 -0.59 ** Ec~i dS cm-' 63 -0.17 CEC cm01 kg" 63 0.47** TOC g kg-' 63 0.71 ** Total-N S kg-' 63 0.76** Total-P g kg-' 63 -0.5 1 Total-K S kg" 63 -0.23* Macrosrgaaic C B kg'' 63 0.81** Macro-organic N B kg-' 63 0.60- Macro-organic P S kd 63 O. 78**

- f Data with "** refer to correlation is signifiant at the 0.05 levei. Data with "**" refer to coneIation is significant at the 0.0 1 level. After Pasture was heavily degraded (HDGP) or cultivated, considerable amounts of macro-organic C and macro-organic N rich in topsoil were eroded away. Therefore, losses in macro-organic C and macro-organic N can be used as good indicators for soil erosion. Subsoil has a higher pH value, for instance in Tianzhu-A/B, the pH in the plough layer would be raised when subsoil is incorporateci with the top layer afler erosion. As a consequence, soil erosion is negatively correlated with soi1 pH.

5.3 -3 Conclusions Soi1 erosion with cultivation is summarized in Table 5.59. It is clearly shown that the amounts of '37~sloss incrase with cultivation length in Tianzhu. On the aerial

basis, "'CS activity decreases by 5% with 8 yean' cultivation, and about 75% of '"CS activity is lost within 48 years' cultivation

Table 5.59. The effect of cultivation length on soi[ erosion at two locations. Cultivation 131Cs loss Erosion rate Site (~m) (%) (kg m-2 v')

Different ecologid conditions resulted in different soil losses. For instance, soi1 erosion rates in Tianzhu, which is located in a valley with higher precipitation, were higher than in drier Shandan-B, situated on an alluvial plain. Approximateiy 65% of I31Cs activity was lost in Tianzhu with 16 years' cultivation, but only about 15% were lost in Shandan-B, although number of cultivation years in Shandan-B was three years' shorter. In general, dope also has a great impact on soi1 erosion. The annual erosion rate in Tianzhu-C (average dope 37%) is 4 kg soü m-' anrmaily over 40 y=, while a soi1 Ioss of 2.7 kg m-' yi' was observed in Tianzhu-B (5% slope) over the same period. Since ecological conditions are the same, the diirence indicates the influence of slope on soi1 erosion. Results fiom local scale are consistent with those from regional scale. Once Pasture is put into crop production, soi1 erosion becomes severe (Table 5.57). On regional scale, soi1 13'cs concentration in crop fields that had been cultivated for less than 10 years (Cl-10)dropped to 8.9 Bq kg-', while soi1 fiom unetoded LDGP was 20.2 Bq kg-'. This represents an average declined of 56%. Data from Tianzhu-AIB indicated that "'CS activity declined by 59% dereight years' cultivation, which is very similar to that on regionai scale. 5.4 Variation of plant species composition among degraded pastures

5.4.1 Plant species To determine the vaiidity of classi@ing Pasture degradation based on changes of plant species and numbers of plant species, individual plants were quantified using a quadrat (Figure 5.10). The quadrat has 25 small squares, which makes it easier to count the nurnber of plants. At each location, two to three different degraded pastures were selected to compare plant species changes between LDGP, MDGP and HDGP.

Figure 5.10. The quadrat fiom LDGP in HGD, Eatlzbu County.

A total of 58 vascular plant species were observed in 18 sites at the seven locations. Detailed individual species and their nunibers at each site are presented in Appendix II. in general, four broad groups of range pIants are classified: grasses, grass- like plants, forbs and shrubs (Holechek et ai., 1989; ADF-Johnson, 1990) in this study. Grasses are disthguished by having hollow, jointed stems; henarrow leaves with large parallel veins; and fibrous mot systems. They have srnail green flowers that are usuaily complete, with male and female parts present in the same flower. Grass-like ~Iantscesemble grasses, but have nonjointed, solid stems which are either three-sided (sedge) or round (rush). These plants have leaves and fibrous roots like true grasses. Male and female floral parts are usually found in separate florets. Forbs are non-grass-like plants, having non-woody stems, generally broad leaves with netlike veins. Many colorfiil wildflowers belong to this group. Shmbs have woody stems that branch near the base, and long, couse roots. Trees differ fiom shnibs in that they have a definite tmnk that bmches well above ground. Shbs and trees have stems that remain alive during dormant periods, but the aboveground parts of most grasses and fohs die back to the crown during winter. The basic life-forms for al1 58 plants are presented in TabIe 5.60. In general, grasses and grass-like plants are more palatable than forbs and shnrbs. The more forbs and shbsremah, the heavier is Pasture degradation.

Table 5.60. Plants observed in the research regions. Common name in Scientiflc name Paiatabilityi Life-fomz Chinese if$ 4 Achnatherum indrians P G a Achnatherum splendens tt G @ Adenophora stricta P F 6 k!! ûk g Agropyron cristatum 9f . Ailium chrysanthum i6 E iS Allium condensatum ti-tf G # Anaphalis sinica + F @ Anemonecathayensis P F % $ Aneurolepidium dasystachys +t G K -;FI& Artemisia argyi lévl - S % Artemisia figida fctt S % Z % Astragaius sinicus P F R @ $I S Carex heterostachya ttff GL 3i Rt E $ Carex lanceolata i+t+ GL B ?E g 55 Carex teinogyna ++t+ GL lx % Chenopodium album f t$ Brk f5: Elyrnus nutans Ï@ 1.11 k $k Euphorbia strachyi % X Gentiana macrophyiia P F ;tÈ E! Gentiana sEabra P F % a % Helictotrichon u'beticum tt+ G $&Heteropappus dtaicus -H F 3fiJ & Heteropappus hispidus + F T Palatabrlity: P = poisonous, - = les palatable, ++++ = more pdatable. t G = grasses; GL = grass-Iike plants; F = forbs; S = sbnibs. Table 5.60. PIants obsewed in the research regions (cont'd). Co-on Scientific name Palatabiiityt Life-fom$ in Ciunese Hypecoum erectum Iris tenuifolia Kobresia capillifolia Kobresia humilis Kobresia pygmaea Koeleria cristata Lamiophlomis rotata Leontopodium leontopodioides Microula sikkimensis Orinus kokonorica Oxytropis ochrantha Pedicularis kansuensis Pleurospermum cordolii Poa annua Pocockia ruthenica Polygonum aviculare Polygonum sibiricum Polygonum vivipanim Potentilla acaulis Potentilla bifiirca Potentilla Multicaulis Potentilla reptans Primula malacoides Primula maximowiczii Roegneria kokonorica Saussurera japonica Steiiera chamaejasme Stipa bungeana Stipa Purpurea Taraxacum lugubre Taraxacum mongoiicum Thalictrum alpinum Thermopsis lanceolata TroUius chinesis % a T Wola phiiippica + Palaubility P = poisonous, - = less paiatable, t++t = more paiatable. + + G = grasses; GL = grass-like plants; F = forbs; S = sbbs. A total of three species of grass-like plants were identified in this study, and these three species were more palatable as well, grass-like plants were therefore summarized with grasses. Shrubs accounted for a very small proportion, thus shrubs were also sununed with fohs. Table 5.61 presents the summary results from statistical analyses.

Table 5.61. Proportion of Ki-forms in different degraded pastures (%).

Pasture # Grass + grass-Iike plants C.V. ' Forbs +shrubs C.V. LDGP 12 65 at a 37 35a b 70 MDGP 13 64a a 3O 36a b 53 HDGP 17 45a b 66 55a a 5 5

t Values in the same column followed by the sarne letter are not significantly different at 0.05 (bold letter at 0.20) probability level according to Tukey's HSD test.

hongdifferent degraded pasnires, LDGP, on the average, has a higher proportion of grass and gass-like plants although the differences are not statistically significant with MDGP and HDGP ai 0.05 probability level due to the large variation arnong different locations. The difference between LDGP and HDGP, however, reaches the signifiant at the 0.20 probability level. If Pasture becomes heavily degraded, plant species composition changes accordingly. Plants with less forage value tend to increase, while more palatable plants such as grasses and grass-like plants tend to decrease. To determine if there are any simiiarities of plants between degraded pastures, the IS was calculated based on equation 3-1. The 1s values can be obtained simply by counting the species in the quadm (Appendix-II). The same degraded categoies in different sites were treated as the repliates, thus, the ISJ of 26 LDGP compared to MDGP = (l+11+16)x100=5~h.

26 MDGP compared to HDGP = [Il+li+26)~10~=i~. and

LDGP compared to HDGP = (21i~~iIl)X100 =40%. Based on above calculation, it is evident that pasture degradation has impact on plant species composition; the same conclusion was reached when comparing plant Iife- form changes in the previous discussion,

5.4.2 Plant cover Plant cover is an important indicator used to evaiuate pasture degradation. A sparse plant cover is usually observed when pasture becomes heavily degraded. Soi1 erosion and water loss are concomitant with Pasture degradation. In tuni, plant growth is retardecl when severe soi1 erosion occurs and soi1 loses water. Table 5.62 indicates that pasture degradation significantly reduced plant cover. On the average, plant covers in LDGP, MDGP and HDGP are 99%. 84% and 63%, respectively.

Table 5.62. Statistical analyses on ground cover (%), regional de. Pasture # of quadrats Mean C.V.% LDGP MDGP HDGP + Values in the same column followed by the same letter are not significantly different at 0.05 probability level accordiig to Tukey's HSD test.

5.4.3 Plant palatability Plant palatability is the degree to which the herbage within easy reach of stock is grazed when a range is properly utilized undet the best practicable range management (USDAFS, 1988). Plant palatability can be used to evaiuate Pasture quality. Pasture with more palatable plants is beneficial to grazing animais, and the pasture is considered as lightly degraded. According to their palatability, ail observed 58 plants were classified with the help tiom Dr. Redmann of the Plant Sciences Department, University of Saskatchewan and Mr. Xindai Mo, Professor of the Grassland Department, Gansu AQricuIturaI University. The references of USDAFS (1988) and lia (1987) were dso used to classi@ plant palatabiIity. The most paiatable grass is coded as "+ + + +",and less palatable as "-" (Table 5.63).

Table 5.63. Grass palatabihy and its assigneci numerical value.

Values -0.5 O 0.5 1 1.5 2 t The "P" refers to plants poisonous to animais.

As discussed in section 5.4.1, Pasture degradation causes a change of plant compositions. More grasses and grass-like plants are observed in LDGP, and more forbs and shbs in HDGP. In order to evaiuate the impact of Pasture degradation on plant palatability, the palatability is ranked with a point system (Table 5.63). The most palatable plants has a value of 2, and poisonous plants are valued -0.5. In most cases, the PI in LDGP is higher than in MDGP, and the lowest PI is observed in HDGP. A few cases show no differences or the reverse results. However, on the average, the fiighest PI is found for LDGP. PIS fiom LDGP, MDGP and HDGP are 205, 173 and 151, respectively, based on calculation from equation 3-2 (Table 5-64), but despite the trend, there are no significant diierences between degraded pastures.

Table 5.64. Statisticd analyses on plant pdatability. Pasture # Mean C.V.(%) LDGP 12 205 ai 3 7 MDGP 13 173 a 70 HDGP 17 151 a 74

+ Vaiues in the same column foiiowed by the same letter are not sigdicantiy different at 0.05 probability level according to Tukey's HSD test.

5.4.4 Relationship between soi[ nutnents and above ground vegetation To determine if there is any reiationship between sail nutrient status and changes in plant species composition, five sites were selected, in whicti (forbs + shbs) in the quadrat account for more than 50% of ail plants in the HMSP (Table 5.65). No significaut nutrient changes were observed when pasture was dominated with forbs and shrubs, except bio-available K, which is much higher in HDGP than that in LDGPiMDGP (Table 5.66). Totai organic C and CEC in grass-dominated pasture seem slightly higher than in forbdominated pasture, but no statistical differences are found.

Table 5.65. Proportion of forbs + shrubs in dierent quadrats (%). LDGP/MDGP HDGP

GJ3, Xiahe 97 3 4 1 59 GJ4, Xiahe 77 23 44 56

Average 78 22 27 73

t Abbreviations of sites can be found in Table 3.1 $ G + GL = Grasses and grass-like plants; F + S = Forbs and shrubs.

Table 5.66. Soi1 fertility changes in forb- and shnibdominated pasture. Determinations LDGPIMDGP HDGP (with fohs & shrubs)

CEC (cm01 kg-') 28.0 a 25.4 a

Total P (g kg-') 0.74 a 0.75 a Total K (g kgeL) 19.1 a 20.1 a Bio-avdable-K (mg kg-') 227 b 407 a Bio-available-P (mg kg-')$ 29.9 a 27.8 a

t Vslues in the same row foliowed by the same letter are not si@cantIy different at 0.05 probability level accordhg to T test. $ Bio-avaiIable P includes resin-P and bicarb-Pi ad biwb-Po. Achwhenmi inebrjans is a poisornus plant to most animals. It is an indicator plant for pasture degradation. This plant was found in four sites (GJ3, HCI, LC, and SD2224). To compare soi1 nutrient changes corresponding with the occurrence of this plant, soi1 analysis data are surnmarized in Table 5.67. Tt indicates that TOC, total N, and soi1 bio-available P were slightly lower in Achmtherum inebrims dominated pasture. ûther chemicai properties are alrnost unchangeci.

Table 5.67. Soil fertility changes with occurrence of Achnathemm i~bnazts. Determinations Wibout Achiherum With Achnutherum inebrians

CEC (cmoi kg-') 18.8 a TOC (g kg-9 61.9 a Total N (g kg*') 3.7 a Total P (g kg-') 0.77 a Total K (g kg-') 20.2 a Bio-available-K (mg kge') 311 a Bio-available-P (mg kg'): 18.5 a

t Values in the sarne row foilowed by the same letter are not significantly düFerent at 0.05 probability level accordmg to T test. $ Bio-available P inciudes min-P and bid-Pi and Bicarb-Po.

5.5 Extrapolating research resuits Of the 16.1 million ha of usable grassiand in the province, Gannan, Wuwei and Zhangye prefectures make up 16.9?/i, 17.8% and 15.8% respectively. Thus, these three prefectures, in which the research sites were selected, mver more than half of the total grasland of the province. To extrapolate the results to the ara in the province with a similar ecological conditions, the area between 2,600 to 3,000 m eievation of the whole province, as well as individuai counties, was estimateci. A total of 2.3 million ha land Iies between the elevations of 2,600 to 3,000 m in the province. Based on information provided by local personnel and county statistics about 85% of the area in this elevation is pasture (Section 4.2.1.1), 3.5% of thwe lands are used for cultivaiion (Table 4-23}, and 0.6% for housingkoaddindustry, and 11% for forestryl lakes/rivers/hardly used lands, etc. Although Table 4.23 shows the category of "others" is 22% of the total land in the research areas, this inchdes hardly used lands, for exampIe, steep mountains, desert, swamps, etc., the areas lying between 2,600 to 3,000 m ASL are mostly used for grazing animals. Therefore, the assumption that 85% of this ara is used for pasture is reasonable. This results in 1.95 miIIion ha for grassland and 80,000 ha for cultivated land in Gansu province (Table 5-68). Of the 1.9 million ha grassland, 976,000 ha is regarded as lightly degraded, and another 976,000 ha as either moderately or heavily degraded (Table 5.69), accordhg to the estimation in Table 4.24.

Table 5.68. The estimated areas between 2,600 to 3,000 m ASL in diffeemt regions of Gansu (1,000 ha). Lands between 2,600 to 3,000 m ASL Region Totai land Total Grassiand CuItivated Province 45,400 2,296 1,952 80 Xiahe 868.8 75.5 64 2.6 Tianzhu 714.9 214.5 182 7.5 Sunan 2,388.6 167.7 143 5.9 Shandan 504.6 95.2 8 1 3.3

Table 5.69. The areas of degraded Pasture and cultivated lands in 2,600 - 3,000 m ASL in Gansu (1,000 ha). Land use Area (1,000 ha) % Grassland 1,952 85 LDGP (50%) 976 42.5 MDGP/fIDGP (50%) 976 42.5 Cultivated 80 3.5 Total 2,296 100 Estimations of soil total organic Cl total N and labile P losses were made on regional scaie (Table 5.70). In general the soil plough layer is about 15 cm in village agriculture since no large machinery is available. It is assumed that soi1 bulk density is 0.78 Mg m-3 for Pasture and 0.88 Mg m' for cultivated land, based on the average data fiom the five sites on local scale sampliig.

Table 5.70. Estimation on losses of soi1 nutnents over the research region (tons). HDGP Cultivated land (30-50 years) Soil elements Per hectare Whole region Per hectare WhoIe region

Soi1 organic C 23.3 22.7 x 106 47.7 3.8 x 10~

Soi1 total N 1.9 1.8 x 106 3.9 0.31 x 106 Soi1 labile-Pi 0.0054 5.3 lo3 - -

$ Labile P includes resin-P, bicarb-Pi and bicarb-Po. ,+ Potentially available Po.

It was calculated (fiom Table 5.33) that total organic C and total N losses reached 22.7 and 1.8 million tons on the HDGP,and 3.8 and 0.3 1 million tons on cultivated land (C3 1-50), respectively (Table 5.70). This corresponds to an economic loss of 6.1 biliion RMB (Cdn $1.1 billion) to replenish soil N in the province, based on urea priced at 1,334 RMB per ton (Cm, 2000). It is even harder to restore soi1 C losses if no attention is paid to soil degradation, No estimation was made on soi1 labile P losses in cultivated fields since IabiIe soil P was increased in most cases. But the labile P level was reduced when Pasture became heaviiy degraded. Total labile P lost amounted to 5,300 tons in whole region, corresponding to 54.9 million RMB (Cdn $10 million) lost to compensate with DAP at the pnce of 2,071 RMB per ton (Cm, 2000). The fate of P, as a potentially avaifable source of P, was also evaluated. The total lost in the whole region was about 32,100 tons P, which is equivaient to 332 million RMB (Cdn$ 60 million) if it is replenished with DAP. 5.6 Summary and conclusions

1) Regional ove~ew In Gansu province there are about 16.1 million ha usable grassland, and 5.1 million ha cultivated land. Of the total grassland, 51% are distributed in Gannan, Wuwei, and Zhangye prefectures where this study was conducted. Almost al1 of the lands in the province are above 1,000 m ASL. From 1,000 to about 2,600 m ASL, climatic conditions are relatively favorable for crop production. Irrigation systems are available in some areas. Water sources come fiom the Qilian Mountains along the Hexi Comdor. Thus gwd crop production is ofien achieved. Soi1 erosion control practices such as sheltering cropland are used to reduce wind speed. In some areas where salinity was a problem, planting uees in fields is another practice to improve microclimate and lower the ground water table. Transportation is more convenient than that in upper regions. Farmers therefore can easily trade their products with nearby cities or other provinces, providing for a prosperous local econorny. As a consequence, fmers have the ability and are willing to invest in their land and manage it correctly to get higher production. Organic fertilizers such as animal wastes and composts are part of their fenilization program as well. As a result, soil structure and soil fertility are improved to some extent. Therefore, soil degradation is not as severe as in the upper regions. It was estimated that there were about 2.3 million ha of land lying between 2,600 and 3,000 m ASL in Gansu. Eighty-frve percent of the lands within this range were grazing pastures. The remaining 15% included 3.5% of cultivated fields, which are vital to local fmers for food and feed production, and 11.5% of watersheds, roads, housing, industry, hardly used lands, etc. In this altinidinal belt yields are Iow and management options are resuicted. Wlthin this sub-alpine range haif the grasslands were considered as heavily to moderately degraded. This was because vast areas of pastures were gated at very high stocking rates, far beyond carrying capacity, resulting in severe grassiand degradation. It is almost impossible to find native pasture without soi1 degradation. Farmers cropped lands between 2,600 and 3,000 m ASL regardless of climatic ador topography risks, remltiag in soi1 fertility decline and soi1 erosion. Short growing seasons, around three to four months depending upon elevatioq ofien cause crops to be harvested before maturity. Farmers still exploit these lands either for grains or for forage, without considering the décts on soi1 degradation. The highest elevation at which cropland was found is around 3,050 m ASL. Above this elevation, the land is used as open range because the growing season is so short that crops rarely mature. Land use is tberefore very simple, restricted to grazing animals only duting faIl or summer, These pastutes are usually considered as lightly degraded because they are distant from the winter/spring bases. Areas between 2,600 to 3,000 m ASL have the highest potential risk for soil degradation Therefore, the research of this study was carried out within this elevation range.

2) Grassiand use and degradation a) Vegetation Plant cover could be used to quickly evduate pasture degradation. It was shown that fier Pasture becomes heavily degraded plant cover and species were changed. Plant cover was significantly reduced by pasture degradation. An average 99% plant cover was found in LDGP, while the Lowest plant cover (62%) was observed in HDGP. The proportion of more palataùle plants such as grasses and grass-like plants decreases with pasture degradation, white abundance of plants with lower forage value tends to increase. A palatability index was used to evaluate the impact of pasture degradation on plant cover. The plant pdatability index decreased from 205 in LDGP to 173 in MDGP, and then to 15 1 in HDGP, but changes were not significant due to large variation among sites and locations. AIthough plant species composition had been changed with pasture degradation, no clear links with changes in the soii fertility parameters measured were found.

b) Soi1 degradation After pasture was cultivated, soi1 degradation was evident. A considerable amount of nutrients will be lost if soi1 degradation is not prevented. For instance, soil organic matter decreased dramatically due to pasture cultivation, and potentially available nutrients such as N and P were Iost. The loss amaunted to 2.1 million tons of N and 37,400 tons of P for the total area between 2,600 and 3,000 m ASL. The cost to replenish these losses with fertiiiier would be approximately 6.1 billion of RMB (local currency) to compensate for N lost, and 387 million RMB for P lost. This loss generates a great pressure on the local fiagile economy, and reclaiming degraded lands and preventing lands fiom fbther degradation is therefore extremely important. Three major causes of soi1 degradation were encountered: soil erosion, TOC loss and dition. Severe soil erosion: Soil erosion is major cause of soi1 degradation. Heavily degraded pasture on both local and regional scales was significantly lower in %s concentration than that lightly degraded pasture, indicating that soil erosion occurred in heavily degraded pasture. Cultivation of grassiand worsened soil erosion in ail sites. Soi1 erosion was concomitant with decline in soi1 organic matter and total N, and lowering of soi1 CEC. Forty-one years' cultivation resuIted in reductions of 69% in 137Cs activity (on weight basis) and 65% in TOC in Tianzhu. Similar results were observeci on regiond de,with decreases of 77% in 13'Cs activity and 59% in TOC after more than 30 years' cultivation. Topography had a great influence on soi1 erosion. Based on I3'cs measurement and equation (34, soi1 losses on the steep dope (37% on the average) of Tianzhu-C reached 40 tons ha-' annually within 48 years' cultivation, whereas annual erosion rate was 27 tons ha-' in Tiaruhu-AB wîth 5% slope over 41 years' cultivation. Climatic differences alm flected soi1 erosion. Soil erosion rate on the flatter dopes of Tianzhu, with higher precipitation, was higher than that in drier Shandan-B. Correlation analysis indicated that 137Cs activity was strongly and positively correlated to macro-organic C (r = 0.87.') and rnacro-organic N (r = 0.86**), and to soil total organic C (r = 0.78**) and total N (r = 0.77**)on both local and regional scales. It was also found tiom local dethat sod inorganic C (r = -0.93**) and pH value (r = -0.68**) were negatively comlated with 137~sa&+, likely due to subsoil exposure. Soi1 sand content was another indicator for soit erosion if subsoil was coarser than the topsoil. At Tianzhu-A/B soi1 became coarser with pasture degradation and cultivation length. A negative power hnction was obtained between 137~sactivity and sand contents. Total organic C loss: Results fiom both local and regional scaies showed a slight decline in TOC when pasture was degraded. However, once pasture was put into crop production, soi1 TOC dropped sharply. The longer the cultivation, the less soii organic C remained. During 50 years' cultivation soi1 TOC declined rapidly at the beginning of cultivation years and the loss leveled off with increasing time of cultivation. In Tianzhu- AIB, for instance, about one-fourth of 84.5 g kgw[organic C was lost within eight years' cultivation, while it took another 30 years to lose an additional one-fourth of organic C. Regional results showed 59% of soil organic C was lost after 3 1 to 50 years' cultivation. Soil erosion and mineralization were responsible for C losses as estimated by ')'CS determination. The greatest loss of organic C was found in macrosrganic matter because it is mainly in topsoil. Over 30 years' cultivation macrwrganic C decreased by 84%. while TOC dropped by 5%. Loss of soi1 organic C was affecteci by other factors including salinity, dry clirnatic environment, and initial concentration of TOC. At the drier site of Shandan-B, only about 13% of TOC were Iost atler 29 years' cultivation, whereas 25% of TOC were lost in the humid Tianzhu-NB site within onIy 8 years' cultivation, although dope and land management were similar. Soi1 organic C was strongly correiated with soil total N (r =0.98**, n =171 in Tianzhu-NB) and organic P (r = 0.72**), thus any changes in TOC resulted in similar changes in total N and organic P. For instance, within 41 years' cultivation in Tianzhu- A/B mil organic C, total N and organic P decreased by 55%, 49% and 41%, respectively. Results 6om regional scale sampling followed the same trends with decreases of 59%, 48% and 35%, respectively, within the cultivation range of 30 to 50 years. Soil C/N ratio declined when pasture was degraded or cultivated. Soi1 CEC was strongly correlated with soil clay content (r = 97**) and soil organic C (r = 0.90**). Therefore, lower soil CEC was attributed to los of organic matter and coarser soi1 texture caused by soi1 erosion Results fiom both [ocal and regional de sampling showed that soil CEC decreased by 20% over 30 years' cultivation Soil saiinity: Once pasture is cultivated, soil EC increases in previously saline soils, but decreases in non-saline soil. At Shandan-B soil salinity is a problem, and increasing number of cultivation years results in higher EC, Sodicity is also increased because the dominant water-soluble cation is Na. Exchangeable sodium percentage (ESP)increased from 12% in MDGP to 15% in Cult-13 in Shandan-B. On the contrary, in non-saline soils such as Tianzhu-AIBIC and Shandan-A, soi1 EC decreases with cultivation. Slightly higher EC in Iightly degraded pasme are favorable for maintaining a good soil structure and benefit plant growth because the proportion of K and Ca in water-soluble cations increased. However, sodium increased firom 7% in LDGP to 22% aer41 years' cultivation field in Tianzhu-NB.

3) Soil P dynamics affected by land use Phosphorus fractionation has been usefiil in understanding the impact of soil degradation and cultivation on P dynamics in grassland soils. Conventional methods for extractable Pi are unable to detect the contribution to bio-availability of soi1 P in organic- based systems (Maroko et al., 1999). Phosphorus fractionation was therefore conducted to identify both organic and inorganic forms of P. The amount of labile Pi (resin-P + bicarb-Pi), is slightly higher in LDGP than MDGP or HDGP. More labile Pi in LDGP is probably due to higher amounts of organic C, which maintains a high biologicai activity, in tum accelerating organic C turn-over, resulting in an increase in the proportion of labile P;. Results obtained on local and regionai desindicated that labile Pi in cultivated fields, regardless of cultivation penod, was significantly higher than that in grassland. Mineralization of organic P and application of P fertilizers are responsible for this higher amount of labile Pi in dtivated fields, A pronounced change was observai in Ca-associated Pi, extracted by diiute HCI. Cultivation of pasture increased significantly the concentration of Ca-Pi. The Ca4 concentraîion increased by 50% and 62% in Cult-16 and in CuIt-41, respedvely, in Tianzhu-A/B. About the same magnitude of change was obtained on regional scaie. However, increase of oniy 21% was found in Shandan-B with 29 years' cultivation. Estirnates of the contributions Eom incorporation of subsoil by titlage, fértilhtion, and Po mineralization to Ca-Pi indicated that mineralization of organic P was a major source of Ca-Pi in cultivated fields. Incorporation of subsoil and P fertiiization contributed 3 1% and 24% to the Ca-Pi increase, respectively. Inorganic FdAl-associated P extracted by 0.1 M NaOH increased with length of cultivation in local scale sampling, but no conclusive evidence was found in regional scale sampling. Increasing number of cultivation years increased concentration of Fe/Al-associated Pi, but cultivation for less than 16 years at Tianzhu-NB did not result in a geat change of Fe/Al-Pi concentration. A part of mineralized Po might be converted into Fa-associateci Pi, resulting in a higher amount of Fe/AI-Pi in cultivated fields. The more stable form of HHC1-exuacted Pi was not affècted by land use. Labile bicarb-Po declined significantly when Pasture had been cultivated in Tianzhu-AB. No significant differences were found on a regional scale owing to large variations between locations. Moderately labile Po extracted by NaOH decreased sharply when pasture was put into crop production. For instance, it was reduced by 46%, from 175 mg kg-' in LDGP to 94 mg kg-' in Cult-41 in Tianzhu-AB, and by 1% from 51 mg kg-' in MDGP to 46 mg kg-' in CuIt-29 in Shandan-B. On a regional scale, only about one-third of NaOH- extracted Po fiom pasture was found fier 30 years' cultivation. The more stabIe ûaction of Po extracted by hot HCI afso showed a decline with pamre degradation or cdtivation years, aithough short pend cultivation (less than 16 years at Tianzhu-A/B) was not statisticaily different from pasture, Results on regional scaie did not show any significant impacts of land use on more stable Po. The proportions of Po fractions behaved differently than th5 absoiute amounts, especially for the more stable hetian- in generai, the more stable fiaction of Po declined with cultivation in absolute amount, but it increased in its proportion when pasture was cultivated. This meant that cultivation and pasture degradation caused the more labile mion of Po to be mineraiid, while the more stable fiaction remained in the soil.

4) Recommendations based on the results from this thesis When extrapolating nsearch results to an area with a sirniIar climatic condition, local modifications should be considered. Results showed that there were large variations in soi1 fertility decline and soil erosion even within the same climatic region. if soi1 salinity is a major cause of soil degradation, practices of controlling salt built-up on soil surface should be considered first. Preventing soil erosion is the top priority if crops are cultivated on a steep dope. Therefore, any practices for controlling soi1 degradation should be adapted to local conditions. To prevent soi1 fiom tiirther fertility decline and degradation, the following recomrnendations are made:

To restore pasture to their normal pmductivity, numbers of grazing animais should be restncted to carrying capacity, which is detemined by gras types, grass productivity and type of grazing animais. In sub-alpine meadow pasture with an average gras (fiesh) production of 5,500 kg ha*', 0.38 ha is needed to support one sheep unit. Pasture with a lower gras production of 2,700 kg ha", needs at least 0.78 ha to raise one sheep unit. Within the research region, it is recommended that one sheep unit require at ieast 0.65 ha if the average gras (fiesh) production is around 3,200 to 3,300 kg ha-', based on statistics from Tianzhu (Cao, 1999) and Xiahe (BAH-Xiahe, 1999). Soi1 erosion and TOC decline are major causes of soil degradation. Converting Pasture into croplands greatiy reduced soil organic C and N, as well as organic P, and resulted in severe soil erosion. A regdation on 1) management of cultivated sites to minimize TOC loss and soi1 erosion rate; 2) restriction of Wer breaking of grassland; and 3) conversion of cultivated fields to pasture should be proposed. Theoretically, dl of the cultivated lands that have a high risk in soi1 erosion in the research region should be converteci back to gazhg land. Practically, however, it is impossible to cany out this policy because cultivated land is vital to local farmers. If field conditions are not suitable for cultivation, but lands were already used for crop production, it is recomrnendable that: 1) soil nutrients and organic matter should be repienished; 2) using farm derived plant and other sources of organic matter and materials not only provide soil nutrients but also irnprove soi1 physical properties; and 3) non-native grasses should be seeded siace the grass production is usually 5-10 times higher thaa native grassland (SSO, 1993), this practice would decrease the great pressure on limited Pasture area. Minimizing the population growth me is a positive way to reduce soil lgrassland degradation In recent years, the annual population growth rate has been around 3% in the research regions (Zhu and Cui, 1996), more than 10 times higher than the national average. To get enough food and fiber, fmers are most likely to raise more animals and convert more pasture into croplands, causing even worse soil degradation. 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To determine impact of land use on soi1 fertility, soil erosion and P dynamics, a minimum of two fields were used at the same site:

A: a native gassland SO~,conbnuously used as pasture. B: a cultivated field adjoining to the pasture. A visual identification was used in 1997 in the field to categorize the degradation of grazed pasture (Table A-1). This classification was verified by quadrat method in 1999.

Table A4. Degraded pasture classification used in this study. Category LDGP MDGP HDGP Plant species and diversity More Medium Few Plant density / ground cover fi& Medium Low Zokors effects Rare Moderate Heavy

Two locations were selected dong the Hexi Corridor, Gansu province, namely, Tianzhu Grassland Station, and Shandan Horse Stud Station. These two Iocations are in the area managed by individual stations, which made it possible to get more information on soil genesis, land management, grass species, and climatic data The setected sites and basic information on the two locations are presented in Table A-2.

Table A-2. Basic information at research sites on local de.

Location-site Elevation (m) Soi1 type AP (mm)? AE (mm)? AT (OC) Tianzhu-A 2,940 C hernozem 416 1,592 -0.3 Tianzfiu-B 2,940 Chernozem 416 1,592 -0.3

Shandan-B 2,840 Chestnut 356 1,702 0.2 + AP = annual precipitation. AE = annual evaporation. AT = annual temperature. A; Location-one: Tianzhu Grassland Station, Gansu Agriculturai University (GAU). Host: Mr. Xu Changlin, Director of the Station, GAU)

The Station, Iocated in the east of the Hexi Corridor, is about 150 km northwest of Lanzhou city. It was se? up in 1956. The GPS receiver readings at the Station are 37" 1 1.79' N, 102" 47.05' E, with an elevation of 2,940 m ASL. Totd area of the grassland managed by the Station is 14 ha, of which, 1.4 ha is for cultivated fields with either oats or rapeseed. This type of the grassland and cultivated field management is well representative of the local area. More than 45% of the total precipitation (416 mm) occurs fiom July to August. The Iowest average temperature in January is -12.3T and the warmest average temperature in Suly is 11.2 OC. The main animals raised in this region are Tibet sheep, yak and horses. Native vegetation is dominated by Elymus nu~uns,Pm L. and Kobresia wiIId A natural soi1 profile was found about 150 m away from Tianzhu-A and 50 m from Tianzhu-B. It was in an erosion channel with more than 2 m depth. Four horizons were identified in the profile, named Ah, B, BC and C horizons. BeIow the horizon C two stonelines were observed. Block-lie structure was found in B horizon. Soil was formed fiom various fan-shaped alluvial deposits, coming fiom different directions, thus resulting in different soi1 texture and soi1 layers throughout whole profile. More clays were found in the upper layer. Soil parent materials are alluvial + aeolian deposit, while alluvial is dominant. Soil profile scherne is illustrateci in Figure A- 1. Before native grassland was cropped, about 30 cm of top grassland soils were dug out to make soii/root sods in situ. Those sods were then burnt for activating plant nutrition right &er they were air-dried. Soil fertility could be maintained for about 2-3 years without any yield reduction. if conditions permitted, animal wastes ( 15-20 tons per ha) were apptieû to those newly cultivated fields, This practice was abandoned der chernical fertilizers were introduced to this region in the 1980's. Sice the 1980's, urea has been a commonly applied N source for basai application at the rate of 75 kg ha". The same rate of ammonium nitrate was recommended for top dressing. if rapeseed is to be planmi, an additionai 75 kg diammonium phosphate (DAP) would be added. Average yields are 900-1.500 kg ha' grain + 500 kg ha" straw for rapesed, 1,150 kg ha-' grain + 1,900 kg ha1straw for oats, or 7.500 kg haT'dry matter if harvested for hay because of late mahirity and 7,500 kg ha-' dry matter for alpine barley hay.

Ah Horizon (O-25cm)

B Horizon (25-50cm)

BC Horizon (5040cm)

Figure A-1 . Chernozernic soi1 profile in Tianzhu, Gansu province.

Site one: Tianzhu-A (TZA)

In this site, three land use pattms were selected: a) LDGP, b) MDGP, and c) An oat field cultivated for 8 yeius. Both pastures (LDGP and MDGP) were fenced. The oat field had been rotated with rapeseed, each crop a year. Soi1 sampks were taken dong three transeas fiom southeast (SE) to northwest (NW). The transect layout in Tianzhu-A is shown in Figure A-2. The transect length was 165 m long. The second and chird msects were paraiieled to transect !, with a distance of IO m between each. In each transect, a tord of 34 soi1 samples were cokcted, six in LDGP, t4 in the oat field, and another 14 in MD-. At each samphg point, three cores were randomly sampled within an area with a diameter of 50 cm. Cores were to a depth of 15 cm, which is the plough layer. The iatecval between two samphg points was 5 m. DSampling point #

Figure A-2. Field layout and transect arrangement in Tianzhu-A.

Labeling: TZA 1-t is for the first point in tmsect one, TZA 1-2 is for the second point in the same msect, etc. The TZA2-1 is for the first point in transect two, and so on. A 5% siope fiom south to north was obsetved in the study field. There was a srnail erosion channe1 crossing three transects, between TZA 1-5 and 1-6, TZA 2-4 and 7-6, TZA 3-4 and 3-6. Sample TZA 2-6 was in the edge between LDGP and oat field, while TZA 2-20 was in the edge between the oat field and MDGP.

Site tw~:Tianthu-8 (TZB)

TZB is about 300 m northeast of TZA. Three land use patterns were identified in this site: a) Oat field cultivated for 16 years; b) Oavrapeseed fields cultivated for 41 years, and c) A fenced MDGP. In this site a crop rotation of oat-rapeseed-alpine bariey was practiced each crop a year. Faliow has mt been practiced in this area. Oats are harvested for their hay, but rapeseed and barley for grain andlor hay depending on matunty. Two transects were employed fiom SE to NW (Figure A-3.). The total transect is 210 rn long, including a 40 rn wide ravine crossing the sampling transects, but no samples were taken in the ravine. Transect one is paralleleci with transect two at a distance of 5 m. 1- 1- Total tmsect = 210 rn I

Figure A-3. Field layout and transect arrangement in Tianzhu-B.

Sampling and labeling methods in Tianzhu-B were the same as in Tianzhu-A. In each transect, a total of 35 points were sampled, 14 (tiom TZB 1-1 to TZB 1-14) for 41 years' crop field, 7 (from TZB 1-15 to TZB 1-21) for 16 years' oat field, and 14 (fiom TZB 1-22 to TZB 1-35) for MDGP. The points at TZB 1-14 and TZB 2-14 were sampled at the edge of oatdrapeseed fields before starting drop off to the ravine. Samples of TZB 1-21 and TZB 2-21 were in the edge between MDGP and oat fields (cultivated for 16 years). From TZB 1-32/2-32 dom to TZB 1-351 2-35, a 3% slope existed. A naturd erosion channel might have been there in the pst.

Site three: Tianzhu-C (TZC)

The Tianzhu-C is 4.3 km south east of Tianthu Grassland Station. According to Mr. Li Fengting, an old villager, cultivation at this site began in 1948. Yield of bariey was maintaincd at 750 kg hi1 in the first 12 years. About 15 years later, barley yield began to decline. Shortage of precipitation is the main yield-limiting factor. Steep dope cuitivation also restricts rain water percolation, but increases soil erosion, which in tum hits crop production. It was also found that slopes facing south had a higher cultivation belt than those facing the north because the former are relatively bigh in accumulated temperature. Fertilizer sources and applied rates were almost same as those in TZAIB. Basically, two land uses were selected, one was a non-fenced HDGP, and the other was a cultivated field for 48 years. Oniy one transect fiom nonh north West (NNW) to south south east (SSE) was sampled at 10 m intervals and to 20 cm depth. Three cores were randomly collected within 50 cm in diameter at each samplig point. There was a 140 m drop fiom the top (3,020 m ASL) to the bottom (2,880 m ASL) of the transect, and the level distance was about 380 m. Therefore, the transect was about 400 m long with a slope of 37% on the average. A total of 40 soit samples were taken, 6 for HDGP, 34 for aipine barley fields. The land use pattern Iayout in the fields is presented in Figure A-4. Some special features on sampling are listed in Table A-3.

Edge between HDGP and barley field

cA sntaii area of HDGP

NNW SSE

Figure A-4. Field layout and transect arrangement in Tianzhu-C. Table A-3. Some unusual sample points in Tianzhu-C. Soil sample Description Shoulders TZC1-5 to TZCI-I6 TZC 1-10 tu 1-1 1 Sampled at a very steep slope. 1-12 to 1-16 The dope is more gentle than above samples Midslopes TZC1-17 to TZC1-27 1-17 to 1-19 With a dope about 70%. 1-20 ta 1-21 With a slope of 40% 1-22 to 1-27 With a slope of 25% Footslopes TZC1-28 to TZC1-38 1-28 to 1-3 1 With a dope of 20% 1-31 to 1-37 With a dope of 15% 1-38 Located at concave of two slopes one fiom northwest another fiom south. 1-39 and 1-40 Eroded HDGP, lots of stones on surface

B: Location-two: Shandan Horse Stud Station Hust: Mr. Li Ruwang, Division Chief: Scientific and Educational Technology Transfer, SHSS, Chinese Army, Lanzhou. The Station was set up der the foundmg of the People's Republic of China, but horse ranching in this area can be traced back to the Han Dynasty, about 2000 years ago. The station is located in the middle of the Hexi Comdor, about 200 km fiom Tianzhu Grassland Station. Altitude of the Station headquarters is 2,640 m ASL. The whole land area of the Station is 219,300 ha, and total area of the grassland managed by the Station is around 125,560 ha. A total of 25,000 ha are cultivated fields cropped with spring wheat, rapeseed and alpine barley. Chute around the Station is characterized by 356 mm annual precipitation, 0.2 OC annuai average temperature. The average temperature in Ianuary and Jdy are -14.7 OC and 13.8 OC, respectively. The number of Thtan sheep and yak raised by the Station is approximately 40,000 and 20,000, respectively. Site one: Shandan-A (SDA) The SDA site is located in Section 9, Sub-Station 1, afliliated with the main Shandan Horse Stud Station. This site is 171 km NNW fiorn TiariLtiu Grassland Station. The GPS readiigs were 38' 06.02' north, 101' 12.95' east, with an elevation of 3,O4Orn ASL. Rapeseed is a dominant crop in this Sub-Station. Average grah yield is 1.850 kg ha-'. The residues are burnt after hmesting. Before 1994 each hectare received 37.5 kg urea and 800 kg single superphosphate (SSP) per year. Since then, 60 kg urea and 260 kg DAP ha-' had been applied each year. Organic wastes were never added in this tieid. More than 3,300 ha rapeseed is being cuitivated in the area managed by the Section 9. The native vegetation beIongs to cold sub-alpine meadow grasses dominated by Kobresia capillifolia (capillarykaf kobresia), Polygomm vivipmm (serpentgrass), and Carex heterostachya (hetero st achys sedge). The soil is a Chernozem, an alpine meadow soi1 (Chinese soil classification). Soii profile was dug out based on a 65 cm deep naturaiiy eroded ditch, not far From SDA The horizon A was silt loam, whiie B horizon was clay loarn when they were tested on site. The C horizon was not found even we dug to bebw 1.1 m deep. The description of the soil profle is given in Figure A-5. Soil parent materials are probably mixed alluvial and aeotian deposit.

A horizon (O - 75 cm)

AB horizon (75-87 cm)

B horizon below 87 cm /

C horizon 1

Figure A-5. Soil profile of Chernozem in Shandan-A A total of four land use patterns including LDGP, MDGP, HDGP and a crop field cultivated for 6 years (Cult-6) were identifieci. The crop field was cultivated beginning in 1960, no fertiiizers were added. Severai years later introduced Qrasses such as Efymiis dahirrims (Dahuria wiidryegrass) and El'ls sibiricus (Siberian wildryegrass) were planted when crop yields declined considerably. In spring of 1992, this field was returned to crop again, with monoculture of rapeseed, thus it has been six years' cultivation history since 1992. The transect layout is illustrateci in Figure A-6. In transect 1, only two land use patterns were observe4 namely, LDGP and Cult-6. However, four land uses were identified in transect 2, i.e. LDGP, MDGP, HDGP and Cult-6. Thus, land uses in two transects were different. Soi1 samples were coilected with two transects fiom West south West (WSW) to east north east (ENE). At each sampling point, two cores were randomly taken within a diameter of 50 cm to a depth of 28 cm, which is the plough layer. The interval between two sampling points was 10 m, transect 1 is paralleled with transect 2 at a distance of 70 m apart. Labeling: SDA 1-1 is for the 1' point in transect 1, SDA 1-2 is for the 2"6 point in the same transect-1, ..... While SDA 2-1 is for the first point in transect-2, and so on. In transect one, a total of 42 points were sampled at the interval of 1 O m, 20 points (fiom SDA 1-1 to SDA 1-20) for LDGP, 4 points (fkorn SDA 1-21 to SDA 1-24) for special samples (fiom which about 0-10 cm top soils were removed in 1976 to build a wall as a fence between rapeseed field and the pasture), and 18 samples (fiom SDA 1-25 to SDA 1-42) for rapeseed field. Points ranging between SDA 1-21 to SDA 1-24 were considered as special samples. In transect-2, a total of 47 soi1 samples were taken fiom different degraded pastures including aforementioned speciai samples, 18 samples were fiom the rapeseed field. More information on individual samples in transect 2 is tisted in Table A-4.

Table A-4. Some special sample points in Shandan-A Points Description SDA 2-1 to 2-6 Sampled in HDGP SDA 2-7 Besides zokor (Myospdax fontanierü) hole SDA 2-8 to 2-1 1 MDGP, while 2-1 1 is besides zokor hole SDA 2- 12 and 2- 13 LDGP SDA 2-14 MDGP, SDA 2-15 HDGP and lots of zokor holes encountered SDA 2-16 MDGP SDA 2- 17 LDGP SDA 2- 18 to 2-20 MDGP SDA 2-2 1 to 2-42 LDGP, while 2-35 to 2-42 in small depression SDA 2-43 to 2-47 Special samples SDA 2-48 to 2-65 A rapeseed field cultivated for 6 years (Cult-6)

Site two: Shandan-B (SDB) Shandan-B is located in Section 2 of second Sub-Station, 10.3 km northwest of Shandan-A. The GPS receiver indicates the site is 38" 10.60' north, 10 1" 16.80' east, with an elevation of 2840 ASL, 200 meters lower than in SDA. Fertilmtion and crop yields: before 1985186, about 600-750 kg SSP per hectare was applied for either rapeseed or bariey as a P source. Urea was aiso used if it was available. Since 1985i86, 135 kg DM + 90 kg urea + 75 kg rapeseed meal (residue afler extracting oil tlom rapeseed) per hectare have been added for barley, while 125 kg DAP + 75 kg urea + 75 kg rapeseed meal for rapeseed. The average crop yield is around 1,350 kg per hectare. Native vegetation is dominated by Stip putpurea ( Purpleflower needlegrass) and Am~rolepidumahsystuchys (Comrnon aneurolepidium). A soil profile was found near sampling transects (Figure A-7). It was achidly a big, deep pit. It was not very clear for individuai horizons because aii transitions with the profile were gradual. Soi1 parent material is aeohdeposit. Ah horizon (0-30 cm)

Bm horizon (50-80 cm)

- -- - C horizon (below %O cm)

Figure A-7. Soii profile of Chestnut soi1 in Shandan-B.

Each of the two transects crossed three iand use patterns. The transect 1 included three land uses, a barley field cultivated for 13 years (Cult-13), MDGP, and a rapeseed field starteci to crop in 1997 (Cult-1). The transect 2 included: a) MDGP, a barley field cultivated for 13 years (Cult-13), and c) a bariey field cultivated for 29 years (Cult-29). Soi1 samples were collected fiom east to West in transect 1, while sarnples were taken in the opposite direction for transect 2 (Figure A-8). The length of transect 1 and 2 is 1,525 m and 2,200 m, respectively. Transect 2 is paralleled to transect 1 at a distance of 75 m, ranging front west to east, point 1 is paralleled to 50th sampling point in transect I(SDB 1-50).

EAST WEST

1-. 1-. 1,525 m

Figure A-8. Field hyout and transect arrangement in Shandan-B. Sarnphg and labeiing were the meas in Shandan-A However, interval between two sampling points was 25 m in transect 1, while 50 m in transect 2. In transect 1, a total of 62 points were sampled, 23 points (fiom SDB 1-1 to 1-23) for Cult- 13, 27 for MDGP (fiom SDB 1-24 to 1-50) for MDGP,and 12 for Cult-1 (fiom SDB 1-5 1 to 1-62). In transect 2, a total of 45 soi1 samples were taken, 14 points (fiom SDB 2-1 to 2-14) for MDGP, 16 points (from SDB 2- 15 to 2-30) for Cult- 13, and 15 points (hmSDB 2-3 1 to 2-45) for Cult-29, includig two HDGP (SDB 2-42 and 2-43) (Table A-5).

Table A-5. Some special sample points in Shandan-B. Sarnple point Description SDB 1-17 Sorne stones in 25 cm depth 1-23 In the middle of road, but not in the nit 1-24 Close to the road SDB 2-14 In the rniddle of the road Close to a small road HDGP HDGP APPENûIX LI. Quadrat sampiing and specific information (regional sampling)

1. Site-Luchang (LC), Sunan County

Population: 179 (including those fiom alcohoI factory, antler section, dear station and fm) Altitude: 2,750 m, at E99O33.247' / N38O54.861' Slope: 7-8% Total area: 7,320 ha Pasture: 3,460 ha WGP= 860 ha; MDGP * 1,300 ha; LDGP a 1,300 ha) Cultivated: 27 ha Soi1 type: Light C hestnut Parent materiai: AUuviaVaeolian deposit Annuai precipitation: 253 mm huaievaporation: 1,820 mm Annuai temperature: 0-3 OC.

Records in Quadrat Pasture type MDGP HDGP Plant cover (%) 60 3O # of species 6 6 Dominant indicator Stipa purpurea Stipa bungeana individuai Species and their numbers in Quadrat (0.25 m2) MDGP # HDGP # Stipa purpurea 10 Stipa bungeana 4 Aneurolepidium dasystachys 4 Artemisia tïigida 5 Heteropappus altaicus 20 Hetempappus aitaicus 28 Agropyron cristatum 1 Carex teinogyna 36 Artemisia fngida 2 Actmathemm inebrians 1 PotentiIIa acaulis L. 2 Achathem splendens 1 2. SiteHuangchmg 1 (HCI), Huangcheng Sheep Stud Station, Sunan County Population: 1,300 Altitude: 2,720 m at El0 1°4S.G9'/ N37'52.703' Slope: 10% Total area: 25,000 ha Pasture: 13,200 ha HDGP: 2,000 ha MDGP: 4,000 ha LDGP: 7,200 ha Cultivated: 1,000 ha Soil type: Light Chesinut Parent material: Aeoiian deposit huai precipitation: 362 mm Annual evaporation: 1,112 mm

Annuai temperature: 0.6-3.8 OC

Records in Quadrat Pasture type MDGP HDGP Plant cover (%) 80 50

Dominant indicator Stipa bungeana Stipa bungeana individual Species and their numben in Quadrat (0.25 m') MDGP # HDGP # Stipa bungeana 150 S tipa bungeana LOO Heteropappus hispidus 25 Artemisia tngida 50 Carex teinogyna 68 Aneurolepidium dasystachys 50 Polygonwn avicuIare 15 Heteropappus hispidus 35 ûxytropis ochrantha 10 PoIygonum aviculare 20 Aneurolepidium dasystachys 40 VioIa philippica subsp 6 Anaphalis sinica 20 Achnathenim inebrians 5 3. Site-HC2, Huangcheng Sheep Stud Station, Sunan County

Altitude: 2,990 m Longitude: E101°41.425' Latitude: N3 T'50.729' Soi1 type: Chestnut Slope: 6%

Records in Quadrat Pasture type LDGP MDGP HDGP Plant cover (%) 100 85 70 # of species 7 7 5 Dominant Polygonum Polygonum Potentilla bifùrca indicator vivipanun viviparum lndividuai Species and their numbers in Quadrat (0.25 m2) W)GP # MDGP # HDGP # Polygonum 125 Polygonum 75 Potentilla bifbrca 100 vivipam vivipanim Kobresia 50 Kobresia 50 Potentilla reptans 25 capillifolia capillifolia Thaiictrum 3 Trollius chinesis 3 Primula 5 al pinum maximowiczii Elyrnus nutans 25 Potenda 25 Kobresia humilis 3 muitids Saussurera 10 Oxytropis 2 Pedicuiaris 5 japonica oc hrantha kansuensis Steiiera 1 Stellera 1 charnaejasme chamaejasme Trollius chinesis 5 Anaphalis sinica 10 4. Site-HC4, Huangcheng Sheep Stud Station, Sumn C0un.y

Altitude: 3,000 m Longitude: E101°30.776' Latitude: N37"51.0111 Soi1 type: Chemozem Slope: 8%

Records in Quadrat

Pasture type LDGP HDGP Plant cover (%) 1 O0 50 # of species 8 5 Dominant indicator Polygonum viviparum Polygonum sibiicum

Individual Species and their numbers in Quadrat (0.25 m')

LDGP # HDGP fC Polygonum viviparum 75 Polygonum sibiricum 75 Kobresia humilis 125 Potentilla reptans 25 Troilius chinesis 25 Hypecoum erectum 25 Leontopodium leontopodioises 75 Potentilla bif'rca 25 Potemilla multicaulis 30 Chenopodium album 20 Saussurem japonica 25 PIeurospermum cordolU 3 Stipa purpurea 20 5. Site-HCS, Huangcheng Sheep Stud Station, Sunan CouMy

Altitude: 2,960 m Longitude: E101°37.982' Latitude: N37Y1.719' Soi1 type: Chemozem Slope: 10%

Records in Quadrat

Pasture type LDGP HDGP Plant cover (%) 1 O0 90 # of species 9 8 Dominant indicator Kobresia humilis Poa annua

individual Species and their numbers in Quadrat (0.25m2)

Kobresia humilis 150 Poa annua 75 Carex heterostachya 50 Carex teinogyna 50 Pocockia mthenica 25 Aneurolepidium 25 dasystachys EIymus nutans 45 Artemisia fngida 25 Leontopodium leontopodioises 30 Potentilla bifbrca 20 Viola p hilippica 5 Pocockia nithenka 15 Potentilla muiticaulis bunge 10 Elymus nutans 32 Thermopsis lanceolata . 8 SteUera chamaejasme 5 SteUera chamaejasme 3 6. Site-Section 1 & 5, Sub-Station 1 (SDl 1/15), Shandan Horse Stud Station Population: ~70QO Altitude: 2,760 m a? E10l020.591'/N38"07.756' Slope: 3% Totai area: 83,380 ha Pasture: 53,250 ha HDGP: 8,500 ha MDGP: 15,000 ha LDGP: 29,000 ha Cultivated: 5,330 ha Soi1 type: Chernozem Parent materiai: Aeolian deposit Annual precipitation: 380 mm Annual evaporation: 1,200 mm Annual temperature: -0.5"C.

Records in Quadrat: Pasture type MDGPt HDGP Plant cover (%) 90 70 # of species 6 5 Dominant indicator Carex teinogyna Stipa bungeana t 2,900 ASL

Individuai Spezies and their numbexs in Quadrat (0.25 m2) MDGP # HDGP # Carex teinogyna 25 Stipa bungeana 45 Aneurolepidium dasystachys 25 Aneuroiepidium dasystachys 75 Poa a~ua 45 Heteropappus hispidus 25 Polygonum viviparum 30 Adenoptsora stricta 20 Taraxacum mongoIicum 30 Carex teinogyna Viola philippica 5 7. Site-SD19, Shandan Horse Stud Station Altitude: 3,040 m Longitude: E101°15.548' Latitude: N38"17.1011 Soi1 type: Chemozem Annual precipitation: 400 mm Slope: 3% Records in Quadrat Pasture type LDGP MDGP HDGP Plant cover (%) 100 95 60 # of species 7 7 6 Dominant indicator Kobresia Kobresia Kobresia humilis capiiiifolia capillifolia individuai Species and their numbers in Quadrat (0.25 m2) LDGP # MDGP fC HDGP # Kobresia 75 Kobresia 7 Kobresia humilis 3 capillifolia capillifolia Troilius chinesis 13 Trollius chinesis 8 Polygonum 150 sibiricum Leontopodium 3 PrimuIa 75 Saussurera 2 leontopodioises maximowiczii japonica Saussurera japonica 8 Helictotrichon 36 Leontopodium 6 tiieticum Ieontopodioises Polygonum 16 Astragaius 18 Taraxacum 20 vMparum sinicus mongolicum Pleurospennum 90 Carex 46 Potentilla bifùrca 6 cordolii heterostachya Thennopsis 12 Saussurera 15 lanceolata japonica 8. Site-SDZIJ28, Shandan Horse Stud Station

Population: 5,000 Altitude: 2,875 m at E101°14.231' 1 N38'1 1.239' Slope: 4% Total area: 68,880 ha Posture: 40,990 ha rnGP 14,000 ha MDGP 10,000 ha LDGP 16,000 ha Cultivated: 9,200 ha Soi1 type: Chestnut Parent material: Aeolian deposit and alluvial Annuai precipitation: 356 mm Annuai evaporation: 1,702 mm

Annual temperature: 0.2 OC

Records in Quadrat Pasture type LDGP MDGP Plant cover (%) 1O0 95 # of species 9 8 Dominant indicator Stipa purpurea Aneurolepidium dasystachys

Individual Species and their numbers in Quadrat (0.25 m2) LDGP # MDGP # Stipa purpura 14 Aneurolepidium dasystachys 22 Carex teinogna 20 Stipa purpura 5 Aneurolepidium dasystachys 13 Pocockia ruthenica I Steiiera charnaejasme 1 Potentilla biica 5 Poa annua 2 SteUera chamaejasme 1 Thennopsis lancedata 1 Poa annua 2 Pocockia ruthenica 7 Heteropappus altaicus 1 Leontopodium leontopodioises I Artemisia tngida 1 Poteda muiticaulis 1 9. Site-SD22124, Shandan Horse Stud Station

Altitude: 2,690-2,880m Longitude: E102°46.566' Latitude: N37011.649' Soi1 type: Chestnut Slope: 7-8%

Records in Quadrat

Pasture type LDGP MDGP HDGP Plant cover (%) 90 80 3 5 # of species 8 6 6 Dominant indicator Stipa purpurea Stipa bungeana Stipa bungeana

Individuai Species and their numbers in Quadrat (0.25 m2)

LDGP # MDGP # HDGP # Stipa purpurea 18 Stipa bungeana 6 Stipa bungeana 2 Aneurolepidium 1 1 Potentiila bifiirca 3 Artemisia tngida 1 dasystachys Agrop~ron 75 Aneurolepidium 8 Agropyon cristamm 70 cxistatum dasystachys Carex teinogyna 60 Heteropappus 2 Aneurolepidium 3 altaicus dasystachys Potentilla bifiirca 4 Carex teinogyna 50 Potentdla acaulis 6 ûxytropis 2 hula 1 Acbaatherum 3 ochrantha rndacoides inebrians Iris tenuifioiia 1 Astragalus 5 sinicus 10. Site-SD4, Shandan Horse Stud Station AItitude: 2,640 m at E101°24.828'/ N38°11.995' Slope: 2-3% Total area: 14,290 ha Pasture: 7,220 ha HDGP 3,600 ha MDGP 1,800 ha LDGP 1,800 ha Cultivated: 4,590 ha Soi1 type: Light Chestnut Parent material: Aeolian deposit and alluvial Annual precipitation: 253 mm Annual evaporation; 2,000 mm Annuai temperature: 2.4"C

Records in Quadrat Pasture type MDGP HDGP Plant cover (%) 70 50 # of species 7 6 Dominant indicator Achnatherum splendens Achnatherum splendens

Individual Species and their numbers in Quadrat (0.25 m2) MDGP # WDGP # Achnatherum splendens 1 Ach~thenimsplendens 1 Stipa bungeana 8 Artemisia ûigida 7 Alhm condensatum 5 Heteropappus hispidus 6 PotenMa bifurca 1 Aneuroiepidium dasystachys 7 Heteropappus hispidus 3 Stipa bungeana 5 Artemisia fngida 4 AUiumchrysanthum 3 PotentilIa multicaulis 1 11. Site-TZA+B, Tianzhu Grass Station, Gansu Agricuitural University Altitude: 2,940 m at E102°47.05' / N37"11.79' Slope: 3% Total area: 16 ha Pasture: 14 ha (MDGP = 12 ha, LDGP = 2 ha) Cultivated: 1.5 ha Soil type: Chemozem Parent materiai: AUuvial+ aeolian deposit Annuai precipitation: 416 mm Anaual evaporation: 1,592 mm

Annual temperature: -0.3 OC

Records in Quadrat Pasture type LDGP(TZA) MDGP(TZA) MDGP(TZB) Plant cover (%) 1O0 1 O0 1O0 # of species 1O 8 9 Dominant indicator Elyrnus nutans Elymus nutans Elymus nutans

Individuai Species and their numbers in Quadrat (0.25 m2) LDGP(TZA) # MDGP(TZA) # MDGP(TZB) # Elymus nutans 25 Elymus nutans 25 Elymus nutans 25 Koeleria cristata 75 Kobresia humuiis 75 Poaannua 50 Kobresia capillifolia 75 Koeleria cristata 25 Koelena cristata . 50 Polygonum 25 Poa annua 25 Potentilla multicaulis 25 vivipanim Trollius chinesis 3 Polygonum 25 Oxytropis ochrantha 25 avicuiare Pleurospermum 25 Polygonum 25 Trollius chinesis 25 cordolii viviparum Gentiana macrophyiia 25 Oxytropis ochrantha 25 Gentiana macrophylla 25 Leontopodium 25 Troüius chinesis 25 Leontopodium 25 leontopodioides Ieontopodioides Polygonum aviculare 3 Kobresia humuiis 25 Oxytropis ochrantha 25 12. Site-Nanniguo (NNG),Tianzhu Autonomous County Population: 504 Altitude: 2,970 m at E102"46.566' / N3P11.649' Slope: 9% Total area: 950 ha Pasture: 800 ha, (half of this lies between 2,600-3,000 rn) Cultivated: 37.6 ha Soi1 type: Chernozem Parent material: Alluvial + aeolian deposit

Records in Quadrat Pasture type LDGP MDGP HDGP Plant cover (%) 1O0 80 70 # of species 9 9 5 Dominant indicator Polygonum Kobresia capillifolia PoIy gonum

Dominant species and their numbers in Quadrat (0.25 m2) LDGP # MDGP # HDGP # Polygonum 15 Kobresia capiliifolia 12 Polygonum 3 viviparum aviculare Kobresia capillifolia 10 Polygonum aviculare 25 Kobresia capiltifoIia 10 Oxytropis ochrantha 4 Polygonum viviparum IO Carex lanceolata 5 Saussurea japonica 10 Saussurea japonica 15 PctentiUa bitiirca 5 Polygonurn avicdare 25 Euphorbia strachyi 8 Taraxacum lugubre 25 Kobresia humuiis 50 Kobresia humulis 50 Carex heterostachya 50 Leontopodium 5 leontopodioides Euphorbia strachyi 5 Taraxacum 5

Steiiera chamaejasme 3 Steliera chamaejasme 5 13. Site-Honggeda (HGD), Tianzhu Autonomous County Population: 74 1 Altitude: 3,040 m at E102°41.918' / N37'13.43 1' Slope: 6% Total ara: 920 ha Pasture: 800 ha (MDGP/HDGP=260 ha, LDGP=540 ha) Cultivated: 38.1 ha Soi1 type: C hernozem Parent material: Alluvial + aeolian deposit

Records in Quadrat Pasture type LDGP HDGP Plant cover (%) 95 80 # of species 8 7 Dominant indicator Polygonum viviparum Kobresia pygmaea

Individual Species and their numbers in Quadrat (0.25 m2)

LDGP # HDGP # Polygonum viviparum 60 Kobresia pygmaea 25 Saussurea japonica 25 Polygonum viviparum 50 Kobresia pygrnaea 25 Leontopodium leontopodioides 2 Poa annua 5 Saussurea japonica Trollius chinesis 3 Pocockia nithenica Leontopodium leontopodioides 4 Trollius chinesis Pleurospermum cordolii 6 Gentiana scabra 14. Site-Sangke(SK), YGahe County Population: Altitude: Slope: Total area: Pasture: HDGP MDGP LDGP Cultivated: Soi1 type: Chernozem Parent materiai: Alluvial Annuai precipitation: 428 mm Annual evaporation: 1,230 mm Annual temperature: 2.0°C Records in Quadrat Pasture type LDGP HDGP Plant cover (%) 1O0 80 # of species 8 6 Dominant indicator Elymus nutans Elymus nutans

Individuai Species and their numbers in Quadrat (0.25 m2) LDGP # HDGP # EIymus nutans 75 Elymus nutans 75 Helictotrichon tibeticum 25 Potentilla multicaulis bunge 10 2 Taraxacum mongolicum 6 2 Artemisia fngida 2 Leontopodium leontopodioises 1 Potentilia reptans 1 Anemone cathayensis 1 Oxytropis ochrantha 3 Carex teinogyna 50 Oxy-tropis ochrantha 1 15. Site-Ganjia I(GJ l), Xiahe County Altitude: 2,930 m at E102°32.112' / N35'23.954' Slope: 7-8% Total area: 77,070 ha Pasture: 71,800 ha HDGP 15,000 ha MDGP 20,000 ha LDGP 36,800 ha Cultivated: 1,650 ha Soi1 type: Chemozem Parent materiai: AlIuviaI Annual precipitation: 342 mm Annual evaporation: I,3 50 mm Annual temperature: 2S°C Records in Quadrat Pasture type MDGP HDGP --- Plant cover (%) 90 70 # of species 6 4 Dominant indicator Stipa purpura Stipa purpurea

Individuai Species and their numbers in Quadrat (0.25 m2) MDGP # HDGP # Stipa purpurea 55 Stipa purpurea 50 Carex teinogyna 50 Aneurolepidium 35 dasystachys Pocockia ruthenica 25 Carex teinogyna 75 Aneurolepidium dasystachys 25 Pocockia nithenica 50

Potentilla biftrca . 25 Roegneria kokonorica 5 16. Site-GJ3, Xiahe County

Altitude: 3,010 m Longitude: El023 1.597' Latitude: N3 5'24.266' Soi1 type: Chernozern Slope: 7-8%

Records in Quadrat

Pasture type MDGP HDGP Plant cover (%) 50 30 # of species 4 4 Dominant indicator Orinus kokonorica Achnatherum inebrians

Individual Species and their numbers in Quadrat (0.25 m2)

MDGP # HDGP # Orinus kokonorica 250 Achnatherum inebrians 2 Poa annua 50 Aneurolepidium dasystachys 3 Potentilla bifùrca I 1 PotentiHa bifurca 10 Stipa purpurea 2 Stipa purpurea 2 Altitude: 3,100 m Longitude: E102"30.138' Latitude: N3S018.1 18' Soi1 type: Chernozem Slope: 5%

Records in Quadrat

Pasture type MDGP HDGP Plant cover (%) 90 50 # of species 7 7 Dominant indicator Elymus nutans Elymus nutans

Individual Species and their numbers in Quadrat (0.25 mz)

MDGP # HDGP # Elymus nutans 22 Elyrnus nutans 7 Carex teinogyna 60 Carex teinogyna 3 1 Pocockia nit henica 15 Pocockia ruthenica 40 Anemone cathayensis 3 Anemone cathayensis 2 Artemisia fbgida 7 Microula sikkimensis 9 Potentilia multicaulis bunge Stel era chamaejasme . 1 Poa annua 5 Poa anma 3 I 8. Site-Nayi 0,Hezuo city Altitude: 3,230 m Longitude: E102O18.958'

Latitude: N34'52.06 1 ' Slope: 5% Total am: 30,860 ha Pasture: 21,400 ha HDGPIMDGP 8,500 ha LDGP 12,900 ha Cultivated: 6,100 ha Soi1 type: Chemozem Parent material: Alluvial Annual precipitation: 588 mm Annual evaporation: 1,233 mm Annual temperature: 1.9"C Records in Quadrat. Pasture type MDGP HDGP Plant cover (%) 100 100 tf of species 8 6 Dominant indicator Elymus nutans Elymus nutans

Individual species and their numbers in quadrat (0.25 ml). MDGP # HDGP # Elymus nutans 25 Elyrnus nutans 25 Ko bresia humilis 25 Saussurem japonica 5 Saussurera japonica 5 Pocockia ruthenica 50 Lamiophlornis rotata 1 Trollius chinesis 25 PotentiUa muiticaulis 3 Taraxacum mongolicum 5 Troliius chhesis 3 Artenmisia argyi 25 Poa annua 4 Taraxacum mongoiicurn 5 APPENDIX m. Principal persons inteMewed dufing three trips to Gansu.

Table Ad. Principal persons interviewed during three trips to Gansu. Locaîion and site Key perwns visiteci Title ot8&tions Date of visit m/d/y Provincial Mr. Zihe Shang Director GGRS 06/11/97 Mr-ZhizhongCao Head DG, GAU 061 t il97 Mr. Tiaawei Guo Director SFI, GAAS 06/10197 Mr. Xuidai Mo Professur DG, GAU 06/23/99 Sunan Mr. Shangwen Wen Director County ATTS 07/04/99 Luchang Mr. Yufeng An Technician DDS 07/05/99 Huang- Mr. hquan Wang Technician SSS 06/30/99 cheng Shandan Mr. Wulin Liu Director M,SHSS 06/1 3/97 Mr. Ruhang Li Director SED,SHSS 08/11/97 Mr. Renpei Dong Director AM, SHSS 08/11/97 Mr. Changgong Jin Director MTD, SHSS 0811 1/97 SDi Mr. Chaowu Tang Depu@ Head SD 1, SHSS 07/02/99

GGRS = Gansu GrassIand Research Institute. DG = Department of Grassland. GAU = Gansu Agriculturai University. sn = Soi1 and Fertilizer [nstitute. GAAS = Gansu Academy of Agicultural Sciences. ms = Agricultural Techaology Tiansfer Section. DSS = Deer Stud Station. SSS = Shep Stud Station. AHD = Animal Husbandry Division. SHSS = S handan Horse Stud Station. SED = Scientitic and Educatiod Division. AN = Agricuitural Research [nstitute. ATTD = Agriculturai TechaoIogy Transfer Division. SD 1 = Sub-Station-one, SHSS. Table Ad. Principal persons interviewed during three trips to Gansu (cont'd).

Location and site Key persons visited Titie Organizations Date of visit ddly Shandan SD1 Mr. Wenhui Lu Leader SD 15, SHSS OS/1 2/97 Ms. Xiaoyun Wang Technician SDI9, SHSS SD2 Mr. Changrong Wang Head SD2, SHSS Mr. Shunji Wang Technician SD2, SHSS SD4 Mr. Jianqi Li Tec hnician SM, SHSS Tianzhu Mr. Yonglin Cao Deputy Dir. County AHD Mr. Ziqian Zhang Head County GS TZA/B Mr. Changih Xu Director Tianzhu GS TZC Mr. Fengting Li Senior Village villager NNG Mr. Shenggao Luo Head Village HGD Ut. Jiaqi Lu0 Technician Vilage Xiahe Mr. Guopeng Hu Deputy Dir. County AHD SK Mr. Huiye Yin Technician County GS GJ Mr. Longxi Ma Head County GS Hezuo Mr. Lao Cai Deputy Dir. Gannan AHD NY Mr. Shumao Wang Head Gannan GS

- -- -- pp -- -- SD 15 = Section-5 of Sub-Station One, SHSS. SD19 = Section-19 of Sub-Station One, SHSS. SD2 = Sub-Station two, SHSS. SD4 = Sub-Station four, SHSS. GS = Grassland Station. TZA/B = Site-A and site-B in Tianzhu, respectively. TZC = Site-C in Tianzhu. HGD = Vüiage of Honggeda, Tianzhu. SK = Sangke Township, Xiahe County. GJ = Ganjia Township, Xiahe County. NY = Nayi Township, Hezuo City. APPENDIX IV. Estimation on soi1 nutrient losses or gains

A: TOC loss at Tianzhu-B

To determine causes of rapid decline in TOC &er cultivation, the following estimation was made at Tianzhu-A/B: 1) About 92% of topsoil(0-15 cm) was lost aller 16 years' cultivation based on the measurement of I3'cs activity in Section 5.3.1 with equation of 3-4. It was assumed that TOC concentration from 15 to 30 cm was constant, with 64.5 g kg-' (calculated based on average concentration of organic matter in O - 30 cm depth was 125 g kg-', Chen et al., 1995). 2) If 92% of topsoil were replaced by subsoil, it would account for a decrease of

TOC to (gx 80.5 + = 65.8 g kg-', usuming pasture wu converted 1O0 1O0 to cropland when it was moderately degraded. 3) The actuai TOC concentration in Cult-16 was 51.4 g kg" (Table 5.13). Mineralization of organic matter should be responsible for the diierence of (65.8 - 51.4) = 14.4 g kg'' TOC. 4) Of the total TOC lost (80.5 - 5 1.4) = 29.1 g kg-', soil erosion and minerdiration accounted for about 5 1% and 49%, respectively.

B. Fertiiiier contribution to total P at Tianzhu-B

To estimate how much added fertilizer P contniuted to soil P pools, the following caladation was made: Annuai fertiiizer input: 15. 1 kg P ha' as diammonium phosphate @Ai'). Crop yietds: Rapeseed 1,250 kg haa grain. 500 kg ha-' straw. Oats 1,150 kg-' grain. 1,900 kg-' straw. P removed Çom: 1) Rapeseed Grain = 1 1.3 kg P hâl assuming 0.9% P in grain (Lin, 1994).

Straw = 2.25 kg P ha-' assuming 0.45% P in straw (Lin, 1994). 2) Oat Grain = 7.48 kg P ha-', assuming 0.65% P in grain (Lin, 1994). Straw = 4.75 kg P ha-', assurning 0.25% P in straw (lui, 1994).

Average annual removai for the rotation of oat-rapeseed:

A total of 16 yean' balance: (15.1-12.9)~16 = 35.2 kg ha". Whole mass of soi1 per hectare in top 15 cm is calculated as: M=AxDxBxlOOO (A-1) where M = mas of wii (kg ha-'). A = area of one hectare (m'), D = sampling depth or plough Iayer (m) B = buik density (Mg m-3). For Cult-16, M= 10000x0.15x0.75x1000 = 1.1 x 106 kg ha".

Thus, fertilizer contribution to P built-up = 35.2xi03 =0-032gpkgml 1.1x106

C. Fertiher conmiution to totd P at Shandan-A

To find out potential contribution of fertilizatiori to soi1 total P, the balance of total P was made accordmg to the foüowing calculation: balfertiluer input: 42 kg P ha' as single super phosphate (SSP). (1992-93). 52 kg P ha*l as DAP, (1994-97). Crop yidds: 1,850 kg ha1grain of rapeseed. P removed: Rapeseed grain = 17 kg P, assuming 0.9% P in rapeseed (Lin, 1994). Crop straw was bumt &er harvesting, loss of P was negligible. Six years' baiance: (42 x 2 + 52 x 4 - 17 x 6) = 190 kg P ha*'. Whole mass of soi1 in top 28 cm accordiig to equation of (A-1):

M = 10,000~0.28 x 0.82 x 1,000 = 2.3 x 106 kg ham' Thus, fertilizer contribution to P built-up was:

D. Fertiiizer contribution to total P at Shandan-B

Annual fertilizer input: 26.1 kg P Idas DAP (26.1 kg P). 0.8 kg P b' as rapeseed meai, assuming 1.08% P in rapeseed meal (Nanjing Soi1 Institute, 1978) Crop yields: 1,350 kg grain per hectare for barley or rapeseed. P removed: 1) Rapeseed = 12.2 kg P ha-', assuming 0.9% P in rapeseeds (Lin, 1994). 2) Barley = 8.1 kg P ha'. assuming 0.6% P in gnins (Lin, 1994).

Annual P removal: (""; 81) = 10.2 kg P lu1(barley-rapeseed rotation).

Al1 of the straw was bumt after harvesting. 13 years' baiance: (26.1+0.8-10.2)~13 = 217 kg ha-'. Whole mass of soil in top 28 cm base on equation (A-1):

M =10,000 x 0.28 x 1.01 x /O00 = 2.8 x 106kg ha-'

217 x /O00 Thus, fertilizer contribution to P bu&-up = ( 2-8 106 ) = 0°8 s kg-'-

The calcu1ation deuly showed that the .@cant increase of 0.08 g P kg" total P in Cult- 13 was tiom addition of P fertilizer and rapeseed meals. E. Estimation on sources of Ca-P; at Tianzhu-B

To determine the causes of higher amount of Ca-Pi in cultivated fields, the following estimation was made: 1) About 92% of topsoil was lost after 16 years' cultivation according to '37~s measurements (Section 5.3.1 with equation of 3-4). if subsoil had Ca-Pi of 204 mg kg-' (Table A-7, assuming the concentration of Cdihm 15 to 50 cm is constant, previous study dso showed there were no difl'erences in TF corn the depth of 15 to 45 cm, Chen et al., 1995), replacing 92% of the top 15 cm by

subsoil would account for an increase of Ca-Pi to 1O0 mg kg" in topsoil &er 16 years' cultivation.

Table A-7. Phosphorus fractions (mg kg") in roi1 profile of Tianzhu-AIB. P fractions MDGP B horizon C horizon ..... Resin-P (1) 20.5 2.0 1.1 Bicarb-Pi (2) 18.1 3.7 1.1

(1) + (2) 3 8.6 5.7 2.2 NaOH-Pi 15.2 4.1 4.4 DHCI-Pi 163.3 209 300 HHCI-Pi 104.6 89 - Total-P 819 780 546

2) In Appendi IV-B, fertüizer P was estimated to contriiute approximateiy 32 mg kg*' to P pools during 16 y-' cultivation. It was assumed that this hction was mainiy in Ca-Pi form. 3) Organic P mineraiization amounted to about 46 mg kg-' from MDGP to Cuit-16 (calculated from Sum-Po column in Table 5.38). 4) Iwrgank P increases in other fractions than Ca-Pi was 16 mg kg", calcdated tiom Table 5.37 as: Pi fi0111 Cult-16 = 165.1 mg kg" (min-P +bi~aïb-Pi+ NaOH-Pi + KHCI-Pi ). Pi fiom MDGP = 158.4 mg kg-' (resin-P +bicarb-Pi + NaOH-Pi + HHCI-Pi ).

This gives a balance of Ca-Pi as shown in Table A-8.

Table A-8. The balance of &Pi (mg kg*') der 16 years' cultivation of MDGP. Ca-Pi source Concentration (mg kg-') Original Pasture soi1 (MDGP) 163 Addition of P fertilizer during 16 years +32 Po mineralkation +46 lncrease in other Pi fractions -16 Incorporation of subsoil 205- 163 = 42 Sum of above five sources 267 Actual &er 16 years' cultivation Balance

The additional 15 mg kg-' Ca-Pi is most likely fiom mineralkation of applied animal wastes. The most likely sources of higher Ca-Pi in Cult-16 are therefore 1) addition of P fertilizer, 2) incorporation of subsoil, and 3) minerakation of Po either fiom organic matter or fiom animal wastes. Organic P mineraiization accounts for 46 mg kg-', Le. 34% of the increase. if mineralization of animal wastes is dso accounted, the total mineralization would contnbute 45% to the totd increase of Ca-Pi. ïhe mineralization rate is quite similar to the estimation on TOC lost by mineralization in Appendii IV-A. incorporation of subsoil and addition of P fertilizer contnbute about 3 1% and 24% to Ca-Pi, respectively. APPENDIX V. Plant paiatabiiity

The paiatability of most of the plants found in this study is characterized as follows: Achnathenim splendens is a perenniai gras, its paiatabiiity is fairly good (Jia, 1987). Anropyon cristatum (crested wheat-grass) is a hardy long-lived perennial bunchgrass. It is highly palatable to aii classes of livestock. Allium (nodding onion) is a perennial herb with characteristic onion-like odor and taste. It is usually succulent and ofhn abundant, is highly palatable to cattle and sheep. But different species Vary considerably. Anauhalis (pearl everlasting) is a bunched or loosely tufted perennial herb of the aster family. It is not an important forage plant. Anemone (globe anmore) is a perenniai herb of the buttercup family. As forage, Anemone is unimportant, being practicaily worthless for al1 classes of livestock. Some species are known to contain poisonous substances. Aneuroleuidium das~stachvs(common anuerolepidium) is a perennial ps. Its palatability is fairly good for goats and sheep when Young. The palatability is usually low in summer (Jia, 1987) Artemisia (saaebrush) is a mshrub, has a low, perennial, woody base. The forage value of this plant is fairy good in palatability for cade and very good for sheep and goats, especiaily during the winter and spring. Astramlus (poisonvetch) is a perennial herb. A considerable number of species in the large Astragdus genus are recognized as poisonous to livestock. Some species are paiatable to ail classes of livestock. Carex (sedges) is a herb of worldwide distribution. It resembies the gras somewhat, and is commonly referred to as grass-like plant, Its forage value is classified as fairly good for sheep and very good for cattle- Elynus (dd-ryes) is a fairly large genus of rather taIl grasses. Generadly speaking, the foiiage of wild-ryes is harsh and is only moderately paiatable to Livestock. Gentiana (gentia.) is an annuai herb. It is relatively low in palatability, hndamentdy not a good forage plant, but used medicinal purpose and therefore much collected. Hetero~ap~usdtaicus (altai heteropappus) is a perenniai herb. It is relatively low in palatability (fia, 1987). -Iris (iris) is a large genus of herbaceous plant. It is wonhiess as forage plant, and sometimes is an important obstacle to range improvement, in that it tends to increase on overgrazed areas. Koeleria (junegrass), also known as mountain junegrass, is a perennial bunchgass. In generai, junegrass is fairly good to good forage. In some localities it is considered very good to excellent forage. ûxytropis (crazyweed), in general, is a shmb, poor in palatability, or poisonous to some animals. Pedicularis (fdeafs) is an annual or perennial weed. It varies in its paiatability, according to the species, fiom practically worthiess to, at best, fair forage for livestock, being more palatable to sheep than to cattle. -Poa (bluegrass) is a perennial valuable gtass. It ranks among the rnost paiatable of al1 grasses, many of biuegrasses being rated as excelient for cattle, horses, sheep, and elk. Pocockia ruthenica (ruthenian medic) is a perennial herb. It is very good in paiatability for dl kinds of animals (Jia, 1987). Polv~onum(knotweed) is an annual herb. It abounds on poor soils, or on areas where such disturûiig influences as overgrating and trarnpling have depieted the perennial plant cover. It is usudy low in pafatab'ity, being practically worthless as forage for cattIe and horse, and only fair for sheep and goals. PoJg~onum aviculare (knotgrass) is a perennid grass. It is good forage for al1 types of animais (Jia, 1987). monun vM~arum( serpentgrass) is a perennial herb. It varies in its paiatability, good forage for goats, but camels do not eat it (fia, 1987). Potentilla (cinquefoil) is a perenniai herb belonging to the rose famiiy. It possesses very Little forage value, ranking as poor to fair for sheep and wonhiess to poor for cattle. On many areas abundance of various species of cinquefoil indicates range deterioration. Roemeria is a perenniai grass. Its paiatabiiity depends upon the species. In generai, it is good to very good forage (Jia, 1987). Steiiera (tuber starwon) is a weed. In paiatability it is fairly good for sheep, and poor to fair or cattle. Stioa (needtegrass) is perenniai bunchgrass. It ranks fairly high as forage plant on most rangeland. Taraxacum (dandelion) is a weed. The presence of dandelion on the range may or may not indicate overgrazing conditions. However, it occurs on sites where the normal plant cover has been depleted as a resuIt of overgrazing or less favorable rnoisture conditions due to abnormal drainage, trampling, and drought. Thalictrum (meadowrue) is perennial herb (shnib). In generai, its paiatabiiity is practically worthless to poor for cattle or sheep. Thermo~sis(goidenpea) is a bitterweed. It is worthless as range forage, low palatability, is suspected of poisoning of livestock.