Sub-Alpine Grassland Sols of Gansu, China
Total Page:16
File Type:pdf, Size:1020Kb
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 The author has granted a non- L'auteur a accordé une licence non exclusive licence aüowing the exchisive permettant à la National Lïbrary of Canada to Bibliothèque nationale du Canada de reproduce, loan, distriiute or selî reproduire, prêter, distribuer ou copies of this thesis in microform, vendre des copies de cette thèse sous paper or electronic formats. La fome de microfiche/fiI.m, de reproduction sur papier ou sur format électronique. The author retains ownership of the L'auteur conserve la propriété du copyright in this thesis. Neither the droit d'auteur qui protège cette thèse. thesis nor substantial exiracts fiom it Ni la thèse ni des extraits substantiels may be printed or otherwise de celle-ci ne doivent être imprimés reproduced without the author's ou autrement reproduits sans son permission. autorisation. PERMISSION TO USE In presenting this thesis in partial fiIfilment of the requirements for a Postgraduate degree fiom the University of Saskatchewan, 1 agree that the Libraries of this University may make it kly avaiIabIe for inspection. I ttrther agree that permission for copying of this thesis in any rnanner, in whole or in part, for schoIarly purposes rnay be granted by the professor or professors who supervised my thesis work or, in their absence, by the Head of the Department or the Dean of the College in which my thesis work was done. It is understd that any copying or publication or use of this thesis or parts thereof for finand gain shall not be allowed without my written permission, it is also understood that due recognition shall be given to me and to the University of Saskatchewan in any scholarly use which may be made of any matetial in my t hesis. Requests for permission to copy or to make other use of material in this thesis in whole or part should be addressed to: Head of the Department of Soil Science 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