The Influence of the LAI Growing Value During the Vegetative Period on the Changing Anti-Erosion Efficiency of Some Crops

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The influence of the LAI growing value during the vegetative period on the changing anti-erosion efficiency of some crops

K. Klima Department of General Plant and Soil Cultivation, University of Agriculture, Kraków, Poland

Abstract

This paper contains results of the research conducted in 2000–2003 in the Mountain Experimental Station in Czyrna near Krynica (southern Poland, 545 m above sea level). The objective of the research was to determine the effect of growth of over-ground parts of fodder beetroot, winter triticale, and horse beans on reduction of intensity of soil losses. The research was conducted with the simulated rainfall on the hillside of 16% slope angle. The simulated 105 mm rainfall of 1.75 mm/min was applied during 7 selected developmental stages of the studied plants. Measurement of the leaf area of the investigated plants was conducted by means of the ‘Sun Scan Canopy Analysis System’ apparatus for LAI. From the results obtained, it was stated that the soil protective efficiency of fodder beetroot, horse beans and winter triticale started respectively at about 60%, 30% and 15% of the plants covering the soil surface. The influence of the growth of over-ground parts of the studied plants on the less intensive soil erosion can be shown by the following regression equations: for fodder beetroot: y = -9,37x + 29,4; (R² = 0,677; n = 82 ); for horse beans: y = -8,44x + 26,41; (R² = 0,698; n = 96) for winter triticale: y = -4,98x = 15,61; (R² = 0,66; n = 112) The results obtained made it possible to verify the nomograms under Polish conditions determining the value of the ‘C’ indicator present in the USLE equation for fodder beetroot, horse beans and winter triticale. Keywords: LAI (Leaf Area Index), water erosion, simulated rainfall, fodder beetroot, winter triticale, horse bean.

1 Introduction

To successfully introduce the empirical model of USLE [18] in Europe it is necessary to verify its indicators in this part of the world. Necessity of such verification was pointed out by Bazoffi et al [3] and Schwertmann et al [16] long time ago. One of the factors responsible for erosion intensity of soil cultivated in agriculture is the kind of plant cover. Plant ability to counteract the erosion depends mainly on the rate of growth of over-ground parts, which protect soil against splashing and decide of interception. Among generally available scientific papers concerning the indicator value of plant cover C in USLE pattern, very few publications describe precisely and dynamically the influence of growth of over-ground parts during their characteristic developmental stages on their soil-protective efficiency. It refers, among others, to sugar beet [4] and also to spring wheat and spring barley [14]. The objective of the research performed was to determine the influence of growth of over-ground parts of fodder beetroot, winter tritacale and horse beans on reduction of intensity of soil losses.

2 Method

Field experiment was conducted on a hillside of mean angle of 16 % in years 2000–2003 in Mountain Experiment Station in Czyrna near Krynica (545 meters above sea level, West Beskid, southern Poland). Description of the Station can be found in Klima’s publication [10]. One-factor field experiment was set up by means of randomising blocks and was repeated four times. Each studied crop plant (fodder beetroot, winter tritacale, horse beans) was cultivated on 4 small fields, their sizes being 22,13 x 1m. Simulated rainfall was applied during the experiment. Józefiaciuk and Józefiaciuk’s sprinkling machine [8] of 0,66 m² (100 x 66 cm) sprinkling area was used. The simulated rainfall of 105 mm and intensity of 1,75 mm/min was applied during seven developmental stages of the studied plants (Table 1). This type of rainfall, according to Chomicz [5] classification, is the type III of torrential rainfalls (B3). For measurement of over-ground area of the studied plants, ‘Sun Scan Canopy Analysis System’ apparatus for LAI was used. LAI was determined on every field directly before sprinkling. Thus, in every year of the performed study (2000–2003) there were taken 4 measurements of intensity of soil losses and LAI during each of 7 developmental stages of studied crop plants. Names of developmental stages have been shown in table 1. The soil on which the experimental fields have been set up, is described as brown, developed from eluvium of flysch rocks, its grain size being of medium skeletal loam. The average grain size analysis was of: 28% of sand, 29% of dust, 43% of silt, 3,1% of organic substances, pH in KCl equalled 5,0. The indicator value of soil susceptibility to runoff, that is the ratio of dust fraction to colloidal slit was 2,1. The slope gradient of experiment fields was determined by means of numerical terrain model using two computer programmes: SURFER (licence number 19498) [9] and DIDGER (licence.

Development and Application of Computer Techniques to Environmental Studies X G. Latini, G. Passerini & C. A. Brebbia (Eds) © 2004 WIT Press, www.witpress.com, ISBN 1-85312-718-3 Development and Application of Computer Techniques to Environmental Studies X 107 number D-5010). The numerical terrain model consisting of x, y, z 5622 points set on the experimental field, was obtained by digitalisation of contur lines on the topografic map. Statistic calculations and chards were made using STATISTICA computer programme (licence number BXXP3080075221FAN5).

Table 1: Developmental stages in which measurement was performed.

Fodder beetroot Winter tritacale Horse bean Gasowski & Ostrowska [7] Zadoks et al [18] Gasowski & Ostrowska [7] Developmental Number Developmental Number of Developmental Number of stage and scale of days stage and scale days since stage and scale days since code of the since code of the the revival code of the seeding stages seeding stages of spring stages time time. vegetation. Mean Mean Mean Germination 9 Beginning of 2 Germinal root 14 (03) spring visible (05) propagation (21) Sprouts (10) 17 Beginning of 11 2nd leaf 32 tillering (30) developed (21) Development of 28 First awns 46 6th leaf 54 three pairs of visible (49) developed (31) leaves (24) 7th leaf is 8 cm 59 Full flowering 58 9th leaf 75 long (31) (64) developed (44) 11th leaf is over 87 Late milk 86 First petals of 99 10 cm long (35) maturity (77) corolla (57) Interrows close- 99 Hard wax 100 Flowering of 116 up (42) maturity (87) first bunches (62) Three week 120 Dead maturity 114 Pods visible in 131 after interrows (92) five bunches close-up (44) (76)

3 Results

From the results obtained it was stated that the soil-protective efficiency of fodder beetroot starts when beetroot plants cover at least 60% of soil, which is equal of LAI value of 0,6 (fig.1). As far as horse beans is concerned the value equalled about 40% (LAI 0,4; fig 2), whereas the value for winter tritacale equalled 16% (LAI 0,16; fig 3). The earlier Klima et al’s research [11] showed potato’s soil-protective efficiency of 80% (LAI = 0,8), spring barley of 30% (LAI = 0,3) and meadow of 4% (LAI = 0,04).

The influence of growth of over-ground plant parts on the reduction of intensity of soil losses proved in the research can be shown in the following regression equation: for fodder beetroot y = -9’37 x + 29, 4; (R² = 0,677; n=82); for horse beans y = -8,44 x + 26,41; (R² = 0,698; n= 96); for winter tritacale y = -4,98 x + 15,61; (R² = 0,66; n=112). Regression importance level was of α = 0,01. The amount of soil loss (mean of 112 fields) received from fodder beetroot fields equalled 23,6 g 1m², from horse beans fields 15,4 g 1m², and from winter tritacale fields 8,1 g 1m². Therefore it can be stated that winter tritacale protected soil twice better than horse beans and three times better than fodder beetroot. Very few scientific publications undertake the problem of influence of growth of over-ground plant parts on their soil-protective efficiency [4,14]. Other works concerning the influence of LAI area on intensity of soil losses, point out that the increase of LAI area is directly proportional to interception [1,6] and inversely proportional to splashing intensity [13]. Nevertheless the authors mentioned above did not describe this interdependence as a mathematical formula, what has been done in this work. Those few works which describe the soil-protectiveness value of plants dynamically, point out that plant anti-erosion activity begins at 20–30% of soil cover [13,14]. The results shown in this work prove that it is substantial simplification of the problem as the soil protective values vary for various plants. The research showed that for fodder beetroot the mean value is 60%, for horse beans 40% and for winter tritacale 16%. The relatively high value for fodder beetroot (60% of soil cover) may be connected with the fact that this root-crop plant is cultivated in wide furrows (60 cm), which according to agricultural science must be opened twice in May. Such technology is almost a provocative factor for soil erosion. The low value for winter tritacale soil cover (16%) proves its high value as soil-protective agent which has been mentioned in several works [13, 15]. In modified USLE equation for Bavarian conditions Schwertmann et al [16] suggested their own classification of cultivation periods and plant development for creation new C indicator charts. In Poland such C indicator charts for Polish conditions have not been created yet. In the work of Banasik et al [2] we can find the C indicator values for crop cover for the certain months of the year. This is one of typical simplification used for parametrical method of erosion prognosis e.g. in the universal soil losses equation USLE [17] in which the C indicator value is read from nomograms. These simplifications are one of the reasons of lack of precision in erosion prognosis because, as this work has proved, LAI value for fodder beetroot increased in May of 0–0,2, winter tritacale of 1,2–2,2 and horse bean of 0,1–0,7. Therefore to be able to give more precise soil erosion prognosis using parametrical equations, one should use data of developmental stages of plants investigated. The necessity of this approach was pointed out also by Laflen [12]. The performed studies allow for the conclusion that the results of this work may be useful for verification of nomograms defining the C indicator value present in USLE equation under the conditions as present in Poland, for fodder beetroot, winter triticale and horse bean.

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4 Conclusions

1. Soil-protective efficiency of fodder beetroot begins when plants cover the soil surface in 60%, for horse beans this value equals 30% and for winter tritacale 16% of soil needs to be covered. 2. The influence of growth of over-ground parts of investigated plants on the reduction of soil loss intensity can be shown in the following regression equation: for fodder beetroot y = -9,37x + 29,4 ; (R² = 0,677; n = 82) for horse bean y = -8,44x + 26,41 ; (R² = 0,698; n = 96) for winter tritacale y = - 4,98x = 15,61 ; (R² = 0,66; n = 112). Regression importance level was of α = 0,01.

References

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