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sur le développement des zones arides et semi-arides

Titre : Characteristics of Soil Macropore on the Loess Plateau and Their Effects on Soil Water

Auteur : 李同川

Grade : Doctoral Dissertation 2017

Université : Northwest A&F University

Résumé partiel
With the advent of large-scale restoration of vegetation in the Loess Plateau,northwest China,there has been an increase in concern about the suitability of loess soil to support permanent vegetation cover.The substantial increase in vegetation cover had a marked effect on properties of the soil,including deepsoil profile water content.This has,however,hindered the sustainable development of vegetation in the plateau region.Because of this,efforts to increase the infiltration and storage of rainwater in the soil have become more urgent.Natural vegetation recovery could improve considerably soil pore characteristics.On the other hand,a substantial increase in vegetation could promote the development of soil-dependant animals by providing abundant food and suitable habitats.The physical activities of soil-dependant animals could dramatically increase the amount of soil macropores.Soil macropore are closely related to water storage and regulating capacity of the soil water reservoir.The quantification of soil macropore characteristics and studying the relationship between the macropore and soil water could be critical in revealing the regulating mechanism of soil macropore on the rainfall and could in turn be used to devise strategies for sustainable recovery of vegetation in this region.In this research,we characterized the macropores associated with different types of vegetation and evaluated the effects of soil macropores on saturated hydraulic conductivity(Ksat)by collecting undisturbed soil cores for four treatments : areas dominated by Quercus liaotungensis(QLI)and Pinus tabuliformis(PTA)in Fu county and by Caragana korshinskii(KOP)and Medicago sativa(MSA)in Shenmu county in Shaanxi Province on the Loess Plateau.Two methods of scanning soil cores with X-ray CT and filling subterranean nests with thin slurry of orthodontal plaster in the field were used to generate three-dimensional images of ants nest(Camponotus japonicus)and their effects on water infiltration and soil evaporation in the Liudaogou catchment.And we assessed the main factors that could affect the characteristic of ants nest.The main conclusions of this study are as follows:1.A medical computed-tomography(CT)scanner and the ImageJ software were used to obtain the macropore data(2D and 3D)in the cores collected from soil under QLI and PTA in Fu county,KOP and MSA in Shenmu county.The 2D characteristics of soil macropore included macroporosity,largest pore area,amounts of macropores,circularity and fractal dimension.The 3D characteristics of soil macropore included macropore surface area density,branch density,junction density and connectivity.Except for the cicularity,the values of all macropore parameters for the four treatments were in the order : QLI > PTA > KOP > MSA.Soil macropore characteristics improved with the increasing time.Soil under KOP40 treatment had better macropore network than that under KOP22.In addition,fractal dimension was significantly(P<0.001)correlated with macropore number(R2=0.928)and macroporosity(R2=0.838).2.The saturated hydraulic conductivity(Ksat)varied greatly among four treatments.The mean value of Ksat was highest in the QLI treatment(0.073 cm/min),followed by PTA(0.063 cm/min)and KOP(0.054 cm/min)treatments.Soil under MSA treatment had the lowest Ksat(0.018 cm/min).The Ksat in KOP40 treatment(0.054 cm/min)was higher than that in KOP22(0.048 cm/min).CT measured macropore parameters(macroporosity,amounts of macropores and fractal dimension)were positively(P<0.001)correalated with Ksat.The fractal dimension accounted for 73.7% of the variation in Ksat.As a single variable,bulk density was negatively correlated with Ksat and accounted for the best variation(80.1%).Bulk density and macroporosity were the best combination of parameters for determining Ksat and accounted for 86.2% of its variation.Macropore 3D parameters correlated positively with Ksat,however,the coefficients of determinations between 3D parameters and Ksat were lower than that of 2D parameters.Moreover,the soil organic matter and soil texture were not significantly(P>0.05)correlated with Ksat.3.The ant nest in the field was composed with vertical tunnel connecting a series of flattened horizontal chambers.Ant nest could reach 60 cm depth in the field,and the diameter of nest tunnels ranged from 4.1 to 6.6 mm.

Mots clés : Macropore； ants； saturated hydraulic conductivity； preferential flow； soil evaporation；

Présentation (CNKI)