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thus grassland productivity. Keywords: Grazing intensity; Spatial variability; Geostatistics; Soil properties; Correlations 1. Introduction 12 Inner Mongolia grassland has been severely deteriorated in recent years because of inappropriate management, that resulted in an increasing degradation of the vegetation cover followed by pronounced soil erosion and nutrient depletion (Li et al., 2000). These processes may cause low water storage capacity and loss of soil fertility, consequently decrease the grassland productivity. Therefore, to develop sustainable management strategies, the processes emerging from pasture degradation by grazing are urgent to be understood as they play a key role in the ecosystem stability. Grazing associated with animal activity altered hydraulic and mechanical soil properties. Greenwood et al. (1997) found significant differences in unsaturated hydraulic conductivity, soil strength and bulk density for the surface soil between ungrazed and grazed pastures. Warren et al. (1986) reported that trampling animals caused soil deformation by exerting high ground contact pressures under their hooves. Besides soil compression, shear stresses further destroy soil structure by kneading and homogenization, which mainly related to a change of macroporosity and the connectivity of the pore system. Destruction of soil structure was observed for sheep grazing (Proffitt et al., 1995), cattle trampling (Pietola et al., 2005), and reindeer herding (Peth et al., 2003). Such changes depend not only on the magnitude of applied stresses, but also on the soil moisture controlled aggregate stability at the time of trampling (Horn and Fleige, 2003; Richard et al., 2001). Furthermore, animal trampling is mostly not static but must be considered as a short time dynamic process, where the soil undergoes repeated sequences of loading, unloading and reloading events (Peth and Horn, 2006). This dynamic soil compression is more intense due to a pronounced inter-particle shear deformation compared to the compaction under static loading. Finally, this will result in an intensive reduction of soil infiltrability
Chapter 2 Spatial variability of soil properties affected by grazing intensity in Inner Mongolia grassland and in a water surplus in the topsoil layer after rainfall, which in turn decreases aggregate strength in the topsoil. Plant available water capacity may be reduced by soil compaction. Reduced plant available water combined with short vegetation periods in the semi-arid grassland limits plant growth and reduces the input of litter, consequently influence the storage of organic carbon in soil. Particularly upper soil layers show high concentration of soil organic carbon and are first affected by management (Kelly et al., 1996). High concentration of organic carbon, especially when it is rich in hydrophobic compounds, restrains water from entering into the soil by increasing the water repellency (Ritsema, 1996). Although this is an important “indirect” effect of grazing on the soil infiltrability it has not yet been well described and quantified. Soil properties have often been reported to show a strong spatial dependence (Shouse et al., 1995; Lophaven et al., 2006). The spatial dependency is commonly characterized and quantified by geostatistical methods such as autocorrelation and variogram analysis. Such spatial analysis is necessary to perform sound interpolation when producing contour maps and to simultaneously provide an estimate of the variance of the interpolated values (Goovaerts, 1998). Kriging, an interpolation procedure, which provides best linear and unbiased estimation, has been universally applied in the environmental sciences to analyze spatial variability and to resolve site-specific problems, e.g. with respect to SWC (Goovaerts and Sonnet, 1993; Famiglietti et al., 1998; Western et al., 1998, Buttafuocoa et al., 2005), shear strength (Cassel and Nelson, 1985; Júnior et al., 2006) and water repellency (Gerke et al., 2001). The correlations between soil properties are very complex, especially on plot or regional scale. These characteristics make it very hard to interpret the various studies and to predict the relevant processes and mechanisms (Ludovisi et al., 2005). Many attempts have been made to establish the relation among texture, structure, aggregate stability, bulk density and organic matter content of the soil and its resistance to water infiltration. Dekker and Ritsema (1994) did not find a significant relationship between the persistence of potential water 13
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Page 5: I Table of contents I Table of cont
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Chapter 3 Factors controlling spati
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Chapter 4 Temporal stability of soi
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Y orientation Chapter 4 Temporal st
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MRD(%) MRD(%) 100 80 60 40 20 0 -20
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Soil water content (%) 40 30 20 10
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Chapter 5 Modeling Grazing Effects
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Chapter 6 Modeling of Coupled Water
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Chapter 7 General discussion and co
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References Chapter 7 General discus
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8. ACKNOWLEDGMENTS Firstly I would
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Curriculum Vitae M.Sc. Ying Zhao Of
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Schriftenreihe des Instituts Neuere
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