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52 SLO: slope (degree); ASP: aspect; CUR: curvature; CAR: upslope contribution area (m 2 ); and WI: wetness index. WDPT: water drop penetration time (s); K: hydraulic conductivity (cm d -1 ); VC: vegetation coverage (%); AGB: above ground biomass (g m -2 ); RE: relative elevation (m); D: dry; M: medium; W: wet; Sand: sand content (%); Clay: clay content (%); SOC: soil organic carbon (g kg -1 ); BD: bulk density (g cm -3 ); SS: shear strength (kPa); Tan(CAR) -0.09 -0.08 0.03 -0.19 -0.03 0.10 -0.02 0.13 -0.07 0.01 -0.10 -0.10 0.01 0.08 0.02 WI 0.05 -0.14 -0.20* -0.12 -0.08 -0.01 -0.06 0.11 -0.07 0.08 0.03 0.1 0.04 0.01 0.03 Cos(ASP) 0.01 0.14 0.03 -0.18 -0.12 0.12 0.30** 0.13 0.00 0.37** 0.40** 0.30** -0.13 -0.07 -0.09 CUR 0.09 0.01 0.00 0.13 0.18 -0.08 0.18 -0.01 0.05 -0.05 -0.02 -0.01 -0.01 -0.06 0.00 Topo RE 0.02 -0.13 -0.20* 0.05 0.18 0.19 -0.26* -0.19 -0.05 -0.25* -0.23* -0.08 0.21* 0.10 0.15 -graphy Tan(SLO) -0.01 0.21* 0.32** 0.06 0.12 0.20* 0.03 -0.01 0.06 -0.08 -0.09 -0.14 0.09 0.18 0.11 Plant VC -0.01 -0.01 0.22* -0.07 0.05 0 -0.12 -0.04 -0.11 -0.25* -0.22* -0.34** 0.26** 0.22* 0.23* AGB 0.04 0.03 0.08 0.1 0.26* 0.33** 0.21* 0.14 0.04 -0.25* -0.26** -0.30** -0.22* -0.22* -0.33** Ln(K) -0.31** -0.12 -0.07 -0.08 -0.07 -0.12 -0.09 -0.17 -0.14 0.01 -0.02 -0.04 0.13 0.00 0.14 SOC 0.27* 0.19 0.13 0.29** 0.23* 0.50** 0.02 0 0.07 0.41** 0.35** 0.39** 0.55** 0.52** 0.52** BD -0.24* -0.19 -0.12 -0.30** -0.23* -0.45** 0.08 0.16 -0.06 -0.32** -0.22* -0.24* -0.38** -0.39** -0.34** SS 0.42** 0.20* 0.1 0.15 0.11 0.27** 0.13 -0.08 -0.02 0.14 0 -0.05 -0.32** -0.19 -0.21* Ln(WDPT) 0.33** 0.18 0.03 0.21* 0.07 0.19 -0.06 0.03 -0.06 0.05 0.06 0.09 -0.35** -0.32** -0.39** Soil Sand -0.14 -0.08 -0.21* -0.28** -0.26** -0.50** 0.07 0.17 -0.05 -0.50** -0.44** -0.47** -0.73** -0.73** -0.83** Clay 0.16 0.09 0.19 0.25* 0.24* 0.55** -0.07 -0.18 0.05 0.55** 0.49** 0.55** 0.62** 0.65** 0.65** D M W D M W D M W D M W D M W Factors Parameters UG 79 UG 99 WG CG HG Table 3.4. Correlation matrix between soil moisture and water-related factors for three soil water statuses for different grazing intensities (P
Chapter 3 Factors controlling spatio-temporal variability of soil moisture using multivariate geostatistics Many studies envisioned soil moisture variability should be strongly controlled by variations in hydraulic conductivity (K), especially under wet conditions (Hawley et al., 1983; Chanzy and Bruckler, 1993; Hébrard et al., 2006). Unexpectedly, we did not detect a correlation between K and SWC (Table 4). K depends strongly on pore size and continuity, wetting properties and SWC. Considerable temporal variability in all of these properties, combined with different impacts on K depending on antecedent environmental conditions, may have confounded any clear trend being observed. The only significant relationship between K and SWC was found for UG 79 when dry. This trend could be caused by the influence of SOC on wettability when the soil was dry, as indicated by the strong relationship between K and WDPT (Zhao et al., 2007). Animal trampling in HG may have caused the negative correlation between shear strength and SWC. The recovery of soil physical structure, reinforcement by plant roots and cohesion by SOC in UG 79 may have reversed this trend as a positive correlation was found. Plant heterogeneity may also control soil moisture patterns as rooting depth, surface cover, and species composition affect evapotranspiration processes. SWC was significantly correlated with vegetation coverage (VG) and aboveground biomass (AGB) in the continuously (CG) and heavily grazed plots (HG), irrespective of moisture condition (Table 4). However, in the ungrazed plots, correlations were only observed under a wet water status in UG 79, and under medium and wet water statuses in UG 99. Reynolds (1970), Hawley et al. (1983) and Francis et al. (1986) found that vegetation coverage was a major factor influencing soil moisture variability. Hawley et al. (1983) further noted that differences were often greater in wet conditions than in dry conditions, but our study did not support this finding. In the HG plot, the negative correlation between AGB and SWC showed the influence of plant transpiration. However, VC was positively correlated to SWC in the HG plot, illustrating the deleterious impact of grazing intensity on both plant coverage and soil physical structure. With minor exceptions, neither surface factors, e.g. relative elevation, slope and aspect (local control) nor subsurface factors, e.g. curvature, upslope contributing 53
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SCHRIFTENREIHE Institut für Pflanz
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Aus dem Institut für Pflanzenernä
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I Table of contents I Table of cont
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controlling soil moisture are of pa
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Zusammenfassung Überweidung wird a
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Die Beweidung beieinflusst besonder
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II List of figures Fig. 2.1. Locati
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measured soil moisture in time stab
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III List of tables Table 2.1. Descr
Page 21 and 22: 1.1 Background Chapter 1 Introducti
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Page 25 and 26: Chapter 1 Introduction water in spr
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Page 29 and 30: Chapter 1 Introduction Krümmelbein
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Page 85 and 86: Chapter 4 Temporal stability of soi
Page 89 and 90: Y orientation Chapter 4 Temporal st
Page 93 and 94: MRD(%) MRD(%) 100 80 60 40 20 0 -20
Page 101 and 102: Soil water content (%) 40 30 20 10
Page 105 and 106: Chapter 5 Modeling Grazing Effects
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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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