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99, from –10.1 to +10.0% at WG, and from –20.1 to +27.4% at HG. Apparently, the absolute span of the MRD is smaller than 15% except for HG, where it reaches 28%. Compared with the results from previous temporal stability experiments (Vachaud et al., 1985; Martinez-Fernandez and Ceballos, 2003), our results have much smaller MRD and also smaller deviations, which may be explained by the smaller spatial area in our study. Due to comparable topographical attributes at the four plots, we ascribed the site-specific differences of MRD to differences of soil and plant properties affected by grazing effects (Zhao et al., 2008a). Compared with the other three plots, the heavily grazed plot (HG) has very sparse vegetation and a weakly structured soil, which accelerates the dynamics of soil moisture and thus decreases the temporal stability. This is consistent with Hupet and Vanclooster (2002), who concluded that the phenology of the vegetation played an important role in the temporal stability of the spatial patterns. Mohanty and Skaggs (2001) found that fields with silt loam soils showed poor temporal stability than those containing sandy loam soils. However, this can not be proofed in our study as sandy soil in HG expresses low temporal stability. This indicates that there should be other contributor to time stability of soil moisture, e.g. low water content itself in HG results in intensive and fast water dynamics, i.e. a low temporal stability. 72 Similarly, the temporal stability of soil moisture is moisture-dependent, that is, the MRD and its deviation for all plots are larger under dry and medium conditions, but smaller under wet conditions (Figs. 2-5). This is consistent with Lin (2006), who indicated that temporal stability is higher when the soil is wetter. It is possibly associated with that during the wet conditions water supply from the subsoil to the topsoil aids to keep the soil from temporal variability. Again some time stability points (TSPs) under wet conditions obviously lose time-stable characteristics under dry conditions. For example, sampling point 34 (denoted as p34) in UG 79 is temporally stable under wet, medium and all conditions, but it is not stable under dry conditions (Fig. 2). However, although the time stability characteristics of some points vary with water conditions, most points were independent on water conditions.
MRD(%) MRD(%) 100 80 60 40 20 0 -20 -40 -60 -80 -100 100 80 60 40 20 0 -20 -40 -60 -80 -100 Chapter 4 Temporal stability of soil moisture and its application in model result validation D W 98 72 34 34 72 98 0 20 40 60 80 100 Ranked M ALL 72 34 98 72 0 20 40 60 80 100 Ranked Fig. 4.2. Ranked MRD of soil moisture in UG 79 in different water conditions during 3-yr measurement period (All: all measurements, D: dry, M: medium, W: wet). Vertical bars correspond to associated time standard deviations, labeled numbers are the time stability points that at least appear three times from four soil water conditions. MRD(%) MRD(%) 100 80 60 40 20 0 -20 -40 -60 -80 -100 100 80 60 40 20 0 -20 -40 -60 -80 -100 D W 12 37 44 46 12 37 41 41 46 72 0 20 40 60 80 100 Ranked M ALL 37 46 1244 41 0 20 40 60 80 100 Ranked Fig. 4.3. Ranked MRD of soil moisture in UG 99 in different water conditions during 3-yr measurement period (All: all measurements, D: dry, M: medium, W: wet). Vertical bars correspond to associated time standard deviations, labeled numbers are the time stability points that at least appear three times from four soil water conditions. 73
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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
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1.1 Background Chapter 1 Introducti
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Chapter 1 Introduction is also unce
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Chapter 1 Introduction water in spr
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Chapter 1 Introduction requires the
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Chapter 1 Introduction Krümmelbein
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Chapter 2 Spatial variability of so
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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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