SCHRIFTENREIHE Institut für Pflanzenernährung und Bodenkunde ...

Recommendations

Info

of grazing intensity could improve soil functions again under pasture. In order to protect and restore degraded soils from intense grazing, we suggest future land use in Inner Mongolia needs to focus on reducing trampling intensity and animal exclusion. Modeling grazing effects on coupled water and heat fluxes (Chapters 4, 5 and 6) 142 Grazing-induced changes in soil properties were parameterized by the coupled water and heat model HYDRUS-1D (Šimůnek et al., 1998). In addition, we introduced the different root densities and boundary conditions for the different grazing intensities. Especially, three improvements is needed to underline when we calibrated the model. Firstly, we worked with the root growth model to consider dynamics of plant water uptake. We considered it important because models designed to simulate agricultural managements are normally limited to simulate crop growing thus keep root constant, e.g. SWAT (Neitsch et al., 2002). Secondly, interception, which can not be calculated by HYDRUS-1D, was estimated by the model SHAW (Flerchinger and Saxton, 1989) since it might occupy a large component of the water budget in our case. Finally, we partitioned evapotranspiration (ET) based on the field measurements, which was particularly essential for the prediction of plant transpiration since it is only determined by root water extraction function related with potential transpiration in HYDRUS code. The modifications in boundary conditions resulted in a significant improvement of the simulation accuracy. We showed that HYDRUS-1D model is capable to reflect the grazing effects on water and heat budgets, and it can be used for the analysis of land management scenarios. Apart from the inverse model, the Laboratory-derived hydraulic parameter (LDP) model showed the best match between simulated and measured water contents as it accounts for soil structural changes resulted from grazing. This result is consistent with the description by Richard et al. (2001), who distinguished textural and structural fractions for the soil pore space and found that soil compaction mainly affected the structural pore space. Our
Chapter 7 General discussion and conclusions results therefore suggest that the detailed laboratory measurements of soil hydraulic properties from undisturbed soil sampling are necessary to reflect the effect of land managements on water flux. Under the prevailing semi-arid climatic conditions in Inner Mongolia, plant available water plays the most key role for the sustainable development of steppe ecosystems. At this moment, some studies have shown that grazing affects water budget (Bremer et al., 2001). However, to which extent grazing affects evapotranspiration, and how far it is partitioned into transpiration and evaporation is unclear. We proofed that the water budget in Inner Mongolia grassland is significantly influenced by grazing. Although there was no apparent difference in evapotranspiration (ET) among different grazing intensities, the components of ET, i.e. interception, transpiration and evaporation significantly varied with grazing intensity. It is obvious that, compared with the grazed sites, interception and transpiration increased and soil evaporation decreased in the ungrazed sites. In contrast to this, evaporation in the grazed sites simultaneously increased. We deem it important information for judgments of water use efficiency in this region. Currently, although snowmelt or lateral soil water movement on frozen soil layers is recognized as an important part for the seasonal water balance, simulations of snow hydrology and soil freezing and thawing are rarely done due to a lack of suitable models that describe the complex processes during phase changes and limited data availability to parameterize or validate such models (Hansson et al., 2004). Especially, the mutual interactions of water and heat flows in frozen soil are limited to laboratory observation and theoretical analysis, but rarely conducted in field applications. Based on this, an extended freezing code was incorporated into HYDRUS-1D to numerically solve coupled equations governing phase changes between water and ice and heat transport (Hansson et al., 2004). The freezing model was proofed to predict well the soil water and heat fluxes under both unfrozen and frozen conditions. This provided a basis for the studies of soil freezing and thawing behavior. It has been found that soil 143
Page 1 and 2:
SCHRIFTENREIHE Institut für Pflanz
Page 3 and 4:
Aus dem Institut für Pflanzenernä
Page 5:
I Table of contents I Table of cont
Page 8 and 9:
controlling soil moisture are of pa
Page 11 and 12:
Zusammenfassung Überweidung wird a
Page 13 and 14:
Die Beweidung beieinflusst besonder
Page 15 and 16:
II List of figures Fig. 2.1. Locati
Page 17 and 18:
measured soil moisture in time stab
Page 19 and 20:
III List of tables Table 2.1. Descr
Page 21 and 22:
1.1 Background Chapter 1 Introducti
Page 23 and 24:
Chapter 1 Introduction is also unce
Page 25 and 26:
Chapter 1 Introduction water in spr
Page 27 and 28:
Chapter 1 Introduction requires the
Page 29 and 30:
Chapter 1 Introduction Krümmelbein
Page 31 and 32:
Chapter 2 Spatial variability of so
Page 33 and 34:
Page 35 and 36:
Page 37 and 38:
Page 39 and 40:
Page 41 and 42:
Page 43 and 44:
Page 45 and 46:
Page 47 and 48:
Page 49 and 50:
Page 51 and 52:
Page 53 and 54:
Page 55 and 56:
Page 57 and 58:
Page 59 and 60:
Chapter 3 Spatio-temporal variabili
Page 61 and 62:
Page 63 and 64:
Page 65 and 66:
Page 67 and 68:
Page 69 and 70:
Page 71 and 72:
Page 73 and 74:
Chapter 3 Factors controlling spati
Page 75 and 76:
Page 77 and 78:
Page 79 and 80:
Page 81 and 82:
Page 83 and 84:
Page 85 and 86:
Chapter 4 Temporal stability of soi
Page 87 and 88:
Page 89 and 90:
Y orientation Chapter 4 Temporal st
Page 91 and 92:
Page 93 and 94:
MRD(%) MRD(%) 100 80 60 40 20 0 -20
Page 95 and 96:
Page 97 and 98:
Page 99 and 100:
Page 101 and 102:
Soil water content (%) 40 30 20 10
Page 103 and 104:
Page 105 and 106:
Chapter 5 Modeling Grazing Effects
Page 107 and 108:
Page 109 and 110:
Page 111 and 112: Chapter 5 Modeling Grazing Effects
Page 135 and 136: Chapter 6 Modeling of Coupled Water
Page 159 and 160: Chapter 7 General discussion and co
Page 161: Chapter 7 General discussion and co
Page 167 and 168: References Chapter 7 General discus
Page 171 and 172: 8. ACKNOWLEDGMENTS Firstly I would
Page 173 and 174: Curriculum Vitae M.Sc. Ying Zhao Of
Page 175: Schriftenreihe des Instituts Neuere
show all

SCHRIFTENREIHE Institut für Pflanzenernährung und Bodenkunde ...

You also want an ePaper? Increase the reach of your titles

Delete template?

Save as template?