Soil and agricultural management practices (AMP) that are able to provide for an increasing population while meeting environmental existential challenges have gained considerable attention in recent times. Such AMP influence the soil profile and hydrological components for varying depths and patterns, depending on site-specific and environmental conditions. Though it is well known that management-induced changes of soil structure have consequences on soil hydraulic properties (SHP) and water fluxes, their dynamics through a season or on a long-term basis are hardly studied. Typically, an invariant soil pore system is assumed when modeling the transport of water and solutes in the soil system which leads to incorrect predictions of the dynamics of water balance components. Ultimately, this may lead to poor decision making and mismanagement of environmental resources. Hence, the present study quantifies the dynamics of SHP from existing studies and evaluates a model that is able to capture soil pore space dynamics following tillage. The objectives were to (1) investigate the quantitative effects of agricultural practices on soil structure and hydraulic properties and the subsequent response of the water balance components (2) evaluate a pore space evolution model for its capability in predicting the evolution of soil pore size distribution (PSD) for two cases: a) when there is a change in the tillage regime and/or land-use change b) in the months following tillage (3) derive corresponding soil water retention and hydraulic conductivity functions to incorporate them in hydrological models
To achieve these objectives, first, a review of contemporary literature was undertaken to analyze the impacts of anthropogenic and environmental influences on SHP. The analysis indicated the relevance of studying temporal alterations of soil structure and SHP. Thereafter, a numerical model was evaluated for its ability to capture the dynamics of soil pore space with respect to time and pore radius using water retention parameter data sets from different parts of the world. The physically based coefficients of the model simulated the processes that were expected to occur after tillage. Furthermore, saturated hydraulic conductivity was obtained from the initial and final pore size distributions. Using the final pore size distribution curve and water retention function, the hydraulic conductivity function was also derived. The resulting water retention and hydraulic conductivity curves can directly be used as input in hydrological modeling studies.
The results of the literature review indicate that, generally, soils show an abundance of large pores immediately after tillage. Those pores are not stable with time mainly due to precipitation and biological activity. Saturated hydraulic conductivity decreases in periods of rainfall along with the number of macropores and the overall porosity. Thus, the infiltration rates and capacities also decrease. However, the results of existing studies cannot be generalized owing to discrepancies in the dynamics of SHP, infiltration rates and soil moisture dynamics for soils under similar agricultural management practices. They are attributed mainly to a lack of standardization of research methodology as well as to site-specific conditions. Furthermore, it was also seen that incorporating the temporal dynamics of SHP in hydrological models produce more reliable and accurate modeling outcomes in comparison to studies with constant SHP as model input.
The evaluation of the pore evolution model illustrated its suitability in capturing the temporal dynamics of soil pore space in response to tillage and environmental influences. High effective rainfalls and plant growth stages at which measurements were done affected the model performance. The use of sink/source terms and providing new initial conditions after high intensity rainfall events were provided as a means to improve the modeling outcomes. Though the model performed quite well in obtaining the water retention function as well as the saturated hydraulic conductivity and hydraulic conductivity functions, the high spatial variability in the sampling sites hampered with the model output. However, the main limitation lay in the lack of availability of sufficient data sets to calibrate and validate the model and its coefficients as well as for the derivation of SHP from the model.
Overall, this study is a forerunner in predicting the temporal dynamics of soil structure and hydraulic properties. The established dynamics in the water retention and hydraulic conductivity functions can be used in hydrological simulations for planning land-use and management measures. The current study also reveals the need for more measurements and data sets that capture the alterations in soil hydraulic properties on a long-term basis.
| Identifer | oai:union.ndltd.org:DRESDEN/oai:qucosa:de:qucosa:72547 |
| Date | 29 October 2020 |
| Creators | Chandrasekhar, Parvathy |
| Contributors | Feger, Karl-Heinz, Schwärzel, Kai, Gerke, Horst J., Technische Universität Dresden, United Nations University (UNU-FLORES) |
| Source Sets | Hochschulschriftenserver (HSSS) der SLUB Dresden |
| Language | English |
| Detected Language | English |
| Type | info:eu-repo/semantics/publishedVersion, doc-type:doctoralThesis, info:eu-repo/semantics/doctoralThesis, doc-type:Text |
| Rights | info:eu-repo/semantics/openAccess |
| Relation | 0.3390/w10121862, 10.1016/j.geoderma.2019.07.017, 10.1016/j.mex.2019.09.014 |
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