Development of Models to Predict Land-Use-Induced Soil Pore-Space Changes and their Hydrological Impacts

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    Kai Schwärzel

    As the demand for agricultural products and the occurrence of extreme weather conditions increase, the resources soil and water become more attractive to the public. Thus, an adaptive land use as a preventative element for soil and water conservation gains in importance. Planning of adaptation strategies are often based on the application of numerical models. With these models, the impact of hypothetical changes in land use under recent and changing climatic conditions on plant growth and water balance components can be estimated and evaluated. As a pre-requisite in existing models, soil hydraulic properties are seen to be temporally constant. However, previous studies have shown that soil structure and with it the soil water retention and hydraulic conductivity functions change significantly as a result of land use. If the dynamics of soil structure are neglected, the uncertainty of the model results increases. This could lead to incorrect planning and a more resources-consuming land use.

    Therefore, the objectives of this study are a) to measure land-use-induced changes in soil structure and in the soil hydraulic properties and b) the implementation of the results into hydrological models that quantify the changes using mathematical equations. These equations describe temporal changes of soil water retention and hydraulic conductivity based on the evolution in the soil pore-size distribution for different land-use practices (e.g., soil tillage, crop rotation, afforestation).

    To derive general principles for the influence of land use on hydrologically relevant soil properties, we will analyse comparable land-use practices with similar soils along a climatic transect from Brandenburg to Styria. For the characterisation of the soil hydraulic properties, field methods (hood infiltrometer and dye tracer experiments) will be combined with laboratory methods (transient evaporation experiments). This approach allows for a better differentiation between macropore and matrix flow domains, which may be fundamental for the development of functions describing land-use-induced changes of the soil pore space. We expect that different land-use measures will have a stronger influence on the macropores.

    The study will increase our knowledge about soil pore-space changes under different land-use practices. Based on a better understanding of the processes involved, we will develop methods and models that are able to quantify the impact of an adaptive land use on the soil hydraulic properties, on components of the water cycle (soil water capacity, groundwater recharge, water quality), and on the production of biomass. This will be the basis for the development and assessment of sustainable land-use systems.