Development of models to predict land use-induced soil pore-space changes

As the demand for agricultural products and the occurrence of extreme weather conditions increase, the protection of our soil and water resources demands greater attention. Consequently, adaptive land uses as a preventative element for soil and water conservation are gaining importance. Planning of adaptation strategies is often based on the application of numerical models. Using these models, the impacts of proposed or potential changes in land use on plant growth and water balance components can be estimated and evaluated under recent and changing climatic conditions. However in existing models, soil hydraulic properties are assumed to be temporally constant; despite previous studies having 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 greater or misdirected resource consumption in 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, under 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 analyze comparable land use practices with similar soils along a climatic transect from Brandenburg,via Saxony and Lower Austria to Styria. For the characterization 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 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 the 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 involved processes, we will develop methods and models that are able to quantify the impact of a given 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 provide a basis for the development and assessment of sustainable land use systems.

As the demand for agricultural products and the occurrence of extreme weather conditions increase, the resources soil and water are more attracted by the public. Therefore, 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 project were a) to measure landuse-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. The project focussed on temporal changes of the water conductance and storage induced by different land use measures (soil tillage, crop rotations, land use change). To achieve this, field experiments were conducted at different sites in Saxonia and Lower Austria and changes of the soil pore structure were modelled. A new combination of different measurement methods enabled an improved differentiation among macropores and matrixpores, which was found to be relevant when describing land use-induced changes of the soil pore space mathematically. The experimental part confirmed that most land use measures mainly affect the larger pore fraction (i.e., macropores). Basing on an improved process understanding, soil pore changes could be described by a model that allows to assess the influence of an adaptive land use on hydrologically relevant soil properties and the water balance. The application of these kind of models can support the identification of site-specific land use systems that are hydrologically sustainable by inhibiting a greater resilience against increasing drought periods.