Assessment of soil structure parameters and functions in agricultural soils

Scientists from six countries worked together during the past 5 years in the field of soil structure assessment, focussing on the importance of physical soil characteristics for agricultural landuse. This multilateral cooperation consisted of 2 projects: The first one (1992-1993) aimed at elaborating a comprehensive concept for the assessment of soil structure in agricultural soils, using standardized methods. For this purpose, -representative soils from the different countries, ranging from light to very heavy textured, were investigated by all partners-using the same methodology. It was found that the diagnostic value of single methods or parameters for describing the soil structure depends on the specific soil function which has to be evaluated. The applicability of all methods for particular soils or specific field conditions was examined. Moreover, in the flame of this first project, new and innovative equipments were developed and tested by the different research groups. Based on the obtained results, a second project was started in 1994 aiming at testing and evaluating Suitable crop-, soil moisture- and ground water models, in which agricultural, meteorological, hydrological and soil parameters were used in order to describe and to quantify transport functions of soil structure as a basis for agricultural plant production. Generally, models for agricultural plant production include two groups of parameters: soil parameters and plant parameters. Time and rooting depth are necessary plant parameters if crop growth should be coupled with soil structure effects. A test of different models showed for instance that the effect of the saturated water conductivity and bulk density alone on crop yield was not significant. But, as soon as root distribution was introduced asa plant parameter, a strong relation to plant growth could be detected as an overall influence of the soil structural status. Moreover, in order to get a complete overview about water transport phenomena, a combination of different field and laboratory methods was found to be useful, especially within a wide range of soil moisture from water saturation to dry conditions. Microscopic studies contributed considerably to the understanding of the spatial organization of soil constituents, their distribution, forms and shapes in the matrix. By interpreting soil features as reflection of processes within the pedon and in the landscape, it becomes possible to understand the type and stability of soil structure and its functionality.