ASSESSMENT OF SOIL-STRUCTURE PARAMETERS AND FUNCTIONS IN AGRICULTURALSOILS

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 multi lateral cooperation consisted of 2 projects: The first one (1992-1993) aimed at elaborating a comprehensive concept for the assessment of so il structure in agricultural soils, using standardized methods. For th is purpose, -representative soils from the different countries, rangin g 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 depend s on the specific soil function which has to be evaluated. The applica bility of all methods for particular soils or specific field condition s was examined. Moreover, in the flame of this first project, new and innovative equipments were developed and tested by the different resea rch groups. Based on the obtained results, a second project was starte d in 1994 aiming at testing and evaluating Suitable crop-, soil moistu re- and ground water models, in which agricultural, meteorological, hy drological and soil parameters were used in order to describe and to q uantify transport functions of soil structure as a basis for agricultu ral plant production. Generally, models for agricultural plant product ion include two groups of parameters: soil parameters and plant parame ters. Time and rooting depth are necessary plant parameters if crop gr owth should be coupled with soil structure effects. A test of differen t models showed for instance that the effect of the saturated water co nductivity and bulk density alone on crop yield was not significant. B ut, as soon as root distribution was introduced asa plant parameter, a strong relation to plant growth could be detected as an overall influ ence of the soil structural status. Moreover, in order to get a comple te overview about water transport phenomena, a combination of differen t field and laboratory methods was found to be useful, especially with in a wide range of soil moisture from water saturation to dry conditio ns. 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 refle ction of processes within the pedon and in the landscape, it becomes p ossible to understand the type and stability of soil structure and its functionality.