Estimation of critical stress ranges to preserve soil functions for differently textured soils

Abstract

The use of heavy agricultural equipment often produces significant changes in soil physical properties through compaction. Soil compaction is one of the environmental factors in agriculture that adversely act on soil functions such as the provision of air, water, nutrients and pore space for root growth affecting crop yields.In this study, critical stress values are defined as the values at which the effects of compaction result in a limitation of soil functions. Soil functions such as water storage, habitat and plant production are influenced to a different degree by soil compaction, so we assume there is not some fixed critical stress threshold for soil, but a range of critical stress values, hereafter called critical stress range. It is investigated, if there are differences in the critical stress values with respect to soil functions leading to critical loads that should not be exceeded to prevent negative effects, and if the critical stress ranges differ for different textures.Using column experiments in a greenhouse classic soil mechanical parameters (dry bulk density, mechanical precompression stress), morphometric parameters obtained with X-ray tomography (macroporosity, pore connectivity) from undisturbed soil samples as well as biological parameters (earthworm activity) and crop factors (grain and straw yield) were investigated for soils with different topsoil textures (top soil 0−15 cm: loam, silty clay loam, silt loam, sandy loam) near field capacity.We found that critical stress values for various parameters and critical stress ranges did not depend on topsoil texture at this matric potential. Studies, which recommend maximum values for mechanical loads to prevent harmful soil compaction solely based on texture, should be treated with caution. Although the soil textures at the four sites were quite different, the middle of the critical stress ranges were similar and concurred with the values of the mechanical precompression stresses which were similar at all four sites, too. The agronomic critical stress values of grain and straw yield mostly were impaired at the lower limit of the critical stress ranges and were, therefore, the most sensitive parameters.