Division S-1 - Soil physics - Time dependence of soil mechanical properties and pore functions for arable soils

Progressive soil degradation due to tillage operations affects crop production and its yield uncertainty, soil erosion by wind and water, and gas emission. The possibility of soil regeneration due to natural or anthropogenic processes is of major concern to sustain soil functions. Material properties like precompression stress, shear strength, and hydraulic conductivity are time dependent, while bulk density is less sensitive to time effects. The hypothesis that the change from conventional to conservation tillage affects mechanical soil strength and pore functions was tested for a stagnic Luvisol derived from glacial till in northern Germany. For more than 7 yr precompression stress, shear strength, and hydraulic conductivity were determined at three depths down to 60 cm. Approximately 3 yr after starting with the Horsch system (annual shallow chiseling in autumn down to an 8-cm depth) as a kind of conservation tillage, soil strength, and the hydraulic conductivity increased in the topsoil by more than 50 kPa and 500 cm d(-1), respectively, even at a higher bulk density as compared with the corresponding values for the conventionally tilled plots. Within the following 2 to 3 yr, these changes were also detected at the 30- to 35-cm soil depth. At the depth of 55 to 60 cm the same trend started after around 7 yr. These changes can be only detected, if the tillage systems were applied continuously and if all tillage and soil operations were performed with light machines, which enable the preservation of newly formed pores and the rearrangement of soil particles creating a more stable soil structure. Thus, the susceptibility to soil deformation will be reduced due to an increased shear strength, which in turn improves pore functioning.