Effects of tillage systems on soil water distribution, crop development, and evaporation and transpiration rates of soybean

Tillage practices are known to affect soil water retention, plant available water and, consequently, crop production. Impacts can be determined by assessing soil hydraulic properties and crop characteristics. In this study, three tillage practices were investigated with respect to vertical soil water distribution and development of soybean. A specific focus was set on determining evaporation and transpiration as fractions of evapotranspiration to obtain additional information on water availability and crop water use. The agricultural practices included conventional tillage, reduced tillage (no plow), and no-tillage. The study site was a long-term field experiment under rainfed conditions. The investigations covered a vegetation period of soybean. The measurements comprised weather and soil water monitoring using sensors and manual monitoring of crop development. Evapotranspiration and its components were determined using scintillometer measurements and an isotope-based water balance technique. In the researched vegetation period with limited water availability, the conservative tillage practices showed better water storage, water use, and crop yields compared to the conventional practice. The weekly evaporation and transpiration rates progressed according to the respective canopy development. Thus, delayed plant development of the no-till practice led to extended green cover and productive water use during the late season, where a large part of the precipitation has fallen. The tillage-induced differences of soil hydraulic properties had a substantial impact on soil water distribution, but a comparatively small impact on the soil surface wetness and thus directly on the evaporation rate. The tillage-induced impacts on soil cover by plant residues, however, showed the substantial reduction effect of plant residue cover on evaporation losses. Hence, assessment of evaporation and transpiration rates contributes to the understanding of differences in water productivity and promotes the efficient use of the available water resources.