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

Tillage practices are known to affect soil water retention, plant available water and, consequently, crop production. Therefore, adjusted and sustainable tillage practices may contribute to an efficient use of limited available water resources. Impacts of tillage can be determined by assessing soil hydraulic properties and crop characteristics. In this study, three tillage practices were investigated with respect to soil water distribution and crop development, with a specific focus on determining actual evapotranspiration (ET) and crop transpiration (T). T/ET ratios should give additional information on soil water availability and crop water use. The practices included conventional tillage, reduced tillage (no plow), and no-tillage and were investigated on a long-term rainfed field experiment with soybean (glycine max l. merr) planting. The long-term experimental field is located in Raasdorf in the agricultural region Marchfeld east of Vienna, Austria (48°14’ N, 16°35’ E; 156 m elevation a.s.l., average annual precipitation of approx. 497 mm). The field is separated in experimental plots of 960 or 1,440 m². The measurements comprised automated monitoring of weather and soil water by means of a telemetric sensor network as well as manual monitoring of crop development. ET and its components were determined using an isotope-based water balance technique. ET rates were determined at the conventional experimental plot based on a water balance and verified with scintillometer measurements on a nearby field of 11.5 ha. 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 T/ET ratios progressed according to the canopy development, which was affected by the tillage-induced soil conditions. In this context, delayed plant development – specifically at the no-till plots – 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 difference of wetness at soil surface, however, did not have a substantial effect on T/ET; even soil evaporation was similar at all plots. Furthermore, the ratios showed the beneficial effect of mulch protection regarding unproductive losses by evaporation, in particular during the initial periods of crop emergence and development. Thus, the assessment of T/ET ratios improved the insights in impacts of management practices and showed potential to promote the efficient use of the available water resources.