Subsoil management as tool for climate-change adapted agriculture

Agricultural production in Central Europe increasingly suffers from extreme drought events. Improving root access to nutrient and water resources in the subsoil below the plow layer is a potential option to maintain productivity during dry summers. Here, we tested a strip-wise subsoil amelioration system that combines subsoil loosening with injections of 50 t per hectare fresh weight organic matter incorporation into the subsoil (biowaste or green waste compost) and compared it with a treatment comprising only subsoil loosening or a non-ameliorated control. Randomized block design field experiments were conducted on Luvisols and Retisols with an argic (Bt) horizon and rotations of spring barley and winter wheat as well as of rye and maize, respectively. We then monitored yields, protein contents as well as physical and chemical soil properties including changes in stable isotope composition as indicators for plant stress and nutrient uptake. We found that subsoil amelioration has the potential to prevent yield losses of up to 20% for cereals and up to 50% for maize after biowaste compost injection, particularly in dry summers, i.e., depending on weather conditions. These benefits were accompanied by a decrease in soil bulk density at the depth of compost incorporation when biowaste compost was used, but not when green waste compost had been incorporated. In contrast, nutrient stocks, nutrient availability, and microbial biomass were not consistently affected by the subsoil amelioration, but root growth was. Differences in crop development could not be explained by any single soil parameter, suggesting that it was rather a combined effect of loosened subsoil and better supply of subsoil resources that increased subsoil root length density and subsequent better crop performance when the summer was dry.