Mean nutrient uptake depths of cereal crops change with compost incorporation into subsoil – evidence from 87 Sr/ 86 Sr ratios

Background and Aims Root restricting layers often hinder crops from accessing the large reservoir of bioavailable mineral nutrients situated in subsoil. This study aims to explore changes in the mean nutrient uptake depth of cereal crops when removing root restricting layers through subsoil management. Methods Subsoil management was performed by deep loosening, cultivation of lucerne as deep-rooting pre-crop, and their combination with compost incorporation. Management effects were evaluated by means of shoot biomass and element concentrations in shoots and soil compartments. The mean nutrient uptake depth was fingerprinted by graphically matching the 87 Sr/ 86 Sr ratios in shoots with the 87 Sr/ 86 Sr ratios in the exchangeable fraction in soil. Nutrient uplift from depth to topsoil was inferred from element concentrations in the exchangeable fraction in soil. Results Shoot biomass remained constant in management and control plots. The mean nutrient uptake depth changed with subsoil management in the order: deep loosening < control < deep loosening with compost incorporation. The latter coincided with a reallocation of compost-derived Na and hence resulted in increased levels of bioavailable Na below the depth of compost incorporation, which may have led to an improved water use efficiency of the crops. Thus, Na relocation triggered the deepening of the mean uptake depth of water and nutrients. Moreover, nutrient uplift from depth to topsoil was evident 21 months after subsoiling. Conclusion Subsoil management by deep loosening with compost incorporation provides a sustainable use of soil resources because otherwise unused deep geogenic-derived nutrient reservoirs were additionally involved in crop nutrition.