Tillage effects on plant water and nitrate uptake compare topsoil to subsoil

Different soil management practices and crop species can significantly influence the plant water and nitrogen use. However, how this affects the plant nitrate (NO₃^-) and water use efficiency from different soil depths, particularly from deep subsoil layers, remains unclear. In this study, we aimed to investigate variations in plant water and nitrogen uptake efficiency across topsoil and subsoil layers under till and no-till soil management practices. A mixture of ²H₂O and Ca (¹⁵NO₃)₂ was injected into the soil columns at depths of 20 cm, 60 cm, and 90 cm using customized suction cups in both till and no-till plots. During the installation of the suction cups, soil samples were taken from 10–20 cm, 50–60 cm, and 80–90 cm depth intervals for subsequent nitrate analysis. Aboveground plant tissues were sampled from winter wheat and maize at two field sites in 2025 as an initial test of the method. We plan to expand this approach to five sites across different European countries in 2026. Plant material was collected on the fourth- and eighth- days following tracer injection, including tillers from winter wheat and top leaves, cobs, and stems from maize. The experimental setup provides a promising approach for tracing plant uptake from different soil depths, especially subsoil. We anticipate that this method will help identify variations in plant water and nitrogen uptake across different soil depths and may become a method that allows more routine inclusion of the subsoil in different studies of plant water and nitrogen uptake. This work will contribute to ongoing efforts to evaluate the impacts of conventional and sustainable soil management practices on resource use efficiency.