Non-inversion tillage benefits soil N retention during bare soil period coinciding with wet spell

Recent meta-analyses suggest risks of increased nitrate (NO3-) leaching with the implementation of reduced tillage practices. This study aimed to quantify effects of a subsidized and commonly implemented form of non-inversion tillage in Switzerland (NIT, i.e. chisel ploughing) in comparison to conventional tillage (CT, i.e. mouldboard ploughing) on NO3- leaching and its driving processes (i.e. water fluxes, soil temperature, plant uptake). A lysimeter experiment was conducted at the lysimeter facility Reckenholz/Zurich in Switzerland, mimicking tillage differences. Results after three years of treatment implementation show that during the following three years, tillage treatment had a significant effect on NO3- leaching in one of three seepage periods for two of three soil types considered. NIT reduced NO3- leaching in the seepage period 2014/2015 by 42 % on a Cambisol from Reckenholz and 32 % on a Luvisol from Schafisheim, respectively. The observed effect was driven by differences in NO3- concentrations in seepage water rather than seepage water amounts. Differences in NO3- concentrations could be attributable to structural differences in the topsoil, leaving larger amounts of soil N exposed to matrix water flow in the disturbed topsoil under CT than in the largely undisturbed topsoil under NIT. Also, differences in crop residue amount between treatments could have contributed to NO3- concentration differences. The treatment impact on NO3- leaching was most pronounced during and shortly after a bare soil period following sugar beet cultivation, which coincided with above-average spring precipitation. Considering that winter and spring precipitation is expected to increase with progressing climate change in Switzerland, reduced soil management may hold potentials to mitigate NO3- leaching in the face of progressing climate change. However, more research is needed to prove the relevance of this mechanism and its sensitivity to soil, climate and management drivers.