Does no-tillage decrease nitrate leaching compared to ploughing under a long-term crop rotation in Switzerland?

Abstract

The intensification of agriculture in the industrialized countries since the 1950s led to an increase not only in productivity but also in nitrate concentrations of ground and surface waters. In some countries, various policy measures aim at reducing agricultural nitrogen losses to waters. Still, nitrate concentrations of groundwater impair drinking water quality and nitrogen inputs to surface water are elevated in many areas. Since no-tillage (NT) is often promoted as a farming system that reduces nitrate leaching, we conducted a seven-year lysimeter trial at Berne-Liebefeld (Switzerland) to compare impacts of NT with mouldboard ploughing (MP) in a diverse crop rotation. Crop yields were 13 % lower and N removals by harvested products 5 % lower under NT than under MP. Seepage volumes under NT exceeded those under MP by 8 %. Larger seepage volumes under NT were found in nearly all crop-by-year combinations and months of the year. Mean nitrate concentrations of seepage water were 20 % lower under NT than under MP but still exceeded Swiss official limits for drinking water quality. On average, nitrate-leaching rates were more affected by nitrate concentrations than by seepage volumes because nitrate concentrations varied much more between tillage systems, crop types and years than seepage volumes. Mean annual rates of nitrate leached exceeded 50 kg N ha−1 in both tillage systems and crop rotations with a large range from 2 to 221 kg N ha−1 in individual years. NT showed 14 % lower leaching rates than MP. The differences between the two tillage systems were not statistically significant due to elevated coefficients of variation and the small number of replicates. Improvements in experimental design are suggested to increase the statistical power in future trials.