Nitrogen Rate Increase Not Required for No-Till Wheat in Cool and Humid Conditions

An increased nitrogen (N) supply was proposed to avoid grain yield (GY) reductions and successfully implement conservation agriculture (CA). We investigated interactions effects of tillage system and N supply on winter wheat (Triticum aestivum L.) at two sites in the Swiss midlands with no (0 kg N ha(-1)) and high (150-160 kg N ha(-1)) N supply using N-15-labelled ammonium nitrate in selected treatments. Wheat's GY, yield components, N related traits and soil mineral N content (N-min) under conventional tillage (CT), minimum tillage (MT), and no-tillage (NT) were studied following two preceding crops: oilseed rape (Brassica napus L.) and maize (Zea mays L.). Wheat after oilseed rape had significantly higher GY and biomass than after maize while a yield decrease under NT compared with CT and MT was observed regardless of N supply level. Differences in soil N-min among tillage systems were seldom found and were inconsistent. No differences in N-15 fertilizer recovery were found between NT and CT while residual N-min after harvest was lower under NT than CT or MT. In conclusion, we did not found consistent reductions in soil N availability and N uptake under NT that would justify an increased N supply for wheat under CA.