N‐Dynamik des Bodens, Ertragsbildung und Stickstoffentzug von Winterweizen bei unterschiedlicher Höhe und Verteilung der mineralischen N‐Düngung

Abstract NO3 dynamics in the soil, yield formation and N uptake of winter wheat as influenced by dosage and distribution effects of N‐fertilizer application In a 4 year series of field trials carried out with 9 regimes of nitrogen fertilizer application at two trial sites with rather shallow top soil layers but large deviations in soil characteristics, grain yield varied between 50 dt/ ha and 120 dt/ha with nitrogen doses from 0–170 kg N/ha. Soil nitrogen supply for wheat grain formation on unfertilized plots reached 80 kg N/ha/year within the narrow range of 75–95 kg N/ha in different years at both sites which amounts to 1.5 % and 0.5 % of the highly different N‐content of the trial sites. The most successful nitrogen application regimes are characterized by modest fertilizer doses in early spring and the delay of supplemental fertilizer doses until growth stage EC 32. They resulted into modest NO) soil content from EC 29 to EC 32 and/or a noticable decrease of soil NO3 content during growth stage EC 30–32, which seems to be responsible for the development of only modest stand densities and reduced straw yield, while the delayed supplementation with nitrogen fertilizer overcompensated these effects mainly by increased grain numbers/ear and a remarkable improvement of harvest index. The contribution of soil borne nitrogen to kernel yield formation started to decrease with even low dosages of supplemental nitrogen fertilization with the exception of the highest yielding season 1987/88. Top levels of grain yield have been regularly obtained with supplemental nitrogen fertilizer dosages about 40 kg N/ha below grain yield nitrogen extraction if they were added within favorable application regimes.