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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 NO3 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. Zusammenfassung 1. Die Kornerträge eines vierjährigen N‐Dün‐gungsversuches zu Winterweizen, der auf 2 flachgründigen Standorten mit stark unter‐schiedlichen Bodeneigenschaften durchge‐führt wurde, differierten bei Düngergaben zwischen 0–170 kg N/ha im Schwan‐kungsbereich zwischen 50 und 120 dt/ha. 2. Bei verhaltener Anfangsdüngung in Ver‐bindung mit einer verzögerten Erganzungs‐düngung wurden regelmäßig Höchsterträge erzielt. Sie wurden bei einem NO3‐Gehalt der Ackerkrume im Bereich von 20 bis 50 kg N/ha, im Entwicklungsabschnitt EC 29 bis EC 32 und/oder einer deutlichen Verarmung des NO3‐Gehaltes im Boden vor Anwendung ergänzender Düngungs‐maßnahmen im Stadium EC 32 durch eine geringere Zahl ährentragender Halme in Verbindung mit einer überkompensieren‐den Steigerung des Ährenertrages und ver‐bessertem Ertragsindex ermöglicht. 3. Im Vergleich der beiden Versuchsstandorte zeigte sich, daß trotz hoher Nt‐Vorräte der anmoorigen Auenrendzina deren weites C: N‐Verhältnis eine rasche Immobilisie‐rung des mineralisierten Stickstoffs begün‐stigte. Daher war eine stärkere Aufteilung der ergänzenden Düngergaben erforder‐lich, um eine optimale Versorgung der Weizenpflanzen auf diesem Boden sicher‐zustellen. 4. Trotz großer Unterschiede im Witterungs‐ablauf der Versuchsjahre und erheblicher Differenzierung der Nt‐Vorräte beider Stando...

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.

Yield formation in cereal‐rich crop rotations and monocultures in an extensive and intensive crop‐management system In a long duration trial, conducted from 1979/80 to 1992 at TU‐Munich's research station in Roggenstein, the performance of monocultures of winter wheat, winter barley and winter rye, as well as numerous cereal‐crop rotations were compared in an extensive and intensive crop‐management system. The results obtained can be summarized as follows. Over the course of 13 years, the influence of the immediately preceding crop on the yield of the main crops was of much greater significance than the rotation as a whole. With winter wheat, no yield differences could be observed between monoculture and cereal crop rotation (if the rotation did not include oats). Oats, rape, field bean, pea, potato and maize as preceding crops, however, in crop management systems, led to, on average, an increase in yield of 13 dt/ha from the following wheat. Winter barley yields were not significantly different in monoculture, cereal crop rotations and crop rotations containing 66% cereals. Furthermore, winter rye yields were the same in monocultures and cereal crop rotations. With all cereals, intensification of fertilizing and chemical plant protection led to a considerable increase in yield, but did not diminish the effects of the preceding crop. Hence, even with the use of modern agronomical techniques it is impossible to compensate for yield losses due to crop rotation.