Growth and yield of winter wheat in the first 3 years of a monoculture under varying N fertilization in NW Germany

Different preceding crops interact with almost all husbandry and have a major effect on crop yields. In order to quantify the yield response of winter wheat, a field trial with different preceding crop combinations (oilseed rape (OSR)-OSR-OSR-wheat-wheatwheat), two sowing dates (mid/end of September. mid/end of October) and 16 mineral nitrogen (N) treatments (80-320 kg N ha(-1)) during 1993/1994-1998/1999. was carried out at Hohenschulen Experimental Station near Kiel in NAV Germany. Single plant grain yield and yield components at harvest were investigated. During the growing biomass, tiller numbers m(-2), biomass m(-2). season, the incidence of root rot (Gaeunmannomyces graminis) was observed. Additionally, a bioassay with Lemna minor was used to identify the presence of allelochemicals in the soil after different preceding crops. Averaged over all years and all other treatments, wheat following OSR achieved nearly 9.5 t ha(-1). whereas the second wheat crop following wheat yielded about 0.9 t ha(-1) and the third wheat crop following 2 years of wheat about 1.9 that less compared with wheat after OSR. A delay of the sowing date only marginally decreased grain yield by 0.2 t ha(-1). Nitrogen fertilization increased grain yield after all preceding crop combinations. but at different levels. Wheat grown after OSR reached its maximum yield of 9.7 t ha(-1) with 2 10 kg N ha(-1). The third wheat crop required a N amount of 270 kg N ha(-1) to achieve its yield maximum of 8.0 t ha(-1). Yield losses were mainly caused by a lower ear density and a reduced thousand gram weight. About 4 weeks after plant establishment. single wheat plants following OSR accumulated more biomass compared to plants grown after wheat. Plants from the third wheat crop were smallest. This range of the preceding crop combinations was similar at all sampling dates throughout the growing season. Root rot occurred only at a low level and was excluded to cause the yield losses. The Lemna bioassay suggested the presence of allelochemicals. which might have been one reason for the poor single plant development in autumn. An increased N fertilization compensated for the lower number of ears m(-2) and partly reduced the yield losses due to the unfavorable preceding crop combination. However, it was not possible to completely compensate for die detrimental influences of an unfavorable preceding crop on the grain yield of the subsequent wheat crop. (C) 2004 Elsevier B.V. All rights reserved.