Effects of nitrogen source and rate on productivity and quality of winter oilseed rape (Brassica napus L.) grown in different crop rotations

Data from a field experiment (1995-2000) conducted on a fertile sandy loess in the Hercynian dry region of central Germany were used to determine the productivity of winter oilseed rape (Brassica napus L.) as affected by previous crop and nitrogen (N) fertilization. The crop rotations compared were winter barley (Hordeum vulgare L.)-winter oilseed rape-winter wheat (Triticum aestivum L.), and pea (Pisum sativum L.)-winter oilseed rape-winter wheat. Fertilizer was applied to winter oilseed rape as either calcium ammonium nitrate (CAN) or cattle manure slurry. The N rates applied to winter oilseed rape corresponded to 0, 80, 160, and 240 kg N ha(-1) a(-1). Management effects on seed yield, seed oil and crude protein contents, and energy and CO2 storage in the seed were assessed. The different N management strategies influenced productivity of winter oilseed rape. Data averaged across all years indicated that the lowest productivity in terms of seed yield (2.79 t ha(-1)), energy storage (7.90 GJ ha(-1)), and CO2 storage (7.69 t ha(-1)) occurred when unfertilised winter oilseed rape followed winter barley. Highest values for all these traits were obtained at 240 kg ha(-1) mineral N fertilization when the effects of the previous crop were small. Pooled maximum seed yields for the high fertilizer rate ranged from 4.79 to 4.90 t ha(-1). Storage of energy and CO2 by the seeds ranged from 13.6 to 13.9 GJ ha(-1) and 13.2 to 13.5 t ha(-1), respectively. Under high N rates, the lowest oil contents (43.8-44.1%) were observed. In contrast, highest oil concentrations were found for the unfertilised plots (46.8-47.7%). Crude protein contents of 21.6% and 17.7% were measured at high and low N rates, respectively. Results emphasize that N fertilization rate had the strongest influence on the productivity of winter oilseed rape followed by smaller effects due to previous crop and type of fertilizer and interactions between these treatment factors. (c) 2004 Elsevier B.V. All rights reserved.