EFFECT OF PRECEDING CROP COMBINATION AND N FERTILIZATION ON YIELD OF 6 OILSEED RAPE CULTIVARS (BRASSICA-NAPUS L.)

Information about the effect of the cropping history on the seed yield of oil-seed rape is extremely scarce. In 1992/93 and 1994/95, the eff ects of different preceding crop combinations (winter barley and winte r wheat as preceding crops, oil-seed rape and wheat as pre-preceding c rops) on the yield of six double low oil-seed rape cultivars were exam ined in a field trial at Hohenschulen Experimental Farm, north-west Ge rmany. In addition, eight nitrogen treatments (different amounts and d istribution patterns) were tested for their potential to reduce negati ve effects of the preceding crops. Following the cropping sequence of oil-seed rape then wheat, oil-seed rape yielded only 3.12 t ha(-1); af ter oil-seed rape then barley, the yield was 3.43 t ha(-1) compared wi th 3.77 t ha(-1) following wheat then barley and 3.71 t ha(-1) followi ng wheat then wheat. The number of seeds per m(2) showed a similar pat tern, whereas the thousand-seed weight partly compensated for the redu ced seed number. It was highest if oil-seed rape was grown 2 years pre viously. The cultivars differed significantly in their yield potential . Express (3.79 t ha(-1)) yielded 0.6 t ha(-1) more than Falcon (3.18 t ha(-1)). Increasing amounts of fertilizer-N (80-200 kg N ha(-1)) inc reased the seed yield from 3.21 t ha(-1) to 3.84 t ha(-1). Changes in the distribution pattern within one fertilizer amount had no effect on seed yield. In addition, no interactions between preceding crop combi nation and the different cultivars or N treatments occurred. It is con cluded that crop management cannot totally eliminate the negative effe cts of an unfavourable cropping history on the seed yield of oil-seed rape. (C) 1997 Elsevier Science B.V.