EFFECTS OF PREVIOUS CROPPING ON SEED YIELD AND YIELD COMPONENTS OF OILSEED RAPE (BRASSICA-NAPUS L)

Information about the effect of the preceding crop or crop combination on the seed yield of oil-seed rape is extremely scarce. Experiments w ere carried out in northwest Germany to investigate the effect of diff erent preceding crops on the growth, seed yield and yield components o f oil-seed rape. The two directly preceding crops, wheat and oil-seed rape, had only a negligible and non-significant effect on the seed yie ld of the following oil-seed rape crop. Oil-seed rape grown after whea t had more pods per plant, due to an increase in the number of pods on the higher category branches. In contrast, the seed yield and yield c omponents were more affected by the cropping sequence, i.e. the crops 2 years before. Averaged over two experimental years, the greatest yie lds were observed in oil-seed rape following the sequence peas-wheat ( 694 g m(-2)), whereas the smallest seed yield occurred after 2 years o f oil-seed rape cropping (371 g m(-2)). The differences in the seed yi eld were again associated with more pods per plant, which compensated for the lower number of plants m(-2), whereas the number of seeds per pod and the mean seed weight were almost unaffected by the previous cr opping. It was not possible to relate the described differences to the crop development, since differences in the biomass caused by the prev ious cropping were only significant at maturity. Oil-seed rape grown a fter 2 years of oil-seed rape had the highest ratings of stem canker ( Leptosphaeria maculans) as well as verticillium wilt (Verticillium dah liae). But the general level of the diseases was low, and therefore ot her causes for the effects described must be considered. (C) 1997 Else vier Science B.V.