EFFECT OF DIFFERENT PRECEDING CROPS AND CROP ROTATIONS ON YIELD OF WINTER OILSEED RAPE (BRASSICA-NAPUS L)

To determine the effect of different preceding crops and crop rotation s on the grain yield of oil-seed rape, a long-term rotation experiment was conducted at the Hohenschulen experimental station in Kiel, NW Ge rmany. Additional factors included the nitrogen fertilization and the fungicide application. The results reported herein are based upon the harvest years 1988 to 1993. Averaged over the different rotations and husbandry treatments, the grain yields in the 6 experimental years var ied between 2.71 t ha(-1) and 3.99 t ha(-1). In contrast, the effect o f the different husbandry treatments was smaller and non significant. Averaged over 6 years, only the fungicide application caused small yie ld increase of 0.2 t ha(-1). The highest grain yields of 3.77 t ha(-1) or 3.65 t ha(-1) occurred when oil-seed rape was directly following p eas. Low yields between 3.15 t ha(-1) and 3.33 t ha(-1) were obtained when oil-seed rape was grown after oilseed rape. The lowest grain yiel d of 3.13 t ha(-1) was produced with oil-seed rape grown in monocultur e only. In rotations with oil-seed rape following a preceding cereal c rop (wheat or barley), the grain yields averaged between 3.22 t ha(-1) in a two course rotation and up to 3.44 t ha(-1) in a four course rot ation. In general, the yields of oil-seed rape increase with the lengt h of the rotation and the length of the break between two oilseed rape crops. The yield component number of seeds per m(2) was affected by t he previous cropping accordingly, whereas the thousand seed weight did not respond to the cropping history. Based upon disease assessments i n the first years of this experiment, we argue that an increase in the incidence of fungal diseases has considerably contributed to the yiel d decrease of oil-seed rape in short rotations.