New crop management to improve perform-ance of Organic Winter oilseed in a network of farmer’s fields

Summary

In organic systems in France, the yields of WOSR are known to be low and variable due to the lack of references on suitable crop management. The aim of our study was to assess four different crop management strategies for organic WOSR in geo-graphically broad network of farmer’s fields. Theses strategies were built in order to limit the impacts of the main limiting factors, i.e nitrogen / weeds and insects. Experiments comparing the four strategies were performed on a network of farm fields in four contrasted regions over 2 years. This study investi-gated also the potential use of turnip rape trap crop to control insect pests on organic winter oilseed rape during the third year. The cropping strategies differed in sowing date, crop density and row spacing, in order to use mechanical weeding. Decision rules concerning the utilisation of mechanical harrow were tested. Hypothesis on the effects of each crop management strategy on crop growth, on pests and environmental conditions were formalized and tested. An early sow-ing date decreased the attack of autumn insects and slugs and blackleg incidence. The smothering effect of oilseed rape on weeds depended on the interaction between the sowing date, the amount of available soil nitrogen at crop emergence, the crop density and the soil management. Attack of blossom pollen beetle were more important on turnip rape than on WOSR but in some cases the trap effect was not sufficient enough to limit pollen beetle damage in WOSR