Rapeseed (Brassica napus L. var. oleifera) response to nitrogen fertilizer following different previous crops

This study was conducted in the crop years 2007-1010 and aimed to evaluate the effects of previous crops and use of nitrogen (N) fertilizer on rapeseed productivity in Ahwaz, Iran. The previous crops were: i) barley + clover; ii) rapeseed; iii) corn; iv) mung-bean; v) rice; and vi) wheat. N fertilizer was applied to rapeseed at rates of 0, 100, 160 and 220 kg ha-1. The effects of management on yield, and product oil content and oil yield were assessed. The effect of the previous crop and the use made of N fertilizer both affected rapeseed productivity. The results of two repeated experiments showed that the lowest seed and oil yields were obtained when unfertilized rapeseed followed rice. The highest seed and oil yields were obtained when rapeseed production followed mung-bean as the previous crop (range 160-220 kg ha-1 N rate). Among yield components, previous crops and N rates significantly influenced the silique number per unit area, and this showed a similar variation to that of seed yield. Data averaged across 2-year periods indicated that the highest oil content occurred in unfertilized rapeseed plots when the effects of the previous crop were not significant. Nevertheless, rapeseed following mung-bean receiving 150-220 kg ha-1 N rates produced the highest yield in the two years in which the experiment was repeated. Rapeseed following mung-bean and receiving 160 kg N.ha-1 had also the highest nutrient use efficiency parameters.