The effect of nitrogen fertilizer rates and withheld irrigation stress on yield and yield components in different growth stages of oilseed rape

Oilseed rape (Brassica napus L.) is one of the most important oilseed crop which in recent years was attentioned, therefore; cultivation, production and its management in order to increase grain yield is very important. Thus, a two year (2006-2008) field experiment was conducted at the Experimental Research Field of College of Agriculture, Shiraz University, to study the effect of nitrogen (N) rates (0, 75, 150, and 225 kg ha-1) and drought stress (full irrigation at all growth stages, withheld irrigation stress at flowering, pod development, and seed filling stages) on yield and yield components of oilseed rape (Talayeh cultivar). The experimental design was split plots arranged in randomized complete block design with four replications. Results showed that full irrigation and 225 kg ha-1 of nitrogen treatment had the highest grain yield, number of pods per plant, and 1000- grain weight. Increased N fertilizer application significantly increased plant height, number of branches per plant, number of pods per plant, and seed yield, but increased N fertilizer application resulted in a decrease in grain oil percentage. Full irrigation and 75 kg ha-1 of nitrogen treatment had the highest grain oil percentage. It is concluded that rapeseed has a high requirement for nitrogen fertilizer. Also, it seems that providing sufficient water to plant during flowering stage is especially important to produce higher yield with high quality at water deficit prone environments.