Effect of water deficit and different nitrogen rates on yield, yield components and physiological traits of rapeseed (Brassica napus L.)

Plants are mostly exposed to environmental stresses. Water and nitrogen availability are two major factors for crop production under different conditions. In order to determine the effects of water deficit and different nitrogen rates on yield, yield components and physiological traits in rapeseed, a field experiment was conducted using a factorial split-plot in randomized complete block desing in 2005 growing season. In this study, two varieties (Zarfam and Modena) in three water regimes(irrigation after 40,60 and 80 percent evacuation of soil water) and four nitrogen rates (0,75, 150 and 225 kg/ha) were studied. Results showed that decreasing soil water and nitrogen rate, caused intensive stress, that caused significant decrease in yield and yield components, that in this case, decreasing the pods in plant was greater than the other components. Physiological traits like stomatal conductance, leaf relative water content, light extinction coefficient and chlorophyll content decreased in water deficit condition, whereas the proline content increased significantly, that this increase was for higher ability of osmotic adjustment in water deficit condition.By increasing the nitrogen rate, all of the physiological traits showed significant increase too. By contrast the two variety, defined that the zarfam had a high tolerance to water deficit condition and lower nitrogen consumption, that the reason of these were higher physiological traits such as stomatal conductance, leaf relative water content, chlorophyll, light extinction coefficient and proline in water deficit and nitrogen consumption conditions. Also, this variety had a high potential of production in normal irrigation and high nitrogen consumption.