effect of nitrogen foliar application on canola yield (brassica napus l.) and nitrogen efficiency across different sowing dates

introduction between oil seeds, from the quality, quantity and nutrition index point of view, canola has the top level . because of the solubility of n fertilizers, the time of urea application, is very important and one of the main reasons of the reduction in n application efficiency is utilization of urea in an inappropriate time. by precisely foliar application of nitrogen, the efficiency of nitrogen transformation to the grain will be very high because in this method the leaf is considered the main organ of nitrogen uptake and a low amount of absorbed nitrogen was transferred to the root and entered the soil. the more division of n application in growth stages and in accordance with plant need and foliar application result in increasing nitrogen use efficiency. the delay in sowing will result in the reduction of yield and this is due to low lai, and thus low radiation absorb in vegetable phase and shorter reproductive phase with high temperature in flowering and subsequent stages that result in low prolific silique and make disorder in transferring stored material to grain. in this experiment using n foliar application to decrease the adverse effect of delay in sowing is objective. materials and methods the experiment was conducted in 2013-2014 in ramin agriculture and natural resource university of khuzestan. experiment was conducted as split plots in a randomized complete blocks design with three replications. in this experiment sowing date]optimum sowing (27 november), 17 december and late sowing (30 december) [were assigned to main plots and several time of n-foliar application with 5 percent density from urea (20 liter per ha), ]to (control), t1 (foliar n application in rosette stage), t2 (foliar n application in budding stage), t3 (foliar n application in flowering stage)[ were placed in sub-plots in randomized way. fertilizing was based on the results of soil examination. therefore, 162 kg ha-1 of pure nitrogen (from resource urea) in the way of dusty application (1/3 after appearance of seedling on the soil, 1/3 in 3-4 leaves stage after thinning and 1/3 at the beginning of steam elongation) and 100 kg.ha-1 super phosphate triple in all plot was applied before planting. each plot was consist of 8 planting line with 20 cm apart from each other and 4 m length. the data were analyzed by using sas and mean comparison of data based on lsd test in 5% probably level. results and discussion late sowing date and nitrogen foliar have significant effect on the yield and efficiency and uptake index of nitrogen. with delay in sowing because the flowering and silique formation stage faced with the heat tension, the vegetative phase, production of photosynthesis matter and growth all treatment like: yield, oil yield, biological yield, oil seed percent, nitrogen harvest index, nitrogen use efficiency, nitrogen utilization of agronomy efficiency and amount of nitrogen uptake, were decrease. but it should be pointed out that with delay in sowing the percentage of nitrogen seed and nitrogen of all bushes was increased. the highest yield with mean of 3406.6 kg.ha-1 was relevant to first sowing date and least yield with mean 1803 and 1499.1 kg.ha-1 was achieved of second and third sowing date, respectively. in foliar treatment the highest yield was obtained from n foliar in budding and flowering stages and the least yield was obtained from control treatment. foliar in budding and flowering stages by increasing the green surfaces of plant, more benefit of sun radiation, increasing in photosynthetic activity were increase and in this way the seed yield and oil yield were increase. as well nitrogen harvest index was increased with increasing of assigned nitrogen to silique in canola and the reduction in wasting of nitrogen will be increased by consume it in appropriate time. with nitrogen foliar application because of availability of nitrogen in appropriate amount and adequate utilization of plant of nitrogen, caused to increase the nitrogen utilization of agronomy efficiency and nitrogen uptake amount. conclusions the results of this experiment showed that with delay in sowing the flowering and grain formation stages were faced to heat tension and can result in reduction in all treatment. the nitrogen foliar in heat stress caused an increase in seed yield, oil yield, dry mater, nitrogen harvest index, nitrogen utilization of agronomy efficiency and amount of nitrogen uptake. as the result, first sowing date and n foliar application in budding and flowering stages were best treatment in this experiment.