Study the effect of defoliation and nitrogen foliar application on yield Physiology of Sunflower

To investigate the effects of defoliation and nitrogen foliar application on yield physiology of sunflower, a experiments was performed in a randomized complete block design with split-plot arrangement in Gonabad region during 2015 and 2016 seasons. Nitrogen consists of two levels of spraying in flowering time (N1) and control (N2) in the main plots. Defoliation consists of five levels: Control (D1), 1/3 defoliation at 8th leaf stage (D2), 2/3 defoliation at 8th leaf stage (D3), 1/3 defoliation at beginning of the flowering (D4), 2/3 defoliation at beginning of the flowering (D5). In nitrogen deficiency conditions, by cutting 1/3 of the leaves at the first of the flowering, grain yield increased by 28% (0.54 to 0.75 kg ha-1) compared to control treatment .In the conditions of nitrogen consumption, after removing the 2/3 of the leaves at the first of the flowering, the amount of dry matter transfer reallocation from the stem to the grain showed a significant increase compared to the control, while in the conditions of non-nitrogen consumption, defoliation treatments had a slight effect on the contribution of stem reserves. Under the conditions of nitrogen deficiency, the negative effect of sink size restriction on grain yield is more than the negative effect of source strength restriction. constraints than the source power limitations On the practice Gain rejection is more. Plant breeders focus their programs to increase the efficiency of nitrogen consumption in order to increase the strength of the sink and reduce extra leaves with low efficiency in grain filling.