Effect of Nitrogen and Defoliation on Assimilate Redistribution and Grain Yield of Maize (Zea mays L.) Under Subtropical Conditions

In order to study the effects of nitrogen levels and defoliation on grain yield, yield components, and assimilate redistribution in maize (single cross 704), a field experiment was conducted in south-west of Iran in 2010–2011. The experiment was split-plot in the form of randomized complete block design with three replications. Main plots consisted of four nitrogen rates (0, 80, 160 and 240 kg N ha^?1) and elimination of some physiological resources including defoliation of upper and lower leaves of the canopy at anthesis stage and control (un-manipulated) were placed in sub-plots. Results indicated that the effect of nitrogen fertilizers and defoliation on grain yield was significant (P < 1 %), but the effect of nitrogen and defoliation interaction on this trait was not. The lowest and the highest grain yield belonged to 0 and 240 kg N ha^?1, respectively. As compared to the un-manipulated treatment, grain yield was 22.2 and 4.2 % lower in defoliation of upper and lower leaves, respectively. Grain yield reduction in defoliation of upper leaves was due to significant reduction of the number of grains and their weight. As the nitrogen rates increased to 160 and 240 kg ha^?1, stem assimilate redistribution increased and somewhat compensated for the effect of defoliation of lower leaves of the maize on its grain yield.