Maize (Zea mays L.) Response to Nitrogen Fertilizer under Drought Stress at Vegetative and Reproductive Stages

In the sub-tropics, water and nitrogen are the most important factors limiting the grain yield of maize. The effect of nitrogen (N) rates and drought stress at different growth stages of maize were investigated. Nitrogen treatments consisted of 100, 150, and 200 kg N ha-1 from the urea source while water stress treatments were composed of irrigation- off since the early 10-leaf stage to emergence of 50% tassel (vegetative), irrigation- off since the emergence of 50% tassel to the end of pollination (reproductive), and well watered plots. Drought condition at both vegetative and reproductive growth stages reduced grain yield 35% and 45%, respectively. Number of kernel per ear and kernel weight also reduced significantly with drought stress especially in reproductive stage. The highest response of maize yield to N fertilizer was observed in treatment with optimal irrigation; however, the increase of N particularly in vegetative stress somewhat led to decrease of drought stress effects on grain yield. Drought stress at vegetative and reproductive stages increased resource limitation with the rate of 67.1% and 77.25%, respectively. Drought stress at both stages caused significant decrease in chlorophyll content and leaf relative water content. In general, the highest negative effect of drought stress on grain yield and physiological traits occurred at reproductive stage and increasing the amount of nitrogen cannot compensate these reductions.