Effect of irrigation on nitrogen uptake and translocation in summer maize

A 2-year field experiment consisting of four irrigation treatments (i.e., 1~4 irrigations during maize growth period) was carried out to study the effects of irrigation amount on the uptake, distribution and translocation of nitrogen in maize plants. The results showed that increased irrigation amount enhanced nitrogen accumulation and distribution in maize stems and leaves at jointing and tasseling stages. However, no significant differences were noted at late grain-filling stage among the different treatments. About 75% of accumulated nitrogen in maize spikes was from post-anthesis assimilation and 25% from translocated nitrogen in stems and leaves. This implied that spikes mainly absorbed N from soil during the stages of grain-filling and maturity. While abundant water supply increased N uptake in vegetative organs, it decreased post-anthesis assimilation rate. It was therefore necessary to maintain moderate water conditions to ensure not only optimum nitrogen absorption, but also increase nitrogen store in stems and leaves. The stored nitrogen would be translocated to grains, which could improve nitrogen use efficiency.