Effects of N application level on yield and premature senescence factor of spring maize in Liaoning province

Premature senescence is a major reason of low yield of spring maize, especially in Northwest Liaoning. The experiment was carried in field, ear leaf chlorophyll content, protective enzyme activity, root dry weight and leaf scorch proportion in the dough stage of spring maize were investigated. Results showed that with the increase of nitrogen level, chlorophyll content, root dry weight increased, leaf scorch proportion decreased; the activities of superoxide dismutase (SOD), peroxidase (POD) reduced at filling stage, milky stage and dough stage. When the nitrogen amount was 240 kg/hm, the activities of SOD, POD could be obviously improved, chlorophyll content, root dry weight achieved higher value. Leaf scorch proportion was the lowest, could defer decrepitude effectively the aging of leaves in late growth stage. The highest yield of maize could be up to 9 284 kg/hm, increased by 40.09% compared to no fertilizer.