Effect of nitrogen management on the relationship of leaf SPAD with nitrogen absorption of corn in cold area

Since there is neither proper distribution ratio nor dressing time of nitrogen fertilizer,nor proper quantified standard for top dressing of nitrogen fertilizer,the nitrogen use efficiency is lower.SPAD of corn leaves and the nitrogen accumulating dynamic were studied by nitrogen management and optimizing dressing,in order to determine the optimum stage of nitrogen dressing and amount.Result showed that the best fertilizer time of corn was ten-leaf stage.At this stage,the SPAD value of the ear leaf decreased gradually,but that of the superior leaf reached maximum at heading stage,and then decreased.The accumulated nitrogen of corn increased.The corn production of dressing of N 150 kg/hm2at ten-leaf stage was the highest among the treatments.