Effects of nitrogen fertilizer rate and combined application of organic manure and chemical fertilizer on yield in summer maize and on soil NO_3~-—N

Under different nitrogen fertilizer level and with combined application of organic manure and chemical fertilizer,a field experiment was carried out to study the varying characteristics of soil NO3——N during the growth period of summer maize.The results showad that: summer maize yield was mainly effected by nitrogen fertilizer rate and not effected by the combined application of organic manure and chemical fertilizer;Soil NO3——N content increased following the rate of nitrogen fertilizer;Combined application of organic manure and urea could guarantee both long-term and short-term provision of the soil N;Increasing application of organic manure could coordinate the provision of soil N,and reduce the soil NO3——N content,thus could decrease the pollution to the ground water.Under the condition of our field experiment,secure fertilizing nitrogen amount of summer maize was within the scope of 200 kg/hm2,and the organic manure and chemical fertilizer with a ratio at 3∶1 was proper.