Effect of Different Application Rate of Nitrogen Fertilizer Under Straw Return on Maize Yield and Inorganic Nitrogen Accumulation

We investigated the influences of different nitrogen fertilizer rate on maize production, nitrogen use efficiency and soil nitrate nitrogen at straw return farmland for two years. The results showed that maize production increased with the increment of nitrogen fertilizer. The maize production was the highest at 216 kg·hm-2(N216)of nitrogen use and began to decrease when the amount of nitrogen use was beyond216 kg·hm-2. There were significant interannual differences on maize production in the same treatment. The maize production in 2010 increased 0.69%~4.75% compared with that in 2009. Nitrogen use efficiency, nitrogen agronomic efficiency and nitrogen harvest index im-proved with the year of straw return. The highest nitrate nitrogen accumulation was found in the treatment of 240 kg·hm-2(N240)in0~100 cm soil layer. Soil nitrate content increased with the depth of soil. This may potentially increased the risk of nitrate pollution on shallow groundwater. Compared with N240, the nitrate nitrogen accumulation of N168(168 kg·hm-2),N192(192 kg·hm-2)and N216(216 kg·hm-2)were equally reduced by respectively 39.87%, 35.84% and 29.38% in 0~100 cm soil layer. Considering the maize production, nitrogen use efficiency and ecological environmental benefits, the optimum amount of nitrogen use should be 200 kg·hm-2.