Fertilization Rate Effects On Nitrogen Absorption By Maize And Nitrogen Residue In Soil In The Hexi Corridor Irrigation Area

Maize is the high yield crop in the Hexi Corridor and the planting areas are very large.Adequate fertilizer and water supply are very important for developing maize high yield potential,but the excessive fertilizer and water result in the decrease of nutrient and water use efficiency, at the same time bringing a series of environmental problems. In order to determine appropriate nitrogen fertilize application and irrigation amount by maize, we have conducted field trials research for three years in Shuangta Village,Xindun Town,Zhangye City,Gansu Province from2013 to 2014（the first experiment） and from 2014 to 2015（the operations research experiment）.The experiment was arranged as a randomized complete block design. The first experiment set seven nitrogen levels including pure N 520（N520）, 455（N455）, 390（N390）, 325（N325）, 260（N260）,195 kg·ha^-1（N195） and no nitrogen（N0）, in order to determine the appropriate nitrogen fertilizer by maize under the local conventional irrigation amount. Dry matter accumulation by maize, nitrogen absorption and distribution, variation of soil inorganic nitrogen, yield, nitrogen use efficiency and soil inorganic nitrogen residue after harvesting were systemly measured in experiments, according ly estimating nitrogen balance under different treatments. In the second experiment, N300 and N375 under reduced irrigation（W1） in the operations research experiment were simply compared with N325 and N390under conventional irrigation（W2） in the first experiment in the aspect of yield,water use efficiency, soil inorganic nitrogen residue and nitrogen balance,in order to determine the best combination of the amount of nitrogen fertilizer and irrigation.The results show that:The first experiment:Dry matter accumulation of no nitrogen fertilizer in plants’ life was lower than other nitrogen treatments. In the early stage of the growth period, nitrogen or no nitrogen fertilizer has no significant effect on total dry matter accumulation.In the mid-late growth period, dry matter accumulation increased with the increase of nitrogen application.In the mature period, when total dry matter accumulation and dry matter accumulation of grain reached the best value, the nitrogen fertilizer point is respectively 390 kg·ha^-1 and 325 kg·ha^-1, more than the piont of nitrogen fertilizer,dry matter accumulation would not significantly increase.Nitrogen uptake of no nitrogen fertilizer was lower than other nitrogen treatments in the whole growth period.In the early stage of the maize growth period, when nitrogen application ≥325 kg·ha^-1, the total nitrogen uptake would no longer significantly increase with the increase of nitrogen application.In the late growth period, when nitrogen application≥390 kg·ha^-1, the total nitrogen uptake and nitrogen uptake of grain would no longer significantly increase with the increase of nitrogen application.Compared with no nitrogen fertilizer,nitrogen application significantly enhanced the grain yield of maize in 2013 and 2014.When nitrogen application≥ 390 and 325 kg·ha^-1,the grain yield of maize would not significantly increase with the increase of nitrogen application in 2013 and2014.When nitrogen application ≥ 390 kg·ha^-1,the average of grain yield for two years would not significantly increase with the increase of nitrogen application.When nitrogen application≤ 325 kg·ha^-1,nitrogen use efficiency increased with the increase of nitrogen application in 2013,exceeding 325 kg·ha^-1,nitrogen use efficiency would drop.When nitrogen application ≥ 390 kg·ha^-1,soil inorganic nitrogen residue fundamentally increased with the increase of nitrogen application in 0¹00 cm soil layer in 2013.When nitrogen application ≤325 kg·ha^-1,there was no significant difference in different soil layers and each treatment.Low nitrogen treatment could reduce the residual soil inorganic nitrogen(≤325 kg·ha^-1)and the mid-high nitrogen treatment causeed of soil inorganic nitrogen accumulation(> 390 kg·ha^-1).Nitrogen apparent loss was significantly lower than that nitrogen treatments and there was no significant difference between these nitrogen treatments in 2013 and 2014.Above all, recommending the local average annual best nitrogen mass is 325 390 kg·ha- 1.The second experiment:In terms of yield and water use efficiency,W₁N₃₀₀ and W₁N₃₇₅were high and significantly higher than W2N325 and W2N390.At respacts of soil inorganic nitrogen residuen in 0¹00cm,nitrogen apparent loss and nitrogen surplus, W₁N₃₀₀ and W₁N₃₇₅ were lower than W2N325 and W2N390.Compared with W2,W1 saved water for 280 mm and water saving rate reached 46.67%. In terms of yield,water use efficiency,plant absorb and soil nitrogen residues,there was no significant difference between W₁N₃₀₀ and W₁N₃₇₅.In terms of soil apparent loss and nitrogen surplus,W₁N₃₇₅ were greater than W₁N₃₀₀, but there was no significant difference between them. Considering water saving,nitrogen saving and high yield, the single irrigation water for 80 mm and nitrogen application rate for 300 kg·ha^-1 should be regarded as the local optimal dosage of water and nitrogen.