| With the increasing of population,it is urgent to increase crop yield to alleviate the problem of grain supply.The application of nitrogen fertilizer could significantly increase crop yield.Therefore,the excessive input of nitrogen fertilizer is more obviously.Excessive input of nitrogen fertilizer could increased the loss of nitrogen fertilizer,which resulted in the increasing of eutrophication.Water environment is seriously damaged.The eutrophication of Chao Lake is becoming more and more seriously.But there is a lack of long-term monitoring of Chao Lake 's research.At the same time,there is also lacking of the study of nitrogen inputting threshold.In view of the above problems,this study had selected the appropriate monitoring points of rice wheat rotation in the Chao Lake Basin.And on this basis,the different levels of nitrogen fertilizer were set up.The samples of rainfall runoff,leaching water,ammonia volatilization,plant straw and soil samples were collected and analyzed.The characteristics of nitrogen loss and the utilization of nitrogen fertilizer in the farmland of Chao Lake Basin under different nitrogen application levels were obtained.The corresponding loss coefficient was calculated,and the threshold value of nitrogen fertilizer input which ensure the security of farmland environment and the security of grain production was raised.The main results are as follows:1?The yield of wheat and rice was significantly increased which using nitrogen fertilizer compared with that of no nitrogen fertilizer.The highest yield of wheat was under the treatment of 125%N(N application rate 262.5 kg/hm~2)and 150%N(N application rate 315 kg/hm~2),which were 3502 kg/hm~2,4172 kg/hm~2,3777 kg/hm~2.The highest yield of rice was under the treatment of 100%N(N application rate 225 kg/hm~2)and 125%N(N application rate 281.25 kg/hm~2),which were 8478 kg/hm~2,7889 kg/hm~2,8819 kg/hm~2.2?The amount of nitrogen accumulation in wheat and rice showed a significant positive correlation with the amount of nitrogen application.But the utilization of nitrogen showed a decreasing trend.The nitrogen accumulation of wheat was 20.27-137.37 kg/hm~2,and the utilization rate of nitrogen fertilizer was about 19%-33%.The nitrogen accumulation of rice was 20.27-137.37 kg/hm~2,and the utilization rate of nitrogen fertilizer was about 19%-33%.3?After fertilization,the concentration of total nitrogen in the surface water reached its peak in the first day.After one week,the total nitrogen concentration in surface water was decreased to the lowest and stabilized.In three years,the highest concentration of each treatment reached to 9.20-173.75 mg/L in 2012,11.26-194.18 mg/L in 2013 and 12.45-154.21 mg/L in 2014.The change of total nitrogen concentration in surface water of N blank treatment was not obvious.The total nitrogen concentration in the surface water of other high nitrogen treatment was significantly higher than that in the low nitrogen treatment.Thus,it is necessary to control the loss of nitrogen in a week after fertilization.4?The nitrogen runoff loss of wheat and rice increased with the increasing of nitrogen application rate.Nitrogen application increased the loss of nitrogen.The loss of nitrogen in wheat season was 5.78-23.98 kg/hm~2,and the loss rate was 1.84%-5.78%.The loss of nitrogen in rice season was 6.85-15.42 kg/hm~2,and the loss rate reached 0.74%-3.89%.The runoff loss was lower than that in wheat season.5?The rule of nitrogen leaching loss in rice season was the concentration of nitrate,ammonium and total nitrogen in the leaching water was increased with the increasing of the amount of nitrogen application.Nitrogen fertilizer significantly increased the concentration of different forms of nitrogen in the leaching water.Ammonium nitrogen accumulation in the 20-40 cm soil layer,gradually reduced from top to bottom.Nitrate nitrogen in 90 cm soil layer in the majority,gradually increased from top to bottom.The nitrogen leaching loss was mainly in the form of nitrate nitrogen.In base fertilizer,tillering fertilizer and panicle fertilizer for about five days,the total nitrogen concentration reaches a maximum value and then starts to decrease.The amount of total nitrogen leaching was between 5.74-27.57 kg/hm~2,and Leaching loss rate reached 3.04%-5.34%.With respect to the nitrogen loss from runoff,the total amount of leached nitrogen loss was higher than that of runoff.6?Ammonia volatilization was significantly increased after the application of nitrogen fertilizer in rice reason.Compared with the nitrogen runoff and leaching loss,the loss of ammonia volatilization was higher,and the proportion of nitrogen fertilizer was higher too.The amount of ammonia volatilization in rice reason was 5.92-99.77 kg N/hm~2,and the ammonia volatilization rate was 8.7%-24.51%.7?After wheat and rice harvest,the majority form of soil mineral nitrogen accumulation was nitrate nitrogen.In wheat season,the content of ammonium nitrogen is almost no higher than 5 mg/kg,and the rice season is almost no higher than 4 mg/kg.The application of nitrogen fertilizer could increase the residual nitrogen in the soil.The accumulation amount of mineral nitrogen in wheat season was 6.84-18.91 mg/kg,and was 4.04-9.75 mg/kg in rice season.Long-term excessive increase in nitrogen fertilizer,soil mineral nitrogen accumulation gradually increased.At the same time,the risk of loss was also increased.8?Considering the yield and economic benefits,the threshold range of wheat nitrogen fertilizer was 247.1-291.9 kg/hm~2,threshold range of rice nitrogen inputs for 229.8-305.2 kg/hm~2.Based on the environmental factors and yield efficiency,the threshold range of wheat nitrogen fertilizer input was 229.73-306.3 kg/hm~2,and the threshold range of rice nitrogen fertilizer input was 196.5-262.02 kg/hm~2.Considering the yield,economic and environmental benefits,the threshold value of nitrogen fertilizer input was 247.1-291.9 kg/hm~2,and the threshold value of rice nitrogen fertilizer input was 229.8-262.02 kg/hm~2. |
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