Effects Of Nitrogen Reduction Combined With Iron Powder Application On Ammonia Volatilization, Greenhouse Gas Emissions And Mineral Nitrogen Leaching In Rice Field

In paddy field habitats,in addition to the absorption and utilization of nitrogen by crops,processes such as greenhouse gas emissions,ammonia volatilization,and mineral nitrogen leaching also occur.Studies have shown that the nitrogen fertilizer application per unit area of rice in my country is 180 kg N/hm²,which is 75%higher than the world average.The current situation is that the input of nitrogen fertilizer is too high and the utilization rate is low,which aggravates the negative environmental effects corresponding to these processes.Namely global warming,atmospheric haze pollution,groundwater pollution.The reduction of nitrogen fertilizer application can reduce the negative effects of the environment,but it will bring about the risk of yield reduction.In this study,iron powder was applied exogenously after reducing the amount of nitrogen fertilizer,in order to reduce the negative environmental effects under the condition of ensuring stable rice yield.The effects of nitrogen reduction and iron application on rice yield,greenhouse gas emissions,ammonia volatilization,and mineral nitrogen leaching in paddy fields in the Yangtze River Delta are still unclear.Therefore,this study set up a test site in typical paddy fields in the Yangtze River Delta,and conducted a three-year field in-situ experiment in the rice season from 2019 to 2021.A total of 7 experimental treatments were set up,namely the traditional nitrogen application rate（100%N）,80%conventional nitrogen application rate（80%N）,80%conventional nitrogen application rate+iron（80%N+Fe）,60%conventional nitrogen application rate（60%N）,60%conventional nitrogen application rate+iron（60%N+Fe）,no nitrogen fertilizer（0%N）,no nitrogen fertilizer+iron（0%N+Fe）,the rice yield,greenhouse gas emissions,ammonia volatilization and mineral nitrogen leaching were measured for each experimental treatment,so as to explore nitrogen reduction The main research results of the impact of iron application on the production and environmental benefits of paddy fields in the Yangtze River Delta region are as follows:（1）Reducing nitrogen fertilizer application will reduce rice yield.The treatment with iron powder always maintains a state of increasing yield under the same nitrogen reduction level.The 80%N+Fe treatment is 1.43%-9.68%higher than the 80%N treatment,and 60%N+Fe treatment is 8.73%-13.94%higher than 60%N treatment.Compared with pure nitrogen reduction,the addition of exogenous iron powder has a positive effect on the yield;80%N+Fe treatment is always the same as 100%N treatment in terms of yield.Maintaining the same level has a positive impact on the stable yield of rice.（2）The peak of ammonia volatilization basically appeared within 3 days after fertilization,and then decreased slowly,and ammonia volatilization basically stopped after one to two weeks;compared with the p H of field water,the concentration of ammonium nitrogen in field water was the main physical and chemical property affecting ammonia volatilization;Ammonia volatilization was positively correlated with nitrogen application level,and ammonia volatilization decreased significantly after nitrogen reduction;Ammonia volatilization and ammonia volatilization intensity of 80%N+Fe treatment showed a continuous downward trend in the three-year rice season,until they appeared with 100%N treatment.Significant difference,80%N+Fe treatment can better balance the environmental impact of ammonia volatilization and the production benefit of stable rice yield.（3）N₂O emission is easily affected by fertilization and field water conditions,and CH₄emission is easily affected by the length of field flooding period;N₂O emission decreases with the decrease of nitrogen application level,which is positively correlated.Nitrogen reduction can significantly reduce N₂O emission,while There is no obvious relationship between CH₄emission and nitrogen application level;under the same nitrogen reduction level,compared with the simple nitrogen reduction treatment,the treatment with iron powder has a tendency to increase the N₂O emission,but the CH₄ emission reduction effect will appear and maintain,and the 80%N treatment group The emission reduction is 57.54%-62.16%,and the emission reduction of the 60%N treatment group is 30.95%-71.46%;the GWP and GHGI of the80%N+Fe treatment are lower than those of the 100%N treatment,which is more advantageous in terms of greenhouse gas emission reduction.It can better balance the environmental impact of greenhouse gas emissions and the production benefits of stable rice production.（4）The leaching of mineral nitrogen is mainly nitrate nitrogen（NO₃^--N）,and the leaching process of NO₃^--N is affected by nitrogen application level and field water conditions;at three different soil depths of 30cm,60cm,and 90cm,Under the same nitrogen reduction level,compared with the simple nitrogen reduction treatment,the treatment with iron powder increased the leaching of nitrate nitrogen,but the increase rate gradually decreased in the three-year rice season,and even decreased;The addition of iron powder at the nitrogen level of 20%is beneficial to reduce the risk of nitrate leaching in deep soil leachate.To sum up,the negative effects of the environment will be weakened after nitrogen reduction,but the yield of rice will also be reduced.Under the level of nitrogen reduction of20%,the treatment of exogenous iron powder addition has a positive effect on the stable yield of rice,and at the same nitrogen reduction level,it is relatively nitrogen reduction alone reduces ammonia volatilization,greenhouse gas emissions,and mineral nitrogen leaching from deep soil leachate.Based on the three-year rice season experiment,the treatment of adding iron powder after reducing nitrogen by 20%can better balance the environmental benefits and production benefits.