Effects Of Optimized Fertilization And Atmospheric Deposition On Nitrogen And Phosphorus Balance In Rice Field In Chaohu Lake Basin

Nitrogen and phosphorus balance in farmland ecosystems is an important reference for nitrogen（N）and phosphorus（P）nutrient management as well as its environmental effects evaluation.Fertilizer application is the main way of nitrogen and phosphorus input to farmland,however atmospheric deposition of nitrogen and phosphorus to farmland can not be ignored.Experiment of rice optimal fertilization as well as atmospheric nitrogen and phosphorus deposition were conducted in the Chaohu Lake Basin in 2019 to analyze the contribution of optimized fertilization and atmospheric deposition to nitrogen and phosphorus balance in rice field.This results provided scientific guidance for the comprehensive management of N and P in rice fields ecosystems as well as surface water quality protection.The main results are as follows:1.A database of the relationship between fertilization and rice yield in the Chaohu Lake Basin was established by using the maximum economic return methods,by which obtained an optimized rice fertilization based on total nutrients control.In Chaohu Lake Basin,the application rates of optimized N,P and K for the yield benefits in rice were 246,112 and 158 kg/hm²,the economically benefits optimized N,P and K were 223,95 and 140kg/hm²,the environmentally benefits optimized N,P and K in rice were 207,95 and 140kg/hm²,the socially benefits optimized N,P and K in rice were 188,95 and 140 kg/hm²,respectively.Rice yield from field experiments showed the law of the Yield benefits optimization fertilization>Economic benefits optimization fertilization>Formulated fertilization>Conventional fertilization>Non-fertilization treatment,and there was no significant differences among the treatments（p>0.05）.The economic benefits followed the rule of the Economic benefits optimization fertilization>Yield benefits optimization fertilization>Formula fertilization>Conventional fertilization treatment.From the perspective of environmental nitrogen loss and nitrogen use efficiency,compared with conventional fertilization,the total loss of active nitrogen in environmental and social benefits optimal fertilization reduced by 10.3%and 18.4%,respectively,while the nitrogen production efficiency of the formulated fertilization and economic benefits optimization fertilization increased by 12.2%and 8.8%respectively.2.The nitrogen surplus in rice field ranged from 189.2 kg/hm²to 221.2 kg/hm².The nitrogen surplus showed the rule of Yield benefits optimization fertilization>Conventional fertilization>Economic benefits optimization fertilization>Formula fertilization treatment,and the highest nitrogen surplus was 221.2 kg/hm²in the yield benefits optimized fertilization treatment,and the lowest nitrogen surplus was 189.2 kg/hm²in the formulated fertilization treatment.The range of phosphorus surplus in rice farmland was48-85 kg/hm².The phosphorus surplus showed the rule of Yield benefits optimization fertilization>Economic benefits optimization fertilization>Conventional fertilization>Formula fertilization,and the highest phosphorus surplus was 85 kg/hm²in yield benefits optimized fertilization treatment,and the lowest phosphorus surplus was 48 kg/hm²in the formulated fertilization treatment.The fertilizer nitrogen,nitrogen deposition and crop straw returning nitrogen accounted for 72.1%～75.2%,14.7%～16.5%and 10.2%～11.4%of total nitrogen input in rice field.Fertilizer nitrogen input was the main source of nitrogen input,followed by nitrogen deposition and crop straw returning nitrogen in rice field..The Fertilizer phosphorus,crop straw returning phosphorus and phosphorus deposition accounted for 92.3%～94.9%,3.9%～6%,and 1.1%～1.7%of total phosphorus input in rice field.Fertilizer phosphorus input was the main source of phosphorus input,followed by crop straw returning phosphorus and phosphorus deposition input in rice yield.Different from nitrogen deposition,the contribution of phosphorus deposition to phosphorus input in rice field is relatively small.3.The annual deposition fluxes of total nitrogen（TN）and total phosphorus（TP）were 98.23 and 3.26 kg/hm²,respectively in the monitoring period.Atmospheric TN deposition is dominated by dissolved organic nitrogen（DON）,accounting for 49.5%of the total TN deposition,while dissolved inorganic nitrogen（DIN）is dominated by NH₄⁺-N（14.48 kg/hm²）,and NO₃^--N is relatively low（5.85 kg/hm²）.Atmospheric TP deposition is dominated by dissolved inorganic phosphorus（DIP）（2.36 kg/hm²）,while the content of dissolved organic phosphorus（DOP）was low.The TN deposition fluxes in the rice season（from June to October）were 45.8 kg/hm²,which accounted for 20%of the total nitrogen fertilizer application in the current season.It was estimated that the annual TN and TP atmospheric deposition on the Chaohu Lake surface were 7661.94 t and 254.28 t,respectively,accounting for 48.4%and 32.5%of TN and TP input from the main rivers entry to lake.Above results indicated that nitrogen and phosphorus deposition in the Chaohu Lake Basin is an important source of nitrogen and phosphorus input to the rice field ecosystem and the Chaohu Lake water body.