Study On Characteristics And Influencing Factors Of Nitrogen And Phosphorus Runoff Loss In Rice Field Under Extreme Rainfall Conditions

As a large agricultural country,the contribution rate of agricultural non-point source pollution to TN and TP is greater than that of domestic sewage and industrial wastewater,which is the main cause of eutrophication of water bodies.The water consumption of rice accounts for 60-70%of the total agricultural water.The rice fields are located in areas with abundant water resources,and the environmental problems caused by the loss of water caused by the eutrophication of adjacent water bodies cannot be ignored.According to the IPCC Fifth Assessment Report,the possibility of global extreme weather events in the 21st century has increased and expanded.Compared with developed countries,the occurrence of extreme rainfall events may cause more serious damage to the farmland ecological environment in developing countries.Therefore,under the extreme rainfall conditions,the law of rice field loss is revealed,the important influencing factors are determined,and the simulation study of nitrogen and phosphorus loss in regional rice fields is carried out to add theoretical basis for optimizing rice paddy rmanagement and forming a rice paddy production system with harmonious food production and environmental friendliness.After several decades of research,the mechanism and regularity of runoff loss in rice fields under natural rainfall conditions have been rationalized,which has promoted a more rational fertilization management and farming system.However,it is a new research hotspot to quantitatively analyze the nutrient loss process in rice fields by artificially simulating rainfall test and to establish the model to determine the risk of nitrogen and phosphorus loss in rice fields.In 2018,we conducted a field experiment on artificially simulated extreme precipitation events in Jingzhou City,Hubei Province,simulating precipitation events of 60,120,180 and 240 mm/h intensity during each rice growth period,while high-frequency monitoring of surface water and RunofIf liquid nitrogen and phosphorus concentrations to further analyze and understand the influencing factors and response relationships of nitrogen and phosphorus runoff losses in paddy fields.On this basis,we carried out parameter verification for the OCHIDEE-CROP loss part of the farmland ecosystem process model,and used the 2017 Jingzhou and 2018 Panjin,Gao'an,Anlu,Chaohu.Fangzheng natural rainfall observation site data to verify the model.The following conclusions were obtained:(1)Under different precipitation conditions,the runoff water volume has no significant difference during the growth period of rice.The runoff loss of total nitrogen has no significant difference at each growth period at the intensity of 60mm/h and 120mm/h.while the runoff loss of TN at the precipitation intensity of 180mm/h and 240mm/h at the three-leaf and tillering stages is about other fertility One to two times the period.The risk of loss of TP is higher in the tillering period than in other growth stages(2)Attribution analysis showed that the total amount of runoff water was significantly positively correlated with precipitation intensity and surface water height(p<0.001).At the same time,with the growth and maturity of rice,the change of leaf area index and crop interception ability showed Positive correlation,but the impact of precipitation intensity on runoff water is much greater than the impact of surface water level and rice leaf area index.The runoff losses of nitrogen and phosphorus were significantly positively correlated with the precipitation intensity and the corresponding initial water concentration before precipitation(p<0.001).The effect of both on the runoff loss of nitro(gen and phosphorus was much greater than surface water level and leaf area index.(3)The model results have a good fit with the observed values(R2>0.9,p<0.001.BIAS<20%).The above prediction model is used to evaluate the risk of nitrogen and phosphorus runoff loss under different intensity rain intensity.The runoff loss of nitrogen is less risky when the rainfall intensity is less than 75%,but it increases exponentially with the increase of rainfall intensity.There is no significant difference in runoff risk during the four growth periods.The runoff loss of phosphorus only increases exponentially with the increase of rain intensity during the tillering period,and the risk is relatively small and relatively stable in other periods.When the local precipitation intensity in Jingzhou reached 95%,the risk of runoff loss of nitrogen and phosphorus increased significantly(p<0.05).The results of this study are helpful to further analyze the characteristics of nitrogen and phosphorus nutrient loss in paddy fields under rainfall conditions,and make further attempts to study the model of rice field loss and risk assessment.