| With the rapid development of social economy,water scarcity both in sources and quality are superimposed on each other,which aggravates the contradiction between supply and demand of water resources.One of the factors affecting water scarcity is the deterioration of water ecological environment caused by eutrophication.The occurrence of water eutrophication is closely related to the loss of nitrogen and phosphorus in farmland soil.It is of great significance to study the law of nitrogen and phosphorus loss under different conditions to reduce the risk of eutrophication and guide production practice.There is abundant rainfall in the south of China.The loss of water and fertilizer is closely related to rainfall intensity and fertilization mode.In this paper,the rape field was taken as the research object.In the early flowering stage of rape,the runoff of agricultural field,nitrogen and phosphorus content of runoff(total nitrogen,nitrate nitrogen,ammonium nitrogen,total phosphorus,soluble phosphorus)and soil nutrient content before and after rainfall(total nitrogen,nitrate nitrogen,ammonium nitrogen,total phosphorus and available phosphorus)under different rainfall intensity(4mm/h,7mm/h and 13mm/h),interval between fertilization and rainfall(2 days,5 days)and fertilization method(spraying,liquid application)was measured by the method of simulated rainfall.The characteristics and main forms of nitrogen and phosphorus loss under different treatments were studied,and the variation characteristics of soil surface nutrients before and after rainfall and eutrophication risk were discussed.The main results are as follows:(1)Runoff variation of secondary rainfall and variation characteristics of nitrogen and phosphorus with runoff.The smaller the rainfall intensity is,the longer the runoff generation time is.The relationship between rainfall intensity and runoff generation duration is power function.After runoff generation,runoff increased with the increase of runoff duration,the relationship between runoff and runoff duration is logarithmic.Nitrogen loss concentration decreases with the increase of runoff duration and there is a power function relationship between nitrogen loss concentration and runoff generation time.The phosphorus loss concentration increases and decreases on the runoff duration and the relationship between phosphorus loss concentration and runoff generation time is exponential function.(2)The total amount,average concentration and form of nitrogen and phosphorus loss.The total amount of nitrogen loss was positively correlated with rainfall intensity,and negatively correlated with the interval between fertilization and rainfall.The average loss concentration of nitrogen was negatively correlated with rainfall intensity,and negatively correlated with rainfall interval.The average loss concentration of spraying treatment was higher than that of liquid treatment.The main form of nitrogen loss in runoff is inorganic nitrogen,and the proportion of nitrate nitrogen is much larger than that of ammonium nitrogen.Rainfall intensity was positively correlated with total phosphorus loss and negatively correlated with total soluble phosphorus loss.There was a negative correlation between the interval between fertilization and rainfall and total loss of total phosphorus and soluble phosphorus.The total loss under the treatment of spraying is greater than that under the treatment of liquid application.Rainfall intensity has a negative correlation with the average loss concentration of total phosphorus.It has a significant negative correlation with the average loss concentration of soluble phosphorus.There was a negative correlation between the interval of rainfall and total phosphorus,soluble phosphorus.The average loss concentration of phosphorus in the treatment of spraying was higher than that in the treatment of liquid.The main form of phosphorus loss is granular phosphorus.(3)Changes in soil nutrient content before and after rainfall and eutrophication risk.After rainfall,the content of total nitrogen and nitrate nitrogen decreased,the content of ammonium nitrogen increased,but the content of total phosphorus and available phosphorus did not change significantly.The NO3--N/DP rate and NH4+-N/DP rate increased with the increase of rainfall intensity and the interval between fertilization and rainfall.The effect of fertilization mode on NO3--N/DP rate and NH4+-N/DP rate were not significant.The NO3--N/DP rate was in the risk area of eutrophication under the treatment of 2 days interval between fertilization and rainfall,and the higher the rainfall intensity,the lower the risk of eutrophication under the treatment of 5 days interval between fertilization and rainfall.The above results can be used as reference for fertilization guidance,rainfall runoff drainage control,farmland wetland design,etc. |
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