Effects Of Different Rainfall Intensity And Fertilization On The Loss Of Nitrogen And Phosphorus In Vegetable Fields In Southern Hebei

The application of chemical fertilizers is the simplest and most effective way to increase food production.In actual production,farmers usually applied fertilizers higher than the recommended fertilization level to pursue high yields.This behavior caused the excess and accumulation of nitrogen and phosphorus in the soil,leading to a series of environmental problems such as the deterioration of vegetable crop quality,the deterioration of vegetable geography,the eutrophication of watersheds,and the nitrate pollution of surface water and groundwater.Agricultural non-point source pollution caused by the loss of nitrogen and phosphorus nutrients in farmland has become one of the hot environmental problems.In response to this problem,this research was based on artificial simulated rainfall experiments,with cinnamon soil vegetable field in southern Hebei of the North China Plain as the research background.The paper compared the improvement of the growth status of pakchoi by different fertilization schemes（control check,conventional fertilization,optimized fertilization）and analyzed the effects of fertilization scheme and rainfall intensity(54 mm·h^-1,75 mm·h^-1,90 mm·h^-1)on the change trend of dissolved nitrogen and total phosphorus in vegetable field runoff,and establish a regression model between the loss of different forms of nitrogen and phosphorus in runoff and multiple factors such as rainfall intensity,fertilization,and runoff.This study provides a theoretical reference for the study of soil nutrient loss and agricultural non-point source pollution control in the southern plains of Hebei Province.The main findings are as follows:（1）The application of chemical fertilizers has a significant impact on the growth of pakchoi,and the application of zeolite can improve the soil water and fertilizer retention capacity.The application of chemical fertilizers significantly improved the growth index of pakchoi.After using chemical fertilizer,the root length,plant height,dry weight,and fresh weight of pakchoi increased by 24.6%～32.5%,31.8%～35.4%,42.1%～49.0%,and52.4%～61.9%respectively.There was a significant difference in the morphological index data of pakchoi under fertilization treatment and no fertilization treatment（P<0.05）.After the application of zeolite,the average weight water content of soil increased by 2.3%-15.5%,and zeolite improved the water retention capacity of 0～10 cm soil layer most obviously.Under the rainfall intensity of 54 mm·h^-1and 75 mm·h^-1,the surface runoff of the optimized fertilization group was reduced by 3.13%～9.40%and 6.01%～7.66%,respectively.Compared with optimized fertilization,conventional fertilization treatments did not significantly improve the morphology and yield of rapeseed.Properly reducing the amount of chemical fertilizers can reduce production costs and maintain the normal growth of vegetables.（2）The rainfall intensity has a significant impact on the loss of ammonia nitrogen and nitrate nitrogen in different fertilized vegetable fields.The concentration of dissolved nitrogen in surface runoff reached its peak in the early stage of runoff and was a descending stage within 0-15 min of runoff,and then stabilized.The concentration of dissolved nitrogen in initial runoff was negatively correlated with precipitation intensity.The loss of dissolved nitrogen from vegetable fields in interflow was dominated by nitrate nitrogen,which accounted for more than 95%.Surface runoff is the main approach for the loss of dissolved nitrogen,which accounted for more than 91%and showed a negative correlation with rainfall intensity.Under 54 mm·h^-1and 75 mm·h^-1 rain intensities,the dissolved nitrogen loss of the optimized fertilization group was reduced by 33.0%and36.8%,respectively.Reducing the use of nitrogen fertilizer had an extremely significant effect on inhibiting the loss of dissolved nitrogen.（3）The intensity of rainfall has a significant impact on the loss of dissolved phosphorus and particulate phosphorus in different fertilized vegetable fields.The total phosphorus concentration in surface runoff showed a trend of first decreasing and then fluctuating smoothly,and the initial runoff concentration was positively correlated with rainfall intensity.The change trend of the total phosphorus concentration in interflow was not obvious,but the total phosphorus concentration varied significantly under different rainfall intensities.The impact of increasing rainfall intensity on the loss of total phosphorus in interflow was much higher than that of surface runoff.Particulate phosphorus was the main component of phosphorus loss from vegetable fields,accounting for more than 90%.Surface runoff was the main approach of total phosphorus loss,accounting for more than 92%.The phosphorus loss coefficient in runoff and rainfall intensity showed a positive correlation trend.（4）Analysis of relevant factors affecting the loss of N and P in vegetable fields.Under simulated rainfall conditions,there was a significant linear relationship between the cumulative loss of dissolved nitrogen and total phosphorus in vegetable field runoff and runoff（r²>0.92,P<0.05）.The relationship between the goodness of fit of different forms of nitrogen in surface runoff and interflow was dissolved nitrogen>nitrate nitrogen>ammonia nitrogen.The goodness of fit between the loss of different forms of phosphorus in surface runoff and runoff was as dissolved phosphorus>total phosphorus>particulate phosphorus;and in interflow,it is represented as total phosphorus>particulate phosphorus>dissolved phosphorus.The regression model results indicated that the comprehensive effects of rainfall intensity,fertilization,and runoff on the loss of N and P in vegetable fields can be accurately described by linear equations.The results of the correlation analysis indicated that the amount of fertilization was the main factor affecting the loss of dissolved nitrogen in surface runoff,and runoff and rainfall intensity were the main factors affecting the loss of dissolved nitrogen in interflow;runoff and fertilization were the main factors affecting the loss of total phosphorus in surface runoff,and runoff and rainfall intensity were the main factors affecting the loss of total phosphorus in interflow.