Study On The Loss Flux Of Nitrogen And Phosphorus In Tea Garden Slopes Under Different Rainfall And Fertilization Conditions

Agricultural development has brought serious surface pollution to the water environment in the hilly area of the upper reaches in Lake Taihui Basin.As the key development type of agricultural comprehensive development in the local hilly area,the tea garden is seriously lost by nitrogen and phosphorus in the tea garden slope due to its unique farming methods(high-intensity fertilization and regular pruning),coupled with the large soil gap and weak soil layer in the hilly area.At present,many experts and scholars have made in-depth research on the loss of nitrogen and phosphorus on the hilly slopes of Taihu Basin,but lack of long-term observation and comparative study on the rhythm of nitrogen and phosphorus output on the slopes of tea plantations on different scales,and pay less attention to the nitrogen and phosphorus output routes in tea plantations,which affectthes the accurate prediction of the current output flux of nitrogen and phosphorus on the slope of tea plantations.As the main way of pollution into the lake from farmland surface source,rainfall runoff effectively evaluates and analyzes the transmission and transfer law of related pollutants,summarizes the regularity characteristics,and provides the basis for the quantitative study of nitrogen and phosphorus output and flux in the tea garden slope under longterm conditions.The typical tea plantation slope and,which located in Tianmuhu watershed in the upper Lake Taihu basin,are selected for experiment.Respectively,the laying of runoff and slope areas in the tea garden slope,through the laying of automatic weather station,soil moisture monitoring system,runoff collection barreland and water level station high-frequency monitoring system to obtain relevant data.Based on the meteorological data,soil moisture,surface runoff and rainfall monitoring sampling obtained simultaneously from 2018 to 2019,the spatial and temporal distribution of soil moisture was studied by comprehensive statistical methods,and the characteristics of rainfall production and flow in runoff and slope areas,the migration process of nitrogen and phosphorus pollutants,and the initial flushing effect of related pollutants are discussed.Using the average concentration of events(EMC),the output of nitrogen and phosphorus in runoff and slope areas is calculated,the nitrogen and phosphorus output flux of the natural rainfall subrunwater area and slope area was estimated,and the main ways and forms of nitrogen and phosphorus output were clarified.The main findings are as follows:(1)Under the influence of rainfall and slope,there are obvious differences in space-time distribution of soil moisture in slope.In the process of soil moisture response to rainfall,under the influence of rainfall and soil moisture lateral transportation,there are obvious differences in the response of different slope and deep soil moisture to rainfall,and the deep soil in the slope and at the bottom of the slope is an active layer of nitrogen-phosphorus nutrient exchange.The rainfall runoff on the slope of tea garden is mainly in the soil,the surface yield is relatively small,and the surface runoff and the middle flow coefficient are 0.099 and 0.206,respectively.In the process of rainfall runoff,the peak of rain strength and surface runoff are well coordinated correspondence,each rain peak point corresponds to the existence of a peak flow point,the rain peak-flow peak response is more rapid,the response interval is more than 5-10 min,and the heavy rain event rain strong peak-flow peak response is faster than the rain storm.(2)Under the two research scales,the concentration of nitrogen and phosphorus pollutants also showed peak fluctuation characteristics in the migration process,the concentration of rainfall was higher in the early stage,and then with the progress of the rainfall process,the concentration of nitrogen phosphorus pollutants generally showed a decreasing trend.Rainfall has a greater effect on the fluctuation of concentration in the surface runoff nitrogen-phosphorus migration in run-off area than in the soil,and the greater the rainfall intensity,the greater the fluctuation of pollutants,especially particulate-state pollutants,in the process of nitrogen-phosphorus migration,and shows a certain initial flushing effect.(3)Nitrogen and phosphorus pollutants in runoff and slope areas are the main output routes in surface runoff.The main output nitrogen form in the runoff cell in the soil is nitrous nitrogen,and the main output phosphorus form is granular phosphorus and dissolved normal phosphate.Rainfall intensity will make the runoff area,slope area nitrogen and phosphorus output EMC value become larger,the impact of rain strength on total nitrogen(TN)is also reflected in the output path,heavy rain strong total nitrogen surface runoff output EMC value is greater than the soil medium flow;Fertilization treatment will affect the proportion of particulate phosphorus in surface runoff and total nitrogen concentration and nitrogen ratio of soil flow in the runoff area.Higher and lower intensity fertilization increased the proportion of particulate phosphorus in surface runoff and the proportion of nitrous nitrogen flowing in the soil.As the fertilization gradient increases,the total nitrogen output EMC value in the soil is significantly higher than the surface runoff.The total nitrogen output flux of runoff area is mainly output by the medium flow route of the soil,which is 1.38-7.48 times the output flux of surface runoff,while the total phosphorus(TP)output flux is mainly output by surface runoff,which is 1.22-3.33 times the flow flux in the soil.The greater the rainfall,the larger the nitrogen and phosphorus output flux in the runoff area and the slope area.Where the total nitrogen output flux isn’t affected by the strong rain,the total phosphorus output flux becomes larger with the strong rain.Under the high-intensity fertilization input,phosphorus is more easily lost than nitrogen,and with the increase of fertilization gradient(20%),the total nitrogen output flux in the runoff area increased by 13.34% and 14.55% in turn,while the total phosphorus output flux increased by 24.44%.