Characteristics And Mathematical Models Of Nutrient Loss On Loess Slope Under Different Conditions

In this paper,a large number of artificial rainfall simulation experiments and water erosion tests were carried out,and the mechanism of soil water and nutrient was studied The rainfall experiment focused on the influence of humus layer thickness on the surface runoff and nutrient;Water scouring experiment mainly studied the length of slope,vegetation types and other factors on the influence of slope soil nutrient loss,and established the corresponding conditions of water and nutrient loss model;The effects of vegetation filter belt length,vegetation type and vegetation density on nutrient control efficiency were also studied.The main conclusions were as follows:(1)Under the conditions of rainfall,runoff time increased with the thickness of humus layer;Humus thickness increased,while the amount of runoff was small;The humus layer for slopeland saving natural rainfall has good effect;Three kinds of nutrient concentration in runoff with the increase of the thickness of humus layer generally decreased,but did not show the significant difference(P>0.05);The total loss of 3 runoff nutrients were increased with the increase of the thickness of humus layer was decreased;the thickness of humus layer increase can reduce the loss of soil nutrients.(2)The mathematical model of water erosion of slope flow condition could well simulate the surface runoff,the coefficient of determination was above 0.96,the relative error was 2.35%(Caragana)and 2.32%(soybean)respectively,which showed that the simulation precision of the model was high.(3)The effective mixing depth model of surface runoff on the Loess Slope under the condition of water erosion was established.The results showed that the model has good simulation effect,and the coefficient of determination was above 0.9.The incomplete mixing model to calculate runoff nutrient accumulated loss of nutrients,when the nutrient was nitrate nitrogen,the relative error between the results and the measured values were 6.6%(Caragana)and 5.9%(soybean),and nutrient were water soluble phosphorus,the relative error were 5.1%(Caragana)and 6.3%(soybean)respectively.(4)The equivalent mixed depth model had a good effect on the simulation of runoff nutrient concentration,and the determination coefficient was above 0.96.Through the equivalent mixing depth model for calculating runoff nutrient accumulated loss of nutrients,when the nutrient was nitrate nitrogen,the relative error of calculation and the measured values were 1.6%(Caragana)and 7.1%(soybean)respectively;When the nutrient was nutrient water soluble phosphorus,the relative error were 7.9%(Caragana)and 5.3%(soybean)respectively.(5)With the increase of vegetation filter length,vegetation filter cut effect on runoff increased,but the runoff reduction rate and water cut rate did not increase with the length of vegetative filter strips and present the corresponding linear growth relationship;The leaching loss of absorbed nitrogen and phosphorus increases with the increase of the length of the filter belt;With the increase of length,the average reduction rate of dissolved nitrogen and phosphorus decreased gradually.(6)When the vegetation types of vegetative filter strips was maize,the runoff reduction rate was highest;Alfalfa was better than other vegetation in reducing the loss of absorbed nitrogen and phosphorus;Corn filter strips on runoff dissolved nutrient reduction is better than other vegetation filter;The interception efficiency of Maize to total nitrogen was higher than that of other vegetation,and the interception efficiency of soybean to total phosphorus was higher than that of other vegetation.(7)The average runoff reduction rate and the average water cut rate increased with the raised of VFS planting density.The greater the planting density of vegetation,the less sediment yield;The total loss of adsorbed nitrogen and phosphorus were decreased with the increase of vegetation planting density;The average concentration of dissolved nitrogen and phosphorus reduction rate with the increase of vegetation planting density;Total nitrogen and total phosphorus reduction rate increased with the increase of planting density;In surface runoff loss of nitrogen and phosphorus was mainly dissolved loss,total nitrogen and total phosphorus content had significant correlation with runoff and sediment.(8)The mathematical model of vegetation filter strips for runoff nutrient could simulate the change of nitrate nitrogen concentration in runoff with time.The coefficient of determination was above 0.78,and the relative error was maintained between 14.73%-18.22%,indicating the simulation accuracy of the model was better.