Study On Soil Erosion And Nutrient Loss Of Sugarcane Slope Land Based On RUSLE Model And ²¹⁰Pb_ex

Intensive sugarcane planting on slopes in Guangxi has caused serious soil erosion.Nutrients such as nitrogen and phosphorus in the soil enter the river water body with runoff,resulting in eutrophication of lakes and reservoirs,and aggravating agricultural non-point source pollution.This has brought great pressure to the sustainable development of regional economy and beautiful ecological environment.However,there are few studies on the temporal and spatial characteristics of soil erosion and nutrient loss in intensive sugarcane planting areas.Therefore,this study takes the Nala small watershed in the intensive sugarcane planting area of Guangxi as the research target area（the watershed is divided into three sub watersheds:SW1,SW2 and SW3）.Based on GIS technology,using rainfall data,digital elevation model（DEM）and remote sensing image and other data in the study area.Firstly,using the modified universal soil loss equation（RUSLE）,the soil erosion rate of the small watershed from 2017 to 2021 is estimated,analyzing the soil erosion status of different slope and land use types.Secondly,through RUSLE model and field sampling,the temporal and spatial variation characteristics of soil erosion and loss of organic carbon（SOC）,total nitrogen（TN）and total phosphorus（TP）in four growth periods of sugarcane slope land in small watershed in 2020（seedling period:February,March and April,tillering period:May,June and July,elongation Period:August,September and October,maturity period:November,December and January）are analyzed,and the effects of vegetation cover and rainfall on soil erosion of sugarcane slope land are explored.And the relationship between the stall rate of soil nitrogen and phosphorus flow and the amount of fertilization in sugarcane slope land.Then,²¹⁰Pb_exnuclide tracer technology is used to analyze the²¹⁰Pb_exarea activity and soil erosion or deposition change characteristics of six slopes in small watershed,analyze the SOC,TN,TP content and loss change law of different slopes and slopes in each sub watershed,and explore the impact of slope on soil erosion.Finally,the applicability of the soil erosion model is analyzed by comparing the RUSLE simulation results with the ²¹⁰Pb_excalculation results.The main results are as follows:（1）Using RUSLE model,the average soil erosion rate of Nala small watershed from 2017 to 2021 was estimated to be 37.05 t/（hm²·a）,belonging to moderate erosion level;Soil erosion mainly occured in the slope range of 5°-25°,which was a key area for preventing and controlling soil erosion;Among different land use types,the forest land（Eucalyptus）had the largest average erosion rate,which was 78.93t/（hm²·a）,while the slope land（sugarcane）had the largest erosion amount,which was 3425.03 t/a.The slope land（sugarcane）,forest land（eucalyptus）,roads and other land use types in the basin should be reasonably planned and managed,the targeted and effective water and soil conservation measures should be taken.（2）The RUSLE model was used to estimate the soil erosion rate of sugarcane sloping land in Nala small watershed in 2020,and the variation characteristics in different growth stages were tillering stage>jointing stage>seedling stage>mature stage.The temporal variation characteristics of soil SOC,TN,and TP loss rates of sugarcane slope land in the watershed were consistent with the temporal variation of sugarcane slope soil erosion rate.The soil erosion rate of sugarcane sloping land in the watershed was greatly affected by rainfall in different growth periods.The effect of vegetation coverage on sugarcane sloping land in jointing and mature stages was not obvious.The loss rate of TN and TP was significantly positively correlated with the application rate of nitrogen and phosphorus fertilizer respectively.Effective measures should be taken to prevent soil erosion and nutrient loss according to the characteristics of soil and water loss on slopes during sugarcane growth.（3）Through ²¹⁰Pb_extracked soil erosion technology,the ²¹⁰Pb_exbackground value of Nala small watershed was 9437.19 Bq/m².Due to the influence of nuclide sedimentation characteristics and soil surface organic carbon,²¹⁰Pb_exon the watershed slope was mainly distributed in the soil surface（0-15cm）.The maximum value of the area activity of²¹⁰Pb_exof the soil of 6 full slopes is generally located in the lower half of the slope（the middle and lower part of the slope,the lower part of the slope and the bottom of the slope）,and the minimum value was generally located in the upper part of the slope（the top of the slope,the upper slope and the upper middle of the slope）.It showed that the content of nuclides was related to the different influences of soil particles on rainfall and runoff erosion and transportation at different slope positions and slopes.The erosion/deposition rate of the six full slopes was-54.42 to 182.60 t/（hm²·a）,and the average soil erosion rate of the watershed was 30.73 t/（hm²·a）.The maximum value of slope soil erosion rate was generally located in the upper half of the slope,and soil deposition mainly occured in the lower half of the slope.There was a positive correlation between slope soil erosion and slope,which further explained the impact of slope on soil erosion.The greater the slope,the more serious the erosion.The ²¹⁰Pb_exmodel was used to estimate soil erosion rates of 33.81 t/（hm²·a）and 14.03 t/（hm²·a）for sloping land（sugarcane）and forest land（eucalyptus）,respectively,it showed that different land use types,vegetation cover,tillage and other management practices also affected soil erosion magnitude.The contents of soil SOC,TN and TP basically showed a downward trend with the change of soil vertical depth,which reflected that the content of soil nutrients was affected by surface vegetation coverage,human activities such as farming and fertilization,and the migration characteristics of soil elements.The loss laws of soil SOC,TN and TP in different sub-watersheds and different slope positions were generally consistent with the soil erosion laws,which showed that soil SOC,TN and TP nutrient loss were closely related to soil erosion rates,and nutrients were attached to soil particles and varied with soil erosion.However,due to the different background values of soil nutrients,there were also differences in their loss patterns.（4）The soil erosion results of slope land（sugarcane）in Nala small watershed estimated by RUSLE model were generally consistent with those calculated by ²¹⁰Pb_ex,which showed that the soil erosion status of Nala small watershed can be characterized by RUSLE model to a certain extent,and had high reliability and applicability.