Soil Salinity Inversion And Soil Quality Assessment In Oasis Of Manas River Basin

【Object】The Manas River Basin,one of the four major irrigated agricultural areas in Xinjiang,is the first area in China to achieve large-scale drip irrigation.Long-term drip irrigation conditions affect the law of soil salt transport,so it is particularly important to explore the temporal and spatial changes of salinized soil,influencing factors,and comprehensive evaluation of soil quality at the catchment scale.【Methods】The oasis of Manas River Basin is selected as the research area.Based on the combination of remote sensing data and field measured data,an inversion model of soil salinity is constructed.The spatio-temporal evolution characteristics of soil salinization in the study area are explored.Based on SEBS model,the regional evapotranspiration is inversed in order to analyze the effect of evapotranspiration on soil salinization.And the soil quality of salinized soil is evaluated using soil quality comprehensive index method.【Results】The main research results are as follows:(1)The remote sensing indexes selected in this paper are normalized vegetation index,ratio vegetation index and soil regulation vegetation index,and the correlation coefficients with soil salinity are-0.746,-0.663 and-0.733,respectively.The coefficient of determination(R~2)of the combined model constructed by the single prediction model is 0.797,and the root mean square error(RMSE)is 3.111.Compared with PLSR and BPNN model,the R~2 of the combined model is improved by 0.038 and 0.094,respectively.Compared with the single model,the combined model can more accurately predict the current status of soil salinization in the study area.(2)Surface soil salinity from 1996 to 2019 inversed using the combined model.The analysis shows that the saline soil in the study area has gradually changed to heavy and moderately salinized soil,and the moderately and heavily salinized soil has gradually changed to lightly salinized and non-salinized soil.The area of moderately and heavily salinized soil is large,and there is a potential risk of secondary salinization.78.02%of the soil salinization in the study area has been sign SQIcantly improved,and 10.09%of the soil salinization has been sign SQIcantly worsened.Soil salinization has been prevented effectively after a long time and large area drip irrigation under the mulch.(3)The daily evapotranspiration in the study area based on SEBS model inversion has obvious spatial distribution.The evapotranspiration in the area close to the Tianshan Mountains is smaller,and the evapotranspiration in the desert area is larger.The R~2of normalized vegetation index(NDVI),surface emissivity,surface temperature and surface albedo,and surface soil salinity are 0.791,0.729,0.635,and0.269,respectively.Normalized vegetation index(NDVI),surface emissivity and soil salinity show a non-linear negative correlation,and surface temperature,daily evapotranspiration and soil salinity show a non-linear positive correlation,and surface albedo has little effect on soil salinity.(4)The degree of nutrient deficiency in the salinized soil of the oasis in the Manas River Basin showed the order of available potassium>available phosphorus>alkaline nitrogen>organic matter.The minimum data set of soil quality evaluation consists of 7 indicators:soil salinity,organic matter,pH,sodium ion,magnesium ion,alkali hydrolyzable nitrogen,and soil texture.The soil quality in the study area is mainly grade II(0.65<SQI≤0.85)and grade III(0.45<SQI≤0.65),accounting for 36.44%and 47.30%respectively.【Conclusion】Compared with the PLSR model and the BPNN model,the combined model can more accurately invert the soil salinity content.The degree of soil salinization in the study area is significantly reduced,and the saline soil gradually becomes heavy and moderately salinized.Change,heavy and moderately salinized soils gradually change to lightly and non-salinized soils.The transformation of salinized soil is greatly affected by NDVI,surface emissivity,surface temperature and evapotranspiration.The soil quality is mainly gradeⅡandⅢ,and the overall quality is in the middle and lower level.