Characteristics And Evaluation Of Soil Quality In The Middle And Lower Reaches Of The Yihe River Basin

Yihe River Basin is located in China’s ecological transition zone and ecological environment fragile zone.Land use types,farming methods,fertilizing irrigation and other factors affect the changes of soil properties and soil quality.So far,little work has been done on the assessment of soil properties and quality in the area of the Yihe River Basin.Taking the middle and lower reaches of the Yihe River Basin as the research object,the physical and chemical indexes of soil quality were systematically determined by the methods of data collection,field investigation,field test and indoor analysis.Their statistical and spatial distribution characteristics are analyzed.The evaluation index system and evaluation model of soil quality in the study area were established,and the fuzzy mathematics comprehensive evaluation method was used to analyze the overall status of soil quality.Furthermore,the spatial distribution of soil quality was predicted,and the law of spatial differentiation of soil quality was discussed,which provided an important guiding ideology and scientific basis for the sustainable development of agriculture in Yihe River Basin.The main findings of the study are as follows:1.Physical index characteristics of soil quality:In the study area,the soil particle size was mainly distributed in the range of 0.01~0.05 mm,with coarse powder as the main particle.The average content of each particle compare: coarse silt > coarse clay > fine silt > fine sand > coarse sand > fine clay.The soil particle size composition and content of 0~20 cm and 20~40 cm soil layer have little change.According to the spatial variation,the soil in the middle and lower reaches belong to loam.The overall trend of particle size from middle to lower reaches is from fine to coarse,clay content decreases,silt and sand content increase.According to the coefficient of variation of each grain level,the content of coarse silt tends to be stable in space,and the fine clay and coarse sand have strong variability.The average soil bulk density was between 1.23 and 1.43 g.cm-3.In terms of soil compactness,the soil in the middle reaches of 0~20 cm soil layer is in a suitable state of compaction,and in the middle reaches of 20~40 cm soil layer and in the lower reaches of the two soil layers,the soil is in a tight state.The coefficient of variation of soil bulk density in different soil layers was about 10% in different regions,indicating that the soil bulk density in the study area was relatively stable.The mean value of soil moisture content in the level(middle and lower reaches)and vertical(0~20 cm and 20~40 cm)did not change obviously,both of which were about 20%,indicating that the soil moisture was at a more suitable level.In general,the physical properties of the soil in the study area are suitable for crop growth.2.Chemical index characteristics soil quality:The content of organic matter in the soil of the study area is in the middle and upper level,the total nitrogen content is extremely short,the inorganic nitrogen content is short,the total phosphorus and available phosphorus content is rich,the total potassium content is extremely rich;The contents of iron,manganese and zinc were not higher than the national standard,and the contents of boron and copper were enriched.In addition to inorganic nitrogen,boron and p H values were higher in the deep layer than in the surface layer,and the other indexes were higher in the surface layer than in the deep layer.The average contents of organic matter,active organic matter,total nitrogen,inorganic nitrogen and trace elements in the middle reaches were higher than those in the lower reaches in the 0~20 cm soil layer,but there was no significant difference in the average contents of most chemical indexes between the middle and the lower reaches in the soil layer of 20~40 cm.The available phosphorus in the study area showed strong variability,and the p H value showed a weak variability.The other indicators showed moderate variation on two soil layers.Compared with that,these elements in carbon,nitrogen and phosphorus were greater than those in boron,copper,iron,manganese and zinc.In general,carbon,phosphorus and potassium in the study area are more suitable for the growth of crops,and nitrogen is relatively deficient.According to the regional distribution characteristics of soil quality indexes in 0~20 cm and 20~40 cm soil layers,the spatial variation was complex,the nutrient content in the surface layer was higher than that in the deep layer,and the nutrient content in most middle reaches was higher than that in the lower reaches.3.Soil quality was evaluated by integrating soil physical and chemical indexes.First,the minimum data set for evaluation was determined.The MSD of 0~20 cm soil layer is: clay content,bulk density,water content,total organic matter,total nitrogen,inorganic nitrogen,total phosphorus,available phosphorus,total potassium,iron;The MSD of 20~40 cm soil layer is: clay content,bulk density,water content,total organic matter,active organic matter,total nitrogen,total phosphorus,available phosphorus p H value,copper,iron.The membership function of organic matter,active organic matter,total nitrogen,inorganic nitrogen,total phosphorus,available phosphorus and total potassium is S-type membership function.The evaluation indexes of clay content,bulk density,water content,p H value,boron,copper,iron,manganese and zinc use parabolic(trapezoidal)function.Then calculate the membership value of each index.The weight of each index was determined by principal component analysis.Finally,the soil quality comprehensive index(IFI)was obtained by using fuzzy mathematics to synthesize the soil single factor physical and chemical indexes after quantification.The comprehensive index analysis of soil quality in the study area shows that most of the IFI in the soil layer of 0~20 cm is in the medium and high level,and only a few of the IFI are in the low and high quality level.The IFI of 20 ~ 40 cm soil layer is generally in medium level,1/3 is low level,and a few belong to low level and high level.The soil quality in the middle reaches was higher than that in the lower reaches,and the variation degree of IFI in the middle reaches was lower than that in the lower reaches.4.Through the analysis of the global trend effect of IFI in the study area,it can be seen that the trend effect of IFI in the two soil layers is both second-order.From the fitting results of semi-variance function,it is found that IFI accords with linear model in 0~20 cm soil layer and Gao Si model on 20~40 cm soil layer.The variation of IFI in space is as follows: the gold coefficient is 0~20 cm soil layer(60.82%)> 20~40 cm soil layer(39.84%),The IFI of the two soil layers is of moderate spatial correlation,and the IFI of the surface layer is strongly influenced by random factors than that of the deep layer.From the interpolation map,it can be seen that the overall distribution trend of IFI in the soil layer of 0~20 cm is similar to that of 20~40 cm in height in the middle and north of the middle side and in the north side of the east side.Soil quality shows regular spatial variability under the combined effects of topography,vegetation,and human cultivation and fertilization.