Study On The Geochemical Characteristics Of Farmland Soils In Yanqi Basin

In recent years,with the rapid development of regional social economy,human disturbance has strongly affected the safety of farmland ecosystems.Industrial three wastes,domestic waste,pesticide residues,chemical fertilizer pollution,sewage irrigation and other serious endangered farmland ecosystems,leading to a decline in the quality of agricultural products,affecting the sustainable development of agriculture.At present,most of the environmental bases of China's land quality are unclear,and regional land use and agricultural layout are not appropriate.Therefore,it is particularly important to realize the scientific planning of agriculture and to identify the agricultural geological environment.The geochemical assessment of land quality is based on a survey of land geochemistry,guided by ecological geochemistry,and an overall evaluation system that scientifically evaluates land quality.This paper studies the geochemical characteristics of farmland soils in Yanqi Basin,and provides basic data and scientific basis for farmland soil environmental protection and sustainable agricultural development under the influence of high-intensity economic activities.The main findings of this study are as follows:(1)From the results of analysis of the geochemical characteristics of heavy metals in farmland soils in the study area,the mean values of Cr,Cd,Cu,Ni,Zn and Pb in the farmland soil of the Yanqi Basin are 1.44,1.67,1.15,1.30,respectively.1.67 and 2.11 times.As is non-polluting,Mn is slightly polluted,Cu,Cr,Zn,Ni and Cd are mildly polluted,and Pb is moderately polluted.The distribution of As,Cd,Cr,Cu,Mn,Ni,Pb and Zn exhibits an island-like distribution pattern,and high content areas appear in each element in some areas.The pollution load index(PLI)of wheat,pepper,tomato,sunflower,sugar beet and corn was slightly polluted.The average potential ecological risk index(E)of each heavy metal element in farmland soil is in the order of Cd,Ni,As,Cu,Pb,Cr and Zn,showing a slight ecological risk.The average values of Cd,Cr,As,Ni,Cu,Pb and Zn in the six types of farmland in the study area did not exceed the national soil environment level II standard;8 elements in six farmland types(As,Cd,Cr,Cu,Mn)The unidirectional pollution index(CF)of Ni,Pb and Zn)reflects different environmental risks.The average PLI of the six farmland types is slightly polluted;Cd,Cr,Cu,Mn in different farmland soils The single potential ecological hazard index(E)and the comprehensive potential ecological hazard index(RI)of Ni,Pb and Zn all showed a slight risk level.From theperspective of spatial distribution pattern,the RI of the six farmland types showed a slight ecological risk in space.(2)From the analysis of soil nutrient geochemical characteristics in farmland,the variation of soil organic matter(OM)in the Yanqi Basin is affected by both structural and random factors,pH,conductivity(EC),available phosphorus(AP),effective zinc(AZ)and available potassium(AK)are affected by human factors.Soil fertility in the study area was moderate and low,soil OM was in a state of deficiency,AP and AK were abundant,and AZ was at a low level.The spatial variability of soil EC and AZ is strong.The soil fertility factors in the study area showed moderate variation,and the variation intensity of AZ was larger.The comprehensive fertility index of soil samples ranged from 0.276 to 0.897.The SFI grades in the study area accounted for 5.15% of grade I,43.30% of grade II,47.94% of grade III,and 3.61%of grade IV.(3)According to the analysis of soil salinity geochemical characteristics of farmland,the soil salinity(DS)and electrical conductivity(EC)of the Yanqi Basin showed strong variation,and the pH CV showed weak spatial variation.The soil DS and EC high value areas are distributed in the low-lying areas of the Bosten Lake and the southern farmland of Hejing County,mainly distributed on the banks of the river in a strip-like pattern;the high pH area is mainly located in the farmland north of the lakeside wetland in the southwest of Bosten Lake,and From south to north,there is a step-like distribution pattern.(4)According to the results of the Canonical Correspondence Analysis(CCA),the heavy metal pollutants in the farmland soil in the study area are mainly Cd,Ni,Cr and Zn,followed by Pb and As.The spatial variation of As,Cd,Pb and Zn is large,while the spatial variation of Mn and Ni is small.The relationship between different soil properties and heavy metals is different.The available potassium has a good correlation with various environmental factors.The cation exchange capacity has a good correlation with organic matter and heavy metals Pb,Ni,Mn and Zn,and represents effective phosphorus and the point of the salt content is far from the arrow of the heavy metal,and has an opposite gradient,and the correlation is weak.The selected eight heavy metals have a certain degree of influence on the spatial distribution of soil properties.Among them,heavy metals have a greater impact on soil organic matter,available potassium and cation exchange,but weaker on effective phosphorus and salt content.(5)The relationship between soil properties and selected environmental factors(soil moisture,land use patterns,soil thickness,altitude)was studied using CCA.The results showed that the variation of cation exchange capacity,available phosphorus,available zinc and soluble salt was larger than that of pH value,available potassium and organic matter,and the variation of pH value,available potassium,available phosphorus and organic matter was similar.Different soil properties and environmental factors have different correlations.Soil pH,soluble salt and soil moisture have good correlation.Available phosphorus is mainly affected by land use type.Effective zinc is mainly affected by soil thickness,and quick effect.Potassium has a good correlation with altitude.The order of influence of environmental factors on soil properties is from soil water content > land use > soil thickness > altitude.In addition to the small influence of soil pH,different land types have a great impact on soil properties.