Study On Environmental Quality And Degradation Causes Of Greenhouse Agricultural Soil In Shaanxi Province

High intensity utilization of greenhouse agriculture has a significant impact on soil production function and pollutant behavior,which leads to soil degradation.As one of the main facility agricultural production bases in Northwest China,greenhouse vegetable production(GVP)has become the leading industry of increasing farmers'income in Shaanxi Province.However,compared with the traditional agricultural production mode,the high planting intensity and the excessive investment of chemical fertilizers and pesticides in GVP have brought a series of soil quality deterioration problems,and gradually become the limiting factors for the sustainable development of GVP in Shaanxi Province.Therefore,in order to characterize the characteristics of soil degradation in GVP,analyze the causes of soil degradation,evaluate its ecological and health risks,and comprehensively assess soil quality,this study selected 165 GVP bases in Shaanxi province to conduct research,and analyzed soil samples from GVP bases by region.The current situation and characteristics of soil degradation of GVP in southern Shaanxi,central Shaanxi and northern Shaanxi were clarified,so as to provide data support for soil rotation,fallow and remediation of GVP in the next step,and provide reference for local or similar decision-making departments to develop facility agriculture industry.The main results are as follows:(1)Soil acidification and secondary salinization has occurred in the GVP.Average p H value in greenhouse soil was 0.53 lower than that in open field,and EC value in greenhouse soil(547.11 u S cm^-1)was more than triple that in open fields(157.14 u S cm^-1).Soil nutrient accumulation was also found in the GVP,the soil organic matter(SOM),total N(TN),total P(TP),total K(TK),available P(Pav)and available K(Kav)in GVP soil were 27%,49%,42%,3%,200%and 54%greater than those levels in open fields,respectively.The average nutrient balance of N,P and K were 1407.0,682.9 and 1169.1 kg ha^-2season-1,respectively.Soil P/K ratio in GVP systems reflected that nutrient surplus in the Southern Shaanxi(0.080)and the Central Shaanxi(0.077)were greater than those in the Northern Shaanxi(0.061).Soil p H and nutrient contents had significantly differences among three regions,soil p H declined by 0.59 in the Northern Shaanxi,which was higher than that in the Central Shaanxi and Southern Shaanxi.The differences in nutrient accumulation and soil p H changes among different regions were the comprehensive results affecting by both fertilization and soil types.Totally,fertilization in GVP in Shaanxi Province was excessive,which may further accelerate soil nutrient accumulation,acidification and secondary salinization.Soil nutrient imbalance,acidification and secondary salinization will increase with the extension of planting years to some extent.To sum up,GVP in Shaanxi Province is facing challenges brought by unreasonable fertilization,and it is necessary to develop reasonable nutrient management strategies to maintain the sustainable utilization of soil.(2)The seven heavy metals of Cd,Hg,As,Pb,Cr,Cu and Zn in the GVP system were higher than those in the open field system.The concentrations of Cd,Hg,Pb,Cr,Cu and Zn in the Southern Shaanxi were higher than the standard values.The concentrations of Cd,Pb and Zn in the Central Shaanxi were higher than the standard values.The concentrations of Pb and Zn in the Northern Shaanxi were higher than the standard values.The pollution of heavy metals was worse in the Southern Shaanxi,followed by the Central Shaanxi,and the lighter was in the Northern Shaanxi.The geo-accumulation index showed that soils with a high risk of Cd contamination,while other heavy metals with low risk of contamination.Potential single ecological risk index showed that soils with a high risk of Cd and Hg contamination and had a higher risk.From the pollution load index,the pollution of heavy metals in GVP system was significantly higher than in the field.The pollution of heavy metals were with the order of the Southern Shaanxi>the Central Shaanxi>the Northern Shaanxi.To solve the problem of soil heavy metal pollution in Shaanxi Province,the most effective way is to control the industrial and agricultural sources of soil heavy metals pollution,whether in GVP or open field production system.Relevant departments should implement strict pollutant discharge standards and carry out appropriate agricultural management to control the importation of heavy metals into the soil.(3)In the GVP system,leafy vegetables contained higher concentrations of heavy metals than fresh fruits and fruit vegetables from both areas.Concentrations of heavy metals were with the order of Zn>Cu>Cr>Pb>As>Cd,and the heavy metals in the Northern Shaanxi were higher than those in the Central Shaanxi.The heavy metal transfer factors for fresh fruits and fruit vegetables were as follows:Cu>Zn>Cd>Cr>As>Pb,and for leafy vegetables were as follows:Cd>Zn>Cu>Cr>As>Pb.The heavy metal transfer factors in the Northern Shaanxi were higher than those in the Central Shaanxi.The target hazard quotient of heavy metals in vegetables were with the order of As>Cu>Zn>Cd>Pb>Cr.The heavy metals of As?Cu?Zn?Pb?Cr had higher target hazard quotient in the Northern Shaanxi than in the Central Shaanxi.(4)Soil quality index values in Shaanxi province was within the medium grade,which was resulted principally from imbalance of soil fertility.Soil quality was correlated with environment quality.According to the soil quality index of 0.6-0.8 from the corresponding sample points,we infer that suitability threshold of soil minimum data set were with p H of6.0-7.1,Total N of 0.8-1.28 g/kg,Available P of 73-184 mg/kg,Cu of 15.9-17.1 mg/kg and As of 6.8-7.3 mg/kg.Therefore,in view of the soil quality problems in the GVP system in Shaanxi Province,the balanced fertilization should be optimized according to the background conditions of different regions.In the Northern Shaanxi,the principle of small amount and multiple fertilization should be adopted,and the application of potassium fertilizer should be increased appropriately.In the Central and southern Shaanxi,we should reduce the amount of manure and supple the amount and intensity of topdressing.Furthmore,we should carry out appropriate management policy of planting mode with rotation,intercropping and intercropping,reasonable irrigation,thus to achieve the reasonable combination of fertilization,irrigation and planting technology,finally effectively solve the problem of soil degradation of facility vegetables,improve the soil quality,and then realize the sustainable development of greenhouse vegetables.