Characteristics and Risk Assessment of Soil Heavy Metal Contents in Facility Agriculture of Guangxi

[Objectives]To study the characteristics of soil heavy metal contents in facility agriculture of Guangxi and analyze its risks.[Methods]The heavy metal content of 30 surface soil samples taken from facility agriculture in Guangxi was analyzed.The status of soil heavy metal pollution in facility agriculture of Guangxi was evaluated by the single factor index method,geo-accumulation index method and Hakanson potential ecological risk index method with reference to the soil background value in Guangxi.[Results]Compared with the soil background value in Guangxi,the over-limit rates of heavy metals cadmium,lead,arsenic,chromium,mercury,copper and zinc in soil samples were 56.67%,56.67%,16.67%,30.00%,50.00%,60.00%and 80.00%,respectively.Compared with the screening values of the Soil Environmental Quality-Risk Control Standard for Soil Contamination of Agricultural Land(for trial implementation)(GB15618-2018),the overlimit rates of the heavy metals cadmium,arsenic,copper and zinc in the surface soil of agricultural facilities in Guangxi were 56.67%,10.00%,16.67%and 23.33%,respectively.Except for the average content of soil cadmium exceeding the screening value,the evaluation content of the other six soil heavy metals did not exceed the screening value.According to the evaluation results of the single factor pollution index method,the surface soil arsenic and chromium of the agricultural facilities in Guangxi belonged to the clean level,lead,mercury,and copper belonged to mild pollution,and cadmium and zinc belonged to moderate pollution.According to the evaluation results of the geo-accumulation index,the lead,arsenic,chromium and mercury in the surface soil of the agricultural facilities in Guangxi belonged to the pollution-free level,while the cadmium,copper and zinc belonged to the mild-moderate pollution.According to the evaluation results of the potential ecological risk index method,the potential ecological risks of the heavy metals of lead,arsenic,chromium,copper and zinc in the soil of agricultural facilities in Guangxi belonged to low potential ecological risk level,and the potential ecological risks of cadmium and mercury belonged to moderate risk level.The potential ecological risk index(RI)of the seven heavy metals in the soil was 132.46,which belonged to moderate potential ecological risk.The largest contribution of soil heavy metals to the potential ecological risk index was cadmium and mercury.[Conclusions]Taking the soil of facility agriculture in Guangxi as the object,this paper studied the characteristics of heavy metal content in facility agricultural soil and its risk assessment,in order to provide a scientific basis for facility soil heavy metal risk prevention and control and provide safe technology for facility agriculture.

Nutrient Accumulation Characteristics of Facility Soils with Different Planting Years in Lateritic Red Soil Region of Guangxi

[Objectives]To explore the nutrient accumulation characteristics of facility soil in different planting years in the lateritic red soil region of Guangxi.[Methods]The soil samples of facility cultivation and open field cultivation were collected in the lateritic red soil region of Guangxi,and the changes of soil pH,water-soluble salts,organic matter,available nutrients and total nutrients were analyzed.[Results]The acidification of the facility soil in the lateritic red soil region of Guangxi became more obvious with the extension of greenhouse planting years,the soil pH decreased by 0.34 units after continuous planting for 10 years,and the water-soluble content was more than 3 times that of the open field and it increased with the extension of the planting years.In addition,the degree of secondary salinization in facility soil became more serious,mainly moderate and mild salinization.The contents of soil organic matter,alkali-hydrolyzed nitrogen,available phosphorus,available potassium,total nitrogen and total phosphorus in the facility soil increased significantly,while total potassium did not change significantly.[Conclusions]This study is expected to provide a scientific basis for facility soil fertilization management,and to promote the sustainable and healthy development of facility cultivation industry.

Improving the Facility Soil by Combining Soil Amendment with Agronomic Measures

[Objectives]To study the remediation methods of secondary salinization and cadmium pollution in facility soil.[Methods]Two kinds of soil amendments,potassium fulvic acid and limestone powder,were selected to be applied alone or combined together to plant maize to carry out field experiments.Their effects on watermelon yield,watermelon cadmium content,soil available nitrogen,phosphorus,potassium and water-soluble salts were studied.[Results]The application of potassium fulvic acid,limestone powder and their combined application increased the yield and soluble solids of watermelon to different degrees.The contents of seven heavy metals including cadmium,copper,zinc,arsenic,lead,mercury and chromium in the watermelon of all treatments were all lower than the food safety limit stipulated in the national standard.During the harvest period of maize seedlings,all treatments could increase soil pH and decrease soil cadmium availability.In particular,3000 kg/ha of limestone powder and 1500 kg/ha of potassium fulvic acid had the best effect on reducing soil available cadmium content.In reducing soil available cadmium content,there were significant differences between single application of amendment and combined application treatments.In addition,compared with the control CK,all treatments decreased soil available nitrogen,phosphorus,potassium and water-soluble salt content.[Conclusions]Potassium fulvic acid,limestone powder and their combined application can increase the yield of watermelon,and can significantly reduce the available cadmium,nitrogen,phosphorus,potassium and water-soluble salt content in the facility soil of maize cultivation.