Improvement And Safety Evaluation Of Phosphogypsum-Based Soil Amendment In Mitigating Soil Salinity Stress

Soil salinization has become an urgent ecological problem worldwide,and it is of great strategic significance to improve and utilize it.The industrial waste phosphogypsum can be used as a chemical amendment in the improvement of saline-alkali land with high efficiency and economy.At present,the use of industrial waste to improve saline-alkali land has gradually become a research hotspot.Therefore,in this study,based on phosphogypsum,bentonite,humic acid,and organic polymer were combined to prepare a saline-alkali soil amendment with both fertilizer effect and water retention function.The pot experiment was carried out to explore the effect,mechanism,and safety of its application in improving saline-alkali land,in order to achieve the dual purposes of solid waste resource utilization and saline-alkali land improvement.The results are expected to provide a reference for the application of the amendment.The main conclusions of this study are as follows:（1）In this paper,SEM,FTIR,XRD and other methods were used to comprehensively characterize composite material.The mass content of Ca SO₄in phosphogypsum was 81.51%.SEM-Mapping analysis showed that the humic acid surface had characteristic high porosity structure,and contained trace elements such as S（1.45%）,K（2.76%）,and Ca（3.70%）.Bentonite was rich in Si,K,Fe,and other trace elements,which was helpful to improve the quality of saline-alkali soil.The content of heavy metals in each component was within the acceptable range.Therefore,the physicochemical parameters of each component indicated that it has certain application potential in saline-alkali land improvement.（2）In this paper,the effects of different proportions of soil amendments on the physicochemical properties of saline-alkali soil were investigated.Compared with the control group,the EC decreased by 1.51%to 33.49%,the soil salt content decreased by 11.40 to 35.46%,and the soil soluble Na⁺concentration significantly decreased by 39.47 to 63.20%.The contents of alkali-hydrolyzed nitrogen,available phosphorus,and available potassium increased by 8.27%～40.02%,3.20～34.81%,and 4.41%～10.78%,respectively.In addition,the soil microbial community structure was improved in all treatment groups,indicating that different treatment groups could significantly reduce soil salinity index,increase nutrient content,and improve soil structure.（3）In this paper,the effects of soil amendments with different proportions on plant physiological indexes were investigated.The growth parameters（plant height,biomass,and chlorophyll）in all treatment groups were increased to different degrees,and the antioxidant enzymes were increased by 10.68%（SOD,T2）～207.31%（CAT,T6）compared with the control group.The contents of proline and soluble sugar in the treatment group were significantly increased by 16.00～115.23%and 39.23～177.57%,respectively.The results showed that the amendments promoted the growth of plants,and plants mainly depended on the antioxidant enzyme system and osmotic regulatory factors to resist the oxidative damage caused by salt.（4）In this paper,the improvement effect was comprehensively evaluated based on the physical and chemical properties of the improved saline-alkali soil and physiological indexes of plants.The results showed that T6 in the treatment group had the best improvement effect,and the best ratio of each component was 2.0%phosphogypsum,2.0%humic acid,0.25%bentonite,and 0.03%sodium carboxymethyl cellulose.Different improvement components played different roles,and amendments mainly promoted plant growth by alleviating soil salt stress and improving nutrients.（5）In this paper,the heavy metal content,available heavy metal content and different chemical forms in improved saline-alkali soil and plants were detected.The results showed that the content of heavy metals in the modified saline-alkali soil was lower than the soil risk control value in GB 15618-2018,and the content of heavy metals in plants was lower than the allowable threshold of Chinese food safety standard HMs.In addition,the health risk value of Cr in the improved saline-alkali soil exceeded the acceptable level for adult males and females,and the health risk value of As can not be ignored in all three groups through ingestion of rape.Therefore,the appropriate measures should be taken to reduce the environmental risks of the amendment application.