Effects Of Different Amendments On Salt Removal And Organic Matter Enhancement Of Saline-alkali Soil In The Yellow River Delta

In recent years,with the excessive application of pesticides and chemical fertilizers in China,the limited cultivated land resources have been damaged,and the contradiction between land and population,food has become increasingly prominent.As an important reserve land resource in China,saline alkali soil has not been developed and utilized in China due to its high salt content,lack of nutrients and other factors,so the improvement and development of saline-alkali soil is of great significance to ensure food security and relieve the pressure of population and land.Soil amendments is widely used in the improvement and restoration of saline-alkali soil,which can improve soil structure,promote salt leaching,and increase soil nutrient content.This study took the Yellow River Delta saline-alkali soil as the research object.First,the spatial distribution of salinity and available nutrients in the area was investigated and analyzed.Then,soil column simulation tests were conducted to explore the effects of different organic amendments on the salinity and available nutrients in soil and leachate.As well as the effects of the combined application of organic amendments and phosphogypsum on soil salinity and organic carbon were studied through indoor cultivation experiments,the following results were obtained:（1）The p H value of saline-alkali land（0-60 cm depth soil layer）in this area is 7.89-8.85,and the soil is alkalescent.The range of soil salinity is 0.45-13.7 g/kg,and the average soil salinity is 3.43 g/kg,and the salinization is serious and the degree of salinization is unevenly distributed.The salinity and available nutrients of the soil decrease with the increase of soil depth.The surface soil（0-20 cm）is mainly saline soil,moderate saline-alkaline soil and severe saline-alkaline soil,accounting for 55.36%,30.36%and 10.71%respectively.The alkaline hydrolyzable nitrogen,available phosphorus and available potassium in the surface soil are all at the level 1,that is,the soil available nutrient content is rich,but the available nutrient distribution is uneven.Compared with Caizhai base,the p H value,available nitrogen,available phosphorus and available potassium of surface soil（0-20 cm）in Lvyi base were significantly different,and Lvyi base was significantly higher than Caizhai base.Correlation analysis showed that there was a significant negative correlation between soil p H and salinity,and a significant positive correlation between soil alkaline hydrolyzable nitrogen,available phosphorus and available potassium;（2）Based on soil column simulation test,the effect of organic amendments on saline-alkali soil improvement was studied.The results show that the addition of organic amendments increased the EC value and water-soluble Ca²⁺,Mg²⁺and Na⁺of the leachate,and increased available nutrients in the 0-20 cm soil layer.Leaching makes the 0-20 cm soil salt in the surface layer move to the deep soil layer.After the leaching,the soil EC value,water-soluble total salt,exchangeable Na⁺and ESP of each treatment increase with the increase of soil depth.The best organic amendments for improving soil salinity and p H was white particle organic silicon functional fertilizer,which significantly increases the water-soluble Ca²⁺,Mg²⁺and K⁺in each depth soil layer,and significantly reduced the p H,exchangeable Na⁺and ESP in each depth soil layer compared with CK treatment.（3）The indoor culture experiment showed that the application of different amendments increased the content of soil water-soluble total salt and CEC.The application of organic amendments mainly increased soil CEC and DOC contents,while the application of phosphogypsum mainly increased soil water-soluble Ca²⁺,Mg²⁺,K⁺,and reduced soil p H and SAR.The combined application of organic amendments and phosphogypsum was better than the single application of organic amendments.Among all the treatments,the combination of white particle organic silicon functional fertilizer and phosphogypsum had the best improvement effect on the main saline-alkali indexes（p H value,SAR,exchangeable Na⁺and ESP）of saline-alkali soil.In summary,the salinity of the study area is heavy,and the distribution of salinity is uneven.Among the different organic amendments,the white particle organic silicon functional fertilizer had the best effect on improving saline-alkali soil,and the effect of organic amendments combined with phosphogypsum was better than that of organic amendments or phosphogypsum alone.