Research On Preparation,modification Of Hydrochar And Its Improvement Feature For Soda-saline-alkali Soil

Soda-saline-alkali soil has high p H value and salt content,low organic carbon content and serious lack of nitrogen,phosphorus and other nutrients.The lack of nutrients in the soil and the existence of a large amount of salt have serious harm to the growth and development of crops,so it is urgent to improve the utilization of soda-saline-alkali soil.At present,hydrochar prepared from waste biomass has rich oxygen functional groups,high nutrient content and low p H value,which may have good potential for improving soda-saline-alkali soil.However,in the process of soil improvement,hydrochar is easy to float,low desalting efficiency,and more nutrient loss.Therefore,it is possible to enhance the improvement effect of hydrochar on soda-saline-alkali soil by modifying it.Based on this,this paper prepared pristine hydrochar,aluminum modified hydrochar and iron modified hydrochar by using pure water,aluminum sulfate and ferric sulfate solution as medium,studied the improvement effects of pristine hydrochar and two kinds of modified hydrochar on physical and chemical properties and nutrient content of soda saline-alkali soil under the conditions of soil cultivation and soil washing,and verified the improvement effects through the growth of rice seedlings.The main research results are as follows:（1）Using fungus bran as raw material,pristine hydrochar,aluminum modified hydrochar and iron modified hydrochar were prepared in pure water,aluminum sulfate solution and ferric sulfate solution.The three kinds of hydrochar were analyzed by scanning electron microscopy,infrared spectroscopy,elemental analysis and other technical means.It was found that the three kinds of hydrochar were acidic and had good surface structure and more oxygen-containing functional groups.Among them,the surface structure of the two modified hydrochar is rougher,showing more pores,stronger hydrophilicity,and has more oxygen-containing functional groups and nutrients,and the p H value and Na content of the two modified hydrothermal carbonates are lower,indicating that they have better potential to improve soda-saline-alkali soil.（2）The results of culture improvement test of soda-saline-alkali soil showed that the bulk density of soda-saline-alkali soil improved by pristine hydrochar,aluminum-modified hydrochar and iron-modified hydrochar decreased significantly,the settlement performance of soil turbidity and the number of aggregates with particle size larger than 0.25 mm were improved,and the texture of soil was improved significantly.Soil p H value decreased from 9.21 to 8.75,8.37 and 8.21,alkalinity degree decreased from 25.60%to 24.30%,19.98%and 19.48%,cation exchange capacity increased by 16.38%,28.69%and 35.29%,soil nutrient level also further improved.Among them,two kinds of modified hydrochar have better improvement effect on soda-saline-alkali soil,and their distribution in the soil is relatively more uniform,avoiding the problem of pristine hydrchar floating in the soil.（3）The improvement test results of soil-saline-alkali soil showed that the p H value of the soil decreased from 8.96 to 8.42,8.05 and 7.97,and the alkalinity decreased from 18.16%to15.32%,12.21%and 10.10%,respectively.The exchangeable Na⁺content decreased by 11.66%,22.08%and 33.13%,respectively,and only a small amount of HCO₃^-and CO₃^2-existed in the soil.In the process of soil washing,the three kinds of hydrochar can all reduce the p H value and alkalinity degree of soil and improve the nutrient level of soil.Among them,the two kinds of modified hydrochar can further promote the precipitation of Na⁺and salt in the soda saline-alkali soil,reduce the loss of soil organic carbon and nutrient in the process of soil washing,and provide enough nutrients for the soil.（4）The biomass and nutrient content of rice seedlings increased significantly when growing in soda-alkaline soil modified by pristine hydrochar,aluminum hydrochar and iron hydrochar.In cultivated and improved soil,MDA content of rice seedlings decreased by 18.58%,37.63%,40.81%,SOD activity decreased by 5.94%,10.64%,13.98%,and Na content decreased by 7.61%,18.38%,26.35%,respectively.Soluble sugar content increased by 16.33%,39.01%and 29.02%,and soluble protein content increased by 14.69%,23.16%and 23.65%,respectively.In the washed soil,MDA content of rice seedlings decreased by 38.02%,46.01%,49.85%,SOD activity decreased by 1.78%,10.43%,14.66%,and Na content decreased by 9.55%,30.29%,46.93%,respectively.Soluble sugar content increased by 39.31%,74.08%and 89.21%,and soluble protein content increased by 38.04%,64.13%and 82.07%,respectively.The above research results show that the pristine hydrochar prepared by fungus bran and the hydrochar modified by aluminum and iron have certain improvement effects on soda saline-alkali soil.Among them,the two kinds of modified hydrochar have lower p H value,developed pore structure,more abundant oxygen-containing functional groups,relatively uniform vertical distribution in the soil,not easy to float,and can improve the soil texture structure more effectively.Reducing soil p H value and alkalinity,promoting the precipitation of salt in soil,improving soil nutrient level,reducing the loss of organic carbon and phosphorus in soil,thus promoting the growth of rice seedlings,and providing important theoretical basis and technical support for the efficient improvement of soda saline-alkali soil by using hydrochar.