| Land salinization has become a key problem to be solved urgently in agricultural development and economic construction.Traditional treatment methods have certain limitations.As a soil conditioner with both economic and ecological benefits,biochar has shown good potential in saline-alkali soil improvement.Compared with traditional pyrolytic biochar,hydrochar has weaker alkaline characteristics and has excellent potential for saline-alkali soil improvement.In this thesis,through soil leaching experiments,the improvement effects of pyrolytic biochar and hydrochar on saline-alkali soil in the Yellow River Delta were compared.The main research results are as follows:(1)Peanut shell,wheat straw,corn straw and rice husk were used as raw materials to prepare MBC1,MBC2,MBC3 and MBC4 pyrolysis biochar by Muffle furnace pyrolysis method,and FBC1,FBC2,FBC3 and FBC4 hydrochar were prepared by hydrothermal carbonization in reaction kettle.According to the results of soil leaching experiment,the addition of biochar changed the grain size composition,p H and zeta potential of saline-alkali soil,increased the soil porosity,water content,cation exchange capacity(CEC)and organic matter content,and significantly reduced the soil bulk density,total water-soluble salts content,exchangeable Na~+content and alkalinity(ESP).On the whole,the treatment effect of hydrochar was better than that of pyrolytic biochar,among which MBC1 and FBC1 treatment had the best effect.The total water-soluble salts content in soil was reduced by 11.43%and 23.03%,the exchangable Na~+content was reduced by 16.47%and 45.31%,and ESP was reduced by 30.74%and 55.58%,respectively.Therefore,peanut shell was determined as the optimal raw material for preparation,and the preparation conditions were experimentally studied.The optimum preparation temperatures of pyrolytic biochar and hydrochar were determined as 500℃and260℃,and the optimum preparation time was 4 h and 2 h,respectively.(2)According to the salt reduction effect of saline soil,the biochar impregnation method was determined as the optimal method for the phosphoric acid modification of biochar.By changing the concentration of phosphoric acid modification solution(5%,10%,15%,20%),MGBC1,MGBC2,MGBC3,MGBC4 modified pyrolytic biochar were obtained.And FGBC1,FGBC2,FGBC3,FGBC4 modified hydrochar.According to the experimental soil leaching results,it was found that with the increase of the phosphoric acid solution concentration,the effect of modified biochar on reducing soil p H showed an overall upward trend.At the same time,the reduction effect of modified biochar on total water-soluble salts content,exchangeable Na~+content and ESP was significantly increased.As for other properties of saline-alkali soil,there was no significant difference in the treatment effect of biochar before and after modification.On the whole,the treatment effect of modified hydrochar was better than that of modified pyrolytic biochar,among which MGBC3 and FGBC2 treatments had the best effect,which reduced total water-soluble salts content in soil by about 23.26%and 32.29%,respectively,and the soil exchangeable Na~+content by about 24.27%and 51.39%,respectively.Soil ESP decreased by 16.37%and 26.02%,respectively.(3)Principal component analysis was used to determine the alkaline degree,total water-soluble salts content,bulk density and porosity as the key indexes to evaluate the improvement effect of the Yellow River Delta saline-alkali soil.MGBC3 and FGBC2 were identified as the optimal modified pyrolytic biochar and modified hydrochar,respectively.Further soil leaching experiments showed that MGBC2 and FGBC3 both significantly reduced the contents of major salt ions(Na~+and Cl~-)and the soil sodium adsorption ratio(SAR),among which FGBC3treatment was superior to MGBC2.The addition of MGBC2 and FGBC3 also increased the contents of soil available potassium,total nitrogen,available phosphorus and organic matter,increased the richness,diversity and evenness of bacteria in saline-alkali soil,and changed the relative abundance of soil bacteria.The relative abundance of metabolic functions such as nucleoside and nucleotide biosynthesis,amino acid biosynthesis and carbohydrate biosynthesis increased significantly in saline-alkali soil bacteria.According to all the experimental results,it is concluded that the modified biochar can improve the saline-alkali soil in the Yellow River Delta as follows:On the one hand,the addition of modified biochar is conducive to the improvement of the structure of salt-alkali soil,making soil salinity more likely to sink with leaching water.At the same time,according to the characterization of biochar,after phosphoric acid modification,the specific surface area,pore volume and surface oxygen-containing functional groups of biochar increase,which has a better adsorption effect on salt ions such as Na~+and Cl~-than before modification,and alleviates soil salt-alkali stress.On the other hand,the addition of modified biochar increased the soil nutrient content,changed the diversity and relative abundance of soil bacterial community,enhanced the function of bacterial synthesis and utilization of soil nutrients,and improved the soil nutrient environment.Therefore,the addition of modified biochar effectively improved the saline-alkali soil in the Yellow River Delta,and the soil environment was improved.Among them,the improvement effect of modified hydrochar was better than that of modified pyrolytic biochar.The research results provided theoretical support for the improvement of saline-alkali soil. |
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