Effects Of Biochar And Wood Vinegar On Adsorption,Leaching And Migration Of Salt Ions In Saline-Alkali Soil

Soda saline-alkali soil in Northeast China covers a wide area and has a serious degree of salinization.Soil salinization will seriously affect soil structure and physical and chemical properties,inhibit plant growth and reduce crop yield.As a soil conditioner,biochar can effectively improve soil structure,increase soil permeability,and increase crop yield;Wood vinegar is an acid modifier,which can effectively improve the properties of the soil and improve soil fertility after being applied to the soil.In order to investigate the effects of biochar and wood vinegar on the adsorption,leaching,and migration of salt ions in soda saline-alkali soil,adsorption,leaching,and pot experiments were conducted in this study.Three treatments were designed for adsorption experiments:0.5%biochar（C1）,1%biochar（C2）,and 1.5%biochar（C3）.The leaching test used soil column leaching method,and the pot experiment used rice as the test crop,all including 10 treatments,namely the control treatment without adding biochar and wood vinegar（CK）,30 t/hm²biochar treatment（C1）,60 t/hm²biochar treatment（C2）,90 t/hm²biochar treatment（C3）,0.75 t/hm²wood vinegar treatment（P1）,1.5 t/hm²wood vinegar treatment（P2）,3t/hm²wood vinegar treatment（P3）,60 t/hm²biochar mixed with 0.75 t/hm²wood vinegar（C2P1）,60 t/hm²biochar mixed with 1.5 t/hm²wood vinegar（C2P2）,and 60 t/hm²biochar mixed with 3t/hm²wood vinegar（C2P3）.The experimental results provide reference for the application of biochar and wood vinegar,and provide theoretical basis for the improvement of saline-alkali soil in agricultural systems.The research results are as follows:（1）Biochar effectively adsorbs Na⁺,K⁺,Ca²⁺,and Mg²⁺ions in saline-alkali soil,and as the amount of biochar applied increases,the adsorption capacity of Na⁺,K⁺,Ca²⁺,and Mg²⁺also increase.C3 treatment has the best adsorption effect on Na⁺,K⁺,Ca²⁺,and Mg²⁺.The adsorption process of biochar on salt ions in soil conforms to quasi first and quasi second order kinetic models,but the fitting effect of quasi second order kinetic models is better.Therefore,the adsorption process of biochar on salt ions in soil is more inclined towards chemical adsorption.（2）The application of biochar alone,wood vinegar alone,and the combination of biochar and wood vinegar in the soil column all increased the leaching amount of salt ions in saline-alkali soil.Among them,under C3 treatment,the total leaching amount of Na⁺,K⁺,Ca²⁺,Mg²⁺,CO₃^2-,HCO₃^-,and Cl^-ions in saline-alkali soil is the highest,increasing by 27.91%,59.26%,12.25%,20.86%,58.45%,39.85%,and 62.51%,respectively.However,increasing the application rate of wood vinegar alone cannot significantly increase the leaching amount of various salt ions.（3）Single application of biochar,single application of wood vinegar,and the combination of biochar and wood vinegar significantly reduced the content of Na⁺,CO₃^2-,HCO₃^-,and Cl^-in soda saline-alkali soil,and increased the content of K⁺,Ca²⁺,and Mg²⁺in the soil.Among them,C2P2treatment had the best improvement effect on various salt ions in saline-alkali soil.From the average level throughout the entire growth period,C2P2 treatment reduced the content of Na⁺,CO₃^2-,HCO₃^-,and Cl^-by 27.54%,62.45%,24.39%,and 29.8%,and increased the content of K⁺,Ca²⁺,and Mg²⁺by 53.05%,40.62%,and 62.07%.In addition,biochar and wood vinegar reduced the Na⁺and Cl^-contents in rice plants,and increased the K⁺,Ca²⁺,and Mg²⁺contents.Overall,C2P2 treatment had the best effect on improving salt ions in rice plants,reducing Na⁺and Cl^-contents by 22.71%and 17.79%in rice roots,and increasing K⁺,Ca²⁺,and Mg²⁺contents by 100%,9.52%,and 8.55%,respectively;The Na⁺and Cl^-contents in rice stems and leaves decreased by11.02%and 5.19%,while the Ca²⁺and Mg²⁺contents increased by 10.67%and 6.52%;The Cl^-content in rice grains decreased by 18.02%,while the K⁺,Ca²⁺,and Mg²⁺contents increased by166.67%,48.03%,and 23.72%.（4）Single application of biochar,single application of wood vinegar,and the combination of biochar and wood vinegar effectively reduced the Na⁺and Cl^-contents in rice plants,and increased the K⁺,Ca²⁺,and Mg²⁺contents.From the overall perspective of rice plants,the K⁺,Ca²⁺,and Mg²⁺contents were the highest in C2P2 treatment,while the Na⁺and Cl^-contents decreased the most.The Na⁺and Cl^-contents in rice roots decreased by 22.71%and 17.79%,while the K⁺,Ca²⁺,and Mg²⁺contents increased by 100%,9.52%,and 8.55%,respectively;The Na⁺and Cl^-contents in rice stems and leaves decreased by 11.02%and 5.19%,while the Ca²⁺and Mg²⁺contents increased by 10.67%and 6.52%;The Cl^-content in rice grains decreased by 18.02%,while the K⁺,Ca²⁺,and Mg²⁺contents increased by 166.67%,48.03%,and 23.72%.（5）Single application of biochar,single application of wood vinegar,and the combination of biochar and wood vinegar all reduced the salt content in saline-alkali soil,and increased soil organic matter,and cation exchange capacity;The single application of wood vinegar and the combination of biochar and wood vinegar also effectively reduced p H in saline-alkali soil and improved its chemical properties.Among all treatments,the mixed application of biochar and wood vinegar has a better improvement effect.C2P2 treatment has the best effect on improving soil cation exchange capacity and salt content.The p H of C2P1 treatment decreased the most,reaching 9.24.C2P3 treatment has the best improvement effect on organic matter.（6）Single application of biochar,single application of wood vinegar,and the combination of biochar and wood vinegar all effectively increased rice yield and its components.The biomass of C2P3 treatment,the solid particle number of C2P1 treatment,and the total particle number of P2treatment are the highest.The 1000 grain weight of rice treated with C2,C3,P2,C2P1,and C2P2increased by 25.60%-41.67%.The C2,C3,and C2P3 treatments had the best effect on improving rice yield,increasing by 65.53%,58.30%,and 57.14%,respectively.Overall,biochar can effectively adsorb salt ions in soil,and whether biochar is applied alone or in combination with wood vinegar solution,it effectively increases the leaching effect of salt ions in soda saline-alkali soil,reduces the accumulation of harmful salt ions in soil and rice,and increases the concentration of nutrient ions.In addition,both single and mixed application of biochar and wood vinegar effectively improved the chemical properties of soda saline-alkali soil,and increased the yield and composition factors of rice.Overall,C2P2 treatment has the best improvement effect on soda saline-alkali soil.