Effect Of Combined Application Of Wood Vinegar Acidified Biochar And Nitrogen On Nitrogen Forms And Availability In Saline Soil

Soil salinization is a worldwide problem,and the theme of World Soil Day 2021 is "Prevent Land salinization,Improve Land Productivity".Salinized soil covers an area of 100 million hm² in China,which is mainly distributed in arid,semi-arid,and semi-humid areas.Soil salinization is an important soil degradation problem that affects the utilization of soil resources and food security in northwest China.Due to the influence of the nature of salinized soil itself,the availability of nitrogen nutrients in salinized soil areas is low,increasing the application amount of chemical fertilizer（especially nitrogen fertilizer）,which leads to the under-utilization of nutrients and environmental pollution.Therefore,the study of nitrogen nutrients in salinized soil has always been our concern.It is one of the effective ways to improve salinized soil by using green and environment-friendly new materials to improve its nutrient availability.This study with a range of salinization of soil in northwest China,by adsorption experiments,indoor soil culture experiments and pot experiments,combining with the oxalic acid,citric acid and sulfur powder mutual comparative research,explore the biochar after wood vinegar fluid acidification treatment,the salinized soil nitrogen transformation and its related enzyme and the effect of plant growth.It is expected to provide some scientific basis for improving salinized soil and increasing yield.The main results of the research are as follows:（1）The results showed that with the continuous increase of the NH₄⁺-N concentration in the initial solution,the adsorption amount of NH₄⁺-N in the solution by each treatment of biochar also showed a gradually increasing trend.At 25°C and 35°C,the maximum adsorption capacity of biochar diluted with wood vinegar by 5 times was significantly higher than that of unacidified biochar.The Langmuir isotherm adsorption model has a better effect on describing the adsorption process of biochar in each treatment of NH₄⁺-N,indicating that the adsorption of NH₄⁺-N by biochar in each treatment is monolayer adsorption;while the pseudo-secondorder kinetic model is used for the adsorption of NH₄⁺-N by biochar in each treatment.The kinetic process of adsorption has a good application,indicating that the adsorption process of different biochars is dominated by chemical adsorption,and the adsorption process is a spontaneous chemical endothermic process with increasing disorder.The increase of oxygencontaining functional groups may be an important reason for the increase of NH₄⁺-N adsorption on biochar acidified with wood vinegar.（2）Compared with the single application of urea,the combined application of acidified biochar and urea reduced soil nitrate nitrogen and ammonium nitrogen by 25.26% and 16.93%,respectively.Acidified biochar increased soil dissolved organic nitrogen and total dissolved organic nitrogen.The combined application of acidified biochar and urea increased the soil urease activity,while the combined application of biochar and urea decreased the soil urease activity.The combined application of acidified biochar and urea during the cultivation process reduced the amount of soil ammonia volatilization,which was reduced by 35.92% and 15.85%compared with the single application of urea and the combined application of biochar and urea,respectively.（3）Compared with the single application of urea,the soil ammonium nitrogen,nitrate nitrogen,soil dissolved organic nitrogen and total dissolved organic nitrogen of the biochar +wood vinegar + urea treatment were reduced by 17.33%,64.95%,8.52%,and 43.59%,respectively.It promoted the absorption of nitrogen in pakchoi.Compared with biochar + urea or single application of urea,the soil urease activity of the biochar + wood vinegar + urea treatment decreased by 20.97% and 36.48%,respectively,while the soil nitrate reductase activity increased by 30.62% and 33.71%,respectively.Compared with biochar + oxalic acid+ urea,biochar + sulfur powder + urea treatment,biochar + wood vinegar + urea treatment effectively improved soil urease and nitrate reductase activities.（4）Compared with other treatments,the yield,shoot dry mass,root dry weight,chlorophyll content,net photosynthetic rate,and stomatal conductance of pakchoi treated with biochar + wood vinegar + urea was significantly improved.The utilization rate and the agronomic utilization rate of nitrogen fertilizers also increased significantly,with an increased rate of 19.06% to 69.03% and 19.46% to 127.24%,respectively.（5）Compared with biochar + urea treatment,biochar + wood vinegar + urea treatment significantly increased the catalase activity and superoxide dismutase activity of pakchoi,but inhibited the peroxidase activity.Compared with the treatment of biochar + citric acid + urea treatment,biochar + sulfur powder + urea treatment,the treatment of biochar + wood vinegar+ urea treatment significantly promoted the activities of superoxide dismutase,peroxidase and catalase in pakchoi.Compared with the treatment of biochar + oxalic acid + urea treatment,the treatment of biochar + wood vinegar + urea promoted the peroxidase and catalase activities of pakchoi.The comprehensive analysis found that the biochar after acidification with wood vinegar can increase the adsorption of ammonium nitrogen,better reduce the loss of nitrogen in saline soil,and enhance the availability of soil nitrogen,thereby improving plant productivity,the utilization rate of light energy,nitrogen fertilizer utilization rate,and stress resistance in saline soil,and finally achieve the effect of increasing production.