Preparation Of Poplar-branch Biochar And Effects On The Ecological Improvement Of Saline-alkali Soil

Soil salinization and degradation of ecosystem services in coastal wetlands have become important ecological and environmental problems limiting the sustainable development of agriculture and forestry in coastal areas,and ecological improvement and soil quality enhancement of saline soils have become one of the hot areas of research in soil science and ecology.Biochar is widely used as a soil ecological amendment because of its wide source of raw materials,rich nutrient content,excellent adsorption performance and relatively stable nature.In this study,poplar（Populus sp.L）branches from harvesting and wood processing residues were used as raw materials to prepare biomass char at different pyrolysis temperatures（300-700℃）and pyrolysis ramp rates(10,30 and 50℃min^-1)to investigate the effects of different pyrolysis conditions on the physicochemical properties of biochar.Using Lianyungang saline-alkali soil as the research object,biochar suitable for improving saline-alkali soil was selected and applied at different charcoal-to-soil mass ratios（0,0.5%,1.5%,3.0%and 5.0%）to analyze the effects and action mechanisms of different biochar additions on soil physicochemical properties,enzyme activity and growth of Kosteletzkya pentacarpos Principal component analysis-affiliation function method was used to calculate the comprehensive index of saline-alkali soil quality and comprehensively evaluate the ecological improvement effect of biochar on saline soils.The results of the study can provide a theoretical basis for the application of poplar branch biochar in the ecological improvement of saline soils.The main findings of the study are as follows:（1）The yield of poplar-branch-biochar gradually decreased with the increase of pyrolysis temperature,and the ash content,p H and Electrical Conductivity（EC）increased with the increase of temperature.At the same pyrolysis temperature level,the effect of temperature increase rate on biomass char yield,ash content,p H and EC value was not significant.The content of mineral elements（K,Na,Ca,Mg,P）in biochar increased with the increase of pyrolysis temperature.The content of mineral elements increased with the increase of heating rate at low temperature,and decreased at high temperature.With the increase of pyrolysis temperature,the C content of biochar increased,the N content increased first and then decreased,and the H content decreased.The types of surface functional groups of biochar are basically the same.Considering the yield and physicochemical properties of poplar branch biochar under different preparation conditions,the biochar prepared under pyrolysis conditions of 400℃and 10℃·min^-1is more suitable for coastal saline-alkali soil improvement.（2）Soil p H,salinity,Exchange Sodium Percentage（ESP）and Sodium Adsorption Ratio（SAR）decreased significantly with increasing biomass charcoal application rate,with the best improvement at 3.0%addition.Soil p H,salinity,ESP and SAR showed an increasing trend again when the biochar application was increased to 5.0%.Soil Cation Exchange Capacity（CEC）and Soil Organic Matter（SOM）,Total Potassium（TK）and Total Phosphorus（TP）,as well as K⁺,Ca²⁺and Mg²⁺increased with increasing biochar addition,while adsorption of effective tnutrients such as Alkali-hydrolyzable Nitrogen（AN）,Available Potassium（AK）and Available Phosphorus（AP）was enhanced.（3）Popla-branch-biochar addition significantly affects soil enzyme activity.The increase of biohar addition had a significant promotion effect on soil sucrase activity,while urease activity and catalase activity showed an increasing and then decreasing trend with the increase of biomass charcoal application,and reached the maximum at 3.0%addition.（4）The addition of biomass charcoal alleviated the inhibitory effect of salt stress on the growth of seashore mallow,and its biomass and plant height increased significantly.At the same time,the addition of biohar promoted the increase of leaf area and root growth,and the total root length,surface area,mean diameter and root tip number were significantly increased.3.0%addition had the best promotion effect on each growth index of Kosteletzkya virginica.（5）Soil Quality Iindex（SQI）was calculated by principal component analysis-affiliation function method,and the evaluation results showed that the SQI increased with the increase of biomass charcoal addition,and the SQI was 0.795 and 0.894 for 3.0%and 5.0%addition,respectively;considering the ecological improvement effect,it was suggested that 3.0%addition was appropriate.In summary,the biomass char prepared from poplar branches at a pyrolysis temperature of400℃and a heating rate of 10℃·min^-1has a higher yield and each physicochemical property is more suitable for ecological improvement of saline-alkali soil on the seashore.Based on the comprehensive evaluation of the improvement effects of different poplar branch biochar application rates on the saline-alkali index,nutrient content and enzyme activity of coastal saline-alkali soil and the effect on the growth of Kosteletzkya pentacarpos,it is the application rate of 3.0%is appropriate.