Evaluation Of The Improvement Effect Of Biochar Based On The Study Of Soil Biochemical Indexes

Biochar is a product with strong stability and high carbon content generated by high-temperature pyrolysis of agricultural waste under anoxic or anaerobic conditions.Due to its strong adsorption and extremely slow aging time in soil,it can improve the adsorption capacity of soil to nutrient elements when applied to soil,and plays an important role in the process of soil carbon pool turnover and nutrient cycling.In addition,soil chemical properties,soil microbial biomass,and soil enzyme activities are important indicators for evaluating soil quality.However,there is a lack of comprehensive analysis of these biochemical indicators in the research field of the impact of biochar on soil quality.Therefore,in this study,we select the gray desert soil of Xinjiang and the sandy soil of Yulin to conduct an indoor simulation culture experiment under different proportions of cotton straw biochar,and take samples regularly to determine the soil chemical properties（p H,available phosphorus,ammonium nitrate nitrogen,soluble organic carbon）,soil microbial biomass carbon and nitrogen,and the characteristics of soil enzyme activity（urease,invertast,alkaline phosphatase,catalase）,in order to reveal the effect of biochar on soil biochemical indexes.The following conclusions are obtained:（1）Under the influence of biochar,the p H value of the two types of soils increased significantly,and the contents of soil available phosphorus,ammonium nitrogen,nitrate nitrogen and soluble organic carbon（DOC）also increased significantly.Among them,the soil p H,available phosphorus and soluble organic carbon（DOC）increased with the increase of biochar application,and the increase was the largest at 8%addition;Ammonium nitrogen and nitrate nitrogen increased the most when the amount of biochar was 2%;During the whole culture period,their maximum increases were 8.1%,459.1%,108.0%,83.5 and 54.8%,in grey desert soil and 29.7%,127.8%,130.0%,20.0%and 104.4%in aeolian sandy soil,respectively.（2）During the whole culture period,the 2%biochar addition had the most obvious promotion effect on the soil microbial biomass carbon of these two types of soil.In the 5th week,biochar treatment had the largest increase on soil microbial biomass carbon,and the largest increases of grey desert soil and aeolian sandy soil were 203.7%and 180.8%,respectively.During the whole culture period,the addition of 2%biochar had the most obvious effect on improving soil microbial biomass nitrogen and carbon nitrogen ratio of these two types of soil.The maximum increase of biochar on soil microbial biomass nitrogen during the whole culture period was 238.8%and 217.8%,respectively.In grey desert soil,compared with CK,biochar treatment had the largest increase of MBC/MBN in the 5th week.At the 36th week of the late culture period,biochar treatment had no significant effect on MBC/MBN in both gray desert soil and aeolian sandy soil,indicating that the effect of biochar on soil microbial biomass had a certain timeliness.（3）The application of biochar can improve the soil enzyme activity to a certain extent,but the activation effect decreases gradually with time.In this study,the addition of biochar at 0.5%to 2%had a significant activation effect on the soil enzyme activity of gray desert soil.Under the application rate of 4%～8%,soil enzyme activities were inhibited in both two types of soil.The soil enzyme activity of aeolian sandy soil increased significantly under the condition of biochar application proportion of 2%.When different amounts of biochar was applied to the two types of soil,the change regulation was not the same in different culture periods,but it basically tended to be stable at the end of culture.In the early 5～7th weeks of cultivation,the V_max of soil urease,invertase,alkaline phosphatase and catalase in two types of soils were increased significantly under biochar treatment,especially under 2%application.The K_m of soil alkaline phosphatase and catalase increased under biochar treatment,while the K_m of soil urease and invertase decreased.In contrast to gray desert soil,aeolian sandy soil had higher urease K_m at the 5th week.Compared with the control,the V_max/K_m of soil urease,invertase,and alkaline phosphatase were significantly increased in both types of soils under the different biochar addition in the early 3～7th weeks of culture,especially with 2%addition.The results of redundancy analysis showed that soil nitrate nitrogen and ammonium nitrogen were the main factor affecting soil enzyme activity and soil enzyme kinetic parameters for both tested soils.Based on the analysis of soil chemical properties,soil microbial biomass and soil enzyme activity indexes,the best biochar addition of grey desert soil and aeolian sandy soil was 2%.