Study On Soil Fertilization And Carbon Sequestration Potential Of Different Pyrolysis Temperature Biochar Returning

A large amount of straw will be produced in the process of agricultural production,and serious environmental pollution problems will be caused if those straw are treated improperly.Therefore,people seek a variety of ways to utilizate straw as a resource.Among them,the way of pyrolysis straw to biochar has received a lot of attention.Straw biochar itself is rich in a large amount of nutrient elements,it can also promote the transformation of soil nutrients and play a role in fertilizing the soil after returning to field.At the same time,biochar also has strong stability and good carbon sequestration potential,which can promote soil carbon sequestration after returning to field,it is an important means to slow down the global greenhouse effect.Therefore,it is of great significance to study the effect and reason of straw biochar returning to field to fertilize soil and its carbon sequestration potential.In this research,four kinds of straw biochars were prepared at different pyrolysis temperatures（300°C,400°C,600°C,800°C）using rice straw as raw material.Firstly,the content of available nutrients and carbon elements in biochar was determined,and the stability of biochar was analyzed by XPS,FTIR and water-solubility experiments before biochar returning to field.Then,the effect of biochar on crop growth and the improvement of soil available nutrients,total carbon and organic carbon contents were evaluated through pot experiments.Finally,to analyze the reasons why biochar returning to field could fertilize soil and its carbon sequestration comprehensively according to changes in soil enzymatic activities related to nutrient cycle and carbon cycle,and predicted the potential of biochar alleviate the global greenhouse effect.This research aims to provide a theoretical basis for the preparation and application of high-quality returning biochar.The final conclusions are as follows:（1）Potted experiments showed that biochar promoted wheat growth effectively.Compared with the blank group,the dry weight of wheat increased by 16.45%-43.86%;After medium and high temperature biochar（400-800℃）returning to field,soil ammonium nitrogen and nitrate nitrogen content increased by 11.37%-269.33%and 67.68%-161.89%,respectively,soil available phosphorus and available potassium content increased by4.20%-29.41%and 374.71%-588.63%,respectively.Low temperature biochar（300℃）returning decreasd soil nitrate nitrogen and available phosphorus content because it was still in the transition state from straw to biochar,not in the complete state of biochar,and its action mode in soil was similar to straw.（2）The nitrogen content in biochar was between 0.65%～1.47%,which could provide a large amount of nitrogen to the soil after returning,but the content of available nitrogen in biochar is extremely low,so the supply of biochar’s own available nitrogen is less than the increase of available nitrogen in the soil.But the supply of its own available phosphorus and available potassium is far greater than the increase of available phosphorus and available potassium in the soil after biochar returning to field.At the same time,it was found that the activities of urease,nitrite reductase,and hydroxylamine reductase associated with the conversion of soil available nitrogen increased to varying degrees after biochar returning to field;Acidic,neutral and alkaline phosphatase activities associated with the conversion of soil available phosphorus were reduced after biochar（400°C,600°C,800°C）returning to field.Therefore,it showed that straw biochar increased soil available nitrogen by promoting soil enzyme activity,and increased soil available phosphorus and potassium through its own supply,eventually achieving the purpose of fertilizing the soil.（3）With the increase of the preparation temperature,the total carbon content of biochar increased,the H/C of biochar decreased,indicating that the degree of aroma and carbonization of biochar was increasing,and the stability was also increasing;Returning biochar to field could increase the content of soil total carbon and total organic carbon significantly,and the promotion effect of high temperature biochar was more obvious.The total soil organic carbon content was 5.5 times that of the blank group and 4.14 times that of the straw group when biochar prepared at 800℃returned to field.it was also found that the higher the temperature of biochar,the less soil CO₂ emissions in the soil.（4）The activities of soil amylase,β-glucosidase,soil cellulase and soil peroxidase showed a significant negative correlation with soil organic carbon content after biochar returning to field,biochar slowed the mineralization of the soil’s own carbon,which was conducive to the accumulation of soil organic carbon,showing a good carbon fixation effect.（5）If the straws of the three major food crops in the world are all prepared into 400℃biochar and returned to the field,the total fixed soil carbon can reach 604.84 million tons per year,accounting for 6.22%of the total carbon emissions from fossil fuels and 48.35%of the total carbon emissions from agricultural land;Considering comprehensively from the perspectives of energy consumption,fertilizing and carbon emission reduction effect,400°C is the best choice for preparing biochar.