Effects Of Tea Residue Biochar On Organic Carbon And Aggregate Characteristics In Ming Shan Tea Garden Soil

The tea industry is the leading industry in the Mingshan District of Ya’an City.The quality of the tea garden soil directly determines the sound development of the tea industry.The amount of tea residue produced in the tea production process is considerable,and the utilization rate is limited,which is not conducive to the advancement of agricultural green development.The resource utilization path of the tea residue needs to be explored urgently.In recent years,biochar has received much attention in soil carbon sequestration and soil aggregate structure improvement,but the conclusions obtained are different.Biochar materials and test soil types are important factors that lead to differences in research results.In this study,tea residue was made into biochar at 500 °C.In an attempt to solve the problem of resource utilization of tea residue,tea residue biochar was added to three types of tea garden soils,namely purple soil,paddy soil,and yellow soil,at a mass ratio of 0%,0.5%,1%,2%,and 4%.A 112-day indoor culture simulation experiments was carried out to clarify the effect of tea residue biochar on tea garden soil quality,reveal its effects on tea soil soil organic carbon composition,mineralization characteristics,soil aggregates and organic carbon distribution,anf find the best application ratio and soil of tea residue biochar.Results show:（1）It is feasible to make tea residues as biomass raw materials to make biochar,which is beneficial to the resource utilization of tea waste.The yield of biochar produced by pyrolysis of tea residue at 500℃ for 2.5h can reach 38.19%,and the carbon content is as high as67.95%.The specific surface area and pore volume are large,and it has a highly concentrated and stable aromatic structure.（2）Tea residue biochar can increase the capacity and stability of the organic carbon pool of the three tea garden soils.Tea residue biochar can significantly increase the total organic carbon,microbial biomass carbon,water-soluble organic carbon,and easily oxidized organic carbon content of the three tea garden soils（P<0.05）,of which the yellow soil has the most obvious lifting effect.At the end of the cultivation period,the total organic carbon of purple soil,paddy soil and yellow soil was increased by 96.64%,72.36% and 321.43% compared with the respective CK treatment.The proportion of each active component in the total organic carbon of the soil decreased significantly（P<0.05）,and all showed a significant correlation with the total organic carbon of the soil.The tea residue biochar reduces the carbon pool management index of the three tea garden soils,and the carbon pool stability is improved.（3）Tea residue biochar has an effect of increasing the mineralization rate,cumulative mineralization and mineralization intensity of organic carbon in purple soil and paddy soil,and the higher the addition ratio,the greater the effect.The impact on the mineralization characteristics of yellow soil is related to the biochar addition ratio.The 0.5% addition ratio significantly reduced the mineralization rate and accumulated mineralization of yellow soil,which were decreased by 18.75%,21.88% and 22.84% respectively compared with CK treatment.The ratio increased significantly,but all biochar treatments significantly reduced the mineralization intensity of yellow soil,and the decrease was positively correlated with the addition ratio.The first-order kinetic model can well describe the mineralization process of three soils（P<0.05）.The addition of tea residue biochar can significantly weaken the carbon-fixing capacity of purple soil and paddy soil in tea gardens,and also significantly enhance the soil carbon-fixing capacity of yellow soil in tea gardens.（4）Tea residue biochar can increase the number of >0.25 mm water-stable aggregates in three tea garden soils,improve the stability of the water-stable aggregates,and the improvement effect on yellow soil is better than purple soil and paddy soil.The largest increase in the content of organic carbon in purple soil is <0.053 mm grain size,10.94%～96.35%,the paddy soil is 0.053～0.25 mm grain size,the increase range is10.45%～74.22%,and the yellow soil is >2mm grain size,from 59.06% to 334.79%,the increase in the organic carbon content of aggregates in yellow soil at all levels is greater than that of purple soil and paddy soil.The influence of tea residue biochar on the organic carbon contribution rate of aggregates at all levels in the three tea garden soils is different,but the relative contribution rate of 0.25～2mm granular organic carbon is the highest in all three soils.In summary,tea residue can be used as biomass raw materials to make biochar to solve the problem of resource utilization of tea residue.Tea residue biochar can significantly increase the organic carbon content,the soil carbon storage capacity and stability,the number of large and medium soil aggregates,and improve the stability of soil water-stable aggregates and content of organic carbon in aggregates by fractions in the three tea garden soils.However,the addition of tea residue biochar to purple soil and paddy soil in various proportions promotes the mineralization of total organic carbon and accelerates the decomposition of organic carbon,adding 0.5% by mass to yellow soil inhibits the mineralization of soil organic carbon.Therefore,considering the three aspects of soil organic carbon capacity improvement,storage,and soil aggregate structure improvement,the yellow soil of the tea garden is considered to be the priority soil for tea residue biochar,and 0.5% is the best addition rate.