Effects of Biochar Application on Soil Nitrogen Conversion and Microbial Community Composition

Abstract In northeastern China, successive years of cultivation have led to a decline in soil quality, a process that is exacerbated by the over-application of chemical fertilizers to ensure staple food production. The large amount of straw produced by cultivation is difficult to effectively use in recent years. There has been an increasing amount of research on the transforming straw into biomass char, but it has often focused on the effects of biomass char addition on soil physicochemical properties, without further exploring the mechanisms of this process and its effects on soil microorganisms. Microorganisms are an important part of the soil system and the process of how biomass char addition affects microorganisms through its effect on soil physicochemical properties should not be overlooked. In this study， the effect of biochar application at different preparation temperatures (300°C, 400°C and 500°C) and addition contents (0.1% and 1%) on ammonia, nitrate and total nitrogen in soil leachates were investigated. The effect of microbial sequencing on the dynamics of carbon and nitrogen was also investigated to reveal the mechanisms contributing to the changes in nitrogen forms. The results showed that biochar had a better adsorption ability on ammonia nitrogen, and biochar promoted the conversion of ammonia nitrogen to nitrate nitrogen by nitrifying bacteria. The addition of 1% biochar (prepared at 500°C) increased nitrate-nitrogen leaching by 86.52% compared to the control treatment. The sequencing of microorganisms also revealed that biochar changed the structure and abundance of the soil microbial community, especially increasing the relative abundance of the Helicobacter nitrification phylum by 2.02%. These results indicates that biochar facilitated the adsorption of ammonium nitrogen and the conversion of nitrate nitrogen, and solving the problem of low nitrogen fertilizer utilization while promoting the formation of beneficial bacteria in the soil.