N2O emission mitigation and microbial activity after Biochar and Cao application in a flooded nitrate-rich vegetable soil

Abstract

ABSTRACTAdding easily decomposable organic materials into flooded nitrate-rich soils can effectively decrease the soil nitrate concentration and repair nitrate-rich soil. However, nitrate reduction is usually accompanied with an increase in N2O emission. This study was conducted to reduce N2O emission in a nitrate-rich vegetable soil flooded for remediation and amended with biochar. Nitrate-rich vegetable soil was placed in five treatment groups: flooding (F); flooding with rice straw (F + RS); flooding with rice straw and 1% biochar (F + RS + 1% biochar); flooding with rice straw and 3% biochar (F + RS + 3% biochar); flooding with rice straw and CaO (F + RS + CaO). Biochar and CaO reduced the N2O emission levels relative to the F + RS group, with the former being more effective than the latter, achieving reduction of 40.70% (3% biochar) and 17.35% (CaO) of cumulative N2O emission. The 3% biochar was more effective than the 1% biochar. Regression analysis showed a positive correlation between the abundance of NO reductase gene (norB) and soil N2O emission flux. In general, biochar and CaO could effectively reduce N2O emissions from a nitrate-rich vegetable soil during flooding remediation, duo to elevating soil pH and altering denitrifying activity. The norB gene was the most important denitrifying gene driving soil N2O emission in the remediation.