[Effects of Straw Returning and Biochar Addition on Greenhouse Gas Emissions from High Nitrate Nitrogen Soil After...

In rice-vegetable rotation systems in tropical areas, a large amount of nitrate nitrogen accumulates after fertilization in the melon and vegetable season, which leads to the leaching of nitrate nitrogen and a large amount of N₂O emission after the seasonal flooding of rice, which leads to nitrogen loss and intensification of the greenhouse effect. How to improve the utilization rate of nitrate nitrogen and reduce N₂O emissions has become an urgent problem to be solved. Six treatments were set up [200 mg·kg^-1 KNO₃ (CK); 200 mg·kg^-1 KNO₃ + 2% biochar addition (B); 200 mg·kg^-1 KNO₃+1% peanut straw addition (P); 200 mg·kg^-1 KNO₃ + 2% biochar + 1% peanut straw addition (P+B); 200 mg·kg^-1 KNO₃ + 1% rice straw addition (R); 200 mg·kg^-1 KNO₃ + 2% biochar+1% rice straw addition (R+B)] and cultured at 25℃ for 114 d to explore the effects of organic material addition on greenhouse gas emissions and nitrogen use after flooding in high nitrate nitrogen soil. The results showed that compared with that in CK, adding straw or combining straw with biochar significantly increased soil pH (P<0.05). The B and P treatments significantly increased the cumulative N₂O emissions by 41.6% and 28.5% (P<0.05), and the P+B, R, and R+B treatments significantly decreased the cumulative N₂O emissions by 14.1%, 24.7%, and 36.7% (P<0.05), respectively. The addition of straw increased the net warming potential of greenhouse gases (NGWP). The addition of coir biochar significantly reduced the effect of straw on NGWP (P<0.05). The combined application of straw and biochar decreased NGWP, and P+B significantly decreased NGWP, but that with R+B was not significant (P>0.05). Adding straw or biochar significantly increased soil microbial biomass carbon (MBC) (P<0.05), and that of P+B was the highest (502.26 mg·kg^-1). The combined application of straw and biochar increased soil microbial biomass nitrogen (MBN), and that of P+B was the highest. The N₂O emission flux was negatively correlated with pH (P<0.01) and positively correlated with NH₄⁺-N and NO₃^--N (P<0.01). The cumulative emission of N₂O was negatively correlated with MBN (P<0.05). There was a significant negative correlation between NO₃^--N and MBN (P<0.01), indicating that the reduction in NO₃^--N was likely to be held by microorganisms, and the increase in the microbial hold of NO₃^--N also reduced N₂O emission. In conclusion, the combined application of peanut straw and coconut shell biochar could significantly inhibit N₂O emission and increase soil MBC and MBN, which is a reasonable measure to make full use of nitrogen fertilizer, reduce nitrogen loss, and slow down N₂O emission after the season of Hainan vegetables.