Synergistically Mitigating Nitric Oxide Emission by Co-Applications of Biochar and Nitrification Inhibitor in a Tropical Vegetable Soil

Abstract

Vegetable soils are the hotspots of nitric oxide (NO) emissions from agro-ecosystems due to intensive management. Biochar application has been recommended as an important countermeasure, however, its mitigation efficiency is limited as biochar largely stimulates soil nitrification. Therefore, co-applied with nitrification inhibitor could maximize the mitigation potential of biochar. Herein, an incubation experiment was conducted to investigate the effects of biochar and nitrification inhibitor applied alone or in combination on NO fluxes, mineral nitrogen intensity and the populations of nitrifiers and denitrifiers in a typical tropical soil under intensive vegetable cultivation. Results showed that biochar or nitrification inhibitor alone significantly decreased NO emissions by 41.6% and 43.5%, respectively, and their co-applications decreased it by up to 68.5%. Soil NO 2 − −N intensity, along with gene abundances of AOB- amoA and nirK were significantly and positively correlated with cumulative NO emissions. Nitrification inhibitor weakened the stimulating effects of biochar on AOB- amoA and total comammox- amoA gene abundances, as well as NO 3 − −N intensity, thus weakening nitrification-driven NO production. Biochar increased qnorB abundance in soils following nitrification inhibitor addition, thereby promoting NO consumption during denitrification. Moreover, biochar or nitrification inhibitor alone decreased nirK gene abundance and NO 2 − −N intensity and these reductions become greater with their co-applications. The present study highlights that co-applications of biochar and nitrification inhibitor can achieve a higher potential to decrease NO emissions from vegetable soil, which should be further verified in the field considering the complex environment conditions in tropical regions.