Nitrous oxide emissions from soils amended with polyphenols and cowpea residues

Abstract

Polyphenols can influence the rate of N2O emission and N mineralization in leguminous crop residues by affecting the activities of residue decomposers or by forming protein complexes. A laboratory microcosm incubation study was conducted to assess the effect of three concentrations of ferulic, vanillic and tannic acids on N2O emissions and inorganic N dynamics in a tropical soil amended with cowpea residue. The results show that N2O emission and mineral N concentrations in the sole cowpea amended soils were significantly higher than in all the polyphenol treatments. Decrease in N2O emissions and N concentrations showed a direct relation with the polyphenol concentrations. However, at the same concentration, the polyphenols did not differ significantly in their ability to decrease N2O emissions and N concentrations even though tannic acid showed the highest numerical decrease. The tannic acid lowered N mineralization and N2O production through protein binding while ferulic and vanillic acids decreased N2O production through N immobilization by stimulating microbial activity. It is concluded that the addition of polyphenols to tropical soils amended with cowpea residue is likely to lower N2O emissions and inorganic N concentration, but the magnitude of reduction will depend on the type and concentration of the polyphenol compounds added