Trade-off between C and N recycling and N2O emissions of soils with summer cover crops in subtropical agrosystems

Abstract

The use of summer cover crops (SCCs) as residue inputs in agricultural systems can lead to a potential environmental trade-off between the amount C and N retained and the emission of N as the potent greenhouse gas, nitrous oxide (N2O). Our objectives were to relate N2O fluxes to the quality of SCCs residues and to select SCCs species with high C and N addition and low N2O emissions. We measured SCC biomass production and N2O fluxes after SCCs termination – velvet bean, pearl millet, dwarf pigeonpea, sunn hemp, showy rattlebox and jack bean - under subtropical no-till conditions. The N2O fluxes in the first 30 days after SCCs termination corresponded to 65% of cumulative N2O emissions measured during 165 days in 2010 and 150 days in 2011. The cumulative N2O emissions varied from 0.46 to 1.38 kg N ha-1 and were not proportional to aboveground biomass N addition. Cumulative N2O emissions were positively correlated to water-soluble C and N and the N content of crop residues and negatively correlated to cellulose and hemicellulose content. The N2O emission factor values varied from 0.24 to 0.64% and did not differ among SCCs. Sunn hemp and dwarf pigeonpea are the most suitable species for inclusion in crop systems because they combined high C and N input and low N2O emissions.