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

background: and aimsthe 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. methods: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. results: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. conclusion:ssunn 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.