Trade-off between C and N recycling and N2O emissions of soils with summer cover crops in subtropical agrosystems
2018
Weiler, Douglas Adams | Giacomini, Sandro José | Recous, Sylvie | Bastos, Leonardo Mendes | Pilecco, Getúlio Elias | Dietrich, Guilherme | Aita, Celso
BACKGROUND AND AIMS: 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. 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. CONCLUSIONS: 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.
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