Atmospheric concentrations of nitrous oxide (N 2 O) have increased in recent decades, contributing significantly to climate change. In Brazil, the agricultural sector is the main source of N 2 O emissions, and sustainable practices such as no-tillage and cover crops (CCs) have been adopted to reduce national emissions of N 2 O. Although the inclusion of CCs in no-tillage systems has been suggested as a strategy to mitigate N 2 O emissions from tropical soils, the magnitude and impacts remain uncertain and highly dependent on CCs species, residue quality, and soil–climate interactions. This study compared soil N 2 O emissions from a maize-cover crop sequence in response to nitrogen in a long-term no-tillage system in the Cerrado. The study was conducted at Embrapa Cerrados, in the Federal District, Brazil, on plots where maize with and without N side-dressing, was followed by different CCs ( Cajanus cajan , Crotalaria juncea , Raphanus sativus and Mucuna aterrima ). The experiment was arranged in a randomized complete block design with split plots and three replications. Fluxes of N 2 O were measured using the static chamber method and the N 2 O concentration was analyzed by gas chromatography. To indicate the action of nitrifying and denitrifying microorganisms, mineral-N (NH 4 + and NO 3 − ) analyses were performed. Daily N 2 O fluxes increased by 38% and 23% following N side-dressing application to maize in the first and second years, respectively. Cumulative N 2 O emissions were ≤2.98 kg ha −1 and emission factor ranged from 0.13% in Cajanus cajan to 0.49% in Mucuna aterrima . N 2 O emissions in treatments with N topdressing enhanced nitrifying activity, mediated by nitrifiers microorganisms. The succession of maize with Mucuna aterrima in the first year and Crotalaria juncea in the second year increased N 2 O emissions. In contrast, during the first year, the maize– Crotalaria juncea sequence exhibited higher nitrogen fertilizer use efficiency (NFUE) than the maize– Mucuna aterrima and maize– Raphanus sativus systems. Notably, the maize– Cajanus cajan sequence showed the lowest cumulative N 2 O emissions, indicating its superior effectiveness in mitigating N 2 O emissions. • Nitrous oxide emissions from a maize-cover crop sequence were ≤2.98 kg ha −1 . • Plots with Cajanus cajan maintained the lowest emissions in both years of the study. • Yield-scaled N 2 O emissions were unaffected by the N rate and cover crop species. • The emission factor was below the IPCC levels for all maize–cover crop sequence systems.
Carvalho et al. (Wed,) studied this question.