Tillage and nitrogen fertilization in irrigated maize: key practices to reduce soil CO2 and CH4 emissions

Abstract In newly irrigated Mediterranean agroecosystems, the combined effect of tillage and N fertilization on soil carbon dioxide (CO 2 ) and methane (CH 4 ) fluxes is at present poorly understood. The goal of this study was to quantify both soil CO 2 and CH 4 emissions as well as crop performance under different tillage systems and N fertilization rates during three maize ( Zea mays L.) growing seasons (2015–2017) in a semiarid area converted to irrigated. Three types of tillage (conventional tillage, CT, reduced tillage, RT, and no-tillage, NT) and three mineral N fertilization rates (0, 200, and 400 kg N ha −1 ) were compared in a randomized block design with three replications. Weekly soil CO 2 and CH 4 emissions, soil temperature and gravimetric moisture were measured. Moreover, maize above-ground biomass, grain yield, and above-ground C-inputs were quantified. Carbon dioxide emissions ranged from 173 to 4378 mg CO 2 -C m -2 d -1 . No-tillage showed a greater mean soil CO 2 flux than CT when applying the highest rate of N (400 kg N ha -1 ). Although some emissions of CH 4 were observed, all treatments acted as net CH 4 sinks during most of the experimental period. A linear multiple relationship between soil CO 2 fluxes and soil gravimetric moisture (0–5 cm depth) and temperature (10 cm depth) were found. In the 2015 growing season, greater cumulative CO 2 emissions were found under NT and RT compared with CT, while in 2016 N T showed the highest values compared to CT with intermediate values in RT. Differently, in 2017 no differences between tillage systems were found. When applying N fertilizer, NT and RT increased maize grain production and above-ground C-inputs compared to CT, since a severe soil crusting occurred in this last, which caused crop water deficit. The results suggest that tillage intensity and N fertilization rate reduction can increase maize biomass production and yield which leads to greater C-input that returns to the soil.