Maize diversification and nitrogen fertilization effects on soil nitrous oxide emissions in irrigated mediterranean conditions

Abstract

Maize is a major irrigated crop in Mediterranean areas and its typical intensive management may impact soil nitrous oxide (N$_{2}$O) emissions. In these irrigated continuous maize systems, the legumes incorporation as well as adjusted nitrogen (N) fertilization might be interesting strategies to reduce soil N$_{2}$O emissions. The objective of this study was to assess the impact of cropping diversification and different N rates on soil N$_{2}$O emissions in flooded irrigated maize under Mediterranean conditions. To achieve this, two cropping systems (maize monoculture system, MC; and pea -maize rotation, MP) and 3N rates (unfertilized, 0N; medium rate, MN; and high rate, HN) were evaluated in a field experiment established in NE Spain during 2 years (2019; 2020). During the studied period, the N rate had a significant effect on soil N$_{2}$O emissions, with a non-linear positive response of cumulative soil N$_{2}$O emissions to N rates. In both systems, quick and high increases of soil N$_{2}$O fluxes were observed immediately after the N application reaching 55 and 100 mg N$_{2}$O-N m$^{−2}$ day$^{−1}$ in MC and MP, respectively. Both years, the pea phase of the MP rotation showed greater cumulative N2O emissions than the fallow of MC. However, N$_{2}$O losses in the maize phase were similar (2019) or even higher (2020) in MC than in MP. Moreover, in both seasons, the MN treatments showed lower yield-scaled N$_{2}$O emissions and N emission factor than the HN treatments, being this last lower than 1% in all cases. The results obtained showed that in irrigated Mediterranean conditions the replacement of a fallow by a legume, together with an adjusted N fertilization are favourable strategies to mitigate soil N$_{2}$O emissions in high-yielding maize systems