The use of double-cropping in combination with no-tillage and optimized nitrogen fertilization reduces soil NO emissions under irrigation.

The irrigation systems of the Ebro valley can lead to high NO emissions. The effects that crop diversification, such as double-cropping in combination with conservation tillage and different N fertilizer ratios, has on soil NO emissions have not been extensively studied in this region. The goal of this research was to measure NO soil emissions and determine the tillage practices and N fertilization rates that provide the lowest emissions when combined with double-cropping systems. The work compared monocropping maize (MC) versus legume-maize double-cropping (DC) with two tillage systems (conventional tillage, CT; and no-tillage, NT), and three mineral N fertilization rates (zero, medium and high). Pea for grain (2019), vetch for green manure (2020), and vetch for forage (2021) were the legumes employed. The NO emissions ranged from 0 to 15.5 mg NO-N m d and were concentrated in the fertilization periods. Soil temperature and water filled pore space (WFPS) content significantly influenced soil NO emissions. For both cropping systems, the conditions with the highest NO emissions were soil temperatures above 20 °C and a WFPS of 50-60 %. The use of legumes facilitated reduced N fertilization in DC without affecting crop yield and led to reduced NO emissions in this cropping system. DC reduced the emission factor (EF), which in all cases was lower than the default IPCC EF (1 %). With DC, a medium N fertilization rate produced similar yields to the high rate commonly applied by farmers, and also entailed lower NO emissions. The no-tillage system, although producing higher levels of NO, achieved lower yield-scaled NO emissions due to greater crop yields. This work underlines the advantages of using double-cropping no-tillage systems combined with medium rates of N fertilization to reduce soil NO emissions.