The use of double-cropping in combination with no-tillage and optimized nitrogen fertilization improve crop yield and water use efficiency under irrigated conditions

Maize is one of the main irrigated crops in northern Spain. However, the traditional cropping system used for its cultivation has relied on intensive monoculture, demanding significant inputs, and resulting in occasional unprofitable yields. A promising practice to increase the sustainability of farms is the use of double-cropping systems. The aim of this study was to evaluate the combined impact of introducing a legume prior to maize, together with different tillage systems and mineral N fertilization rates on crop yields and water productivity under Mediterranean irrigation conditions. The study compared monocropping maize (MC) versus legume-maize double cropping (DC) with three tillage systems (conventional tillage, CT; minimum tillage, MT; no-tillage, NT), and three mineral N fertilization rates (zero, medium and high). The legumes employed were pea for grain (2019), vetch for green manure (2020), and vetch for forage (2021). The highest yields were found in DC. On the one hand, the benefits associated with legume cropping allowed for increased grain yield of DC maize; on the other hand, the combined biomass of the legume plus maize led the DC systems to achieve significantly higher total biomass (sum of grain and stover) than the MC systems. In addition, a better adaptation of the maize DC phenological cycle to environmental conditions favoured higher yields in this system. Higher water consumptions in DC systems resulted in lower yield water use efficiency (WUEy). However, when only irrigation water was taken into account, DC was the system with the highest irrigation water use efficiency for yield (IWUy). Similarly, the high biomass values generated in the DC system resulted in higher water use efficiency for biomass (WUEb). The tillage system with the highest yields was NT. These results, together with a higher water retention capacity in NT made the water productivity (WUEb, WUEy and IWUy) of these systems higher. The use of high N fertilizer rates did not show any yield or WUE advantage over the medium rate. The results of this study indicate that in Mediterranean agroecosystems, the use of legume-maize double cropping systems together with NT systems and reduction of N fertilization can be a good strategy to maintain crop yields, while saving N fertilizer, and to improve WUEb and IWUEy.