Under Mediterranean irrigated conditions cover cropping (CC) and double cropping (DC) are diversification/intensification strategies that can increase grain yield and resource use efficiency of the traditional winter fallow-maize (Zea mays L.) system. Four cropping systems were evaluated in terms of productivity, water and nitrogen use efficiency (WUE and NUE) under sprinkler-irrigated conditions during three growing seasons in the Ebro Valley, Spain: (1) long-season maize with winter fallow (F-LSM), (2) long-season maize after a leguminous cover crop (common vetch, Vicia sativa L.) (CC-LSM), (3) short-season maize after a cereal crop (barley, Hordeum vulgare L.) (B-SSM), (4) short-season maize after a leguminous crop (winter peas, Pisum sativum L.) (P-SSM). The introduction of the vetch winter cover crop required an additional 5% irrigation water but allowed to reduce the nitrogen fertilizer applied by 20%, increasing the system grain yield synthetic nitrogen use efficiency (NUEsynt-g) by 27% without affecting the cropping system grain yield and WUE. DC systems required 12% more irrigation water than the traditional F-LSM but produced more grain. The B-SSM was the most productive system (21.9 Mg grain ha-1) and increased the WUE by 32% compared to the F-LSM system, but required a 39% more nitrogen fertilizer. Compared to the traditional F-LSM system, the P-SSM cropping system increased the grain yield (+16%), protein yield (+66%), NUEsynt-g (+20%), and the WUE (+10%). The diversification and intensification of the traditional F-LSM system increased yield (with the DC systems) and resource use efficiency (WUE with the DC systems; NUE with CC-LSM and P-SSM cropping systems).