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Over the last decades, non-cereal crops have been displaced in European cropping systems leading to a signif-icant dependency on imported soybean. Continuous maize cropping under Mediterranean irrigated conditions can lead to agronomic and environmental problems. The objective of this work was to assess diversified Medi-terranean irrigated cropping systems to maximize protein production while reducing synthetic N fertilizer use. A field experiment was carried out from 2019 to 2021 in an irrigated area in NE Spain. Four cropping systems, (i) continuous maize (MM), (ii) soybean in a rotation one out of three years (MSrt), (iii) barley-maize double cropping system (BM), and (iv) barley-soybean double cropping system (BS) were assessed at the crop, pre-crop and cropping system level. Productivity in terms of grain, energy and protein yield was measured at the crop and calculated for the cropping system level. As well, synthetic N fertilizer use efficiency was calculated for each cropping system. At the pre-crop level, soybean introduction led to a 28% yield increase in the following cereal (maize or barley) mainly due to the residual N effect. At the cropping system level, soybean in rotation (MSrt) did not lead to a significant increase in total protein production compared to MM (from 895 to 947 kg ha-1 yr- 1), but it mildly increased synthetic N fertilizer use efficiency. Protein production in the BS system (1778 kg protein ha-1 yr- 1) was significantly higher than in all other cropping systems (990 kg protein ha-1 yr- 1 on average). As well, BS was the cropping system with the highest synthetic N fertilizer use efficiency compared to the other cropping systems (251 and 88 kg grain kg synthetic N fertilizer-1). Our results demonstrate that introducing soybean as a double crop following barley is a successful strategy to reduce environmental impacts resulting from N fertilizer use and increase protein production, contributing to plant protein self-sufficiency and cropping systems diversification.