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Under Mediterranean rainfed areas, no-till cereal-based systems have been adopted to cope with water availability and increasing input costs. However, the increased risk of biotic stresses, high N-fertilizer dependence, and current EU policies warrant cropping systems re-design. Evaluate diversification and N fertilization as strategies to improve N use efficiency at the cropping system level and quantify its productivity. Four crop sequences combined with four levels of N fertilization were assessed in a three-year field experiment in semiarid rainfed north-eastern Spain. Crop sequences were continuous winter wheat (WCS) and three-year diversified rotations with pea (PCS), faba bean (FCS), or a multi-service cover crop (MSCS) and two years of cereals. Crop, pre-crop and cropping system levels were considered. Agronomic evaluation included crops above-ground biological N fixation (Ndfa), net N balance (Ndfa minus N removed by grain), soil N mineralisation productivity, energy to N tradeoff (ENT), and N use efficiency of protein (NUEp) production. Pea yields ranged from 0 to 766 kg ha−1 and Ndfa from 24% to 54%. Faba bean yield ranged from 1378 to 4251 kg ha−1 and Ndfa from 32% to 72%. Net N balance was close to neutral for pea while in faba bean it ranged from 41 to −21 kg N ha−1. Alternative pre-crops led to greater soil N mineralisation (51 kg N ha−1, on average) and higher wheat yield (564 kg ha−1, on average) compared to wheat as the pre-crop. N fertilization increased protein yields, with FCS presenting the highest yields at all N fertilizer rates. This effect led to a stable NUEp (1.69 kg protein kg N supply−1), as the protein yield increased proportionally to N supply. Diversification improved the succeeding wheat performance and grain legumes N fixation exceeded grain N removal. Introducing legumes into cropping systems led to a decrease in energy productivity compared to the cereal-based system. However, protein production in the FCS was higher than in any other cropping system regardless of the N fertilizer rate. Crop diversification adds challenges and risks in dry Mediterranean areas. However, the study shows that crop diversification with faba bean can decrease cropping system's N-fertilizer dependence and increase protein productivity, contributing to cropping systems' sustainability. • Effect of crop diversification and N fertilization to support N efficient cropping systems. • Multiscale assessment including crop, pre-crop and the cropping system level. • Pea and faba bean supported cropping systems N use efficiency through biological N fixation. • Faba bean cropping system showed the greatest protein yields regardless of the N fertilizer rate. [ABSTRACT FROM AUTHOR]

Over the last decades, non-cereal crops have been displaced in European cropping systems leading to a significant 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 Mediterranean 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. • Four cropping systems were assessed at the crop, pre-crop and cropping system level. • Soybean introduction in single cropping systems did not increase protein yield. • Soybean pre-crop effect increased the following cereal yields by 28%. • Barley-soybean double cropping increased protein yield at the cropping system level. • Synthetic N use efficiency was highest in barley soybean double cropping system. [ABSTRACT FROM AUTHOR]

Mediterranean cropping systems, characterised by continuous cereal cropping, are largely dependent on synthetic inputs, such as N fertilisers. On the other hand, they face difficult pedoclimatic conditions, exacerbated by climate change. Diversification is seen as a way to increase cropping systems resilience. The aim of this study was to co-design diversified cropping systems based on the expertise of local stakeholders and co-assess their performance, using modelling data. Our case study is the Ebro valley in Spain, a Mediterranean area with great potential for diversification, particularly where irrigation is available. Two workshops were organized to i) define the reference system in the study area and its limitations ii) co-design diversified systems to overcome these limitations and iii) co-assess reference and diversified systems. Between the two workshops, the STICS soil-crop model was calibrated with local experimental data, enabling to simulate the inter-annual (2000–2021) agronomic and environmental performance of the reference and diversified systems. An economic analysis was conducted. Stakeholders evaluated all economic, agronomic and environmental aspects. The reference system was a continuous winter cereal crop based on synthetic N fertilisation and intensive tillage. The four diversified co-designed systems consisted in introducing pea and/or rapeseed every 2 or 4 years, reducing tillage and partially replacing synthetic N fertilisation with locally sourced livestock manure. Simulation results showed that wheat and barley grain yields remained stable with diversification. Pea and rapeseed yields were lower in rotations where both were introduced compared to when each was the only break crop over 4 years. At the system level, protein yield remained stable with diversification, however, energy yield decreased by 20 % when break crops were introduced twice and by 10 % when introduced once. Gross margins improved with diversification only when pea was introduced once (12 %), mainly due to reduced expenses (-31 %), while incomes remained stable compared to RCS. However, incomes decreased by 5 % when rapeseed was introduced once, and by 10 % when both break crops were introduced. Unexpectedly, environmental performance deteriorated with diversification, with increased N losses through ammonia volatilisation and nitrate leaching in the years following pea and rapeseed cropping, due to greater N availability in the soil. An increased use of pesticides was predicted by the stakeholders in diversified systems, where the environmental impacts were exacerbated with the higher presence of break crops. The reference system presented slightly lower N availability and increased soil organic carbon storage. Overall, the approach proved useful in identifying a diversification strategy that improved agronomic and economic performance, with the system including pea once every four years being the most efficient. However, the environmental trade-offs associated with the increased presence of pea and rapeseed in the crop rotation must be considered in order to mitigate the environmental risks. • Participatory workshops and modelling were combined to assess diversification. • Introducing pea and rapeseed maintain protein yield but decreased energy yield. • Continuous cereal was the most efficient in raising long-term soil organic carbon. • Gross margin increased only when introducing pea once in a 4-year rotation (+12 %). • Diversified cropping systems increased N availability and risk of losses. [ABSTRACT FROM AUTHOR]