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 and Ndfa from 24% to 54%. Faba bean yield ranged from 1378 to 4251 kg ha 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. Alternative pre-crops led to greater soil N mineralisation (51 kg N ha, on average) and higher wheat yield (564 kg ha, 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), 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.

中文翻译：

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蚕豆的引入使得蛋白质生产减少了对地中海免耕系统中氮肥的依赖

在地中海雨养地区，采用免耕谷物系统来应对水资源供应和不断增加的投入成本。然而，生物胁迫风险的增加、氮肥的高度依赖以及欧盟当前的政策需要重新设计耕作系统。评估多样化和氮肥施肥作为提高种植系统水平氮肥利用效率并量化其生产力的策略。在西班牙东北部半干旱雨养地区进行的为期三年的田间试验中，评估了四种作物序列与四种施氮水平的结合。作物序列为连续冬小麦（WCS）和三年多样化轮作，包括豌豆（PCS）、蚕豆（FCS）或多用途覆盖作物（MSCS）和两年谷物。考虑了作物、作物前和作物系统水平。农艺评价包括作物地上生物固氮（Ndfa）、净氮平衡（Ndfa减去谷物去除的氮）、土壤氮矿化生产力、能量与氮的权衡（ENT）和蛋白质生产的氮利用效率（NUEp）。豌豆产量为 0 至 766 千克公顷，Ndfa 产量为 24% 至 54%。蚕豆产量为 1378 至 4251 公斤公顷，Ndfa 产量为 32% 至 72%。豌豆的净氮平衡接近中性，而蚕豆的净氮平衡范围为 41 至 -21 千克氮/公顷。与预作小麦相比，替代预作作物带来了更高的土壤氮矿化（平均 51 千克氮·公顷）和更高的小麦产量（平均 564 千克公顷）。施氮肥提高了蛋白质产量，FCS 在所有施氮量下产量最高。这种效应导致了稳定的 NUEp（1.69 kg 蛋白质 kg N 供应），因为蛋白质产量与 N 供应量成比例增加。多样化提高了小麦的后续性能，豆类谷物的氮固定量超过了谷物的氮去除量。与以谷物为主的系统相比，将豆类引入种植系统会导致能源生产率下降。然而，无论氮肥施用量如何，FCS 中的蛋白质产量都高于任何其他种植系统。作物多样化增加了地中海干旱地区的挑战和风险。然而，研究表明，蚕豆作物多样化可以减少种植系统对氮肥的依赖，提高蛋白质生产力，有助于种​​植系统的可持续性。