Cover crops play an increasingly important role in improving soil quality, reducing agricultural inputs and improving environmental sustainability. The main objectives of this critical global review and systematic analysis were to assess cover crop practices in the context of their impacts on nitrogen leaching, net greenhouse gas balances (NGHGB) and crop productivity. Only studies that investigated the impacts of cover crops and measured one or a combination of nitrogen leaching, soil organic carbon (SOC), nitrous oxide (N₂O), grain yield and nitrogen in grain of primary crop, and had a control treatment were included in the analysis. Long‐term studies were uncommon, with most data coming from studies lasting 2–3 years. The literature search resulted in 106 studies carried out at 372 sites and covering different countries, climatic zones and management. Our analysis demonstrates that cover crops significantly (p < 0.001) decreased N leaching and significantly (p < 0.001) increased SOC sequestration without having significant (p > 0.05) effects on direct N₂O emissions. Cover crops could mitigate the NGHGB by 2.06 ± 2.10 Mg CO₂‐eq ha⁻¹ year⁻¹. One of the potential disadvantages of cover crops identified was the reduction in grain yield of the primary crop by ≈4%, compared to the control treatment. This drawback could be avoided by selecting mixed cover crops with a range of legumes and non‐legumes, which increased the yield by ≈13%. These advantages of cover crops justify their widespread adoption. However, management practices in relation to cover crops will need to be adapted to specific soil, management and regional climatic conditions.

European grassland‐based livestock production systems face the challenge of producing more meat and milk to meet increasing world demands and to achieve this using fewer resources. Legumes offer great potential for achieving these objectives. They have numerous features that can act together at different stages in the soil–plant–animal–atmosphere system, and these are most effective in mixed swards with a legume proportion of 30–50%. The resulting benefits include reduced dependence on fossil energy and industrial N‐fertilizer, lower quantities of harmful emissions to the environment (greenhouse gases and nitrate), lower production costs, higher productivity and increased protein self‐sufficiency. Some legume species offer opportunities for improving animal health with less medication, due to the presence of bioactive secondary metabolites. In addition, legumes may offer an adaptation option to rising atmosphericCO₂concentrations and climate change. Legumes generate these benefits at the level of the managed land‐area unit and also at the level of the final product unit. However, legumes suffer from some limitations, and suggestions are made for future research to exploit more fully the opportunities that legumes can offer. In conclusion, the development of legume‐based grassland–livestock systems undoubtedly constitutes one of the pillars for more sustainable and competitive ruminant production systems, and it can be expected that forage legumes will become more important in the future.

• The impact of grazing on SOC is climate-dependent. • Grazing increases SOC for C4 but decreases it for C3 and C3-C4 mixed grasslands. • Grazing increases TN and BD but has no effect on soil pH.

Emissions of N ₂ O were measured from different agricultural systems in SE Scotland. N ₂ O emissions increased temporarily after fertilization of arable crops, cultivation of bare soil, ploughing up of grassland and incorporation of arable and horticultural crop residues, but the effect was short‐lived. Most of the emission occurred during the first two weeks, returning to ‘background’ levels after 30–40 days. The highest flux was from N‐rich lettuce residues, 1100 g N ₂ O‐N ha ⁻¹ being emitted over the first 14 days after incorporation by rotary tillage. The magnitude and pattern of emissions was strongly influenced by rainfall, soil mineral N, cultivation technique and C∶N ratio of the residue. Comparatively large emissions were measured after incorporation of material with low C∶N ratios. Management practices are recommended that would increase N‐use efficiency and reduce N ₂ O emissions from agricultural soils.

Open Access Under a Creative Commons license Article Accepted Date: 10 September 2014 Acknowledgements The authors would like to thank the UK Department for Environment, Food and Rural Affairs (Defra) for funding this study as an addition to the InveN2Ory project (AC0116) aimed at establishing the Global Research Alliance Modelling Platform (GRAMP). Rothamsted Research receives strategic funding from the Biotechnology and Biological Sciences Research Council (BBSRC).Peer reviewedPublisher PD