• Energy Research

Agricultural activities are important sources of nitrous oxide (N2O), methane (CH4) and carbon dioxide (CO2). They contribute approximately 10% of the total emitted greenhouse gases (GhG) in the European Union. We search for evaluating GhG emissions at the farm level and designing mitigation options. As emissions occur at many stages within the farm operation, it is crucial to consider nutrient cycling and farm working. Our proposal comprises three characteristics: an integrated farm approach which combines empirical and mechanistic modelling through describing C and N fluxes through two coupled models of land use: a farmers’ practices description; and system boundaries limited to the farm gate, but including also pre- and post-chain effects. We used a case study located in semi-continental conditions (Mirecourt – North-Eastern France). The simulated farming system is a mixed dairy and crops system so as to account for a rather generic farming system.

SummaryRecent reviews confirm and extend previous observations that elevated carbon dioxide (CO2) concentrations stimulate photosynthesis, leading to increased plant productivity. Elevated CO2concentrations tend to reduce the sensitivity of grassland ecosystems to low levels of precipitation but induce progressive nitrogen (N) limitations on plant growth which can be alleviated by supplying a significant external input of N in the form of mineral fertilizer or through the increased use of N‐fixing legumes. Other nutrients, such as phosphorus, can act as the main limiting factor restricting the growth response in legumes to atmospheric CO2concentration. The botanical composition of temperate grasslands is affected by the rise in atmospheric CO2concentration, possibly through a decline in the relative abundance of grasses. Elevated CO2concentration will also alter the feeding value of herbage to grazers both in terms of fine‐scale (for example, crude protein concentration and C:N ratio) and coarse‐scale (legumes vs. grasses and C3‐ vs. C4‐species) changes. The management guidelines of grasslands will need to be adapted to global atmospheric and climatic changes and to increased variability in climate.

Abstract In Europe, grassland is one of the dominant forms of land use. Within 20 years, the area of permanent grasslands and pastures in Western Europe has declined by 12%. Semi-natural grasslands are often hot spots of biodiversity and are threatened both by intensive farming and by the abandonment of farmland in marginal areas. In this review, we show that biodiversity, climate change, C sequestration and farming systems issues are highly interconnected in grassland ecosystems. In this context, there are new risks (induced by climate change), new opportunities (linked to carbon sequestration and biodiversity conservation for example) and new challenges (concerning farm management and agricultural practices) for managed grasslands. An assessment of the current research perspectives underlines some key questions: (i) How to reduce the sensitivity and increase the resilience of grassland biodiversity to heat waves and droughts in an altered climate? (ii) How to protect soil organic carbon stocks under global warming? (iii) How to preserve the habitat for rare or endangered species, while managing the functional diversity of the vegetation for agricultural purposes? (iv) How to maintain the heterogeneity and diversity of grassland vegetation at the farm and landscape levels? (v) How to design innovative farming systems that integrate the impacts of farm activity on biodiversity, water and air quality, fossil energy use and greenhouse gas effect? (vi) How to produce integrated knowledge taking account of the consistency of the different management practices and their feasibility at farm level according to four criteria (profitability, labour, agricultural and environmental performance)?

European grassland-based livestock production systems are challenged to produce more milk and meat to meet increasing world demand and to achieve this by using fewer resources. Legumes offer great potential for coping with such requests. 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 abundance of 30-50%. The resulting benefits are a reduced dependency 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 bioactive secondary metabolites. In addition, legumes may offer an option for adapting to higher atmospheric CO2 concentrations and to climate change. Legumes generate these benefits at the level of themanaged 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 in order 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 only be expected that legumes will become more important in the future. Opening sessionOpening session

Les questions sur la stabilité du climat, au-delà de sa variabilité que l’on pourrait qualifier de naturelle, ne datent pas d’aujourd’hui, et les progrès des sciences ont permis progressivement d’en reconstituer l’histoire, marquée par des fluctuations de grande ampleur (Acot, 2004). Pour en rester à l’épisode le plus récent (l’Holocène) qui a suivi la dernière grande glaciation, il s’est traduit par un retour à des conditions moins froides, en gros supérieures de 4 à 5° C en température moyenne globale, qui sont restées globalement stables (dans une fourchette de 1° à 2° C) depuis environ 12 000 ans, et ceci malgré des fluctuations locales assez rapides (jusqu’à 10° C en une centaine d’années, découverte récente à partir d’analyses de sédiments) ou des variations plus globales correspondant, de manière schématique et pour l’Europe, aux périodes de l’optimum médiéval du Xe au XIIIe siècle ou du petit âge glaciaire allant du XIVe au XVIIIe, bien mises en évidence par les historiens, à partir de l’analyse des séries historiques d’avancée des glaciers ou de dates de vendange (Le Roy Ladurie, 1983). Dans les années 1970, le climat apparaissait globalement stable, à condition que l’on élimine les fluctuations inter-annuelles par la prise en compte d’une durée minimale de 30 années, suivant les normes fixées par l’Organisation météorologique mondiale (OMM). Et les projections futures pariaient sur un retour inéluctable à des conditions glaciaires… dans 10 000 ou 20 000 ans. C’est alors que sont apparues les interrogations sur l’accroissement de l’effet de serre par l’action de l’homme et ses conséquences sur un réchauffement du climat, du coup tout aussi inéluctable, avec des ordres de grandeur de la même ampleur (de l’ordre de 4 à 5° C), mais cette fois à l’échéance du siècle à venir.

AbstractA potential strategy for mitigating nitrous oxide (N2O) emissions from permanent grasslands is the partial substitution of fertilizer nitrogen (Nfert) with symbiotically fixed nitrogen (Nsymb) from legumes. The input of Nsymb reduces the energy costs of producing fertilizer and provides a supply of nitrogen (N) for plants that is more synchronous to plant demand than occasional fertilizer applications. Legumes have been promoted as a potential N2O mitigation strategy for grasslands, but evidence to support their efficacy is limited, partly due to the difficulty in conducting experiments across the large range of potential combinations of legume proportions and fertilizer N inputs. These experimental constraints can be overcome by biogeochemical models that can vary legume‐fertilizer combinations and subsequently aid the design of targeted experiments. Using two variants each of two biogeochemical models (APSIM and DayCent), we tested the N2O mitigation potential and productivity of full factorial combinations of legume proportions and fertilizer rates for five temperate grassland sites across the globe. Both models showed that replacing fertilizer with legumes reduced N2O emissions without reducing productivity across a broad range of legume‐fertilizer combinations. Although the models were consistent with the relative changes of N2O emissions compared to the baseline scenario (200 kg N ha−1 yr−1; no legumes), they predicted different levels of absolute N2O emissions and thus also of absolute N2O emission reductions; both were greater in DayCent than in APSIM. We recommend confirming these results with experimental studies assessing the effect of clover proportions in the range 30–50% and ≤150 kg N ha−1 yr−1 input as these were identified as best‐bet climate smart agricultural practices.