Mitigation strategies for greenhouse gas emissions from animal production systems: synergy between measuring and modelling at different scales

Animal production systems are large and complex sources of greenhouse gases (GHG), especially nitrous oxide (N2O) and methane (CH4). Emissions from these systems are expected to rise over the coming decades due to the increasing global population and shifting diets, unless appropriate mitigation strategies are implemented. In this paper, we argue that the main constraints for such implementation are: (i) the complex and often poorly understood controls of GHG sources in animal production systems; (ii) the lack of knowledge on the economic and social costs involved in implementing mitigation strategies; and (iii) the strong political emphasis on mitigating nitrate leaching and ammonia volatilisation, rather than GHG emissions. We further argue that overcoming these three constraints can only be achieved by initiating integrated mitigation strategies, based on modelling and experimental work at three scales. At the `laboratory and field scale¿, basic causal relationships with respect to processes of GHG formation and other detrimental fluxes need to be experimentally established and modelled. As management options are considered at the `farm scale¿, this is the ideal scale to evaluate the cost-effectiveness, feasibility and possible pollution swapping effects of mitigation measures. Finally, at the `national and supra-national scales¿, environmental legislation is implemented, effectiveness of environmental policies and emissions abatement measures are being monitored, and the social costs of various scenarios are being weighed. We illustrate the need for integral measures and working across different scales using our own work on the relationship between nitrogen surplus and fluxes to the environment. At the field scale, a clear positive relation between nitrogen surplus and N2O emission, NO3¿ leaching and NH3 volatilisation was experimentally established. At the farm scale, the model DAIRYWISE was used to evaluate effects of minimising nitrogen surplus on the nutrient flow and economic viability of an average Dutch dairy farm. Even after including trade-off effects of CH4 emissions from cattle and manure storage, there was still a clear positive relationship between farm gate nitrogen surplus and GHG emission. At this scale, the prime issue was balancing environmental gains with economic viability. Finally, at the `national and supra-national scale¿ we developed the MITERRA-EUROPE model, and used it to quantify the effects on GHG emissions of environmental policies aimed at reducing NO3¿ leaching and NH3 volatilisation in the 27 Member States of the European Union (EU-27). This showed the intricate relationship between different environmental goals, with both positive feedback (balanced fertilisation reduced both NO3¿ leaching and N2O emission) and negative feedback (`low-emission¿ manure application reduced NH3 volatilisation but increased N2O emission) possible. At this scale, there is a clear need for an integral approach towards reducing environmental assessment to the environment. Our studies so far suggest that `balanced fertilisation¿ is among the most promising mitigation measures for simultaneously lowering N2O emission, NO3¿ leaching and NH3 volatilisation, without pollution swapping to CH4 emissio