Controlling nitrous oxide emissions from grassland livestock production systems

There is growing awareness that grassland livestock production systems are major sources of nitrous oxide (N2O). Controlling these emissions requires a thorough understanding of all sources and controlling factors at the farm level. This paper examines the various controlling factors and proposes farm management measures to decrease N2O emissions from intensively managed grassland livestock farming systems. Two types of regulating mechanisms of N2O emissions can be distinguished, i.e. environmental regulators and farm management regulators. Both types of regulators may influence the number and size of N2O sources, and the timing of the emissions. At the field and farm scales, two clusters of environmental regulating factors have been identified, i.e. soil and climate, and three levels of management regulators, i.e. strategic, tactical and operational. Though the understanding of these controls is still incomplete, the available information suggests that there is large scope for diminishing N2O emissions at the farm scale, using strategies that have been identified already. For example, model calculations indicate that it may be possible to decrease total N2O emissions from intensively managed dairy farms in The Netherlands in the short term from a mean of about 19 to about 13 kg N per ha per year by more effective nutrient management, whilst maintaining productivity. There is scope for a further reduction to a level of about 6 kg N per ha per year. Advisory tools for controlling N2O emissions have to be developed for all three management levels, i.e. strategic, tactical and operational, to be able to effectively implement emission reduction options and strategies in practice. Some strategies and best management practices to decrease N2O emissions from grassland livestock farming systems are suggested.