Search

In a field experiment, annual nitrous oxide (N2O) emissions and grassland yield were measured across different plant communities, comprising systematically varying combinations of monocultures and mixtures of three functional groups (FG): grasses (Lolium perenne, Phleum pratense), legumes (Trifolium pratense, Trifolium repens) and herbs (Cichorium intybus, Plantago lanceolata). Plots received 150 kg ha−1 year−1 nitrogen (N) (150 N), except L. perenne monocultures which received two N levels: 150 N and 300 N. The effect of plant diversity on N2O emissions was derived from linear combinations of species performances' in monoculture (species identity) and not from strong interactions between species in mixtures. Increasing from 150 N to 300 N in L. perenne resulted in a highly significant increase in cumulative N2O emissions from 1.39 to 3.18 kg N2O-N ha−1 year−1. Higher N2O emissions were also associated with the legume FG. Emissions intensities (yield-scaled N2O emissions) from multi-species mixture communities around the equi-proportional mixture were lowered due to interactions among species. For N2O emissions scaled by nitrogen yield in forage, the 6-species mixture was significantly lower than L. perenne at both 300 N and 150 N. In comparison to 300 N L. perenne, the same N yield or DM yield could have been produced with the equi-proportional 6-species mixture (150 N) while reducing N2O losses by 63% and 58% respectively. Compared to 150 N L. perenne, the same N yield or DM yield could have been produced with the 6-species mixture while reducing N2O losses by 41% and 24% respectively. Overall, this study found that multi-species grasslands can potentially reduce both N2O emissions and emissions intensities, contributing to the sustainability of grassland production.

As part of its international obligations, Ireland faces emission reduction targets with respect to greenhouse gases (GHG). These reduction targets are to be achieved both in the short term and over the coming decades. Agriculture is a substantial source (33%) of Ireland’s GHG emissions. Whereas the economic welfare of farmers has been the dominant force in shaping agriculture policy for several decades, there has been a notable increase in environmental concerns and a gradual emergence of environmental policies which are relevant to agriculture, particularly in the last 10 years. The future evolution of the agri-food sector in Ireland must therefore be seen in the context of both the economic growth objectives of national agricultural policy, as well as national environmental policy objectives arising from international obligations. In light of the recent proposals with respect to the EU Common Agricultural Policy (CAP) post-2020 (EC, 2018), environmental objectives will become an increasingly important subset of the CAP objectives and the implementation of the CAP in Ireland. The EU Effort Sharing Decision (ESD) requires that Ireland reduce its non-ETS GHG emission by 20% by 2020 relative to the 2005 level. The reduction target for the non-ETS sector for 2030 is 30%, but incorporates so called flexibility mechanisms designed to make the achievement of this target less onerous. A partial equilibrium model of Irish agriculture is used to explore differing future outcomes in terms of the sector’s size and associated GHG emissions to 2030. The scenario analysis employed demonstrates the implications of different future pathways for bovine (dairy and beef) agriculture, the dominant sector in Irish agriculture and the principal source of its GHG emissions. Mitigation actions are then factored in to provide measures of future levels of emissions inclusive of this mitigation capacity. While technical mitigation actions are largely grounded in interventions that are based on science, the scenario analysis makes clear that the scale of the ultimate challenge in mitigating agricultural GHG emissions will be determined by the overall size of the agriculture sector and the intensity of production per hectare. The dairy and beef sectors in Ireland are noteworthy for their contrasting levels of profitability; dependence on support payments; and farm income. Now that the EU milk quota has been eliminated, from the perspective of economic development, an increase in the size of the dairy sector and entry into the dairy sector are desirable economic policy objectives. However, the paper demonstrates the strong contrast between dairy and beef farms, not just in terms of income but also in terms of intensity of production per hectare and the associated level of emissions produced. It follows that a transition from beef production to dairy production, while desirable from the point of view of farm income, could have adverse consequences for emissions.

Over the last century an increase in mean soil surface temperature has been observed, and it is predicted to increase further in the future. In order to evaluate the legacy effects of increased temperature on both nitrogen (N) transformation rates in the soil and nitrous oxide (N2O) emissions, an incubation experiment and modelling approaches were combined. Based on previous observations that gross N transformations in soils are affected by long-term elevated-temperature treatments we hypothesized that any associated effects on gaseous N emissions (e.g. N2O) can be confirmed by a change in the relative emission rates from various pathways. Soils were taken from a long-term in situ warming experiment on temperate permanent grassland. In this experiment the soil temperature was elevated by 0 (control), 1, 2 or 3 °C (four replicates per treatment) using IR (infrared) lamps over a period of 6 years. The soil was subsequently incubated under common conditions (20 °C and 50 % humidity) and labelled as NO315NH4 Gly, 15NO3NH4 Gly or NO3NH4 15N-Gly. Soil extractions and N2O emissions were analysed using a 15N tracing model and source-partitioning model. Both total inorganic N (NO3− + NH4+) and NO3− contents were higher in soil subjected to the +2 and +3 °C temperature elevations (pre- and post-incubation). Analyses of N transformations using a 15N tracing model showed that, following incubation, gross organic (but not inorganic) N transformation rates decreased in response to the prior soil warming treatment. This was also reflected in reduced N2O emissions associated with organic N oxidation and denitrification. Furthermore, a newly developed source-partitioning model showed the importance of oxidation of organic N as a source of N2O. In conclusion, long-term soil warming can cause a legacy effect which diminishes organic N turnover and the release of N2O from organic N and denitrification.