Nitrous oxide emissions – can they be abated by forages in ruminant agricultural systems?

Abstract

Nitrous oxide (N2O) emissions account for approximately 10% of global greenhouse gas emissions, with about 90% of these emissions derived from agricultural practices. In New Zealand, the single largest source (60%) of agricultural N2O is animal excreta (urine and dung) deposited during grazing while nitrogen fertiliser use currently directly contributes only 2.7% of agricultural emissions. Currently available options to reduce N2O emissions (e.g., dietary interventions or using enhanced fertilisers), are more suited to more-intensive animal production while fewer options are available for more extensive grazing systems. The aim here is to examine possible forage solutions that might reduce N2O emissions from grazed pasture systems. Plant-based options that could lead  to reduced N2O emissions include using plants with
chemistry that divert excess nitrogen into faeces rather than urine and/or by influencing soil N transformation
processes. Faeces degrade more slowly than urine and as a result the slow mineralisation of organic N results through a slow supply of ammonium results in a reduced rate of N2O emissions. The challenge will be to improve the agronomic characteristics of these plants which currently limits their usefulness. This could be approached through plant breeding and/or use of forb-based pastures. This thought piece on how New Zealand grassland farmers can reduce N2O emissions
without having to disrupt current management systems will seek to identify practical opportunities.