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Most Nitrogen Lost from Grassland Not a Climate Concern

08 December 2015

IRELAND - Newly published research into soil processes discovers that over half the nitrogen applied to grazed grassland soils in temperate regions was lost as environmentally benign di-nitrogen (N2) gas.

The research, published in the Nature Scientific Reports Journal, was led by Teagasc’s Environment, Soils and Land Use Research Department at Johnstown Castle in collaboration with partners in Northern Ireland (Agri-Food and Biosciences Institute) and New Zealand (Lincoln University and AgResearch).

Grazed grasslands are common agricultural systems in temperate climatic countries due to the long growing season more suited to grass growth.

Grazing is associated with low nitrogen use efficiency, which means that, typically, only 15 to 30 per cent of the nitrogen applied is captured in farm produce. The remainder of the nitrogen is either stored in the soil, or lost to water or the atmosphere. Of particular concern is the loss of nitrous oxide (N2O), which is a powerful greenhouse gas that is responsible for approximately a third of greenhouse gas emissions in Ireland, where Teagasc is based.

Research to date has focused on the loss of nitrogen gases that are directly detrimental to our health, the climate and the environment.

Losses of di-nitrogen (N2), which comprises 78 per cent of the air we breathe, are still poorly understood, due to difficulties in measuring them and the complexities of the processes involved. That means that – thus far – our scientific understanding of both nitrogen losses and greenhouse gas emissions from agriculture has been incomplete.

This collaborative cutting edge research has now completed the jigsaw, by using advanced isotopic methods to measure these benign di-nitrogen (N2) emissions from grazed grassland soils.

These were found to account for 57 per cent of the nitrogen applied in the form of cow urine to soil. The source of these benign emissions is a little known process called co-denitrification which has been seldom studied. By contrast, emissions of the potent greenhouse gas nitrous oxide (N2O), accounted for merely 0.7 per cent of the applied nitrogen.

Dr Karl Richards, Principal Investigator on the research project said: “This discovery suggests that our grassland soils are able to convert a large part of the nitrogen losses into benign di-nitrogen (N2) gas.

However, we have to keep in mind that this nitrogen loss, while not environmentally damaging, it still represents a significant economic loss of nitrogen to the farmer. Further research is required to see if this soil process can be manipulated to increase nitrogen use efficiency in grazed grasslands.”

According to Dr Gary Lanigan, coordinator of the Irish Agricultural Greenhouse Gas Network: “If we can understand the process further then manipulation of co-denitrification in soil may be a feasible option for reducing greenhouse gas emissions from grazed grasslands.

"This underlines the advances by the Irish agricultural greenhouse gas network in finding solutions for low carbon-agriculture, as highlighted at the COP21 in Paris this week.”

Further Reading

You can view the full report by clicking here.

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