Direct losses of nitrous oxide from N fertilisers are relatively small. In grazed pastures, urine patches are the main contributor to these emissions, Lincoln University's Professor Hong Di told the New Zealand Agricultural Greenhouse Gas Research Centre's recent conference.
Di is a Professor of Soil and Environmental Science and had worked closely with Professor Keith Cameron of Lincoln University on nitrification inhibitor technology, marketed by Ravensdown as ‘eco-n'.
His theme in a short speaking slot was manipulating nitrification processes to reduce N2O emissions in winter forage systems. A large number of cows lumped tightly together on wet, possibly pugged soil brings together all the ingredients for high N2O emissions, he said.
Trampling of a cow's hoof can make the soil less aerated and more favourable to the production of N2O, he told the conference, adding that at Lincoln, a robotic hoof had been used to simulate the repetitive action of an adult Friesian cow in winter.
In a comparison of trampled pasture with soil not trampled, emission levels more than doubled on the trampled soil.
Urine and a nitrification inhibitor (DCD treatments had been applied to both areas in mid June, the results measured using lysimeters and gas chambers.
The DCD significantly reduced total nitrate leaching by about 66%, and reduced N2O emissions by 58-63% in both areas.
In response to a question, Di said the highest level of recorded N2O reductions by DCD was about 82%.
It is not clear why a 100% reduction hadn't been achieved but he noted an 82% reduction in emissions was ‘spectacular' and hoped this would help NZ to reduce its agricultural greenhouse gas emissions. Further research is underway to improve our knowledge and the performance of DCD.
A delegate also asked about possibilities of DCD doing harm in human food chain. Comprehensive toxicology reports from New Zealand and overseas had cleared it of these possible effects in its use in New Zealand, Di said.
He later told The New Zealand Farmers Weekly that while urine patches on pugged winter soil was strongly linked to high levels of nitrate leaching and nitrous oxide emissions, it did not over-ride the benefits of New Zealand's pastoral farming system. Nor was the solution as simple as just housing cows, or putting them on stand-off pads, as this could create other complications, he said.