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Research Needed into Nitrate Inhibitors

A significant body of research now underway could answer questions about the use of nitrate inhibitors to manage nitrate leaching losses and greenhouse gas emissions from farming, soil scientist Dr Dough Edmeades told this week’s Environment Waikato Environment Committee meeting.

Dr Edmeades, of AgKnowledge, said combined losses of various forms of nitrate to the environment were large, representing a significant loss in economic efficiency as well as affecting groundwater quality and greenhouse gas emissions. About 30-40 percent of total nitrogen going into pastoral systems was being lost, at a cost of about $60 million in the Waikato Region alone.

Greenhouse gas emissions from nitrogen loss represented about two million tonnes in the Waikato each year – 15 percent of the national total.

Nitrate inhibitors restricted the microbial conversion of ammonium to nitrate and nitrous oxide gas and much research had gone into identifying nitrate and urease inhibitors. They were not biocides so did not kill bugs, were not known to be toxic, acted on specific enzymes and were biodegradable.

“There is a huge amount of scientific literature on these chemicals. Most is on the effects when used with fertiliser and manures on arable farming.”

They could reduce nitrate leaching and greenhouse gas and ammonia emissions, increasing nitrogen efficiency. However there had been variable results. Their effectiveness depended on soil temperature, pH, moisture and organic matter content, and the size of the effect depended on soil nitrogen states, leaching and the degree of water logging.

Dr Edmeades said the New Zealand effects on pasture were unique, as the urine patch from grazing animals was the primary source for nitrogen losses, rather than fertiliser nitrogen. Research in New Zealand was limited, with most on small plots, and while some very large beneficial effects had been reported, subsequent results were less encouraging.

No New Zealand trials had examined the effectiveness of the chemicals on a large scale and on paddocks covered with a mosaic of urine patches. More investigations under New Zealand climate and soil conditions were needed, he said.

One short-term trial had been done in the Waikato where very large effects were reported, but it was difficult to extrapolate the results so that the concept could be proven at a larger scale.
Future research was essential to quantify the costs and benefits across the whole range of soil and climatic factors which influenced their effectiveness.

“I am very positive about this work and I say, bring on the research. If we do not conquer it, this problem of nitrogen loss to the environment is a lid on our agricultural production and there is a significant body of research underway which may or may not answer these questions.”

Cr Jenni Vernon said she supported the research into nitrate inhibitors and was keen to see new technology provide benefits for agriculture as well as the environment.

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