Nitrogen management on the farm

NIWA scientists are testing the effectiveness of nitrous oxide inhibitor dicyandiamide (DCD) on a Methven dairy farm. The product is claimed to be able to reduce nitrate leaching, increase pasture production, as well as reduce greenhouse gas emissions.

Nitrous oxide is an unwanted by-product of pastoral agriculture. It is also a potent greenhouse gas with about 300 times the global warming potential of carbon dioxide (CO₂).

New Zealand has an unusual greenhouse gas emission profile amongst developed nations with about half of our CO₂ equivalent emissions coming from methane and nitrous oxide. Practically all of the nitrous oxide is emitted by agricultural soils and this accounts for about 16% of New Zealand’s gross emissions.

“A lot of dairy farms are intensively managed. The amount of nitrogen involved is large, when compared to sheep farming, for example. With changing land use and a greater intensity of nitrogen in the system, it seems inevitable that nitrous oxide emissions will rise,” says NIWA principal scientist, Dr Mike Harvey.

However, help is at hand and research at Lincoln University has developed a nitrification inhibitor product based on dicyandiamide (DCD). DCD is a non-toxic compound that has been shown to have multiple benefits on pasture. It reduces conversion of urea into nitrate, which in turn reduces subsequent nitrate leaching. It also gives increased efficiency from nitrogen fertiliser use, as well as lowering nitrous oxide emissions.

Over the last four years, scientists at NIWA have been working with Landcare Research and Agriculture Canada on a system that is the first of its kind in New Zealand. This system makes continuous atmospheric measurements of nitrous oxide emission rates from farmland.

It uses a laser to monitor one-hectare plots of land in a way that gives accurate total emission data. This has previously been very difficult as emissions are 'patchy'. They vary over time and are different over each part of the land which emission rates are being measured.

NIWA scientists are very excited by the capability they have developed and tested with help from dairy farmers. This system can play an important role in independently verifying the mitigation potential of greenhouse gas inhibitors like DCD.

On Craige MacKenzie’s dairy farm in Methven, the NIWA team is measuring emissions on five one-hectare-sized plots of land over a couple of months. “Each plot is grazed at a normal grazing intensity. On one of the plots dicyandiamide was applied after grazing and one plot received selective applications reducing the amount of inhibitor. This selective treatment design has been developed by Craige. “We are continuously measuring the nitrous oxide emissions from those plots,” says NIWA atmospheric scientist Dr Andrew McMillan.

“There is economic benefit to farmers from more effective use of nitrogen. There are also benefits to the country from being able to reduce our greenhouse gas emissions and this technique helps to verify those reductions,” says Dr Harvey.

This work is funded by the Ministry of Agriculture and Forestry, and the Foundation for Research Science and Technology.