'Greener' pastures could help farms slash emissions

Using an alternative plant type like plantain (pictured) in grazed pasture could help cut nitrous oxide emissions from soils. Photo / File

Shifting to "greener" pastures could help our farms slash their greenhouse gas emissions.

Findings of a new Kiwi study suggest using an alternative plant type, like plantain, in grazed pasture could help cut nitrous oxide emissions from soils.

The AgResearch study set out to compare emissions of the potent greenhouse gas, nitrous oxide, from soils containing different types of forage – perennial ryegrass, white clover, plantain and lucerne - over different seasons at a Waikato dairy farm.

Agricultural soils, and the urine deposited by grazing animals, are the main source of nitrous oxide emissions globally and are a major contributor to greenhouse gas emissions resulting from human influence.

"A significant finding from this study was that in autumn and winter, nitrous oxide emissions were 39 to 74 per cent less where plantain was planted, compared to perennial ryegrass," senior scientist Dr Jiafa Luo said.

"Lucerne also saw lower emissions compared to the ryegrass in winter and autumn, but smaller reductions than in the case of the plantain.

"In summer, we found emissions from the plantain and lucerne were actually higher than the ryegrass, which is something that needs to be explored further."

Previous studies had shown plantain can reduce the amount of nitrogen excreted in the animals' urine.

But in this latest study, the same urine type - from animals fed ryegrass and white clover - was applied to all of the plant types tested.

"So other factors may be involved, and one may be that plantain releases biological nitrification inhibitors into the soil which reduce the nitrous oxide emissions," Luo said.

"What this research tells us is that incorporating plantain into grazed pastures could be an approach to reducing emissions.

"However, we do need to do further work to examine the process by which the emissions are reduced, and how this is impacted by different conditions across the different seasons."

What to do about about agricultural greenhouse gas emissions - making up about half of our inventory - has long been a headache for New Zealand and its efforts to combat climate change.

Much of those emissions can be put down to methane belched from ruminant livestock like sheep and cows.

At nearly six times the global average, New Zealand now has the highest methane emission rate in the world.

The new AgResearch study was funded by the New Zealand Agricultural Greenhouse Gas Research Centre, which has been at forefront of efforts to tackle the problem, and whose work has helped produce hundreds of rumen microbial genomes for scientists to study.