The link between lower nitrate in waterways and reduced losses of it as nitrous oxide to the atmosphere can be strongly influenced by some farm management decisions, Waikato University freshwater scientist Professor Troy Baisden said.
Linking greenhouse gas and freshwater policies is timely and more closely integrating them could help farmers work towards achieving the new regulatory demands quicker and more seamlessly.
Nitrogen from livestock converts to nitrate in soils that can enter waterways through leaching and to nitrous oxide gas released into the atmosphere.
Nitrous oxide represents about 20% of all farm gas emissions with methane making up the rest. But its global warming potential is significantly greater than methane.
While methane has a global warming potential of 28-36 times more than carbon dioxide on a 100-year time-scale, nitrous oxide has a warming potential of 265-300 times carbon dioxide.
It also lasts far longer with a life in the atmosphere of about 110 years compared to methane’s 15 years.
“Except for destocking, progress on methane requires a very big silver bullet that can be developed only by big, government-funded science.
“In contrast, nitrous oxide can be dealt with at a farm management level now.”
But nitrous oxide is invisible and expensive to measure. Yet most of the solutions are very similar to what farmers will be considering to reduce nitrate leaching.
Traditionally, reducing nitrate losses means lower stocking rates, less bought-in feed and lower nitrogen fertiliser application.
But emerging solutions include alternative feeds such as plantain or diverse pastures and rethinking practices when paddocks are wet.
“The wins come from limiting the extent of excess nitrogen, mainly from urine patches, in very wet soils.
“It’s the amount of demand beyond what plant and soil can take up that matters so small reductions or changes in timing can make a big difference.”
Better nitrate management will deliver a win-win-win in terms of keeping nitrates in the soil rather than waterways, improved production and lower gas losses from farms.
But Baisden is concerned much of New Zealand’s modelling on nitrates and nitrous oxide gas has been done in isolation.
“There are people running nitrous oxide models nationally that should also be including nitrate leaching too but I don’t see that happening. The challenge is how do we get the two connected?”
Past reports trying to link the two have also involved complete land use change as a solution when farmers are instead looking at how they can farm better to achieve the reductions.
“My feeling is past work hasn’t looked in detail at what innovative mitigation on-farm may evolve. The researchers asked regional councils, not farmers, what to model.
“Farmers risk being left to sort through an accumulation of information and risk facing people who are basically trying to sell them snake oil to solve the problems – farmers will demand a better job from universities and researchers to sort through the sales pitches.”
This is going to also involve some sort of validation of technology claiming to help farmers.
“What farmers can do is consider how they can reduce these nitrogen losses as part of farm environment plans.”
It might also help to start talking about how that creates value, either through production gains or using less fertiliser or by feeding into ways to get a certification label for environmental performance that adds value to products.
He believes Overseer might better set up to estimate gases than water quality parameters.
“The greenhouse gases are driven by farm-scale data such as cow numbers, all scaled up to a national inventory.
“However, it is harder to put in individual on-farm mitigation inputs and calculate how much we reduce nitrates by doing so.”
He hopes the top 20% of farmers who understand how to get farm environment plans in place and to optimise them will help lead the rest of the sector.
“Researchers and academics like myself will contribute but the solutions have to come from farmers at a farm level.”
Pastoral Greenhouse Gas Research Consortium general manager Mark Aspin said research on nitrates and nitrous oxide relationships is thin on the ground but is an area demanding greater attention.
“By reducing nitrate losses in soils you have the potential to reduce nitrous oxide.
“But with nitrous oxide it is only lost under certain conditions, such as fully waterlogged soils, colder conditions and off urine spots after heavy rain.
“Generally, the losses are greatest over autumn-winter and more the further south you go.”
