DPIRD Grains Industry Day drills into crop emissions

In a Department of Primary Industries and Regional Development (DPIRD) trial at Xantippe looking at nitrogen for very early sown canola, it was discovered that while increasing rates of nitrogen fertiliser, particularly urea, led to increased yield, it also caused an increase in emissions from the crop.

That increase ranged from 0.4 tonnes of carbon dioxide equivalent per hectare at 65 kilograms of urea, up to 1.4t/ha of CO2 equivalent at 390kg.

The findings were presented at last week's DPIRD Grains Industry Day, held at Optus Stadium, by Jackie Bucat, who is part of the team looking into agricultural emissions.

"No one is saying to stop applying fertiliser, but there are ways of reducing the amount we use without affecting the profitability and productivity of the farming operations," Ms Bucat said.

"If growers start counting and measuring their emissions, they will be best placed to look at opportunities to evaluate different mechanisms to reduce emission at no loss to profit."

According to Ms Bucat, there are benefits in measuring emissions for farm businesses, in large part because of the market signals hinting at premiums for low emission or carbon neutral grain.

There is also an expectation that as suppliers and business partners work through trying to manage their risk of exposure to climate change, they will want a carbon account from the farmers they work with.

"Emissions from agriculture are more difficult to abate - we don't have solar cows or wind grown crops and those sorts of renewable technologies are available to other industries," Ms Bucat said.

"But it doesn't really matter that it's not fair because at the end of the day, we still have to do our bit to save the world."

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It's important to note that not all gases are the same and the warming potential of the various onfarm gases varies.

Carbon dioxide is the biggest greenhouse gas and is the standard for measurement, but 1t of methane has the same warming as 28t of CO2 and 1t of nitrous oxide (fertiliser) is equivalent to 285t of CO2 .

In the agricultural sector, enteric fermentation, meaning it happens in the intestines of animals, dominates emissions.

Whereas for broadacre, agricultural soils, liming and fertiliser application are the big contributors.

In WA, where evapotranspiration is at least 80 per cent of rainfall, there are a lot less emissions from agricultural soils.

That is mainly in the lower rainfall zones as there is reduced nitrification and denitrification, no leaching or runoff and lower volatilisation.

Whereas in the high rainfall zones, the emissions are far greater.

"When it comes to nitrification and denitrification, nitrous oxide is either a byproduct of one or an intermediary of the other and it oozes from the system to accumulate in the atmosphere," Ms Bucat said.

"All nitrogen fertilisers are similar for nitrification and denitrification, volatilisation and leaching, however urea has an additional area of loss.

"Carbon dioxide is absorbed when urea is formed, so when it is used that carbon dioxide is released which gives it a higher carbon footprint than the other nitrogen fertilisers."

Overall, for every 1t of urea there is 4.5t of carbon dioxide equivalent produced.

That does not mean growers should stop using urea, but anything they can do to reduce volatilisation and leaching, or better match urea application to crop growth, would be a benefit to overall emissions reduction.

"If we want to reduce emissions, we need to reduce nitrogen and the best way to do that is by having a better match to the actual need of the crop," Ms Bucat said.

"That includes variable rate applications, timing to crop demand and using more legume and pasture crops in the rotation."

For growers wanting to measure their emissions, DPIRD suggests using the Greenhouse Accounting Frameworks for Australian Primary Industries toll created by the Primary Industries Climate Challenges Centre.