Researchers discover pastures absorb carbon dioxide

Dairy UP researchers are measuring the kilograms of greenhouse gas emitted or taken up by different pasture types and management practices to help the industry understand its baseline emissions.

University of Sydney researchers have found that 8kg of the total carbon dioxide emitted each day by the average cow was immediately taken up by a hectare of dairy pasture system.

These 8kg represent 73 per cent of the production from each cow.

These findings are part of a Dairy UP and NSW Environment Protection Authority partnership project investigating greenhouse gases on NSW dairy farms and identifying and evaluating options for carbon neutral dairy production.

Dairy UP project leader Professor Luciano Gonzalez said dairy customers and the broader community wanted dairy to have the least impact on the environment.

He said these findings were very encouraging, but needed more detailed understandings of the full benefit.

“To reduce emissions, the industry needs to accurately understand the production and removal of GHG and how different management practices and farming systems affect output and carbon sequestration,” Prof Luciano said.

“This project will help NSW dairy meet industry emissions reduction targets and also fill knowledge gaps within the industry, to enable dairy farmers to estimate their farm’s emissions with increased accuracy, while providing practical ways to decrease emissions and increase carbon uptake.”

This project is using the Australian Dairy Carbon Calculator and the Dairy Greenhouse Gas Accounting Framework and has included a global literature review — examining studies from across the world — as well as on-farm trials and monitoring studies.

Trials at the University of Sydney Camden research farm are measuring the flows of GHG from different pasture types and management practices.

The GHG are measured using eight chambers and a greenhouse gas analyser.

Their findings indicate that dairy cows emit about 11kg CO2e cow/day, mainly as methane. Of this, the early results indicate that every hectare of pasture, on average, was taking up about 8kg CO2 e cow/day from the atmosphere.

The uptake may be in additional pasture growth or sequestered in the roots and then soil.

“We want to test the idea that the 73 per cent of the carbon dioxide emitted from a cow each day is part of a carbon cycle and taken up by the pastures.”

Further evidence for the cycle comes from studies of the soil carbon.

The Dairy UP project is collecting up to 120 soil samples per farm from 10 participant farms to analyse soil organic carbon.

Prof Luciano said these data would tell dairy farmers and researchers about the “carbon capital” stored in the soil which will help establish a greenhouse gas emission baseline and provide insight into how different pastures, crops and management practices affect soil carbon.

Initial findings from the University of Sydney Camden farm showed native pasture had the highest soil organic carbon at 4.8 per cent.

This contrasts with findings from the soil and landscape grid of Australia maps which estimated the native pastures would have the lowest soil organic carbon.

“The analysis showed the lowest soil organic carbon area at the Camden property was the cropping paddocks at 1.2 per cent,” Prof Luciano said.

“The rye-grass and Kikuyu pastures sat at about three per cent soil organic carbon.”

Diets of dairy cattle have also been examined, as part of this project, to understand how this affects the production of GHG from feed.

Dairy Australia has pledged to reduce the emissions intensity of the Australian dairy industry to 30 per cent less than 2015 levels by 2030.

“These results are encouraging, but there will be more findings to come that should help us meet those goals,” Prof Gonzalez said.

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