Finding a baseline for methane emissions in rice

The trial is being conducted at the Rice Research Australia Pty Ltd site at Coree, near Jerilderie, which involves 12 bays, four each of aerial sown, drill sown, and drill sown with delayed permanent water.

The main variety was V071, with a small amount of Viand resown because of duck damage in the aerial bays.

Jae Moore-Lambert who manages the trial site said methane, nitrous oxide and carbon dioxide are measured through an automated chamber in the middle of each bay connected to a monitoring trailer.

"Each chamber is closed for roughly an hour and takes four samples from each chamber every 15 minutes, plus calibrations in the middle," he said.

"Then it will open and close for the next four."

Mr Moore-Lambert said by taking the four samples over the hour an actual figure of whether there was significant gas emissions being emitted from the crop could be calculated by detecting the increase in concentration of the gas in the air samples.

Deakin University Associate Professor Wendy Quayle said the trial had so far shown a strong relationship between greenhouse gas mitigation and the number of ponded water days.

The aerial sown rice has been inundated for about 135 days, the drill sown for about 91 days and the drill sown with delayed water for about 69 days.

"The amount of methane from the aerial sown crop is significantly higher than the other two treatments," she said.

"Drilling crops causes an 86 per cent mitigation of methane compared with the aerial sown crops and if you go to delayed permanent water we've only got four pc of the methane that is in the aerial sown crops.

"We've got about five tonnes of carbon equivalent so far from aerial sown crop, a tonne from the drill sown and about half a tonne from the delayed permanent water."

Prof Quayle said if the industry was looking to reduce emissions and move towards net zero then moving from an aerial sown or broadcast was a really good potential method of achieving that.

"The problem is when we move to fewer days of inundation there is a chance we can get nitrous oxide produced which is generated when there is fertiliser around and the soil conditions aren't completely saturated," she said.

"So we're also measuring nitrous oxide which has a greater global warming potential than methane.

"We found we get significant mitigation of methane and we are getting some NO2 produced but not to an extent where it's still a very good trade off in our mitigation of methane towards global warming."

While similar research had been conducted, predominately in Asia and the USA, Prof Quayle said it was important to conduct their own with growing conditions very different in Australia.

"We have relatively very high yield potential, our soils are different, we're under temperate conditions, we have advanced water management strategies and fertilisation strategies, as well as different residue management and different varieties," she said.

Prof Quayle said the research was important because rice was globally well known to be a large methane emitter.

"It's estimated that 20pc of all the greenhouse gases that are emitted from agriculture come from rice cultivation," she said.

"The primary driver of methane is water. We're always striving to try and improve our water productivity.

"We knock off two environmental targets - water use as well as methane."