Rice study could save farmers billions

Breeding rice plants that retain more phosphorus in the straw, which is returned to the soil after harvest, could reduce the use of phosphorus fertiliser and save farmers billions of dollars, according to Southern Cross University (SCU) researcher Dr Terry Rose.

Dr Rose, a research fellow with the university’s Southern Cross Plant Science and Southern Cross GeoScience research centres, is part of an international consortium that has received around $750,000 over three years to investigate the prospect of breeding rice varieties with reduced phosphorus content in the grain.

“About $11 billion worth of phosphorus is taken off rice farms in harvested grain around the world every year,” Dr Rose said.

“We are aiming to reduce the amount of phosphorus in rice grain by about 20%, which could save billions of dollars worldwide. In some countries, farmers don’t have the money to maintain soil fertility by applying fertiliser, so as phosphorus is exported from their farms in harvested grain, crop yields decline and their livelihood suffers.

“In Australia, our farmers maintain soil fertility through fertiliser application, but that comes at a cost to the farmer which will likely rise over the years.”

The idea is to breed varieties of rice so that the majority of the phosphorous is retained in the leaf and stem of the rice plant, which is left in the ground after harvest and could return the phosphorus to the soil as it breaks down.

“At present, over two million tonnes of phosphorus (equivalent to around 22 million tonnes of superphosphate) is removed from rice fields across the globe in rice grains at harvest time,” Dr Rose said.

“A small proportion of this phosphorus is returned to the soil but most ends up in either landfill or waterways via sewage pathways. Over 70% of phosphorus taken up by rice plants from the soil ends up in the grains at harvest and only the remaining 30% in the straw and roots is returned to the soil.

“In addition, 70-80% of phosphorus in cereal grains is stored as phytic acid, which is considered to be an antinutrient because it cannot be digested by humans (or other non-ruminant livestock) and binds cations such as calcium, zinc and iron - hence, these nutrients are not digested by humans either.

“The project will look to minimise the amount of phosphorus transferred to the grains at maturity, resulting in more phosphorus being returned to the soil in residues and lower levels of the antinutrient in the grains.”

The implications for Australian cereal farmers, particularly wheat producers, could be massive. Last year over 60,000 tonnes of phosphorus ($300 million worth of phosphorus fertiliser at the current price) was removed from paddocks in wheat grain harvested across the country, most of which will be exported overseas.

“Given that phosphorus fertiliser prices are likely to continue to increase, retaining phosphorus in wheat straw to be returned to the soil may be a sound strategy for minimising input costs,” Dr Rose said.

Dr Rose and SCU will work with researchers from AfricaRice, the Japan International Research Center for Agricultural Science and the International Rice Research Institute (IRRI) located in the Philippines. The project is funded by the Global Rice Science Partnership (GRiSP).