Future food needs new underground strategy

A greater focus on roots during plant breeding could ensure staple grain crops continue to feed the world as recycled nutrients substitute conventional fertilisers in the future, a University of Queensland study has found.

The project at the School of Agriculture and Food Sustainability compared how modern varieties of sorghum and traditional or landrace sorghums accessed and used phosphorus from conventional and recycled sources. 

Dr Michael Walsh said nutrients retrieved from waste streams offer opportunities for more efficient, cleaner and cost-effective fertilisers but they need to be able to nourish crops. 

“Growing the sorghum plants in laboratory conditions revealed some stark differences,” Dr Walsh said.

“The traditional sorghum outperformed the plants from a modern breeding program when they were given less soluble and recycled phosphorus – they took up more of this vital nutrient and grew bigger.

“A key difference was in their root exudates, the organic chemicals their roots released into the soil to interact with nutrients. 

“We analysed over 20,000 root-generated chemicals to identify exudates that acted like pickaxes, unlocking phosphorus so that the crop could grow. 

“Years of breeding crops in the presence of easily accessible fertilisers has created high yielding crops for modern farms, but they can be ‘lazy’ underground. 

“As soon as the phosphorus was less soluble and harder to access in our experiments, the modern sorghum was outgrown by the traditional sorghums which had adapted to grow in environments with less available nutrients.”

Phosphorus is a key ingredient in modern agricultural fertilisers and most comes from mined deposits.

Honorary Professor Susanne Schmidt said recycled nutrients will become very important in the future.

“Mined and refined phosphorus is a non-renewable resource, and it is subject to price volatility and supply chain interruptions as only few nations possess deposits,” she said.

“A circular nutrient economy will be the way to a sustainable food future. That means reclaiming agricultural inputs like phosphorus from wastes, including livestock manure and human effluent, and unavoidable food waste.

“This study has shown traditional sorghum was more efficient at drawing phosphorus from the soil, so these landraces are a great source of information.

“Breeding crops with a view of their root exudates could improve phosphorus use efficiency and ensure agriculture is ready for reclaimed nutrients.” 

Having completed the research as proof-of-principle, the team is keen to field test sorghums and other grain crops. 

The research paper is published in Sustainable Agriculture.

Collaboration and acknowledgements