Modern crops may be high performers above ground, but underground they are losing their edge. That gap could become critical as agriculture shifts towards recycled nutrients.
For the seed sector, the signal is clear. Traditional sorghum lines outperform modern varieties when phosphorus is harder to access, pointing to root traits and exudate chemistry as underused breeding targets for nutrient-use efficiency in a circular fertiliser system.
A University of Queensland study published in npj Sustainable Agriculture found that a stronger focus on roots in plant breeding could help staple grain crops remain productive as recycled nutrients begin to replace conventional fertilisers.
The School of Agriculture and Food Sustainability project compared how modern sorghum varieties and traditional landrace sorghums accessed and used phosphorus from conventional and recycled sources, according to a press release.
Dr. Michael Walsh said nutrients recovered from waste streams could offer a cleaner, more efficient and cost-effective fertiliser option, but only if crops can use them effectively.
“Growing the sorghum plants in laboratory conditions revealed some stark differences,” 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.”
Walsh said that a key difference was in their root exudates, the organic chemicals their roots released into the soil to interact with nutrients.
“We analyzed over 20,000 root-generated chemicals to identify exudates that acted like pickaxes, unlocking phosphorus so that the crop could grow, he said.
“Years of breeding crops in the presence of easily accessible fertilizers has created high-yielding crops for modern farms, but they can be ‘lazy’ underground.”
Walsh said 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 an essential component of modern agricultural fertilisers, with most supplies sourced from mined reserves.
Honorary Professor Susanne Schmidt said recycled nutrient sources are expected to play an increasingly important role 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.
Schmidt said 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.”
With the proof-of-principle research complete, the team is now looking to move into field trials with sorghum and other grain crops.
