Making the most of phosphate

Crops need to improve efficient take-up of this vital but diminishing element. Elizabeth Finkel reports.

Granules of a fertiliser containing potassium and phosphorus. – Getty/Science Photo Library

The big black letters, “NPK”, on any bag of fertiliser stand for three things plants just cannot do without: nitrogen, phosphorus and potassium. Nitrogen we take from the air. Potassium reserves in rocks should last for centuries. But phosphorus, also largely mined, is another matter. By some projections, mines could run out by the end of the century.

What makes the problem worse is that modern crop plants are wasteful in their use of phosphate, absorbing only a fraction of what they are given. So a major goal in plant breeding is to create more phosphorus-efficient crops.

That requires some nifty plant engineering – precisely the mission of La Trobe’s Jim Whelan and the multi-nodal team he is part of at the Australian Research Centre of Excellence known as “Plant Energy Biology”. A starting point is the genes of phosphate-efficient rice varieties donated by his Chinese collaborators at Zhejiang University near Shanghai. Whelan probes the plants’ response to starvation: which genes do they activate; what chemicals do they produce? “It helps me understand what they sense, what they think.”

Reverse engineering the system this way reveals which genes are likely to be helpful. For instance, some “starvation-sensing” genes send a plant into fatal shock. “We might just need to tell the plant not to worry about low phosphate,” says Whelan. “Even if we can get a 10% increase in phosphate efficiency, the savings will be enormous.” Australian farmers, whose old soils are particularly deficient, now spend A$2 billion a year on phosphate – about 2% of the world market.

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