Phosphorus mines underfoot by Guy Cotsell

A $10 Billion Lock-Up: The exciting possibility of using a legume, like white lupin, to free up soil phosphorus for a following cereal crop.

Farmers who fertilise to build up the phosphorus bank in their soil may be reaping only a fraction of the potential benefit.

"The rural industry spends $600 million each year on phosphate-based fertilisers, yet often only about 10 to 20 per cent of the phosphorus is directly used by plants in the year it is applied," said CSIRO Plant Industry researcher Alan Richardson.

This is because phosphorus is the hardest of the major nutrients for plants to get out of the soil: much of what is applied remains more or less permanently locked up.

CSIRO researchers estimate that Australian agricultural soils may be holding up to $10 billion worth of phosphorus as a result of past fertiliser applications. This 'bank' of soil P will have increasing value as world resources of rock phosphate become depleted and the cost of P fertiliser increases.

Fellow researcher Peter Hocking said the phosphorus bound in the soil could be released by organic acids secreted by the roots of some plants such as white lupin.

The CSIRO team is examining how plants such as white lupin secrete the acids, and whether other plants can do the same.

"We are looking at the exciting possibility of using a legume, like white lupin, in crop rotations, not only to produce grain and fix nitrogen, but also to free up some of the soil phosphorus for a following cereal crop," said Dr Hocking.

Next, wheat and canola?

The CSIRO team has recently isolated genes that prompt organic acid production in roots. This opens new opportunities, in the long term, to genetically modify crops such as canola or wheat to secrete organic acids and gain direct access to the phosphorus bank in the soil.

If the research allows farmers to use less phosphorus, the environment could benefit from a reduction of phosphorus in farm run-off.

Growers and researchers at a GRDC-sponsored phosphorus workshop in Adelaide last February discussed this and other approaches, and urged a high degree of farmer participation in experiments expected to follow the early research.

Program 2.2.1 Contact: Dr Peter Hocking 02 6246 5049