Scientists from Australia’s Commonwealth Scientific and Industrial Research Organization have identified ways of freeing up phosphorus fertilizer, which has become tightly held in soil.
The research team estimates Australian agricultural soils might hold up to $10 billion worth of phosphorus as a result of fertilizer applications.
Alan Richardson and fellow CSIRO plant industry researcher Peter Hocking said Australia’s agriculture industry spends $600 million each year on phosphate-based fertilizers, yet often only about 10 to 20 percent of the phosphorus is directly used by plants in the year it is applied.
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“The remaining phosphorus becomes locked up in the soil,” Richardson said.
Phosphorus-based fertilizers are essential to achieve economic yields on most Australian soils.
“Our soils are generally among the most deficient in the world for the plant-available form of phosphorus,” said Richardson. “Many of our soils readily bind phosphorus when it is applied, making fertilizer applications relatively inefficient.”
Added Hocking: “We now know that phosphorus bound in the soil can be released by organic acids secreted from special roots of some plants such as white lupin. The plant secretes citric acid which separates phosphorus from clay particles or other compounds such as calcium or iron phosphate, thereby making the phosphorus available for plant uptake.”
The scientists are examining how plants such as white lupin secrete organic acids to release some of the phosphorus reserves bound in the soil.
Researchers are working to find which organic acids are most effective in releasing soil phosphorus and how acids are secreted from white lupin roots. They will also examine other plant species for organic acid secretion.
Some for others
Preliminary greenhouse results show white lupin, as well as making phosphorus available for itself, might also leave some available phosphorus behind for the next crop.
“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 Hocking.
“Field trials will be necessary to test these concepts under farming conditions,” he said.
The team has recently isolated genes that prompt increased organic acid production and secretion. This opens new opportunities, in the longer term, to genetically modify crops, such as canola or wheat, to secrete organic acids and directly access the phosphorus bank in the soil.
The CSIRO scientists with support from the International Wool Secretariat are now examining ways in which pasture plant and soil microorganisms access organic phosphorus reserves.
“We now know that soil bacteria use special enzymes to break down organic forms of phosphorus in soil and release it in a form available to plants,” said Richardson.
“We aim to better understand this process and use gene technology to isolate the enzymes and genes involved.
“In the longer term, these genes could be used to modify plant roots to provide better access to soil phosphorus,” he said.
This research might also lead to environmental benefits with farmers using less phosphorus fertilizer, resulting in farm runoff containing less phosphorus.
