Working out how to extract an element from human waste in order to recycle it back into agricultural crops may not be everyone’s idea of fun, but when Professor Terry Rose starts talking about the phosphorus cycle, he lights up.
A scientist who specialises in sustainable cropping systems, Professor Rose is also a lecturer in the new Regenerative Agriculture specialisation within the Bachelor of Science at Southern Cross University. His research is primarily undertaken on farms in conjunction with farmers (and groups of farmers).
Phosphorus is one of Professor Rose’s key interests as it is necessary for flourishing crops, thus vitally important in terms of Australia’s food security. The mineral is mostly imported in the form of rock phosphate, before being converted into superphosphate or more soluble fertilisers, which crops can more easily absorb. These fertilisers are applied to soils for broadacre crop production (e.g. wheat, canola and rice) where the phosphorus is taken up by the plant, and most of it is transported to the grain or seed, depleting phosphorus levels in our agricultural soils. These grains, oilseeds and pulses are consumed, mostly within our large cities and population centres, or are exported overseas.
Once this produce is consumed most phosphorus is passed into the waste processing system resulting in its loss within the sewage treatment system or through dumping in landfill, with limited amounts returned to agricultural soils. It’s an unsustainable system.
“The world’s phosphorus resources are mostly located in Morocco and China. Australian rock phosphate deposits are less than 1% of the world’s reserves,” said Professor Rose.
“Our phosphorus security therefore relies on being able to access rock phosphate from foreign sources.
“If at any stage there were issues with getting these fertilisers into the country, we’re pretty exposed. We would find our crop yields over time would diminish and agriculture would suffer as a consequence. If we could make that system more robust there would be benefits for both farmers and the environment.”
Recycling bio solids (formally known as sewage sludge) and finding ways of treating this human waste so it can be reapplied to the land, such as using thermal treatment approaches, or extracting the phosphorus before the waste goes into landfill; are all avenues being explored to make the phosphorous cycle more sustainable.
“We’re looking at something called struvite, which is magnesium ammonium phosphate precipitated out of waste waters, to see if we can reuse that as a fertiliser source to replace these rock phosphate-based fertilisers. Because at some point in the future we’re going to run out of rock phosphate, it’s a finite resource. You can mine it for a while, for a few centuries, but at some point, we’re either going to run out or it’s going to be very expensive to obtain. Either way it’s not a great system,” said Professor Rose.
“We’ve also been doing research over the past decade, trying to look to whether we can actually breed crops where less phosphorus goes into the grain, so we don’t take it all off the field every year. Even in organic or regenerative systems, you keep taking it off the field, so at some point it needs to be replaced.
“We think there should be ways that the plant can take up enough phosphorus to yield high amounts of nutritious produce without moving most of the plant’s phosphorus into grains. We think we can minimise that.”
In Western Australia where some soils are particularly impoverished and low in phosphorous, whole ecosystems have developed and some plants have adapted to live without as much available phosphorus.
“For example, Banksias make cluster roots, or proteoid roots, and they can mine phosphorus from the soil. They basically acidify the soil around the roots and strip the phosphorus from these little clusters. The Australian macadamia does the same thing, so another area of research we are doing is looking at macadamias to try and work out how these roots function,” said Professor Rose.
“Plants have also evolved in impoverished soils to form symbioses with different types of fungi, the most widely known are called Arbuscular Mycorrhizal fungi or AM fungi. The fungi links into the plant’s roots and taps into its carbohydrate supply, the plant photosynthesises and then feeds the fungus. In return the fungus makes hyphae which it sends out into the soil to take up phosphorus and a few other nutrients and brings them back to the plant, so they have this little trade.
“Last year we found some evidence that macadamias can both form cluster roots and relationships with fungi, which is really rare.
“There’s obviously a lot of interest in whether we can work out how and why these plants do that and whether we can exploit that somehow in some of the crops we use, to help them out.”
In addition to this research Professor Rose is currently working on a number of projects within the Cooperative Research Centre (CRC) for High Performance Soils, looking at how to improve our agricultural soils to increase their resilience and a number of ARC (Australian Research Council) projects that revolve around plant breeding and new crops.
Learn more about studying Regenerative Agriculture at Southern Cross University
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