Managing microbes to manage nitrogen

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Crop spraying equipment in a paddock

Research into soil microbes may identify ways to keep more nitrogen in the soil and available to crops.

PHOTO: Brad Collis

As growers know only too well, nitrogen is the single largest variable input. It can also be the least effectively used of all farming system inputs, with up to 90 per cent of applied nitrogen never taken up by crops.

Soil microbiologist Dr Lori Phillips is trying to improve this situation through research that is generating a new level of detail on how agronomy, soil chemistry and soil biology interact to influence agricultural productivity. A major factor is nitrogen uptake.

Dr Phillips notes that increasing nitrogen uptake by just 10 per cent represents a significant jump in cost-effectiveness, along with increased yields. Based on 2013 prices, Australian growers spend about $3 billion a year on nitrogen fertiliser. A 10 per cent increase in nitrogen-use efficiency could therefore result in on-farm savings of $30 million a year.

The challenge she is pursuing is how to keep more of the nitrogen applied as fertiliser in the soil and one key seems to be the level of microbial activity.

While “a million different factors affect nitrogen uptake, first and foremost is soil microbial communities and what they do with nitrogen,” she says.

Image of a woman

Soil microbiologist Dr Lori Phillips is working to increase nitrogen uptake in crops.

PHOTO: Brad Collis

Her research, funded by the GRDC’s Soil Biology Initiative II, aims to determine the composition of soil microbial communities, their role in nutrient cycling and how farming practices influence microbial activity.

By studying how nitrogen is processed in soil systems and which microbes are responsible, Dr Phillips can explore how agronomic practices influence those microbial communities and improve nitrogen uptake.

“Understanding which soil microbes are active in nitrogen-cycling at what time opens up new avenues for nutrient management,” she says. “There are all sorts of little tweaks we are looking at that growers could use with existing farming technologies to start shifting the balance in the crop’s favour in terms of which organisms within the soil are working at any given point in time.”

While not yet able to make blanket recommendations, the research in Victoria and Western Australia is pointing to three areas that could improve nitrogen uptake: depth of nitrogen application, timing of application and the role of tillage.

Dr Phillips says soil testing is showing the active organisms that convert fertiliser into a plant-available form vary and exist at different depths according to soil type.

“This suggests that if we change the depth of fertiliser placement depending on soil type we can increase the rate at which that fertiliser is converted to something the plant will use,” she says. “It could be as simple as that.”

Another simple tweak that could improve nitrogen efficiency as indicated by the research is the timing of its application according to crop sequence. For example, most growers know that applying nitrogen at sowing after a legume crop would probably be a waste because the soil is already full of nitrogen-rich legume residues.

“In fact, if you fertilise too soon after a legume crop you can temporarily shut down the organisms that are breaking down those residues and releasing the nitrogen that is already in the system,” she says.

Dr Phillips, who joined the Victorian Department of Environment and Primary Industries from Canada three years ago for this project, says the impressive level of cooperation and communication between Australian growers and researchers is helping to achieve results.

She will be reporting her findings by the middle of the year and hopes to advance her current research streams into farm trials.

In the longer term, Dr Phillips is aiming for her research to feed into the development, globally, of a diagnostic tool for soil microbial communities; much like the tests used to determine a soil’s chemical profile.

“We would like to have a test to determine what microbes are present and how active they are so growers know whether to boost microbe numbers or shift balance to improve the benefit.

“We want to know what’s going on in our soils, who’s there and what they are doing.”

More information:

Dr Lori Phillips
03 9032 7141
lori.phillips@depi.vic.gov.au

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GRDC Project Code DAV00106

Region South, West