Adelaide hosts the nitrogen world

Photo of two men and women kneeling

(From left) Professor Barbara Reinhold-Hurek (Germany), Associate Professor Flora Pule-Meulenberg (Botswana), Dr Michael Russelle (USA) and Dr Mike Ewing (Australia) at the Hart Field Site, South Australia, during the 2014 Australian Nitrogen Fixation Conference.

PHOTO: Rebecca Jennings

The challenges of managing nitrogen in food crops and the technologies and practices being developed to maintain the cost-effectiveness of this crucial element, were aired at the 17th Australian Nitrogen Fixation Conference in September.

The GRDC-supported conference, hosted by the University of Adelaide and the South Australian Research and Development Institute, brought together researchers and students from around Australia and the world.

Speakers included: Professor Barbara Reinhold-Hurek, head of the Department of Microbe-Plant Interactions at the University of Bremen, Germany, who discussed molecular plant–bacteria interactions; Dr Euan James from the James Hutton Institute, Scotland, who discussed plant electron microscopy and nitrogen fixation; and Dr Michael Russelle, from the US Dairy Forage Research Center, who presented on legumes and on-farm nitrogen management.

Conference sessions focused on nitrogen fixation in farming systems and research into organisms that can form nitrogen-fixing relationships with plants – and which present future opportunities for grain growers. There were field tours to research sites in SA’s mid-north to view progress of work into different pea cultivars and their response to inoculation.

Conference co-organiser Dr Maarten Ryder, from the University of Adelaide, said a message for growers from the conference was the need to optimise nodulation using strategic inoculation.

“By not inoculating at all, or not inoculating often enough, growers could miss out on opportunities to get more nitrogen into soils and achieve better yields of grain legumes and pastures, as well as following cereal crops,” he said.

“Rather than just inoculate and hope for the best, it’s important to use recommended methods to ensure sufficient rhizobia are applied at sowing, and then to monitor nodulation by sampling a few plants in early spring to assess results.”

The Australian Nitrogen Fixation Conference is held every two to three years, and the location of the next event has not yet been announced.

Inoculating Legumes: a practical guide is available at: www.grdc.com.au/GRDC-Booklet-InoculatingLegumes

Researchers discuss a global challenge

Ground Cover caught up with four researchers during their visit to the Hart Field Site in South Australia’s upper-north farming region and asked them to share their perspectives on nitrogen research:

Botswana: Associate Professor Flora Pule-Meulenberg, Botswana College of Agriculture
USA: Dr Michael Russelle, research soil scientist, US Department of Agriculture, Agricultural Research Service
Australia: Dr Mike Ewing, deputy chair, GRDC Western Panel, and former principal scientist at the Department of Agriculture and Food, Western Australia
Germany: Professor Barbara Reinhold-Hurek, Department of Microbe-Plant Interactions, University of Bremen

What is your main research area, and what practical tools can it deliver to growers?

Associate Professor Pule-Meulenberg:

Plant/rhizobia interactions. I characterise rhizobia, test them in different crops, measure nitrogen fixation and evaluate wild legumes for use as fodder crops. This has the potential to deliver efficient legume inoculants that fix high N2 as well as provide more efficient water use by fodder species, which are adapted to low-rainfall conditions.

Dr Russelle:

I try to identify ways to keep nitrogen cycling on the farm so it helps grow crops and feed livestock, rather than escape to the water or atmosphere. So I work with fertiliser, manure, legumes, forage and grain crops, dairy cows and, of course, soil, water and air.

Lucerne, as a deeply rooted perennial forage, can deliver an economic and desirable hay and silage product, remove excess nitrate from past fertiliser or manure application, and reduce or eliminate the need for fertiliser nitrogen on the next crop or two of maize.

Dr Ewing:

Introduction and development of new crops and pastures, particularly legumes, and their role in changing farming systems.

Involvement in research initiatives that are delivering new pasture legumes where existing gaps exist.Some of these new plants are already commercial, such as serradellas for infertile sandy soils, but others are only now becoming available, including messina for saline and waterlogged situations and tedera, a drought-tolerant perennial legume with wide soil adaptation.

Professor Reinhold-Hurek:

My long-time goal is to improve nitrogen fixation for cereals. We mainly work with nitrogen-fixing endophytic bacteria that colonise the interior of rice, trying to better understand how they interact with each other.

Another aspect deals with more direct, applied questions: how to improve nitrogen fixation in local pulses for smallholders in Namibia or Angola.

For smallholders and their local pulses, such as cowpea or Bambara groundnut in Namibia, we will hopefully deliver rhizobia as inoculants that are adapted to the harsh conditions there – high soil temperatures and dry seasons. My long-term dream is to give a nitrogen-fixing rice system to growers.

What is the main challenge for growers in your country?

Associate Professor Pule-Meulenberg:

Rainfall. Although its amount may seem adequate (300 to 550 millimetres) distribution is erratic, leading to crop failure.

Dr Russelle:

Slim economic margins in most years, and deciding what equipment and land to buy in the good years. Growers also face the challenges of managing weather risk, the complexity and number of decisions in crop and/or livestock production, labour management, equipment maintenance.

Another challenge that is coming in many areas is increased regulation due to water quality impacts of excessive nitrogen and phosphorus application and, in some cases, manure run-off.  

Dr Ewing:

Increasing production and profit at a sufficiently high rate to offset the continuing impact of declining terms of trade.

Professor Reinhold-Hurek:

A more sustainable use of resources. For example, in areas of sandy soils where I live, many growers struggle with high rates of nitrogen leaching into the groundwater.

Improved root systems in crops such as maize might help to reduce nutrient losses, and perhaps bacterial inoculants may aid in increasing root growth – a research area that has not been fully exploited yet.

What is the main challenge for agricultural researchers in your country?

Associate Professor Pule-Meulenberg:

Funding. In the past the Botswana Government has not committed any GDP for research, but they will start doing so in the next Development Plan.

Dr Russelle:

As fewer citizens grow up on farms, or even know anything about agriculture, funding for agricultural research is more difficult to justify to state and local governments. Most of our research funds come from these sources, although growers and industry also support research through groups similar to, although much smaller than, the GRDC.

Dr Ewing:

Researchers face a huge challenge to continue to deliver profit-enhancing innovations to growers with declining resources available to them and a narrowing skill base at a time when almost all major initiatives demand a strongly multidisciplinary approach.

Professor Reinhold-Hurek:

Attracting students.

What was the ‘take-home message’ for you from the Australian Nitrogen Fixation Conference?

Associate Professor Pule-Meulenberg:

The interaction between research staff and growers here through on-farm research. I wish there was a strong linkage like that between our agricultural research institutions, extension and growers.

Dr Russelle:

From an outsider’s perspective, I’d say the message is that your growers and the agricultural industry are getting a lot from the investment in nitrogen-fixation research: from really exciting discoveries of how plants and their symbiotic partners communicate and regulate each other, to learning how quickly rhizobia disappear from a field in the absence of a legume; from improving inoculum quality to estimating rates of nitrogen release from legume residues; from discovery of new rhizobia types with amazing tolerance to salinity and soil acidity, to development of a new legume crop that tolerates flooding. Amazing.

Dr Ewing:

We cannot assume that because legumes are capable of fixing nitrogen that they will always be operating at peak efficiency. Legumes and their root-nodulating bacteria need to be manipulated and managed to deliver their optimum benefits and this requires ongoing research by scientists with an understanding of field problems and the right set of technical skills.

Professor Reinhold-Hurek:

It is really fascinating how Australian researchers get nitrogen fixation ‘to work’ out in the field.

Looking ahead, what do you think are the biggest challenges and opportunities for growers when it comes to fixing nitrogen?

Associate Professor Pule-Meulenberg:

For Botswana, most growers are aware of the benefits of nitrogen-fixing legumes. However, the inoculant technology is not known in the farming community. This means that even the extension staff is not well-versed in how to handle bacterial inoculants. Regarding opportunities, N2-fixing legumes could provide a solution to reducing greenhouse gas emissions when compared with using inorganic nitrogen fertilisers.

Photo of legumes and their root-nodulating bacteria

Legumes and their root-nodulating bacteria need to be manipulated and managed to deliver their optimum benefits and this requires ongoing research, scientists say.

PHOTO: Brad Collis

Dr Russelle:

A real benefit of nitrogen from legumes in a cropping system is that it doesn’t show up all at once like fertiliser does, but becomes available through soil biological activity. With good crop management, you can capture nitrogen in grain and feed yield. The challenge is that you have to manage crop-protection chemicals to minimise carryover effects on the legume and rhizobia, use the right inoculum for the legume, not let it die by poor handling, follow the legume with a crop that will utilise the extra nitrogen as it becomes available, and reduce the fertiliser nitrogen application rate appropriately.   

Dr Ewing:

The biggest challenge is to have an array of crop and pasture legumes to cover all of our climate zones; soils that are sufficiently profitable to ensure that they are used in rotations and can then deliver the additional benefits associated with nitrogen transfer to following crops and disease breaks.

Professor Reinhold-Hurek:

The legume-nodule system can be well adopted by growers, saving resources while letting the microbes work. However, the biggest nitrogen challenge is with respect to the big three: rice, wheat and maize. We do not have practical solutions, yet, to save nitrogen fertilisers, apart from crop rotation with legumes. 

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Nitrogen benchmarking for better management

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