Increasing the effectiveness of N fixation

WHY THIS PROJECT WAS NEEDED

As well as generating useful income, pulses provide significant benefits to following crops, including nitrogen (N) fixation which can boost nitrogen supplies to following crops. Pulses are estimated to fix about 120 kg N/ha, or more than 220,000 tonnes of nitrogen across Australia, worth about $220 million each year.

However, not all pulses develop nodules well or fix nitrogen to their potential, especially on acidic soils. It was recently estimated that nitrogen fixation could be increased by 25%. Several GRDC project investments have been designed to help reach this target, however these project outputs require further extension and communication to farmers. This GRDC project investment aimed to improve nitrogen fixation of winter pulse crops and to promote their wider adaptation and adoption.

In short: This project aimed to improve nitrogen fixation in winter pulses, focusing on best-practice inoculation and management to counter soil acidity. The project was a collaborative effort, with various organisations aiming to optimise pulse nodulation and improve production outcomes in their regions.

Project focus

Project activities were designed to promote best management inoculation and pulse management practices, raising awareness and knowledge around pulse nodulation and nitrogen fixation. The project also aimed to raise awareness of the impact of soil acidity, especially subsoil acidity.

Demonstration trials were established at St James (lentils and chickpeas) and Bungeet (faba beans) during 2019 to promote effective inoculation and pulse management practices, raise awareness and knowledge around pulse nodulation and nitrogen fixation, as well as the impact of soil acidity on crop yields.

In 2020, a demonstration site at Murchison was sown to faba beans.

Project outcomes

Key messages from the 2020 trial were that:

• Sowing rate, rather than inoculation, was the main determinant of faba bean dry matter (DM) production.
• It was estimated the faba beans in this demonstration trial fixed between 101–129 kilograms of nitrogen per hectare, based on above-ground DM production.
• High harvest indices (HI) in the trial (49–64%) indicated a considerable amount of the nitrogen fixed was removed in the grain.
• A new DNA test available to measure Group E and F rhizobia in soil accurately predicted the moderate levels of nodulation measured in the trial.
• Inoculation responses are more likely in soils with lower pH (<pHca 5.0).

Where faba beans are sown into acidic layers at depth, the likelihood of inoculation responses will further increase.

• Results from the 2020 trial were published in Research for the Riverine Plains, 2021
• Results from the 2019 trial were published in Research for the Riverine Plains, 2020