Increasing N Fixation in Pulse Crops Through Improved Rhizobia, Inoculation and Crop Management Practices

⁠⁠⁠The Grains Research and Development Corporation (GRDC) is a statutory corporation established under the Primary Industries Research and Development Act 1989. It is subject to accountability and reporting obligations set out in the Public Governance, Performance and Accountability Act 2013. It is responsible for planning, investing in and overseeing research and development, and delivering improvements in production, sustainability and profitability across the Australian grains industry.

As well as generating useful income, pulses provide significant benefits to following crops, including nitrogen (N) fixation boosting N supplies to following crops. Pulses are estimated to fix about 120 kg N/ha or more than 220,000 tonnes N across Australia, worth about $220 M each year. However, not all pulses are well nodulated and fix N to their potential, especially on acidic soils. It was recently estimated that N fixation could be increased by 25%.

Apart from narrow-leafed lupins, pulses prefer neutral to alkaline soils and their performance declines on soils below pH 5.5 (measured in calcium chloride). Compared to current commercial inoculants, rhizobial strains for faba bean have been identified with improved tolerance to soils between pH 5.5 and 4.5, which could also be useful for lentil, field pea and vetch. Acid tolerant rhizobial strains were first identified in the glasshouse and limited field experiments have shown their potential to double nodulation and the amount of N fixed by faba bean on acid soils. The improved strains increased faba bean yields significantly and have potential to expand its production in medium and high rainfall areas. Similar improvements in chickpea rhizobia may increase its area of adaption.

Crop protection and trace element seed treatments, herbicides and soil constraints other than acidity are also factors that may be contributing to the underperformance of legume inoculants. Limited tests have shown that the seed fungicides Thiram and P-Pickel T carry a high risk of killing rhizobia and inhibiting nodulation of faba bean, lentil and field pea, while Gaucho is of relatively low toxicity. Zinc sulphate seed treatments are also highly toxic to rhizobia. Herbicides, particularly residues of Group B herbicides, are known to damage legume roots and can potentially decrease infection sites for rhizobia and nodulation. However, such effects are easily overlooked in the field and have not been thoroughly investigated. A recent study showed that field pea crops are sometimes well nodulated, but N fixation is sub optimal. The cause of this poor fixation is not understood, however herbicide effects are suspected. The impact of crop protection chemistry on N fixation and the implication of herbicide tolerant varieties needs to be better understood, especially as pulses expand onto less favourable soils in low and high rainfall areas. In addition, improvements to rhizobial carriers and inoculation methods may be possible, especially when sowing pulses into dry soil.

The GRDC seeks to enhance nitrogen (N) fixation of winter pulse crops through improved rhizobial strains for hostile soils and enhanced inoculation practices that minimise the potential impact of fertiliser and crop protection applications, and maximise rhizobial survival, nodulation and nodule function. These improvements will broaden the adaptation of pulses onto soil types and areas where they are currently not widely cultivated. This three year R&D investment, starting early 2018, will be supported by a separate extension and communication investment to promote awareness of nodulation and N fixation in pulses, and adoption of best inoculation practices.

By June 2022, growers in the southern region have access to improved rhizobial strains compared to the current commercial inoculums for winter pulse crops, plus best management practices for optimising nodulation and nitrogen (N) fixation, including minimising the impact of fertiliser and crop protection applications.

These innovations will enhance N fixation and production of pulse crops with flow on benefits to following crops, and enable expansion of pulses onto soil types and in agro-ecological zones where they are currently not widely grown.

The indicative GRDC investment is up to $1.56 million. The GRDC is focused on delivering value to Australian grain growers; therefore, your application must demonstrate fair market value. Leverage of GRDC funds through in-kind and cash co-contributions is viewed favourably. Applicants should comply with the tender requirements and draft GRDC standard Two Party or Multi-party Research Agreements.

This proposed investment would be undertaken over a three year period from 30 March 2018 to 30 June 2021 and will be delivered across the GRDC Southern Region.