Research producing sweet outlook for pulse crops on acidic soils

RESEARCH is offering hope to grain growers who have been limited in their ability to successfully grow pulse crops on acidic soils in the southern cropping region.

New strains of rhizobia with improved acid tolerance have shown promise in field trials, lifting the prospects of commercialisation and a subsequent expansion of faba bean and lentil crops into areas with acidic soils.

Profitable production of pulses is dependent on successful nodulation of the crop, so growers inoculate seed with rhizobia bacteria that stimulate the production of nodules on the plant roots which fix atmospheric nitrogen for the pulse crop.

This free source of nitrogen ensures a healthy pulse plant with little or no reliance of nitrogen from the soil, and also delivers excess nitrogen that supports crop production in subsequent years.

However, the current commercial strains of rhizobia are typically much more sensitive to acid soils than the host legume plant, so a Grains Research and Development Corporation (GRDC) research investment has been testing the performance of alternative strains of rhizobia that have been identified with improved acidity tolerance.

Research leader Ross Ballard, from the South Australian Research and Development Institute (SARDI), a division of Primary Industries and Regions SA, says field trials over the past three years have demonstrated the effectiveness of the new strains in nodulating faba beans and lentils on acidic soils.

Mr Ballard says the new strains of rhizobia have resulted in a dramatic improvement in nodulation compared to commercial strains when applied at recommended rates of inoculation in acid conditions.

“Increases in faba bean nodulation of about 30 percent have been consistently measured with the new strains where soil pH is less than 5.0 when measured in calcium chloride,” Mr Ballard said.

“The new strains are improving nodulation and ultimately that results in better crop vigour early in the growing season, as well as improved nitrogen fixation and yield.”

Mr Ballard, who has been undertaking the rhizobia trials with fellow SARDI researcher Liz Farquharson, says further evaluation of the strains will be undertaken this year and that a new strain for faba bean (and possibly lentil) could be commercially available in 2022, subject to further positive results.