Grower options for inoculants expand as new strains arrive

At a recent Mid North High Rainfall Zone research update, SARDI researcher Liz Farquharson gave an overview of the latest southern Australia trials for Group E and F, legumes.

These groups include field pea and vetch in E and lentils and faba beans for F, which only had two rhizobia strains available in the past.

Rhizobia, the soil bacteria which nodulates the roots of legumes, plays a key role in plant performance and yield, according to Dr Farquharson.

"Within those nodules, is where the magic of nitrogen fixation takes place and where nitrogen in the atmosphere is converted to a form which is available to the plants," she said.

Effective pulse legumes can fix about 30 kilograms of nitrogen per tonne of dry matter, Dr Farquharson said, and this relationship between the crop species and the rhizobia species, was "special".

"It has to match up because only certain species will nodulate certain legumes types," she said.

Dr Farquharson said very poor persistence of present E and F rhizobia strains in acidic soils with a pH less than 6, was a major driver for the research.

"We had multiple reports of peas, lentils and beans nodulating very poorly on acidic soils and stunted yellow crops early in the season," she said.

"There was also a desire to extend legume options."

Data from multiple trials of rhizobia strains on acidic soils has shown a significant improvement in yield and nodulation in group E and F legume crops.

As acidic soils increasingly become an issue, researchers conducted 60 replicated trials across 24 locations, to form a collaborative project across multiple states.

SARDI researcher Liz Farquharson said once soil pH levels were below 6, the number of nodules per plant, dropped off considerably.

Dr Liz Farquharson was pleased two new strains were ready to go this season.

"With the previous strain, it was optimal nodulation generally above pH 5.5 and sub-optimal and poor nodulation below pH 5," she said.

"Whereas for the new strains, we are shifting optimal nodulation down to pH 5. But in some cases, there is probably sub-optimal nodulation."

Growers could still expect poor nodulation below pH 4.5 .

"It is not the panacea of acid soils for legumes but rather, another tool in the tool box," Dr Farquharson said.

It is a big undertaking when researchers are selecting rhizobia strains for a commercial inoculants.

There is a rigorous process in Australia, which looks at nitrogen fixation, capacity, and effectiveness, as well as the host range for commercial production, does it survive well on seed.

Multiple trials are then ran in the main growing regions for the crops, to look at the strains' ability to survive for multiple years in the soil.

The new strains showed big gains in biomass production in soil just under pH 5, while grain yield hit an average of 15 per cent improvement for lentil, peas and vetch.

For faba beans, the SARDI 969 strain, consistently performed better when compared with other strains in the trial, while across seven sites, there was a 65pc improvement in nodulation on acidic soils with the new strain.

Nitrogen fixation was measured in faba bean trials and recorded a 24pc improvement of fixation, with significant grain yield improvements across two of the seven sites.

When there is a soil pH of greater than 5, trials revealed the new strain was comparable to the old strain.

But, this showed there was a big improvement was on acid soils.

"This strain is an outright replacement and it will work anywhere. But, the big bang for buck is the improvement on the acid soils," Dr Farquharson said.

A bean trial at Giles Corner acted as a preliminary evaluation of the new strains in different formulations and rates. Previously, the old strains required double the rate of peat but the new strain, had significantly better nodulation with the standard rate.