By Mark Olson

Questions abound when it comes to the inoculation of pulse crops: Is it necessary to inoculate at all? After I have grown a specific pulse in the field once before, do I have to inoculate again? Is there any merit in “double-inoculating” a pulse crop? What about using rhizobia inoculants in combination with growth promoting organisms?

In many parts of the world where there is a long history of growing pulse crops, inoculation is not actually as common. Comparatively, Western Canada has a relatively short history of growing annual crops and nitrogen-fixing annual grain legumes such as pulses. As well, each pulse-kind has a specific bacterium to which the symbiotic relation is formed, and these bacteria are necessary to optimize the benefits of nitrogen fixation. There is no question that applying an inoculant to the seed (or in the seed row) to meet the pulse crops’ nitrogen requirements is more cost-effective than applying a manufactured nitrogen fertilizer and is of huge benefit in lowering a cropping system’s overall environmental impact.

Although rhizobia introduced into the soil environment by inoculation do survive, the bacteria’s exponential reproduction over several years before growing a pulse again may make the residual populations less effective at fixing nitrogen. For that reason, applying inoculant every time when growing a pulse crop is considered a best management practice and lowers risk to the grower dealing with poor or zero nitrogen fixation in their crop.

Fields that have never had a pulse species of any kind are often referred to as “virgin fields” and some growers will inoculate with two different formulations of inoculant (i.e. liquid and granular) for the first time growing that pulse species on the field. This is referred to as “double” or “dual” inoculation and is a common practice within the soybean industry upon ‘first’ and ‘second-time’ soybean land. In pulse crops, research on dual inoculation is limited and whether a grower chooses to double-inoculate on virgin fields is dependent on their propensity for risk and the planned economics of doing so.

The addition of other and/or multiple biologicals to inoculants has become increasingly common. Tag Teamâ and Jumpstartâ, as examples, contain Penicillium bilaiae, a naturally occurring soil fungus which is able to solubilize the tightly bound soil nutrient phosphorous. Phosphorous is critical to root development and the inclusion of Penicillium bilaiae results in a visibly more extensive root systems which in turn increases water, macro, and micro-nutrient uptake from the soil. These product/product combinations were one of the first-generation biologicals to appear in markets across Western Canada.

In addition, there are numerous plant growth promoting rhizobacteria (PGPRs) in combination with inoculants on the market. Nodulator Duo SCGâ is just one example of a granular inoculant that combines the nitrogen-fixing of Rhizobium leguminosarum for pea and lentil together with a bacteria Bacillus subtilis. The addition of Bacilis subtilis increases root and shoot biomass which in turn enhances water and nutrient absorption as well as assists the crop ability to survive under less than ideal environmental conditions

“LCO” or ‘lipochitooligosaccharide’ technology is where a specific molecule amplifies the communication (sometimes referred to as “Nod factor”) between the plant and rhizobium, initiating the formation of nodules regardless of poor environmental conditions.

Tagteam BionQâ is another example of a product but with LCO technology and multiple organisms: Rhizobium leguminosarum, Penicillium bilaia, Bacillus amyloliquefaciens and Trichoderma viren. All these products are added to increase nodulation and root mass for enhanced water and nutrient uptake.

It should be noted that this is not an exhaustive list of product or product combinations with inoculants. The product names mentioned as examples are not an endorsement of their effectiveness and whether they are of economic benefit. Pulse growers are encouraged to talk to their local agrologist as to which inoculant product fits best with their farming operation.