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New inoculant offers added benefits

'New' bacterium complements the old.


February 16, 2008
By Ralph Pearce


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For most growers, the practice of inoculating soybeans has been a bit of a tough sell in recent
years. Whether it is the perceived inconvenience of applying the inoculant or the added cost of having a seed dealer apply it or the debatable value of the bacterium is not known for certain. However, one company recently launched its new line of inoculant for soybeans, adding a ‘new and different‘ species of bacteria and the potential for higher yields.

 22a
Soybean plants treated with HiStick N/T (left) versus untreated plants (right) provides a visible advantage and could provide a yield boost of more than 1.5bu/ac.

In September 2007, Becker Underwood Canada released its new HiStick N/T inoculant for soybeans,
featuring its BioStacked technology that offers the combined action of Bacillus subtilis with existing Bradyrhizobium japonicum. The inoculant is available in both liquid and sterile peat formulations, and DeKalb and Pride Seeds are making the inoculant available on their varieties.

The addition of B. subtilis is considered significant on several different levels. According to a brief from the US Environmental Protection Agency (EPA), Bacillus subtilis is a common and naturally occurring bacterium, found in air, water, soil and decomposing plant material. It can produce a number of proteases and other enzymes that allow it to break down various natural substrates and residues, and helps promote nutrient cycling. The bacterium also produces an endospore that enables it to survive extreme conditions of heat and dessication, and as a pathogen or a disease causing agent, B. subtilis is considered benign. (www.epa.gov/oppt/biotech/pubs/fra/fra009.htm)

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Another benefit of this bacterium is that it is considered a plant growth promoting rhizobacterium (PGPR) which can, in some fields, stimulate early growth in soybeans and promote earlier canopy closure. “It also appears to provide some protection against root rots,” says Dr. Dave Hume, professor emeritus at the University of Guelph and a consultant with Agri-Trend Agrology. “That’s our experience, and you don’t always see it, so it probably means that in some soils, the organism makes a lot of headway against the disease organisms that are in the soil, and in other soil types it doesn’t.”

Since 2002, Hume has tested the HiStick N/T formulation against its predecessor, HiStick+ and has found there to be some advantages. On new soybean fields containing no populations of soybean rhizobia, the average yield gains have been 1.5bu/ac higher using the N/T compared to just HiStick+ inoculant, which contains only the soybean rhizobia. “Adding the HiStick+ gave us, on average, about a
35 percent yield advantage on new soybean soils, which you would expect,” explains Hume. “But then on average, we got another 1.5 bushels from having the B. subtilis in there.”

In fields that have grown soybeans before, Hume has found an average field response of about 1.5bu/ac from inoculating with HiStick+. There has not been enough research done yet in Ontario on fields previously cropped to soybeans to know if there will be any additional yield response when the B. subtilis is included in the inoculant.

Results from other regions
In trials at seven sites in Manitoba, comparisons of HiStick N/T to HiStick+ indicated yield increases of 1.6bu/ac. In Ohio, the average response in five trials of HiStick N/T versus uninoculated checks was 2.1bu/ac, and in Wisconsin, the yield advantage was 3.5bu/ac in seven trials comparing HiStick N/T to HiStick+. One trial in Maryland also showed an 8.1bu/ac advantage for the same comparison. “All of those US tests were obtained using ApronMaxx RTA as a seed treatment and so are ours,” says Hume. “What we don’t know yet is whether this 1.5bu/ac or 1.6bu/ac boost that we’re talking about is on top of the 1.5bu/ac that we averaged just from adding the inoculant to soils that have grown soybeans previously. If it is, 3.0bu/ac from a grower’s perspective would be an easy choice. Even at 1.5bu/ac, to me, with $10 soybeans, that’s something I’d be looking at.”

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A close-up of the treated soybeans confirms the root mass is thicker, denser with more nodules for fixing nitrogen.

Tough sell made a little easier
For Bill Lester, the challenge of convincing growers of the benefits of inoculants is made a bit easier by
showing them that HiStick N/T is a new category of inoculant. As Becker Underwood’s district manager for eastern Canada, he acknowledges that inoculating soybeans has lost some of its lustre, and is perceived as an ‘old practice’. Yet he traces the past 10 to 15 year history of inoculants, including
the passage from non-sterile types to sterile formulations.

“With a lot of growers in southwestern Ontario that have been growing soybeans for a long time, the last time they would have used an inoculant, it was likely a non-sterile formulation, which from data that we have from universities, suggests that non-sterile formulations typically will only give you a yield response of half a bushel per acre on rotated ground,” details Lester. A large deficiency in the old, non-sterile formulations is the presence of other competitive, non-beneficial organisms. “But most growers in the southwest had gone away from using inoculants before the sterilized inoculants started to come on stream. According to third party research through universities, sterilized inoculants have been proven to give anywhere from 1.5bu/ac to 2.5bu/ac yield response. That’s starting to get into the range where growers would notice that.”

Even at 1.5bu/ac yield response, Lester believes the value of HiStick N/T, at roughly $3.00 per acre, would require just a half bushel per acre increase to justify the expense. “In a year like 2007, where we have yields all over the board on soybeans ranging from as low as 5.0bu/ac to some yields upwards of 50bu/ac or more, if you’re in that range of 25bu/ac or 30bu/ac, an extra two or three bushels may mean the difference between making money or not,” says Lester.

He likens the notion of inoculating to keeping a vehicle properly tuned. “If you thought about the extra mileage, the fuel economy that you can get out of a vehicle by rotating the tires and changing the oil on a regular basis, you’d never know what you were giving up unless you’re doing that, and keeping track of the extra economy you’re getting.”

Smoothing out the rough spots
From the perspective of an inoculant providing a protective quality, Lester points to the benefits in variable sections of a field. Relying on indigenous species of rhizobium to efficiently fix nitrogen in soybeans may cost a grower money. “The zones that typically would get a yield boost from an inoculant are the areas that are tough on the survivability of these organisms,” says Lester.

“If you have eroded knolls in the fields where the organisms would dessicate due to lack of moisture or if you have flooded hollows in the field that basically choke off the rhizobium without an oxygen source for an extended period of time, those are hot zones where an inoculant will really give you a return.”
Convincing growers to ‘come back’ to using inoculants will not happen overnight, and Lester is quick to
concede to that. “But as more growers come on with good experiences, definitely the use pattern will gain some more popularity.” -end-