Farm Industry News

Inoculants in rotation

YOUR NEIGHBORS would probably look at you funny if you started throwing around terms like Bradyrhizobium japonicum. But say “soybean inoculant” and most everyone in soybean country would know exactly what you were talking about.

Soybean inoculants such as those containing the friendly bacterium B. japonicum have been around for more than 40 years. The mutually beneficial relationship between nitrogen-fixing bacteria and soybean roots has long been known to improve root nodulation, nitrogen uptake and yield on fields that have not been planted to soybeans for a few years.

In recent years, however, farmer interest in soybean inoculants has increased to include treating soybean seed more often, even in standard corn-soybean rotations. New strains of bacteria, increasing acceptance of inoculant technology, and evolving customer needs have been driving the trend.

In the field

Steve Webb farms a corn-corn-bean rotation in central Indiana and says that he always puts an inoculant on the seed in his drill box.

“At less than $3 an acre, why wouldn't I use an inoculant?” Webb asks. “It is one of the cheapest things I can do to increase my soybean yield. Farmers spend a lot more on corn seed for less return.” Last season Webb used a brand called HiStick, a dry peat-based formulation produced by Becker Underwood.

Daryl Bridenbaugh of Pandora, OH, also uses HiStick. “I have been using inoculants for several years,” Bridenbaugh says. “It takes some time to mix in with the beans, but I think it is worth it — several dollars in return for every dollar spent. I used it on all my fields, including beans after corn.”

Bridenbaugh says he used to inoculate beans in the '60s and '70s and then quit taking the time to do it. He started again about 10 years ago when he bought a 750 John Deere no-till drill with a bigger seed box that made it easier to mix in inoculant. “I probably would have started again anyway, because the inoculants were getting better,” Bridenbaugh says. “I don't have any research to prove anything, but I think using an inoculant today is just something you can't afford not to do, especially since the inoculants they have today are so super powered.”

Sweet spot of a trend

As farms get bigger and farmers become inoculant believers, more are willing to pay their seed providers extra for pre-inoculated soybean seed. Advanced Biological Marketing believes its new 60-day encapsulated inoculant, Excalibre, is the right product to help dealers and retailers offer their customers inoculant treatment services. Dan Custis, president of the company, says regional seed companies are showing interest in offering Excalibre as a value-added option.

“Increased interest is due to a number of things,” Custis says. “These include introduction of new strains of Bradyrhizobia, including some that can inoculate soybeans in cool or hot planting conditions. We're also seeing more retail dealers custom treating and inoculating soybeans.

“There's also an increased cost of nitrogen for the corn crop, and soybeans that are well inoculated will produce approximately one pound of free nitrogen per bushel of soybeans produced for the following corn crop.”

Longer-lived rhizobia

Although most seed inoculant products must be applied to the seed immediately before planting, Excalibre is the first product to remain viable on soybean seed for up to 60 days. The product's encapsulated rhizobia remain protected, like the gummy center of a tootsie pop only on a much tinier, bacteria-sized scale. Soil moisture dissolves Excalibre's protective coating after inoculated seed has been planted.

To develop Excalibre, ABM worked with Cornell University on a process in which the end product maintained high levels of live rhizobia over time. It took three years to come up with a consistent, workable encapsulation process. In addition to its extended on-seed shelf life, the product is compatible with most current fungicide and insecticide treatments.

Fewer restrictions, and a larger planting window from treatment to planting, buy farmers and their seed suppliers time and flexibility during the hectic, unpredictable soybean-planting season.

Multiple strains

“The thinking in regards to inoculating your beans every year has changed with the introduction of new strains of bacteria,” Custis says. “If you are on a corn-bean rotation, you can maximize the use of inoculants by alternating brands of inoculants. Not every soybean inoculant contains the same strain of Bradyrhizobia, and some strains work better in specific seasonal soil conditions.”

One competitive product that addresses the “multiple strains” issue is Becker Underwood's Vault. Viable on the seed for 30 days, Vault is billed as a “bio-stacked” inoculant with multiple strains of beneficial rhizobia to help ensure activity in variable soil conditions, including hot, cold, dry or wet. Completing the “stack” for Vault is a biological fungicide called Integral that suppresses common soilborne diseases caused by fungi such as Rhizoctonia and Fusarium.

University tests vary

While almost everyone agrees on the value of inoculants for soybean seed planted to ground that has been absent soybeans for several years, researchers and farmers have been divided on the economic viability of using inoculants more frequently on corn-soybean rotations.

In the late 1990s, the results from six years of research convinced Michigan State University crop scientist Maury Vitosh that using a rhizobium inoculant would not improve soybean yields in fields that have been planted to soybeans in recent years. This supported the widely held assumption that roots of the soybeans themselves ensured that an adequate population of friendly bacteria would be available in the soil for the next soybean crop a year or two down the road.

Vitosh concluded that inoculant use, either as a seed treatment or an in-furrow liquid application, was only beneficial when soybeans were planted on new soybean ground. Only in areas where soybeans were not grown before or were planted every few years did inoculants show an advantage, improving soybean yields by 20 bu./acre or more.

However, more recent research from Purdue University indicates that inoculants may provide a financially significant return on a corn-soybean rotation. The researchers, Shawn Conley and Ellsworth Christmas, looked at multiple soybean plots grown in a traditional corn-soybean rotation in Indiana from 1993 to 2004. Some years showed gains of 2 bu./acre or more, while others registered no gain. Over the 10-year period, comparing yields of seed-applied inoculant plots versus a non-inoculated control showed an average yield gain of 1 bu./acre.

Using a variety of different inoculant products, the Purdue researchers reported inoculant cost per acre ranging from $1.50 to $2.75/acre. With an expected marketing year average price of soybeans between $5.00 and $5.80/bu., the Purdue results indicate that soybean inoculants will more than pay for themselves over the long haul, even in a corn-soybean rotation.

“We're not necessarily recommending that every grower in Indiana put inoculant on every acre of soybeans, but we are suggesting that some of the newer technologies are making it more grower friendly,” Conley says.

In light of the 1-bu. yield advantage he and Christmas found, Conley recommends farmers initiate their own side-by-side strip trials to test efficacy on their specific soils and soybean varieties.

Large-scale acceptance

Don Schafer, senior soybean product line manager for Pioneer Hi-Bred International, notes that Pioneer does not sell inoculants specifically, but that a growing number of Pioneer sales reps do offer the service to their customers, coating the seed with inoculant just prior to delivery or customer pickup. To service their customers, these seed reps have invested in treatment equipment that costs anywhere from a few hundred dollars to more than $25,000.

Pioneer leaves inoculant services to its sales pros largely because the inoculum on soybean seeds still has a relatively short shelf life. Though ABM's Custis says he hopes Excalibre will win over large seed companies like Pioneer, Schafer says even 60 days of on-seed viability is not long enough to accommodate Pioneer's seed supply chain.

“We produce soybean seed at over 25 production locations throughout North America,” he says. “The product gets moved around all the time. Challenges in movement and planting would be too great for us to get involved with inoculating soybeans at the seed production facilities. With the planting window now from late March in the Delta to mid-July for double-crop after wheat, the logistics become impossible. The longer-lived inoculant products are primarily a benefit to the grower who is looking for more just-in-time planting flexibility.”

Schafer says Pioneer doesn't track the number of customers who request inoculant-treated seed from their sales reps, but he notes that enough growers must see economic return to view the practice as worthwhile. “Geographically, some areas have a greater interest in inoculated soybeans. North Dakota, South Dakota and Wisconsin are relatively high in inoculant use,” Schafer says. “We don't really know why inoculants are more popular in some regions than others, but we do know that growers in Wisconsin, for example, often inoculate 100% of their beans.”

Schafer notes that Pioneer takes no position on the cost-effectiveness of soybean inoculants in different rotations, pointing out that growers are the ultimate judge and vote with their dollars. He says, “Since the trend seems to be an increase in inoculant use, we can assume that farmers see value in the money spent.”

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THE CLOCK starts ticking the moment a soybean inoculant is applied to the seed. Depending on the product, the live rhizobia might stay viable on the seed for a few hours or a few days. This has traditionally required farmers to apply inoculant in the planter box just before planting or to hire their seed supplier to apply a liquid formulation for just-in-time delivery. Either option can add to the stress of an already busy planting season.

Addressing the time crunch, Advanced Biological Marketing is the first company to bring an encapsulated inoculant to market. The product, called Excalibre, extends the effective life and efficacy of the live rhizobia to 60 days on the seed before planting. The encapsulated rhizobia remain protected and dormant on the seed until planted in the soil, giving more flexibility in planting date management and choice of insecticide and fungicide. An added benefit is the compactness of the product package; a 1-lb. package of Excalibre dry powder is enough for a properly equipped seed supplier to treat up to 60 50-lb. bags of soybean seed. The product is applied at a low rate of just 0.02 oz. for 100 lbs. of seed.

Contact Advanced Biological Marketing, Box 222, Van Wert, OH 45891, 877/617-2461, visit or, or circle 219.

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