Over The long term, soybean inoculation appears to be profitable throughout the Midwest, says Jim Beuerlein, crop science professor, Ohio State University. This is due in part to continued improvements in inoculants over the last several years.

Beuerlein, who has evaluated soybean inoculants since 1995, notes that today's inoculants contain “many-fold” more bacteria cells per gram or milliliter of material than those of a decade or so ago. Moreover, the development of extenders, made out of complex sugars, has improved the shelf life of inoculants. Some extenders can help inoculants remain viable for up to 120 days.

Some inoculants, such as Optimize, developed by EMD Crop BioScience, Brookfield, WI, also include growth promoters. Optimize LCO (Lipo-chitooligosaccharide) Promoter Technology activates a soybean plant's genes to begin cell division in roots and shoots independent of soil conditions.

Some inoculants, such as Vault LVL, developed by Becker-Underwood, Ames, IA, and Excalibre, developed by Advanced Biological Marketing (ABM), Van Wert, OH, feature more than one strain of bacteria, which can help them work better at higher or lower temperatures, Beuerlein says.

Vault LVL combines multiple strains of beneficial rhizobia with Integral biological fungicide and a conditioner.

Excalibre and ExcalibreQR, encapsulated inoculants, feature three strains of Bradyrhizobium bacteria. ExcalibreQR is a preformulated combination of Excalibre and QuickRoots, which contains Bacillus subtilis var. amyloliquefaciens and Trichoderma virens Gl-3. It was developed to improve root growth, soil exploration by microbes and nutrient efficiency.

Soybean inoculants work best at 40 to 80° F. If too hot or cold, bacteria cannot survive. Inoculants also can dry out quickly if left in sunlight too long.

Try them again

Some growers quit using inoculants several years ago after they experienced problems with handling them or they found the inoculants had poor compatibility with fungicides. If you have not used inoculants recently, Beuerlein suggests trying them again. “They're much different now than they were five years ago,” he says.

Growers will probably not see visual differences in color or height of soybean plants but will likely see greater yields at harvest, Beuerlein claims. Over the last several years, in test environments (with good rotation schemes, drainage, etc.), Beuerlein has seen a yield improvement averaging about 2 bu./acre each year.

In a paper entitled, “Soybean Inoculation: Its Science, Use and Performance,” Beuerlein reports an average yield increase from 64 Ohio trials of 1.94 bu./acre, which produced a profit of about 300% when soybeans were worth $6.00/bu. and when the cost of the inoculant was about $3.00/acre.

“Today's commercially available inoculants do a very good job at a cost of $2.50 to $4.00/acre, and you can get 2 to 6 more bu./acre using inoculants,” Beuerlein says.

Some growers, however, are looking for more. Growers often ask Palle Pedersen, Iowa State University Extension soybean agronomist, if any of today's products will result in significantly higher yields. “If we can document a significant yield increase from adding the inoculant, then soybean price doesn't matter,” Pedersen says.

Several growers who use inoculants point to recent highs in farm gate prices for soybeans, noting that at more than $6.00/bu., inoculation (averaging $3.00/acre) is a “no-brainer.”

Record holder's insights

Kip Cullers, Purdy, MO, harvested a world record soybean yield of 154 bu./acre last year growing Pioneer brand variety 94M80 (RR) at a rate of 225,000 seeds (final stand)/acre. The 2007 yield topped the previous record he held in 2006 for producing 139 bu./acre.

Cullers treated the soybeans with the liquid Optimize inoculant last year. He says that the root mass of the inoculated soybeans was twice that of nontreated soybeans. “Having good root structure in the first 4 in. of soil translates to better yield,” he says. “If you can build twice the root mass there, you can get good yields.”

The southwestern Missouri farmer inoculated the soybeans himself a couple of weeks before planting, also treating the seed with Cruiser Maxx Pak, the seed treatment insecticide/fungicide combination.

The soybean yield record holder's advice to others? Plant the best genetics for your area; use an inoculant, fungicide and insecticide seed treatments; and protect those treatments at the R2 stage with a fungicide, such as Headline.

Victor Menold, who is a partner in Menold Bros. with his brother Dean near Hiawatha, KS, started inoculating soybean seed about three years ago. After five years of not using inoculants because of their compatibility issues with fungicides, they started inoculating again.

The Menolds have produced an average 55 bu./acre over the last three years with soybean seed that has been inoculated with Becker-Underwood products by Ag Partners Cooperative, Hiawatha, KS. They farm 3,400 acres — half corn and half soybeans. “We like the convenience of having the seed inoculated by our supplier in a timely manner,” Menold says. “If applied too close to planting, there can be plantability issues.”

All of the Kansas farm's soybeans are inoculated. Although the Menolds do not conduct yield tests themselves, their cooperative has tested inoculants in the area and has observed yield improvements of 2.5 bu./acre over non-inoculated seed.

“It's easy to justify the cost of inoculants with today's nitrogen prices at $700/ton,” says Menold, adding that inoculation costs him about $2.75/unit of seed ($3.60/acre). They plant approximately 1.3 units of seed/acre, he says. “It takes just a third of a bushel per acre improvement to pay for the cost of inoculant,” he says. “It seems like the right thing to do.”

“Even $4.00/bu. soybeans would easily pay for the inoculant,” says Bob Krabbenhoft, owner of Krabbenhoft Seed & Supply, Sabin, MN. “With current market prices [$11.00/bu. in January 2008], you would need only a one-third to one-half bushel per acre yield increase to make inoculants pay.”

Soybean yields in Krabbenhoft's region of western Minnesota vary from year to year, ranging from 25 to more than 60 bu./acre, but his plot data have shown an average increase of 2 to 3 bu./acre with inoculated seed.

James Nelson, who farms 3,000 acres (about 1,000 of which are planted to soybeans) near Moorhead, MN, began using inoculants about three years ago after not using them for some time. He had experienced handling problems when he mixed inoculants with peat several years ago and felt they were too expensive at the time as well.

But three years ago, he began using Krabbenhoft's seed treatment service and has inoculated all of the soybeans since. He does not conduct side-by-side comparisons but averaged just less than 40 bu./acre last year and 50 bu./acre in 2006. Heavy rainfall last year hurt the crop somewhat.

Nelson has not seen any inoculant/fungicide compatibility issues but notes that sometimes wet treated seeds can stick together and form chunks.

Multiple seed treatments can result in high-volume liquid seed loading. Seed may come out of a treater so wet that it bridges in handling equipment and occasionally in the planter. Seed coats can tear off the seed when bridged soybeans break apart, says Marty Robinson, ABM's vice president of sales and marketing.

ABM developed Excalibre and MegaPack Low Volume Liquid to reduce the amount of liquid the seed must handle, leaving more room to apply multiple seed treatments without damaging seed quality, Robinson says. These products feature a seed conditioner and extender for better seed flowability and improved water imbibition, less handling damage and improved cool temperature germination, he says.

Bacterial populations

Krabbenhoft says most growers in his area choose to inoculate soybeans because they are on a two-year or longer rotation and can lose rhizobia population in the soil in as little as one to two years. This has been the case with saturated soils in the Red River Valley the last few years, he says.

Inoculants may not be effective under two scenarios, says Ohio State's Beuerlein: heavy rain for a week or two after planting, or if the soil is very dry at planting or for a few days after planting.

If you have a low population of Bradyrhizobium bacteria in the soil, you can add it to the seed and have a nitrogen source from this, says Iowa State's Pedersen. “On average, we expect to get around 50% of our nitrogen requirement for soybeans from nitrogen fixation,” he says. “The other half comes from the soil from microbial activities.”

If soil has a low population of the bacteria or is low in organic matter, then inoculation can help. If the population of bacteria and organic matter levels are adequate, inoculants may be unnecessary, Pedersen says.

“I see an increase almost every year in the percent of acres with inoculated seed,” Krabbenhoft says. “Last year, the growers I work with chose to inoculate nearly two-thirds of the soybeans I sold them.”

Ninety percent or more of the soybeans that Krabbenhoft sells are inoculated before delivery. “Very few farmers inoculate their own soybeans because it takes time and custom applicators can inoculate much more precisely using liquid inoculants,” Krabbenhoft says.

The Minnesota retailer uses ApronMaxx fungicide with inoculants and has not had compatibility issues. He uses separate mixing tanks and applicators so that products do not come into contact with each other until directly applied to the seed.

Because inoculation takes time and the proper equipment, more growers are having their suppliers treat the seed. Suppliers with seed treaters can inoculate more easily and at proper rates. Moreover, now that extenders are available, seed can be treated up to 120 days before planting without loss of viability.