Inoculants support soybean farmers

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WEST LAFAYETTE, Ind. – Small crop yield increases add up to extra dollars in a farmer’s pocket. And when it comes to growing soybeans, few management decisions improve yields like inoculation.

Research shows coating soybean seed with inoculant is a cost-effective way to boost production, say Purdue University and Ohio State University Extension agronomists.

The numbers. “My data over the last eight years indicates that the average yield response is about 1.25 bushels per acre,” said Purdue’s Ellsworth Christmas. “That ranges anywhere from zero yield response to nearly 3 bushels per acre yield response.

“Depending on seeding rate and row spacing, it’ll cost a farmer from $1.50 per acre to just under $3 per acre to inoculate. At current bean prices and at a 1.25-bushel increase per acre, you’ll get roughly $3 in return for every $1 invested.”

What is it? Inoculant is a naturally occurring bacterium that maintains a symbiotic relationship with the soybean plant.

The organism, which grows on the plant roots, converts nitrogen gas into nitrate, which the plant needs for growth, said Jim Beuerlein of Ohio State.

“The soybean plant nourishes the bacterium and the bacterium helps the plant to grow,” Beuerlein said. “It’s a pretty unique relationship and can be profitable for the farmer.”

Soybeans prefer nitrogen from natural sources to nitrogen fertilizers. Fertilizer gives plants a greener color, but offers no yield advantage to farmers, Christmas said.

The old view. A decade ago agronomists believed there was no need to inoculate soybeans before planting in a field that had grown soybeans in previous years, because there was adequate inoculum in the soil.

But with the increase in no-till practices, narrower crop rows, earlier planting, higher seeding rates, a switch from continuous corn to rotational corn-soybean acreage and other factors, that thinking is changing, Christmas said.

New inoculant products give producers another reason to consider treating their seed, Christmas said.

Many new products start with a sterile base, meaning the inoculant contains larger bacterial counts per ounce. Some also carry a “sticker” agent that helps the inoculant adhere to the seed.

Most common. The most common inoculants come in liquid and powdered peat forms. The products are applied directly to the seed in the planter or drill box, just before the farmer is ready to plant.

“Most of the products will say to plant within two hours after inoculating the beans,” Christmas said. “If you’re using the liquid inoculants you can buy a little metering device you can use at the base of the auger that feeds the bulk beans into the drill or planter, and inject the material at the base of the auger.

“By the time the seed has traveled up the flighting and into the drill or planter, the inoculant-coated soybeans are dry.

“You can mix it by hand or with a stick. I know a farmer who uses a paint stirrer he’s rigged up to an electric drill.”

How to apply. Application methods for peat-based inoculant are similar to liquid products, although some labels recommend seed be moistened with water ahead of time to promote better inoculant adherence.

The amount of inoculant necessary to treat soybean seed varies from product to product, so read and follow the instructions on the label. Inoculant also can be applied to the soil.

“It is important to maintain the recommended concentration per 1,000 linear feet of row to be effective,” Christmas said.

“If a row spacing less than 30 inches is used, the cost increases accordingly, and usually is not cost-effective.”

Profits increased. Seven years of Ohio State research indicates inoculants greatly increase profits for soybean producers.

OSU conducted 40 field trials with more than 2,600 plots across Ohio. The data show annual seed inoculation can increase profits 400 percent to 500 percent.

A yield increase of one-third bushel per acre is profitable and a 2-5 bushel per acre increase is common. The 2001 trials evaluated 14 different inoculant products at six sites. Average yields increased more than 6.5 percent, generating an additional profit of $5 to $12 per acre.

Other ways. Improving a crop’s health through the use of fungicide seed treatment is another way a farmer can boost profits.

“Farmers need to pay special attention to the diseases they have in their fields and then choose a fungicide package to control diseases for the varieties that may not be resistant to them,” Beuerlein said.

Phytophthora, Pythium and Rhizoctonia are three root rot diseases that can cause major crop losses if not adequately controlled.

“Proper variety selection and proper seed treatment can eliminate those diseases as a potential problem,” Beuerlein said.

Seeding rates. Adding fungicide treatment to the inoculated seeds resulted in as much as $15 in extra profit per acre. A farmer can save money by reducing seeding rates.

A 2001 Ohio State seeding rate study indicated that reducing seeding rate by 50,000 seeds per acre could potentially save a farmer as much as $10 per acre.

Study results showed that maximum soybean yields were realized when seeding rates ranged between 150,000 and 175,000 seeds per acre.

“Farmers tend to plant 25 percent more seed than they need to,” Beuerlein said. “Some of that is to compensate for poor equipment or lack of calibration.

“Some of it is just habit, but some producers feel that the high seeding rates are needed for better weed control. Most people can reduce seeding rate by 25 percent without affecting either weed control or yield, and therefore increase profits.”

Proper calibration of equipment to achieve the desired number of seeds planted per acre, or the number of seeds per foot of row, is an important step in reducing production cost.

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