Seed inoculation Helps Soybeans Get Nitrogen
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Three years of research done at Ohio State shows that seed inoculation is an inexpensive way to improve soybean yields by increasing nitrogen availability to plants.
Soil inoculation promotes a naturally occurring, symbiotic, process to increase plant nitrogen use. Inoculants are useful bacteria that infect roots, then consume plant sugars and carbohydrates in exchange for fixing nitrogen for use by the plant.
Farmers can apply bacterial materials to seed before planting, as was done in this study. This year, Ohio State researchers will look at other means of inoculation, such as spraying a bacterial solution into the furrow at planting, and other methods.
Studies from 1995 through 1997 saw soybean yields increase on average 1.55 bushels per acre compared to control plots when inoculants were planted at 16 test sites around the state. The increases ranged from a high of 4.4 bushels per acre for a commercial inoculant to a low of .6 bushel per acre for regular humus.
Beuerlein calculated that soybean inoculation increased profit by $10.10 per acre at a cost of less than $2 per acre.
Seed inoculants give farmers control over one of three important inputs that affect yield. Water is the most important input, but its uncontrollable. Nitrogen availability is a close second, followed by sunlight, which also can't be controlled.
"Increasing the supply of any of these three inputs will increase yield," Beuerlein says.
Using seed inoculants also is cheaper and more effective than mid-summer direct applications of nitrogen, Beuerlein says. Direct applications give only small yield increases probably due to the root system's demise during pod fill when nitrogen need is greatest.
The use of seed inoculants for two consecutive plantings also can generate an improved nitrogen-fixing process in the soil. Fields planted to soybeans for the first time may require special treatment because there may not be enough bacteria to fix adequate nitrogen.
After using inoculants for the first time, farmers may need to apply 75 pounds nitrogen per acre at flowering. The following spring, they should use seed inoculants and plant soybeans for a second year.
The USDA and commercial entities have developed improved inoculants, but newer materials are coming. "More productive strains are being developed using recently developed gene transfer technology and will enter the market in about two years."
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