Back to Beans

ST. LOUIS (DTN) -- It's time to consider getting inoculated.

Flu season may be winding down, but first-year soybeans will require some doctoring this spring, Michigan State University Extension Educator Mike Staton warns.

As some growers consider a move from continuous corn fields to soybeans, they will need to consider a host of management steps, agronomists told DTN. Inoculation will be the most important one, Staton stressed. Checking on proper nodulation this summer will help growers gain that oft-reported bean yield bump following corn. Growers should also test soil for the proper levels of pH, phosphorus, and potassium, and some may need to plan ahead for managing heavy corn residue during planting.

INOCULATE, THEN FOLLOW UP

If you've been out of the soybean game for three to four years, a soybean inoculant is imperative, Staton told DTN.

Like the friendly legume they are, soybeans are able to create a mutually beneficial relationship with the microscopic bacteria living in the soil around their roots, Staton explained.

"The soybeans give bacteria the food it needs, and the bacteria takes atmospheric nitrogen, which is not usable to the soybean plant, and converts it to a form that is usable," he said.

After years of no soybeans, the neglected bacterial population of your soil will decline, and their departure can hit you in the pocketbook, Staton added.

"Soybeans need so much nitrogen that if you don't have that bacteria functioning properly, you're going to lose a tremendous amount of yield, 10 to 12 bushels," he warned.

University of Arkansas soybean specialist Jeremy Ross has done extensive studies of inoculants on the market and said there seems to be little difference between the available products, so finding a good inoculant shouldn't be difficult. Their benefits are so well established that university agronomists in Michigan and Ohio actually recommend using an inoculant every year, regardless of your rotation, Staton said.

Don't relax once the seed is inoculated and in the ground, Staton warned. "Producers really should dig up some roots in representative areas in the field just before the plants blossom, in late June to early July, and look for these root nodules on the roots," he explained.

NODE CHECK

Dig -- don't pull -- the plants up, and carefully clean the delicate root system off. Look for small, hard nodules on the roots. If you find roots sprinkled liberally with these nitrogen-fixing bumps, you're in good shape. If you don't see at least seven nodules on the roots, your beans will need supplemental nitrogen, as soon as possible, Staton warned.

The nitrogen needs to be applied at R1 (first blossom) or R2 (full bloom), or growers won't see benefits, he added.

Nodulation can be unsuccessful for several reasons, Staton noted. The bacteria in the inoculant may not be viable, soil pH levels could be too high or low, soil conditions could be too wet or dry following planting, or residual nitrogen in the field could be too high.

"Residual nitrogen from manure or commercial fertilizer will make soybeans lazy," Staton explains. "If they have nitrogen available -- the magic number is 40 pounds per acre in the soil at planting time -- those plants might not nodulate."

You can find more information on identifying and responding to poor nodulation in this article from Michigan State University Extension's Field Crops website: http://goo.gl/….

FERTILITY CHECK

Continuous corn can lower the pH of a field faster than other crops, thanks to the acidifying nature of the added nitrogen those fields require, Staton warned.

If soil isn't frozen, it isn't too late to take some soil samples and send them to a lab to check pH and various nutrient levels. If that isn't possible, don't despair -- any soil test done in the past two years should give an accurate assessment of soil fertility, Staton said.

Soybeans prefer a pH between 6.0 and 6.5. A lab test can identify soil pH levels of your soils. Another test known as the buffer pH or lime index can indicate the amount of lime needed to correct a low level.

Take special note of potassium levels, which are especially important to soybeans. Crop uptake can lower potassium levels relatively quickly in fields, and in course-textured soils, leaching losses are possible, Staton said.

Most land-grant universities publish recommended levels of nutrients for common crops like soybeans, he added. For example, you can find the combined recommendation of Purdue, Michigan State, and Ohio State universities here: http://goo.gl/….

MANAGE RESIDUE

Some continuous-corn growers might be faced with a thick mat of corn residue at planting, Staton added. If you want to use tillage to smooth it out, options are likely limited to some type of shallow vertical tillage. Soils may be too wet for deeper tillage implements in the spring.

No-tillers shouldn't be put off by patches of heavy corn residue, added University of Nebraska Extension Engineer Paul Jasa. "Soybeans are extremely forgiving," he told DTN. "I can put them on top of residue or 3 inches deep and they'll still grow and still yield."

Jasa discourages the use of residue-moving attachments that some farmers put on the front of their planters to clear away residue. "Anytime you put a residue-mover on the planter, it detaches the residue, and now it can move around with the wind or flowing water," he warns. "I'd rather leave the residue standing upright, anchored, and attached -- then the planter and drill can pass across it. If I knock the residue loose, then it moves with the implement, and it will cause plugs and problems."

For more information on a simple way to improve drill and air seeder performance, see this article from Michigan State University Extension's Field Crops website: http://goo.gl/….

Emily Unglesbee can be reached at Emily.unglesbee@dtn.com

Follow Emily Unglesbee on Twitter @Emily_Unglesbee.

(PS/AG)

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