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Corn+Soybean Digest

Sorghum Strengths | Adding Sorghum to Rotations Can Reduce Weeds and Disease

Justin Knopf’s no-till sorghum and soybeans contribute to a solid rotation and help generate more consistent yields for both crops, as well as wheat also grown in the mix. But sorghum’s help in breaking up weed and disease cycles helps the most in keeping the crop in his rotation.

He likes how all three crops complement one another in his Salina, KS, dryland operation that receives about 30 in. of precipitation annually. Knopf, his dad Jerry and brother Jeff farm together and also raise alfalfa and have a few acres of corn – acres that are expected to grow in number down the road.

Knopf doesn’t necessarily see exceptionally high yields coming from the sorghum-bean portion of his rotation. It’s fewer weed problems that attract him the most.

Research by Paul Hay, University of Nebraska Extension agronomist, shows that sorghum can yield well in a rotation, but won’t regularly promote higher yields in the following crop.

“Diversity and weed management are significant aspects of having both soybeans and sorghum in our rotation,” he says. “We have a winter annual grass with wheat, a summer annual grass with sorghum and soybeans give us a summer annual broadleaf. Each crop has its own limitations in weed control, but when grown in a diverse rotation, those limitations can be managed.”

Kansas is the nation’s leading sorghum-producing area, partly because the crop works well on marginal land seen in some areas of the state. It’s often in a wheat-soybean rotation.

Tesfaye Tesso, a sorghum breeder at Kansas State University in Manhattan, learned much about milo from research in his native Africa. Sorghum is a huge crop for human and animal food in Africa, so growers know a thing or two about it. And Tesso feels U.S. growers can benefit from what African producers have experienced.
“Growing sorghum will usually help soybeans that follow it,” he says. “It goes along with the cultural practice of growing different crops to change the weed flora. Sorghum following soybeans is especially helpful because Roundup Ready beans (treated with glyphosate) can provide weed control for sorghum the next year.”

As for yields, Tesso says residual nitrogen remaining from soybeans or other legumes should enhance a sorghum crop that follows. “This can sometimes contribute to higher sorghum yields,” he says. “In Africa, they try to plant sorghum in fields that were previously planted in any kind of beans.”

Hay points out that sorghum acres are down substantially in eastern Nebraska and blames it mostly on the higher corn prices. Hay conducted a survey of 10 years of data from some 2,000 growers in eastern Nebraska. He says sorghum yields were respectable, even though other crops rotated after sorghum might see a slight drop in yields, but still perform well.

For example, in his survey of conventional producers, sorghum following soybeans yielded 82.3 bu./acre, compared to 72.1 bu. following corn, 89.3 bu. following wheat and 75.5 bu. in continuous milo. In no-till situations, sorghum following soybeans averaged 94.5 bu., compared to 104.9 bu. following wheat, 101.9 bu. following corn and 87 bu. in a continuous-milo environment.

Soybean yields in conventional-tillage programs averaged 33.7 bu. following sorghum, 40.5 bu. following wheat, 37.3 bu. following corn and 36.6 bu. in a continuous-beans situation. No-till soybeans averaged 35.2 bu. following sorghum, 41.1 bu. following wheat, 38.4 bu. following corn and 35.7 bu. in continuous beans.

In Hay’s survey, corn following conventional sorghum averaged 78.2 bu., compared to 106.3 bu. following soybeans, 109.4 bu. after wheat and 83 bu. on continuous corn. In no-till, corn yielded 79.3 bu. after sorghum, 107.2 bu. after soybeans, 125.4 bu. after wheat and 85.5 bu. in continuous corn.

For wheat in conventional programs, yields averaged 41.2 bu. after sorghum, 46.4 bu., after soybeans, 49.2 bu. after corn and 47.4 bu. after wheat. In no-till, wheat yielded 49.9 bu. after sorghum, 50.9 bu. after soybeans, 60.2 bu. after corn and 52.4 bu. after wheat.

“The results of the long-time survey showed that like corn, sorghum is really responsive to rotation,” says Hay. “If they’re grown after soybeans, you see a yield increase. There’s an even bigger increase if sorghum follows wheat.”

That’s Knopf’s rotation and it fits his need for better weed control in sorghum. “I think most sorghum growers will tell you that effective weed control options for the crop are a limitation,” he says. “But with our sorghum usually following two years of wheat, we have controlled troublesome summer annual weeds during the fallow periods, which means weed pressure going into the sorghum year is much less.”

The operation has been in no-till around 10 years. Residues of previous crops help protect soil against wind and water erosion. “There’s more grace for crops in hot, dry periods,” says Knopf. “More residue gives us a few more days in those situations before we start hurting yields.”

Those yields have been especially high the past few years. Sorghum, which had normally yielded 70-90 bu./acre, has hit over 100 bu. Soybeans have been 45-55 bu./acre, compared to 30-40 bu. in the mid-2000s.

“Our dryland corn actually yielded over 150 bu., in 2009,” says Knopf. “Certainly timely rainfall has been the most significant factor in these higher yields, but we feel no-till is also making a difference.”

Knopf sees adding more corn to his rotation, due partly to the success of his no-till program. “No-till should help corn become a more consistent crop for us,” he says, adding that those acres will prob-ably come from ground normally planted in sorghum.

“Traditionally, sorghum can handle drier, hotter weather. But drought and heat tolerance in corn hybrids continues to improve, so I’m anti-cipating that we may have more corn acres in the future.”

Hay believes in sound crop rotation and sorghum fits into that category because of its weed control. “We should have as many crops in the portfolio as we can,” he says.

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