In the last three to four years, grain sorghum acres have enjoyed a resurgence in Plains states like Nebraska. In years such as 2015, when cash bids for sorghum in some locations were as high as 50 cents per bushel over corn, it's not hard to see the value in adding sorghum to the rotation. Near the end of 2017, grain sorghum prices inched within 5 cents of local corn prices in some parts of Nebraska.
However, sorghum brings a non-monetary value to the rotation as well. Research and grower experience in Nebraska and other Plains states shows sorghum can give a boost to the following corn crop.
Rick Kochenower, agronomist at Sorghum Partners seed company, compared irrigated corn yields when planted in rotation with irrigated corn, soybeans and sorghum in 2001, 2002 and 2004 at the Oklahoma Panhandle Research and Extension Center near Goodwell.
While the corn-on-corn rotation yielded the lowest all three years, all years benefited from a diverse rotation. Corn planted after grain sorghum yielded 20 to 30 bushels more than continuous corn.
"This was on ground that had been in continuous corn since '98," Kochenower says. "I found a 16% to 17% yield increase. The corn-soybean rotation averaged 171 bushels per acre, and corn-sorghum rotation averaged 170, while the corn-on-corn rotation averaged 141."
"One thing I can attribute it to is the massive root system of the sorghum crop. It may not make much sense rotating a grass with a grass, but there are always benefits to rotating crops," Kochenower says. "A sorghum plant basically has twice the root mass of a corn plant. It roots deeper, and that's the reason the sorghum plant is so drought-tolerant."
"The roots grow out and break compaction," says Lynn Belitz, a sorghum grower from Fullerton, Neb., who has realized these yield benefits on his own field. "When the root decays, it opens up the window for the water to get in."
Another driver is the amount of residue left behind in a sorghum field.
"It has to do with planting corn into milo stalks. It's usually 20 to 30 bushels, but it depends on the year. Sorghum doesn't use as much moisture as corn, and the stalks give you more cover so the moisture doesn't evaporate over winter," Belitz says. "There was a dry spring several years ago when we were still disking, and we got to a field that was still milo stubble, and it was still moist. None of the cornstalk fields looked moist. That may be because the milo didn't use all the moisture like the corn did, and it didn't evaporate as easily as the cornstalks in the spring. Meanwhile, when the root decays, it opens up the window for the water to get in."
Slater Chandler, who has grown grain sorghum on his farm near Imperial, Neb., for two years, notes he saw a smaller yield increase in the following corn crop this year. However, it was in a part of the state that receives around 20 inches of annual rainfall, and a continuous crop rotation that doesn't hurt corn yields is a rare thing.
"Last year, I had a 10-bushel boost on the corn after sorghum. This year we didn't have much of a boost, but we didn't have rain for about 60 days. It sure didn't hurt it either, though," Chandler says.
For Chandler, it's more about return on investment, and because sorghum residue holds more water for the following crop, it's also allowed him to break up his wheat-fallow rotation.
Residue plays a big role for Chandler, who grows sorghum on 15-inch rows. While it may seem counterintuitive to have more plants in the field using water in a borderline semiarid climate, he says it also prevents water being lost to evapotranspiration — not to mention water being used by weeds.
Chandler cites research by Bob Klein, Nebraska Extension cropping systems specialist, that shows it takes only a 40-bushel winter wheat crop to give about 100% surface cover, while it takes a 160-bushel grain sorghum crop to give about 100% surface cover. However, both winter wheat and grain sorghum residue last longer than corn residue, because they have a higher carbon-to-nitrogen ratio.
"The residue is so good at holding water on the field. There's a lot more leaf area in milo residue," Chandler says.