Released: March 19, 2002

K-State Study: Soybeans Benefit From Crop Rotations, Too

TOPEKA, Kan. – It’s pretty well known that when corn and grain sorghum crops are rotated with soybeans, the corn and sorghum benefit from the rotational effect. But researchers at Kansas State University have shown that rotations help boost soybean yields, too.

"Some people may not be aware of it, but soybeans in a rotation benefit from the rotation effect," said Larry Maddux, Agronomist-in-Charge of the K-State Research and Extension Kansas River Valley Experiment Field. "It’s not unusual to see a 10 to 15 percent [soybean] yield increase due to the rotation."

By rotating crops, Maddux said, the disease, insect and weed pressures are lessened compared to a monoculture system where one crop is continuously grown. The pests are constantly kept off balance when crops are rotated.

Maddux’s research was done on irrigated land and included crop rotations of corn-soybeans; corn-corn-soybeans; continuous corn; and continuous soybeans. Four nitrogen treatments were used on the corn in each of the rotations – 0, 75, 150 and 225 pounds per acre.

In his research, continuous soybeans yielded 60 bushels per acre, while soybeans in a rotation yielded an average of 65 bushels per acre – about an 8 percent yield increase. The higher yield was attributed to greater weed problems in the continuous soybeans, compared with those grown in rotations

The soybeans did not respond to the residual nitrogen from treatments applied to corn.

Researcher Ken Kelley at the K-State Research and Extension Southeast Agricultural Research Center got similar results on a dryland cropping study. Those rotations included continuous sorghum; continuous soybeans; sorghum-soybeans in a two-year rotation; soybeans grown for one, two, three, four and five years after sorghum; and sorghum grown for one, two, three, four and five years after five years of soybeans. Two nitrogen rates – 60 and 120 pounds per acre – were applied to the grain sorghum.

"The four-year average yield for continuous soybeans was 24.6 bushels [per acre], while the yield of soybeans in the sorghum-soybean rotation was 28.4 bushels," Kelley said. "That’s about a 13 percent yield response."

Kelley said one interesting finding of the research was that the longer soybeans were continuously planted, the more the yields declined.

There was a 14 percent yield increase [to 106 bushels per acre] for grain sorghum at the 120-pound of nitrogen rate in the sorghum-soybean rotation compared to the continuous sorghum that yielded 91 bushels. When 60 pounds of nitrogen per acre was applied in the sorghum-soybean rotation, the effect was a 23 percent yield advantage for the grain sorghum – to 91 bushels per acre – compared to continuous sorghum, which yielded 78 bushels.

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K-State Research and Extension is a short name for the Kansas State University Agricultural Experiment Station and Cooperative Extension Service, a program designed to generate and distribute useful knowledge for the well-being of Kansans. Supported by county, state, federal and private funds, the program has county Extension offices, experiment fields, area Extension offices and regional research centers statewide. Its headquarters is on the K-State campus, Manhattan.

Story by:
Mary Lou Peter, Communications Specialist
mlpeter@oznet.ksu.edu
K-State Research& Extension News