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Research Highlights

Research Highlights
Improving yield in double-cropped soybeans

Wheat harvest and soybean planting take place at the same time on the Kejr Farm in Kansas. Photo by Josh Kejr.

By Carol Brown, USB database communications

Photo by Josh Kejr

Growing soybeans in a double-cropping system is becoming a common practice in Kansas as well as in other states. Pairing grains such as wheat, barley or other winter crop with soybeans can increase farm income by growing two cash crops on the same land in the same crop year.

Kansas researchers have shown that planting soybeans earlier and in narrow rows can improve soybean yield in a double-cropping situation.

“Double-cropping can be an excellent option for farmers to increase productivity,” said Ignacio Ciampitti, lead project investigator. “We are looking at intensifying production using the same units of land. We also explored several factors to find the best combination of inputs for improved yield.”

Ciampitti, an associate professor in agronomy at Kansas State University, received checkoff support from the Kansas Soybean Commission to determine how farmers could improve productivity with double-cropped soybeans. In a double-cropping system, soybeans are planted in fields that would traditionally have grown a cover crop or left fallow. Historically, soybean yield lags in the double cropping system compared to full-season soybeans.

Increased soybean production is being pursued as the world’s population continues to grow. More soybeans will be needed to contribute to the global food system in the next 25 years. Researchers across the country are studying how to increase production without using more land. Farmers growing two cash crops in one year can increase supply without placing more acres into production.

Research results

Ciampitti and his research team addressed the potential yield limiting factors for soybeans in a double-crop system: planting date, seeding population, soil moisture, residue from the winter crop as well as fertilizers, pests and diseases.

Season length is a major factor for soybean maturity,” Ciampitti said. “As soon as the winter crop is out, you want to get your soybeans in right away.”

If farmers harvest their winter crop in the third week of June, that means the soybeans are planted the third or fourth week of June, which can impact the system, he said. In some tests, they harvested wheat 15 to 20 days earlier than usual. Ciampitti said the winter crop had a little more moisture, but the earlier harvest days helped with getting the soybeans established sooner.

“It is a compromise between waiting until the winter crop is truly finished and maximizing the double-cropping system,” he said.

Other factors that have an impact soybean yield in a double-cropped system include seeding rates and row width, according to Ciampitti’s research. Increasing seeding rates as well as having more rows could compensate for the lack of time the soybean has to grow.

 “We tested increasing seeding rates at 10 and 15 percent compared to what was recommended for full-season soybean planting populations,” he said. “The increased population forces the plants to compete faster for resources, such as sunlight. They have fewer days to produce branches and close the canopy much sooner than lower populations, increasing the number of pods produced at the canopy-level.”

For all site years except one, high seed population contributed significantly to higher yields; and earlier planted soybeans had greater yields in high population treatments.

Ciampitti cautioned that late soybean planting can have the potential of freeze damage. The probability that the crop will not reach maturity is increased as planting is delayed.

Other factors to consider

Another factor to be aware of, Ciampitti said, is to ensure machinery is calibrated for uniformity of residue size and distribution from the winter crop. This will help with soybean emergence.

“I have seen situations with farmers who did all the right things for their soybeans but had a lack of uniformity on the winter crop residue. This impacts the survivability of that soybean,” Ciampitti said.

Although Ciampitti did not officially research environmental impacts, double cropping has some positive benefits.

“If you compare the soybean double-crop system to a full-season system, the ability to control weeds was better because we kept most of the ground covered the entire year, similar to a cover crop,” he said. Additionally, with continuous ground cover soil erosion is reduced as well.

One of the disadvantages of planting soybeans after wheat or other winter crop is decreased soil moisture, especially on non-irrigated acres.

“If you have a very high yielding winter crop, most likely that crop is capturing and using quite a bit of water and nutrients,” Ciampitti said. “Those factors have an impact on the following crop. It will be even more impactful if you are depending only on precipitation, not irrigation. The system is very susceptible to not having enough moisture to establish the soybean crop.”

The research project was conducted over two growing seasons, with eight site years in two locations. Soybeans were planted after two different wheat harvest dates.

Other resources: Double-crop Soybeans After Wheat: A Review

To find research related to this Research Highlight, please visit the National Soybean Checkoff Research Database.