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Increasing net returns by double-cropping soybean

By double cropping soybean after winter wheat, farmers can increase their net returns. These increased returns come without needing to farm additional acreage, a new study shows.

Double cropping is a practice where farmers harvest one crop, and then plant and harvest a second crop in the same field – all within the same year. “Often, research is focused on single crop soybean,” says Carrie Knott, member of the American Society of Agronomy and researcher at University of Kentucky. “But there is a real need for research in double crop systems, as well.”

A new study from Knott and her team has determined soybean characteristics that can maximise chances that farmers profit from double cropping soybean. The research was published in Agronomy Journal.

The researchers tested several soybean relative maturity groups and seeding rates. “These are two agronomic practices every producer must consider,” says Knott.

Soybean relative maturity groupings are a numerical scale that describe how fast soybean varieties develop in relation to day lengths in different regions. In general, the lower the number, the faster the soybean plants are ready for harvest.

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Because of changing weather patterns in the past 30-40 years, updated data on intensive double crop soybean production was needed to keep farming recommendations current. - Photo: Carrie Knott
Because of changing weather patterns in the past 30-40 years, updated data on intensive double crop soybean production was needed to keep farming recommendations current. - Photo: Carrie Knott

Maximise seed production and profitability

Much of the previous research on double cropping soybean is 30 to 40 years old. Knott and her colleagues wanted to make sure that the current recommendations for double crop soybean were still valid to maximise seed production and profitability.

“Weather conditions have changed during that time,” says Knott. “They are predicted to keep changing in the coming years, as well.”

Double crop soybean accounts for about 10% of soybeans produced in the Upper Mid-South and Ohio River Valley regions in the United States. However, that figure was as high as 36% of the region’s soybean production in the past. “The logistics of the double crop system can be very demanding at times,” says Knott.

Identify profitable farming strategies

There is potential for reduced profitability. There are also some increased risks associated with producing double crop soybean.

Knott and her colleagues set out to identify profitable farming strategies for double crop soybean. They also aimed to understand the various risk factors.

Study sites were in western Kentucky. Four soybean relative maturity groups at five different seeding densities were tested over two growing seasons. The researchers determined the relative maturity groups and seeding densities that produced the highest yields.

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A recent study found the longest soybean relative maturity groups led to the highest yield in double crop soybeans. - Photo: Carrie Knott
A recent study found the longest soybean relative maturity groups led to the highest yield in double crop soybeans. - Photo: Carrie Knott

Risk analyses

According to the study, the longest relative maturity groups had the highest yield. Also, the highest seeding rates led to the highest yields.

But Knott and her colleagues wanted to learn about more than yields. They also used risk analyses to find which relative maturity groups and seeding rate combinations maximised the likelihood of positive net returns for farmers.

Results show that planting soybean relative maturity group 4.7 at 200,000 seeds per acre would have the highest probability of creating a positive net economic return.

How double-cropping helped transform Brazilian agriculture

From 1980 to 2016, grain production in Brazil increased more than fourfold, and the country now stands as the world’s largest soybean exporter and the second largest exporter of corn. The two main drivers of this increase in food production were cropland expansion and double-cropping.
A new study by University of Delaware, published in Nature Food, quantifies for the first time the impact that double-cropping also had on helping Brazil achieve its national grain boom.
According to the study, the increase in grain production in the Brazilian Centre-West – which produces 46% of the country’s grain – can be attributed to cropland expansion as well as double-cropping. Contributions from double-cropping in the region reased from 19% to 33% from 2003 to 2016. While the increase in soybean production was largely due to cropland expansion, the increase in corn production could be linked to the practice of double-cropping.
In the Centre-West, the agricultural area for second season corn – or the corn grown after the first season soybean is harvested – increased from 26.3% to 66.6% from 2003 to 2016, and in 2012, the second season corn crop surpassed the corn grown during the first season as the main source of corn nationwide.
From 2003 to 2016, double-cropping in Brazil offset the equivalent of about 76.7 million hectares of arable land for corn production, that is, more than twice the annual harvested area of corn in the United States.

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