Double cropping is not a new invention and in the right environment, it can have a positive impact on farm profitability by maximizing time and resource in a single season. In South Carolina, farmers continuously farming irrigated corn in sandy soils on the Coastal Plains have been experimenting with double cropping corn and soybeans – with some success.  

“This is not really a new concept. We're growing a crop, coming in with harvest immediately, and planting something else,” said Clemson University Extension specialist Michael Plumblee. “We've done this for several years in South Carolina with small grains and soybeans. That was our rotation for a long time, and we have kind of again shifted away from that, just because we're not growing as much wheat.”  

Farmers were looking for another double cropping solution to break up continual corn production, for profitability, but also to impact soil health, weed and disease pressure. The result was to test out a system the state’s Georgia counterparts had likewise tried – following corn with soybeans in a single season. 

“About four years ago, we estimated we had 3,000 to 5000 acres of this being tried at varying levels, and a lot of different recommendations and different practices going on,” Plumblee said. “Since we've been doing this research, we've probably increased the acreage at least in a few counties, to over 20,000 acres, and we have more of a consistent effect.” 

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The gist is this: Grow a full-season corn crop with the normal focus on yield and management, cut it quickly at high moisture and immediately plant soybeans with the goal to make a crop before first frost as cheaply as possible. 

Simple? Sure. Plumblee said the strategy holds up even with farmers ruthlessly in pursuit of the best profitability for their farms.  

“A lot of our growing mentality in that area is very similar to Mississippi, where they're very aggressive,” Plumblee said. “They’re going to make sure it pencils out and then they're going to do it right.” 

What are the keys to success? 

Planting Date  

Planting dates were equally critical for both the corn and soybean crops. Planting the corn in March and following with soybeans no later than the first week of August seemed to be the sweet spots on-farm. 

“The hybrid selection on corn didn't matter as much as relative maturity, but the march planning dates seem to be critical,” Plumblee said. “As well as harvesting at 20% moisture content or higher - anywhere we let it field dry was way too late when we got the soybeans in to stand a chance.”  

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Knowing a March plant date and high moisture picking worked best helps guide planting for the soybean crop – in which timing was equally critical. 

“When we looked at the soybean yield across all these different planting dates, we had some plots that we were pushing 50 bushels, but I'd say the average is probably 25 to 30 bushels on some of our earlier planting dates,” Plumblee said. “The later we plant, we're really reducing our yield.”  

Yield reduction to the tune of a .4 bushel-per-acre per day after harvest farmers waited to plant the soybean crop – a significant drop to signify time is of the essence. 

“A lot of the guys double cropping are seriously chasing the combine with the tractor, planting behind it,” Plumblee said. “They'll plant all night if they have to just try to get the soybeans in, because they know that every day matters.” 

Residue management after corn harvest is a critical component for soybean stand establishment for farmers attempting a double cropping system. (Photo courtesy of Michael Plumblee)

Residue Management  

Planting behind the combine brings up another challenge to the double cropping system – managing tall corn residue. For farmers intent on pursuing double cropping, Plumblee said investing in residue management tools like row cleaners or choppers helped the system flow more smoothly. 

“A lot of the growers that have really adopted this have started to invest in some equipment to help with some of these challenges,” Plumblee said. “One of those being a stalk chopping corn head, so that after they're done harvesting corn, the field is basically prepared to be planted. Confetti chain rolls also are a big help in this system, to chop up the residue ahead of the planter.” 

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Managing residue helps the soybean crop establish more quickly, which is important when time is of the essence. 

Plant Height 

“One thing that we identified very early with some of the farmers that were already doing this practice is that plant height is absolutely critical,” Plumblee said. “We can make 30 bushels, but if the plants are only five inches tall and we can't get them into the combine header, we're not really doing a whole lot of good.”  

Soybean varieties with a tall stand and a maturity group five performed best in trials and on farm. Plumblee said group four did not perform well in the system, despite high expectations.  

Overall, soybean planting is highly dependent on corn planting, so variety selections need to be made in tune with one another. 

Where does it fit?  

For double cropping to be an option, South Carolina has seen the best results in sandy, irrigated soils. With only about 20% of farm ground in South Carolina under irrigation, Plumblee said the system is not a fit for everyone.  

Soybeans grown in the system are continually battling the first frost, which comes at a similar time of year in South Carolina as it does in Delta states. 

“We're kind of on the same latitude as Mississippi, and our first frost date is only about Nov. 8,” Plumblee said. “The first year that we did this work, we did have an early frost about Oct. 16. At that time, a lot of these soybeans were about V6, so it would have been similar to accidentally desiccating too early. We estimated we had about 10% to 15% loss.”  

Although the results were disappointing, Plumblee said experiencing loss actually encouraged some producers to push forward. 

“It wasn't a total flop. We still made some soybeans,” Plumblee said. “I think that made people feel a little bit more comfortable with doing the system after we had an early frost and it wasn't a total failure. Obviously, no crop insurance on these type of soybeans is a little bit more risky.” 

Farmers in South Carolina have chased combining corn with planting soybeans in hopes of higher profitability. After five years of testing, some say there is a method to the madness. (Photo courtesy of Michael Plumblee)

Is it profitable?  

Farmers saw positive profitability results when corn was prioritized. Planting a productive variety at a good planting date and then treating it with an eye toward yield helped producers reach goals they typically would set for single crop corn.  

When following with soybeans, Plumblee said farmers saved money by cutting additional nitrogen applications, which had no impact on yield. As well as backing down their tyical seeding rate for soybeans from 180,000 seeds per acre to closer to 150,000 seeds per acre to save on seed costs.  

With those changes, farmers double cropping essentially had the same profitability projections as full season corn – with some additional drying costs - plus the profitability of the entirety of the soybean crop, which pushed the potential profit for a double crop beyond continual corn. 

“The potential is there. I think the mentality and the mindset to get them in, get them cut, and the equipment set up has got to be there,” Plumblee said. “We keep learning more and more about this system as we go. We're able to spread the cost of equipment across two crops on one calendar year. We're not having volunteer corn come up after we harvest, and we’re seeing a lot of other added benefits.”