When it comes to cover crops, biomass production is key to getting the most bang for your buck, and early planting dates pack the biggest punch. However, harvest operations often push cover crop planting dates later into the season. 

So, what can a farmer do to maximize the return on investment (ROI) and get the most out of cover crops? To investigate, Kip Balkcom, research agronomist at USDA-ARS conducted a six-year study to determine the best planting dates and input rates for a high-residue cover crop. 

Bottom line: management is key. “Cover crops require both a monetary and time investment, just like any other crop,” Balkcom said. “If we expect to get something out of them, we have to put something into them.” 

Balkcom’s study took place at the Wiregrass Research and Extension Center in southeast Alabama from 2015 to 2020. Cereal rye was planted on a Fuquay sand with a range of inputs. Balkcom’s research looked at: 

The goal was to determine whether an increase in inputs on later planted crops could produce the same amount of biomass as earlier planted crops. Balkcom shared the biggest takeaways to maximize your ROI with cover crops. 

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Seeding rates: How low can you go? 

Balkcom explained the seeding rates in the cover crop study. When the study kicked off in 2015, it was believed that higher seeding rates provided better surface coverage. However, that is no longer the case.  

“There is a lot of research out there showing we do not need nearly as much cover crop seed as we once thought,” he said. 

Balkcom tested high and low seeding rates. He planted 90 pounds per acre for the high rate, then cut it to 60 pounds per acre for the low rate. 

In the end, Balkcom said the seeding rate did not impact biomass production, and he believes he could have planted an even lower rate. “Using 60 pounds per acre as our low rate made no difference. I wish I would have cut it to 45 pounds per acre,” he said. 

Of course, the amount of seed you plant affects the cost of production and reducing your seeding rate can boost your bottom line.  

Balkcom said, “We do not have any control over how much seed costs, but we do have control over how much we plant. It is good if we can reduce these seeding rates, but we still have to know how low we can go.” 

Planting dates and nitrogen rates 

Of the four planting dates in the cover crop study, two were planted early and two were planted late.  

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Nitrogen was applied at four rates from 0 to 90 pounds. Biomass was measured to determine the crop response to the fertilizer applications.  

When nitrogen was applied at 90 pounds per acre, both the early and late planted cover crops saw an increase in biomass compared to when no nitrogen was applied at all. The early and late planting produced 2.2 times greater biomass and 2.9 times greater biomass, respectively, when the highest nitrogen rate was applied. 

While the later planted crop showed a slightly higher response to nitrogen, the earlier planted cover crops still produced twice the amount of biomass.  

Balkcom said the big takeaway is early planting. “Across these coarse-textured soils in the southeast, we generally have to plant cover crops by Nov. 15 to produce enough beneficial biomass.” 

He also compared the late October planting date where no nitrogen was applied to the early December planting date where 90 pounds of nitrogen was applied.  

Balkcom said, “For me this is telling. We were not able to overcome the environmental constraints of shorter growing days in the later planted cover crops, even though we threw money at the problem.” 

A look at cost and carbon 

To further examine cost, Balkcom divided the cost of production by the amount of biomass produced to express results in dollars per 100 pounds of biomass. 

For the two early planting dates, the cost of production was consistent at $2 per 100 pounds of biomass. Balkcom said when additional nitrogen was applied on those early planted cover crops, biomass increased enough to offset the cost of the fertilizer. 

This could justify nitrogen applications on early planted cover crops to enhance soil health benefits like erosion control, improved soil moisture, weed suppression, and soil organic carbon. 

“In the past, we put on 30 pounds of nitrogen per acre to keep costs down, but if you plant early and put on 60 pounds or so, I think you could get that cost back in terms of biomass produced,” Balkcom said.  

He also looked at the connection between biomass and soil organic carbon. Balkcom said soil cores were taken across the soil profile to measure organic carbon concentrations. Results indicated that nitrogen fertilizer was necessary to build up soil organic carbon on the Fuquay sand in this study. 

“Sands do not typically build up a lot of soil carbon. When we put on 90 pounds of nitrogen, it produced the most biomass, and that biomass added carbon back in the soil,” he said. 

Balkcom explained that biomass is generally 40% to 45% carbon. “You multiply that by the amount of biomass you produced, and that is how much carbon you added back. In terms of building up soil carbon, we added twice as much when we fertilized, compared to not fertilizing.” 

He also cited the importance of reduced tillage in cover crop management.  

“Soil carbon is generally built up at 0 to 5 centimeters, or the top two inches of the soil. As we get down to 10 to 15 centimeters, about six inches deep, we have basically dissipated that carbon. It does not build up as much in that region. 

“I mention that, so people recognize when you utilize a cover crop, even in conjunction with tillage operations, you want to minimize surface disruption to help preserve the soil carbon you are trying to build up,” he said. 

Of course, Balkcom realizes this study was done on one soil type, at one location in the southeast. Cover crop management may change depending on soil type, climate, and cropping systems, but the benefits are clear. 

“I think the benefits of cover crops are pretty consistent, and they will generally be enhanced as we increase the amount of biomass we produce,” he said.