For many years, burley tobacco growers have used cover crops in the offseason to protect the soil and scavenge nutrients. Because many tobacco growers also produce livestock, a team of researchers at the University of Kentucky is examining the entire enterprise as one system. The team includes assistant professors Ben Goff in forage and grazing systems and Erin Haramoto in weed ecology, as well as Extension professor Bob Pearce in burley tobacco production systems.
The researchers have a two-in-one goal: to study the impact of management of winter forage species on tobacco yields in a strip-tillage system and to determine the impact of tobacco herbicides on the establishment and growth of those forage species. Their study seeks to determine the right combination of forage species, herbicides and weed management to best prepare the soil for tobacco transplanting.
“Tobacco’s the moneymaker, and we don’t want to overlook that fact,” said Pearce. “Margins are fairly tight, so if we can eke out some additional economic benefit from the system, then that’s what we want to do. The idea behind this test is to look at ways that we can utilize the cover crop without doing anything to harm our main cash crop in the process.”
Growers should understand that the value in cover crops is not necessarily as exports themselves but in protecting the land, reducing soil erosion, maintaining the topsoil and recycling nutrients. “If we look at trying to achieve a dollar value out of that cover crop, say a hay harvest, then we cut that material, and instead of returning those nutrients back to that soil, we’re going to export them off of that piece of ground,” Pearce said. “That’s one of the trade-offs that we have to consider.
“I’ve seen few cases where a grower has tried to cut a wheat crop for hay, or make silage out of it, and the tobacco crop has not really done well in some of those scenarios. That’s kind of the thought process behind this—to see if we can we can do some of these things if we manage them well without impacting our tobacco crop.”
Crimson Clover, Over and Over
Historically, burley growers have stuck with small grains—usually winter wheat or winter rye in Kentucky—as cover crops. For flue-cured tobacco, the Virginia Cooperative Extension also recommends a rotation incorporating small grains and fescue or ryegrass. These crops do a nice job of returning nutrients to the soil, but on their own they do not have much forage value. Growers of late have been encouraged to diversify cover crops, and this experiment was designed to incorporate crimson clover with winter wheat in the hopes of returning nitrogen to the soil and improving the forage value of the cover crop.
Tobacco growers have long understood the role of cover crops in maintaining their soil, but integrating these new mixtures could cause skepticism. Growers will want to be confident in results before investing in seeds. “If you’re asking a grower to spend more, he has to be able to see that value and where that value is in terms of a more valuable forage—that you can demonstrate that value that it preserves the soil,” Pearce said. “You have to be able to show that that value is there in order to get that grower to spend that extra money.”
Unearthing the Herbicide Factor
The researchers are also looking at the impact of herbicides commonly used on the tobacco crop on the forage crops that follow. In the first year of this particular program, no major issues came forward, though Pearce said there could be cumulative effects that have not arisen yet.
In his past research, Pearce has found that the best management practices for cover crops involve killing them in early spring so that they can break down, three to four weeks prior to transplanting tobacco. Waiting much longer than that can cause problems such as water being taken out of the soil as well as pest and nutrient problems.
Early burndown means less crop residue is left on the surface, which can also impact weed control.
A cover crop that is killed and left on the surface can act as a mulch for the crop that comes after, but the plant material could also intercept some chemical treatment intended for the soil.
“We can either see suppression or enhancement of weed problems when we have a heavy cover crop,” Pearce said, “so we’re trying to take a look at those things and see if, somewhere in there, there’s an optimum, and can we reach that through proper management.”
The work continues as the researchers evaluate the effects of cover crops and grazing on the tobacco, as well as the timing of harvest. How does an earlier crop fare versus a later crop in terms of nutrients and the use of water? “Those are all excellent questions,” Pearce said, “and ones that we don’t have answers to at this point.”