Switchgrass may be a few years away from being used in cellulosic ethanol production, but its growth curve could make it an option today as a forage companion to tall fescue, according to research at the University of Tennessee, presented at the Milan No-Till Field Day in Milan, Tenn.
Gary Bates, professor, Extension coordinator, University of Tennessee Plant Sciences, said the growth curve of tall fescue shows good development in the spring and the fall, but the plant is not adapted to high temperatures and periods without rainfall, so forage production slumps during the summer.
But warm-season grasses such as switchgrass have the opposite growth curve, he says. “When fescue is starting to slump in June, July and August, switchgrass grows best. So animals could graze on the switchgrass during this time and you could rest the fescue. Last year was perfect example. If you just had fescue to graze, you really struggled.”
Bates says quality objectives for switchgrass are different for forage than for biofuel. “What makes a really good biofuel crop — low nitrogen content, low energy and a lot of fiber — makes a very poor hay crop. For a hay crop, we want a lot of protein, a lot of energy and very little fiber. So it's just a matter of how you manage the crop.”
Research indicates that annual switchgrass yields are not significantly different between a one-time harvest and a two-time harvest. However the forage quality from a one-time harvest late in the year “is pretty rough. The November cut was only getting 2 to 3 percent protein. That is not going to meet the needs of a cow during the winter.”
Work done on two switchgrass varieties, Cave-in-Rock and Alamo, showed that if either is harvested early enough in the year, “you can get a protein content that is 12 percent to 14 percent protein. That's good quality for livestock. But the later you wait to harvest it, the lower the protein. Every forage crop follows this same type of curve. When you cut it early, it's good. If you cut it late, it's bad.”
Other warm-season grasses, bermudagrass, pearl millet and crabgrass, are the same way, Bates says. “If you cut them when they're vegetative and they don't have a seed head, you get 15 to 16 percent protein. If you wait to harvest until they start producing a head, they have 6 to 8 percent protein. So it relates to maturity.”
Extra management is required for switchgrass, Bates stressed. “Traditionally fescue hay is cut when there's a break in the weather, when we have a week to get it laid down and dried. If we cut fescue before it produces a seed head, we can get 14 to 15 percent protein. In west Tennessee, that's going to be in the first week of May. Even if I cut in the first week of June, it will still be 10 percent protein and the cow will do fine. So I have a month window for cutting and still can get a good hay crop.
“We don't have quite as much leeway with switchgrass. Our research showed that quality started dropping long before it produced heavier stems to support a seedhead. You have to get it out when it's relatively young, about 30 inches tall. If you wait past that, you'll start getting lower nutrient quality.”
Producers can also use switchgrass in grazing programs, according to Bates. “Research in Nebraska on two different types of switchgrass indicate gains for steers of 1 to -2 pounds per day. The point is if you get rainfall, you get good gains. If you have a drought, your weight gain might be lower.
“But you have to be careful. The biggest hesitation on using switchgrass as a grazing crop is the harvesting height. If you start cutting or grazing down below 6 to 8 inches, you start to weaken your plants. It's harder for them to come back when you remove the growing points.
“So if you use switchgrass for grazing, you need to have some level of a rotational grazing program. You can't just chunk the cattle out there and say, ‘go at it, girls.’”
In the future, the beauty of switchgrass could be giving the producer flexibility to use it as either a forage or biofuel, according to Bates.
“If it's used as a biofuel, it's allowed to grow for the entire year and gets to 7 to 8 feet tall. The first week in November after a few frosts, it goes dormant, then it's harvested for cellulosic ethanol.”
“If you had 10 to 20 acres of switchgrass that was supposed to go to a biofuel crop, you could take the first cutting off 10 acres for hay, then let everything from that point on go to a biofuels crop. Yes, I'll cut my biofuel yields down a little bit, but maybe the value of it as hay crop early would offset that.”
Planting switchgrass could be a good hedge against weather too, noted Bates. “Think about last year, the Easter weekend when we had that freeze. When producers cut their hay crop in the spring, they knew they had about half the hay crop they needed.
“It would have been good to have some warm-season grass out there.”
Bates doesn't believe switchgrass could turn into a weed problem in other crop fields.
“No. 1, it's not very competitive as a seedling. In fact, our biggest problem is getting it established. We don't think it's going to spread by seed very much and it doesn't have rhizomes. The plots we today are still in the same spots they were when we started them.”