How much fertilizer nutrients do you remove when you bale peanut vines?

It’s becoming an increasingly popular question among peanut producers, and it’s one for which there are no easy answers, says Glen Harris, University of Georgia Extension agronomist.

Harris explored the value of peanut vines during this year’s Southern Peanut Growers Conference, held this summer in Panama City.

“I’ve been in Georgia for 14 years, and over the past three or four years, this is probably the biggest question I get,” says Harris.

For typical peanut production — such as that in south Georgia and north Florida — the nutrient value of peanut hay is probably about 50 pounds of nitrogen, 10 pounds of phosphorus and 60 pounds of potassium, he says.

“That’s what I got when I raked up peanuts by hand and had them analyzed — the vines averaged 1.7 percent N, 0.35 percent P2O5 and 2.1 percent K2O,” he says.

Although current fertilizer prices are extremely volatile, if you consider a nitrogen price at 70 cents per pound, phosphate at 80 and potassium at 50 cents per pound, then the vines would be worth $30 for nitrogen, $8 for phosphate and $30 for potassium for a total of $73 per acre, says Harris.

“I’ve done a lot of research, raked a lot of vines, sampled and weighed a lot of bales, and discussed this issue with our county agents. And when you think about it, how much you’re removing with peanut hay depends on a lot of different factors,” he says.

One of the factors that has been discussed is peanut varieties, and whether or not newer ones yield less vines than older ones. Research in Georgia, says Harris, has shown that most modern varieties yield about the same amount of vines per acre.

There’s also the question of how much a peanut crop yields, and how this affects the amount of hay. “Obviously, the more peanut yield, the more vines, unless the peanut yield is well below average and vine production is obviously reduced. Then vine yields should be about the same regardless of pod yields,” he says.

Baler efficiency also figures into the equation, says Harris. “This really tripped me up until the county agents straightened me out. I have always used the old number — that a 3,000-pound per-acre peanut yield will produce 6,000 pounds of vines per acre. I even raked up some vines from different peanut varieties to verify this. But the numbers the county agents were getting, based on how much their farmers were removing, were not adding up.”

It didn’t take long, he adds, to figure out that when he raked the vines by hand, he was recovering everything — very different from a farmer using a hay baler. Baling efficiency depends on how the vines are windrowed, how dry they become before picking, and how soon you bale them after picking, he says.

Baling efficiency, he explains, is somewhere around 50 percent. So with 6,000 pounds of vines per acres, you’re removing about 3,000 pounds. But the weight of round bales also can vary, anywhere from 800 to 1,200 pounds, with 1,000 pounds being a good average, he says.

The nutrient content of peanut hay is like other nutrient contents — it won’t be the same everywhere, and it would have to be analyzed on an individual field basis. “A lot will depend on how many vine leaves you lose and leave on the ground,” says Harris.

The question of how much the peanuts vines are worth obviously depend on the price of fertilizer at the time, he says. “That round bale is worth more now that fertilizer prices have increased. But one thing we need to realize is that our soils in south Georgia in the Coastal Plain are not high in organic matter to begin with. A lot of people say the definition of sustainable agriculture is leaving peanut hay on the ground. There’s a lot of truth to that when you look at our soils and organic matter.

“If you leave that on, you’re leaving not only the nutrients but also the carbon. I understand the need for feed and cash flow, but if you want to do what is best for the soil — not considering the other factors — then you’ll leave it on the ground.”

And this is not a new discovery, he says. In 1988, a University of Georgia economist concluded that peanut vine removal may not pay. With higher fertilizer prices and the higher value placed on increasing soil organic matter, Harris reaches the same conclusion today in saying that farmers should be looking more at the inherent value in not removing peanut vines from the field.

e-mail: phollis@farmpress.com