Research suggests benefits of pasture burning in August or September
MANHATTAN, Kan. – Uncommonly blue skies prevailed across much of eastern Kansas this April. In most years, springtime means smoke from prescribed burning of pastures and rangeland, but not in dry 2018.
“Most of that reluctance to burn is related to bad weather conditions, and very dry conditions,” said KC Olson, a professor of range beef cattle nutrition and management at Kansas State University. “Folks are worried that if they burn up what forage they have, they might not get anymore.”
Spring pasture burning is a time-honored tradition in the Flint Hills. Prescribed burns are used to control weeds and encourage nutrient-rich, new growth to benefit cattle grazing on those hills (see sidebar).
With so many landowners choosing not to burn in April, Olson said this might be an opportunity to try an approach he’s been encouraging since 2015: prescribed burning toward the end of summer.
The benefits to this strategy begin with weed control.
If Kansas ranchers were asked to name the weed they hated the most, there’s a good chance sericea lespedeza would top the list.
“Sericea lespedeza is a perennial legume,” Olson said. “It’s got a very deep root system and it’s tolerant of thin or poor-quality soils. We have thin soils here in the Flint Hills.”
As a weed, sericea plays a mean game of dirty pool. It thrives in conditions that wither many forage grasses and tamer weed species. Its roots exude a type of chemical that inhibits the germination and growth of other plants nearby. Its leaves are high in condensed tannins, a compound that causes stomach upset to any beef cattle that might ingest it.
Then there are the seeds. “In recent research that we’ve conducted, one stem will produce an average of 864 seeds per year. That’s a four-year average, one stem of a multiple stem plant.”
And it’s in these seeds that Olson believes he’s found an effective strategy: don’t give the plants a chance to develop. The seeds are covered with a thick, protective coating. The seeds must undergo a process called scarification that will crack open that outer coating.
“Fire is the perfect scarifier for sericea lespedeza seed,” Olson said. “The seed doesn’t care if the scarification happens in the spring, in the summer, in the fall – as long as there’s some growing season left, it’s going to germinate, and you’re going to get a juvenile plant. When we burn in the spring and scarify the seed at that time, those juvenile plants have a full growing season to mature, store root carbohydrates, and maximize their survival odds for subsequent years.”
“But,” he continued, “when we burn in August or September, even though we still scarify the seed and still cause germination, that juvenile plant has 10 weeks, maximum, to develop roots, to store carbohydrates, to try to get through the ensuing winter. In our recent four-year study, I believe that the mortality of sericea lespedeza that we observed was due to that effect of burning later in the year.”
Stocker-cattle producers will naturally wonder about the impact to their bottom line. Olson said what might be lost in weight gains will be matched by savings in weed treatment. “I’ve done some mathematics on this. The amount of money that we spend spraying sericea, and accepting the collateral damage to native wildflowers that comes with spraying, completely eclipses the amount of money that we might hope to make by burning in the spring, at what is traditionally considered to be the ‘correct’ time.”
Olson added that there are other research-based reasons for late summer prescribed burning. “Those wildflowers that everybody likes look at out the vehicle window when they’re driving down the road? In our research, fire in August and early September actually stimulated proliferation of wildflowers while suppressing sericea lespedeza, ironweed and Western ragweed,” he said. “As an allergy sufferer, I’m pretty happy to give up a little ragweed.”
This could bode well for people who struggle with allergens and other airborne particulates, including smoke. Instead of suffering twice each year – during traditional spring burning, and during late summer pollen activity – late summer burning just might cut that misery in half.
“I hope that allergy sufferers think about that when they’re irritated by smoke from prescribed burning,” Olson said. “That smoke may be resulting from getting rid of something that makes me feel even worse at a different time of the year.”
With spring burning a missed opportunity for many range managers this year, Olson is hopeful smoke will be a more common sight later in the year.
“A number of people, midstream in this research, decided that they were going to try it because they were so tired of managing sericea with herbicide. I think we’re going to see a lot of acres on fire this August and September,” Olson said.
“Then they’ll wake up one morning in about February of next year and think, ‘You know, I’m going to do that again.’ I hope so.”