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Reduce invasives to increase rangeland soil health

Reducing smooth brome and Kentucky bluegrass to grow more native grasses and forbs improves soil health and resilience against drought.


Stan Boltz, a USDA NRCS rangeland management specialist in South Dakota for 33 years, describes how healthy soil and cattle grazing management can reduce invasive species, bring back native rangeland and increase stocking rates.

Listen to the podcast interview with Robin “Buz” Kloot on Growing Resilience podcasts.

From his town-kid youth, where he viewed his first ranch on a hayrack hoisting bales, Stan Boltz has since spent three decades helping ranchers improve grassland, so more cows harvest paddocks efficiently.

His passion for rangeland plant and soil health grew from a botany class into an NRCS career. It started with rangeland studies in Texas and Nebraska, followed by USDA-Soil Conservation Service work in Nevada for 10 years before moving back to South Dakota in 1997, and eventually serving as NRCS state rangeland management specialist. In 2016, Boltz moved into his current role as regional soil health specialist.

Boltz believes in the impact of dynamic soil properties and how rancher management can affect the plant community above ground—a topic that needs more discussion in rangeland management. “One of the dynamic soil properties that are very affected by management is aggregate stability, and that's very key to erosion. Another is water infiltration due to a combination of soil characteristics. And a third one is organic matter. These big three affect the plant community changes you see above ground.”



Smooth brome kills soil structure

In South Dakota and the Northern Plains, two significant threats to diverse native rangeland are conversion to cropland and invasion of non-native cool-season grasses, primarily Kentucky bluegrass and smooth brome. “Since ranchers can still graze these grasses, perhaps they’re not perceived as a threat,” he says.

“If you dig up soil beneath smooth brome, you’ll notice very shallow roots and the soil lacks structure, pore space that leads to poor water infiltration. Research also shows smooth brome and other invasive species change the soil biology to prevent native species seed from germinating,” Boltz adds.

Kentucky bluegrass does other things that are equally bad for the soil. “Due to reduced fungi and very shallow roots, the breakdown is minimized, which creates a thatch-mat layer with a poor platy soil structure below. Again, rainfall doesn’t make it into the soil profile,” he says.

Rancher strategies to reduce invasive species

In the podcast, Boltz discusses numerous methods that can help ranchers reduce these invasive species so cool-season native species can increase, such as green needlegrass, needle-and-thread and others.

“One method of success is early heavy grazing down to the ground of Kentucky bluegrass and smooth brome before the cool-season native grasses begin to mature. It’s a small window to do it, and some ranchers do it a paddock at a time, then shift the paddock back to moderate grazing. It does work, and ranchers tell me they’ve seen a large increase in native grasses come back,” he says.



Prescribed burning, especially in the eastern part of the state, has shown success in reducing Kentucky bluegrass. “A late April-early May timeframe works best,” Boltz says. “And I know ranchers who have used Roundup to knock back smooth brome and bluegrass to bring natives back.”

Boltz says the key is to try these strategies for a few years under good grazing management and watch if natives start to come back. “One of my favorite quotes is from Jim Faulstich,” says Boltz, “and he says, ‘Use what you’ve got, but manage for what you want.’ He truly understands the importance of managing toward more plant diversity.”

Here’s more of what Boltz had to say in this podcast:

“Plant diversity is the one thing that is going to improve soil health the most over time on grasslands. Diversity above ground increases diversity below ground, making the whole system better able to withstand drought.”

“I really like the 3 R’s idea for rangeland—rotate, rest, recover—as they’re easy to remember. One of the other things I mention to ranchers is grass utilization rate because roots are impacted when you graze off more than 50% by weight. When you move to 60% utilization rate, 50% of roots stop growing for 10-12 days.”