How Soils Affect Native Grasses

Cool season annual grasses and forbs turn fields a lush green

If you were coming down the long drive from our gate to the house in early spring, you might have noticed the green fields stretching out on either side. Ample winter rains in 2019-2020 filled the fields with a bumper crop of little barley (Hordeum pusillum), rescue grass (Bromus spp.), seven weeks fescue grass (Festuca octoflora), annual weeds, and many kinds of wildflowers the Texas Hill Country is famous for.

But if you returned in late May, you would find that the green had turned to straw, leaving mostly bare ground dotted with weeds like croton, western ragweed, silver puff, Wright’s plantain and pepper grass. Warm season grasses were few and far between, limited to a few low-successional species such as whorled dropseed (Sporobolus pyramidata), old field three awn (Aristida oligantha), hairy grama (Bouteloua hirsute) and plains lovegrass (Eragrostis intermedia).

Ever since we bought our place in in 2009, we have been focused on helping the land recover its native grasses. As I have noted so many times in earlier posts, native perennial grasses are desirable because their deep roots help the land function more like a sponge, storing rainfall and releasing it more slowly instead of allowing ground-scouring runoff.  Native grasses evolved over time to become an important part of the ecosystem by providing nesting habitat, cover, and a diverse food source for pollinators, birds, and mammals. Despite years of removing prickly pear cactus and plenty of brush, addressing washed out gullies, and planting native grass seeds in bare burn pile scars, there still remain two large fields that have never recovered a significant number of native grasses.  Our changing weather patterns have reduced the frequency of “average” spring rainfall, and continue to break records for high temperatures, making it harder to plant native grasses and have them survive after germination.

The Natural Resource Conservation Service (NRCS) notes that our area in SW Llano County as a “unique geological region within Texas”, consisting largely of weathered Pre-Cambrian granite, gneiss and schist with limited water-holding capacity. Historically our area was an open savannah rangeland, or mixed woodland-grassland ecosystem characterized by widely spaced trees that allow light to reach the ground to support a continuous herbaceous groundcover consisting primarily of grasses. Thanks to high numbers of re-sprouting woody species (mesquite, lotebush, persimmon and whitebrush), the savannah ecosystem is being replaced by shrubland. Following Texas Parks and Wildlife guidelines for management, we manage our place by maintaining open spaces alternating with shrub thickets for cover and food.

 We had been told that Mason and Llano counties were among the most abused in the whole state.  For instance, our place had been part of a vast tract owned originally by one of the earliest German pioneer families to arrive in the area.  Early settlers raised sheep, goats and cattle, often in numbers that seem astonishing to us now even though that was when there was still plenty of native grass on the range. Some areas were surely cultivated and larger areas leased to folks who were not likely to practice long-term stewardship of the land.  The last owners of our property attempted to raise both horses and cattle on 140 acres, leaving behind entirely bare areas where animals had been fenced.  After 10 years, we are beginning to suspect that there may not be any residual native grass seed in the soil to launch a recovery, even if conditions were right.

I wondered, too, what other factors limiting grass cover might be at play.  Was it because we broadcast the seed instead of using a no-till drill? Did harvester ants and birds haul off the seed we planted? Sometimes the seed would germinate and grow for a year, even producing seed, but not persist.

Summer of 2018 we were awarded a small grant from the Regional Conservation Partnership Program – a federal program funded by the USDA. With the grant we arranged to partner with Texas Parks and Wildlife Department to borrow one of the department’s no-till drills to sow the seed. This offered us an opportunity to learn if the delivery of the seed was the problem.  We are devoting the grant to the purchase of native grass and forb seed, and to hiring a neighbor to pull the drill. 

New research is teaching us more and more about the important relationship of soil microorganisms- particularly bacteria and fungi- to deep-rooted perennial native grasses. These organisms form symbiotic relationships with the plant’s root system, assisting in making otherwise inaccessible nutrients available, and enhancing root development for more uptake.  When the vegetative layer has been grazed to bare ground year after year, these essential soil organisms decline too, resulting in a site that is less able to recruit and nurture young grasses.

I had pieces of the puzzle identified, but I still wondered if there was something about the soils of these two areas that was also making it hard for grasses to grow. To understand more about what we were up against, I needed to learn more about my dirt!

On June 18, Travis Waiser, soil scientist with the Natural Resource Conservation Service (NRCS) in Kerrville, came out to analyze the site. As always, it amazed me that experts working for both state and federal agencies will make “house calls” on smaller properties to help owners understand best management practices for their specific location. Travis’s work focuses primarily on managing the NRCS Web Soil Survey. The NRCS has soil maps and data available online for over 95% of the nation’s counties.  Travis showed up at our place for an onsite investigation of soil quality. He described how he had met with a landowner who wanted to plant a big pecan orchard and wondered if the soils were appropriate (they weren’t). Travis’s process for assessing our soils was fascinating.  He first had to dig a “post hole” pit almost 30” deep in order to identify separate soil horizons. He looked for the presence of organic materials, fine roots, and overall texture.  He took samples from each horizon, and matched them with standard descriptions, including color. Then he took the samples back to his lab for further study and sent me the report.  In summary, he told me: “I did not see anything that would prevent grass plants to not sprout or survive. The only difficult areas are those spots that I believe the surface has been completely eroded away.”

The surface layer in the first field is mostly sandy, gritty loam. The next two layers are sandy clay and sandy clay loam, until they reach the fractured bedrock layer at around 27 inches (86 cm).  The soils are low in organic material and poor in moisture retention. The clay content results in “cemented” hardened crust in the summer, especially in bare areas. Both fields were similar in their composition, and both showed significant erosion- not in gullies, but in over-all loss of soil depth in the top layer.  The surface horizon in the second field was significantly deeper, suggesting less topsoil had been lost.

Looking at the soil layers in several large draws elsewhere on the place told me that at one time a significant rainfall event had scoured the area, probably after it was grazed down to a nub. The exposed arroyo or gully showed the distinct layers of soil, particularly topsoil of a certain depth not perceived throughout the fields. After talking with Travis, I had a better understanding of the toll constant grazing, browsing, and agriculture had taken on our rugged rangeland. It didn’t “look” eroded, but a significant loss of soil and seeds over time had resulted in its current impoverished and degraded condition. This was not a single or even a dozen extreme events, but more like the “death by a thousand cuts” type of demise. We learned from neighbors that the front field had been a dense mesquite thicket 20 years ago.  As everyone knows, mesquites are very good at taking over bare ground caused by overgrazing or abandoned short-term agriculture. The previous owners had bulldozed across the area, and that’s where the dozens of burn piles came from.  More erosion could have occurred when the land was scraped bare and vulnerable to heavy run off during a storm.

 When we first bought the land, I felt confident that with hard work and the right seed, we could make the land turn around – in my lifetime.  Now I accept that I can plant seed, but I can’t make soil! It’s true that change to improve overall ecosystem conditions often rely on humans to remove negative pressures like overgrazing, erosion, invasive species and spreading brush, but ego, some know-how, and “expertise” have their limits, and the main limit is time.   My role going forward will be more observation and awareness of the condition of our place, but with less assertion that it would be me, not Mother Nature, who will be setting the pace for recovery.

 

posted on 9/12/2020