4/10/18 Soils Field Day
Today’s field day introduced us to the soils that we’ll encounter in the surrounding area and how they relate to the vegetation. I’m excited to learn more about soil and geology over the next few months because the more I learn about the natural world, my connection with it expands. Recognizing the plants, animals, geology, and even weather around me gives me a greater sense of place, a deeper connection with nature, reverence for its complexity, and the call to stewardship of the land.
The volcanic (igneous) rock, specifically basalt-dominant, shapes the landscape and vegetation of this region in southern Oregon. The Big Sagebrush, or Artemesia tridentata, is the dominant vegetation and has three subspecies that are telling of the soil it grows in. Sagebrush is a “mirror image” plant, meaning that the height of the plant mirrors the depth of the soil above the bedrock. The two most common grasses in the area are Poa secunda (Sandberg bluegrass) and Achnatherum thurberanium (Thurber’s needle grass). The Oregon Outback has less plant diversity than the Midwest, so I have fewer plants to learn this round, but there are very minute differences between species.
I like that soil sampling can be even more hands on than plant sampling. To describe and identify soil, you have to feel it with your hands, observe it closely, smell it, and the really talented geologists even use taste.
Watching the volunteer geologist’s face scrunch up in thought as he rolled the soil around in his hands and listening to his excitement and funny phrases was like watching a wine connoisseur sampling a fine wine. He sorted through the soil, noting the structural changes in the layer. Soil that separated as blocks had a high clay content. There were also granular structures that resembled rounded rocks.
Part of our soil data collection includes digging small pits to take samples. As we extract the layers from the earth, we lay them on the ground or a tarp. The solid background of the tarp can help you see the subtle color differences as the soil changes with depth.
We sampled soil at four sites. The first site was moderately high elevation for Oregon, in the mid 5,000s ft. There were small, discrete mounds around some of the sagebrush because the silty soil collects dust and creates litter mounds. Here we saw Big Sagebrush, Artemesia tridentata wyomingensis. These sagebrush are shorter, prefer medium soil, and lower elevation.
The second site we visited was chosen so we could see Artemesia arbuscula, or low sagebrush. This sagebrush grows to about six inches tall and prefers claypan soil. Here, we saw vesicular soil crust between the plants. This crust has many large cracks in it due to the expanding and shrinking of the soil. Peeling a sample of the vesicular crust showed that it had aridic characteristics. The surface tension of the water was greater than the organic matter pullback.
This area was also more productive than the first one because it had a greater diversity of grass species. Some of the other grasses we saw were Leymus cinereus (Basin wild rye), Ereogioum (buckwheat), wheatgrass, Elymus elymoides (bottlebrush squirreltail), and Agropyron cristatum (crested wheat). We also observed one of the early spring bloomers dotting the landscape, a small, shiny yellow buttercup.
The third site that we sampled soil at was near Horsehead Lake in an area that fluctuates heavily in the amount of water it holds year to year. Here we found clays with expansive properties, which seal as they wet. This means that they expand and contract in response to water content, essentially making them self-tilling.
The fourth site that we sampled was a hilltop that had a highly productive, deep organic soil. This area received more rain than the others and also had many grasses present.
While driving around to sites, angus calves would gallop alongside our trucks. We also saw chukar birds and antelope. We also saw a lot of juniper encroaching into areas of lower elevation than they had been historically. This is due to an altered fire regime, as they are not fire-adapted trees. The BLM actively cuts back the juniper in this area in an attempt to slow their invasion. We also encountered Bromus tectorum, cheatgrass, the scourge of the west.
I’m already missing the deep, soft, rich, fertile soils of the Midwest, especially now that it’s spring and I should be propagating plants for a garden. However, I am happy to start learning the intricacies of sagebrush land and starting to see individual species and soils instead of a seemingly homogenous landscape.