Written by Megan K. Nasto, Research Scientist, Working Lands Conservation

Overlooking the complex landscape of Three Creeks, Rich County, Utah.

As the temperatures cool, the vegetation browns, and the soils dry, our summer 2022 field season on Three Creeks, Rich County, Utah comes to a close. It is with sore arms and layers of dirt under our fingernails that we put away our augers and probes, and reflect on the season. And what a new and successful season it was!

With an award from the United States Department of Agriculture, National Institute of Food and Agriculture, Agriculture and Food Research Initiative (2022-67019-37134), as well as continued support from a Bureau of Land Management Cooperative Agreement (L20AC00202-02), we were able to officially launch our new soils program.

This program builds upon our pre-existing work of examining how innovative livestock grazing can balance the many ecosystem services of economic, environmental, and societal importance that publicly-owned rangelands in the western U.S. provide. To complement the suite of ecosystem services we already monitor - including, water quality, stream flow, riparian health, forage production, plant diversity, and sage-grouse habitat - we added soil health and organic carbon.

But what is soil health and organic carbon, and why do we care? Well, let me proselytize for a minute.

We define soil health as a living, breathing ecosystem who function supports plants, animals, and humans alike. To put it simply - and perhaps a bit dramatically - without soil we wouldn’t have food, medicine, clothing, or building materials. Without soil we wouldn’t have life. Unfortunately, but not unsurprisingly, soil health is highly sensitive to the never-ending disturbances of human existence. And the disturbance that is the main focus of our soils program is that of livestock grazing. Speaking quite generally, if livestock grazing is managed poorly, soils become susceptible to erosion, the ability to capture and store water declines, and plant growth suffers. On the other hand, if livestock grazing is managed well, soil erosion is reduced, water capture and storage increases, and plant growth is stimulated. This, in turn, can lead to increases in soil organic carbon.

Soil organic carbon is often regarded as the primary indicator of soil health. It determines soil structure, facilitates nutrient retention, and support plant production and biological diversity. The reduction or loss of soil organic carbon lowers soil fertility and leads to land degradation. In Utah specifically, where rangelands comprise 80% fo the state’s total land area, livestock grazing has led to a significant loss of soil organic carbon across 17% of the state’s vital agroecosystem under public ownership. A common approach taken by land management agencies to restore soil health is to sacrifice grazing by reducing livestock numbers or removing them entirely from the rangelands. This, of course, reduces earnings to producers and negatively affects their livelihoods. An alternative management strategy with the potential to balance grazing with soil health and organic carbon is the implementation of grazing practices that minimize livestock’s physical impacts on the soil itself.

Clearly, soil health and organic carbon are intricately linked feeding back into one another and other processes that sustain rangeland systems. A complex view of the interactions between the physical, chemical, and biological components of the soil system is thus required to improve our understanding ability to influence the soil response to changes in livestock grazing management.

We are taking a comprehensive approach to understand how the historical legacy of grazing systems that differ in duration and timing throughout the grazing season, as well as the implementation of an innovative time-controlled rapid-rotation grazing system, affects soil health and organic carbon on a landscape-scale.

We selected six metrics of soil health that are expected to change in response to grazing, and are interpretable either by themselves or in conjunction with on another as a representation of specific processes and conditions relative to rangeland health and the generation of other ecosystem services. These metrics include infiltration, water-holding capacity, structural stability, bioavailable nitrogen, microbial biomass, and microbial respiration. Like I mentioned previously, soil organic carbon is often regarded as the primary indicator of soil health but we are considering it as its own ecosystem service.

Working Lands Conservation’s soils crew! From left: Megan K. Nasto (Research Scientist), Chase Gunnell (Soils Crew Leader), Logan Ballard (Vegetation Crew Leader), and Nathan Omer (Field Technician).

This summer we collected data on these metrics of soil health, as well as organic carbon across gradients of soil moisture and mesic-xeric plant communities within the riparian corridors on Three Creeks. And we collected these data monthly across the grazing season. If we were to collect these data at a singular time within the grazing season, it would provide us only with a snapshot of the ecology underlying the rangeland. Soils - and the microbes that thrive within - are dynamic systems constantly in flux responding to the abiotic forces of precipitation and temperature, and the biotic forces of plant inputs and livestock hooves. These data, collected together and monthly, should provide us with a comprehensive view of how soils respond to the environment throughout the year when livestock are actively grazing the landscape. Such a view will provide insight into the ‘whys’ and ‘hows’ of rangeland processes.

Though riparian corridors only make up a small fraction of the overall landscape on Three Creeks, they are biological hotspots of microbial, plant, and animal life. It is only natural, then for livestock to gravitate to these areas for water, food, and rest. It therefore becomes critical to assess the health these riparian soils in relation to their upland counterparts as the riparian corridors may be playing an outsized role in storing organic carbon.

We must not forget about the sagebrush-steppe uplands, though. The sagebrush-steppe may seem desolate and unassuming, but behind the sea of olive colored brush and golden grasses is a rich mosaic of complexity. A heterogeneity in ever regard. Islands of fertility and microclimate formed by sagebrush themselves. Bare ground of iron red soils hardening as the moisture disappears. Vibrant wildflower pockets of lupin, Indian paintbrush, desert, rose, and sego lily. Rolling mountain tongues awash with annual and perennial grasses. Countless rabbits, gophers, chipmunks, and horny toads finding their own existences.

The uplands of sagebrush-steppe rangelands are full of magic, and that is certainly the case when one looks towards the ground. Yes, it’s true that the soils in these rangelands are limited by little precipitation and cold temperatures. Such conditions constrain the activity of soil microbes responsible for processing and storing organic carbon. But the potential exists for the health of these soils to improve, as well as the capacity to store organic carbon.

We have a strong experimental design in which we are comparing the stocks of upland soil organic carbon across the different grazing systems on Threes to that of a time-controlled rapid-rotation grazing that’s been in place for over 30 years just a few miles to the south. This highly managed grazing systems offers a ‘positive control’, and preliminary data suggest that Three Creeks has the potential reach levels of organic carbon seen here once it fully transitions out of their historical grazing systems and into one that’s similar.

A robust, systemic, stratified, and repetitive sampling approach is what we need, however, to not only map baseline stocks of soil organic carbon on a landscape-scale, but to determine sequestration rates with time since changes in livestock grazing. And that is exactly what we embarked on this summer. In addition to collecting soil health data across riparian corridors, we are also collecting organic carbon data across the entire Three Creeks landscape. We took great care and effort to stratify - or segment - the landscape into all of the different spatial variables that influence organic carbon. These include vegetation type and density, soil type and texture, topography, and historical grazing system. And we took eve greater care and effort to carry out the actual sampling. And, girl, did we sample!

Once the sampling stratification and approach is designed, it may seem like a simple process of bagging soils can begin. We are here to tell you, though, that is far from the truth. One can’t simply - with a trowel in hand - place soil in a bag. One must carefully auger down into the ground and pull out whole cores of soils. Then one must separate the cores by horizon and/or specified depths. Only then can the soil be bagged. But that’s not where it ends. One must also collect what are called bulk density soil samples. These are perhaps the most important samples of all. These samples are what enables us to convert contents - or percentages - fo soil organic carbon into stocks. These samples are what enables us to estimate how much soils organic carbon actually exists on the entire landscape. What is critical about these samples is that they must be extracted from the ground as intact and undisturbed as possible. An incredibly hard feat when working on the cobbly loams of Three Creeks. But a feat we made sure to accomplish. With a little bit of grit and elbow grease we weighed down our field truck and came home with totes full to the brim with bags of soil.

Now is the time for a quick respite before the massive sample processing and analysis effort takes place! Soon enough, though, we’ll have data to curate, a store to share, and maps to present. Stay tuned as the saga of soil health and organic carbon on Three Creeks unfolds!

Our Soils Program Has Officially Launched!