It only seemed fitting that on a bright, sunny day in May, we could be treated to a day of soil sampling with Peter Donovan during some prime photosynthesis time when all the action is happening. By “action” I mean that the plants are hard at work in the brilliant sunshine collecting sunlight, carbon dioxide, and water to produce root exudates feeding the soil microbes, which in return help feed the plant, all the while adding to the soil carbon stocks and water holding capacity below ground.
If you’ve ever met Peter, he’s a somewhat quiet man with a tremendously insightful mind covering philosophy and all things scientific. He has an articulate style of communication that leaves listeners with much fodder for thought. It’s fairly routine to walk away from a conversation with him scratching your head and saying “Wow! I never thought of it that way.”
Peter is part of the Soil Carbon Coalition, which is a nonprofit working toward advancing the practice and awareness of turning atmospheric carbon into growing soil carbon and the inherent qualities it provides—increased water holding capacity and infiltration along with a boost in fertility. He is an incredibly dedicated man as evidenced by the old converted school bus he typically uses to travel the country. Fully equipped with a wood burning stove and an upright piano that remarkably stays in tune through all that travel. Peter has been making stops at a number of farms and ranches to establish a baseline of soil carbon and other data to share in an open source online app called Atlasbiowork. For this stop at TomKat Ranch, Peter is following up on the baseline data 4 years after the initial samples were taken.
What is so unique about the methodology he uses to collect the data is that it is easily repeatable without requiring sophisticated equipment lowering the entry cost for monitoring a very dynamic soil property—soil carbon. While the lab analysis can be somewhat costly, sampling in the field does not have to be. That’s the beauty of Peter’s method. By simply looking for landmarks with defined edges for reference, you can establish a transect line at a site using a common orienteering compass (device that needs no batteries, which can be really handy when sampling in remote areas). If major landmarks are not available, markers can be used to establish the points on your transect similar to the piece of rebar we drove into the ground. The rebar is bent so that there is a rounded eyelet on the top end so it’s not poking out of the surface of the ground. To increase visibility, you can also tie a piece of aluminum wire or something else that will make it easy to locate the marker, but still be safe for wildlife and cattle.
Once the transect was laid out, Peter chose a location on the transect that is representative of the overall cover in the pasture to record the vegetation present within the hoop. The hoop is 94” and made from a plastic coated cable, but could be made with just about anything. The cable is nice because it is flexible, but also rigid enough to hold shape when setting it down on the ground. When conducting this observation, there are many questions that need to be asked while the hoop is laying on the ground. Is solar energy being captured and how much bare ground is present? Is there a litter layer? Is there evidence of capping, where the unimpeded raindrops explosively splash the bare ground sealing the top of the soil preventing infiltration? What species of grasses and forbs are present? Is there evidence of insect and invertebrate activity? There are many more questions Peter has on his website that should be considered before successfully conducting this observation.
After recording the hoop observations, Peter handed out some 10x loupes (magnification lenses at 10x power) for the group to take an up close look at the soil surface. There’s something really fun about seeing four adults lying face down on the ground and listening to the “oohs” and “aahs” as they examine the micro arthropods and textures typically obscured by the macroworld around us. There are so many perspectives when it comes to ecosystem function and this exercise proves just that!
Next, we laid out the water infiltration rings. This test simulates a one inch rainfall event to determine how long it takes for the water to soak into the ground. To paraphrase Peter, we’re using the intelligence of the water molecule to explore soil structure measuring macropores and soil function. Good infiltration means we are capturing and holding the water in the soil, which is why our creek now runs all year long. Poor infiltration means the water is running off to somewhere else and may create a host of issues from erosion to sediment deposits and loss of topsoil. This time of year, the soil is still pretty moist and with all the healthy forage cover, infiltration was reasonably decent.
After infiltration, Peter retrieved his soil core sampler to extract a sample to send to the lab for analysis. Typically, this is a relatively straight forward process. Stab the soil with the core sampler and pull it out with soil intact providing a key look into the soil profile going from 0-40cm. However, our pasture’s soil did not get the memo. Each time Peter tried to take a sample, the probe would collect about a 10cm depth of material and then clog preventing him from getting a solid 0-40cm core. Undaunted by this roadblock, or should we say, probe block, Peter decided to dig a small soil pit to get an accurate set of samples to measure at 0-10cm, 10-25cm, and 25-40cm. This required the aforementioned “pit”, which was really just a small hole, and carefully shaving off enough material from the meticulously measured depths to get enough sample for each analysis. We often talk of how important it is to be adaptive in regenerative management and this was one such case that allowed Peter to be flexible enough to still get the sample and maximize his time in the field.
To finish the day’s sampling, Peter took out the bulk density ring, which happens to be a precisely measured sawed off piece of exhaust pipe from a tractor and collected bulk density samples to help determine the compaction of the soil. Bulk density is the dry weight of a soil divided by its volume which tells us how tightly the soil is packed together within that volume. A high bulk density means that root growth is restricted and infiltration is slowed.
After several hours in the sun and finished with the sampling, many of us felt as if our information infiltration had saturated due to so many scientific insights in such a short amount of time. We learned that the Carbon cycle is not a problem we can fix, but a system we inhabit. And measuring function in soil health, instead of studying problems and addressing symptoms, will go a long way toward understanding how photosynthesis holds our soils together. Since the carbon cycle governs the water cycle, perhaps we should take a closer look at measuring the length of the green season, since it is highly sensitive to management decisions. Particularly, in climates like California. Length of green season might address soil health principles better—soil cover, living roots, and diversity—as a true measure of success. Looking for outliers and working backward could be incredibly informative for understanding regenerative management and the impact of our decisions as we continue to adapt with our working land.