Last Friday night, I went to our family prairie for a last check of fence and water before cattle came in on Saturday. Shortly after the sun dropped below the horizon, I was preparing to head back home when I noticed an old yellow mineral tub that had been sitting upside down at the bottom of a small draw. I’d seen it many times before but had left it there, thinking maybe our lessee (owner of the cattle) would salvage it. This time, I figured I’d waited long enough and just picked it up. That’s when I realized how long it must have been sitting there.
When I lifted the plastic tub and saw the mass of yellow-green grass beneath it, a rapid fire series of thoughts passed through my brain. As I processed all those thoughts, I realized there were a number of interesting ecological observations and conclusions that could be made from the situation. In other words, that empty livestock mineral feeding tub, emptied, blown by the wind, and then abandoned, had accidentally become an educational tool. Here are some of the lessons that I believe we can draw from the yellow tub of the prairie.
Let’s start with a little context. We’re managing our prairie with the ‘Open Gate Rotational Grazing System’ I described in a post a couple years ago. The prairie is split into four main pastures and a couple smaller units. Last year, the pasture containing the yellow tub was grazed intensively for most of the season, resulting in most plants being repeatedly cropped short. This year, it will rest all season, as well as most of next year.
Also, the tub landed in the former location of a big tree the cows used to cluster around for shade until I recently cut it down. That shade and consistent disturbance pushed the plant community toward brome/bluegrass dominance. As a result, most of the yellow-green grasses appear to be Kentucky bluegrass, with a little smooth brome mixed in.
A first observation is that the bluegrass and brome under the tub must have gotten an early start on the season because the tub acted as a kind of hot house this spring, providing much warmer temperatures inside the tub than out. That allowed those grasses to start growing well before most of their neighbors. Apparently, the tub was translucent enough to allow those plants to photosynthesize too, though based on the color of the grasses, they wouldn’t have minded a little more light (more on that below).
However, the disparity in height between the grasses inside and outside the tub seems too great to be explained only by warmer temperatures this spring. Instead, I believe two other factors influenced the height of those in-tub grasses. First, that tub was probably sitting there long enough to protect those grasses from last year’s grazing. The grasses outside the tub have barely managed to grown a few inches tall this spring. Those inside were touching the top (bottom?) of the tub, which is about 16 inches deep. That’s really tall for Kentucky bluegrass, even with an early start.
The impact of grazing on the grasses around the outside of the tub can be seen by looking at the other three pastures across the prairie. For example, in the pasture that didn’t get grazed at all last year, the brome is about 10 inches tall right now. Bluegrass is a little shorter, averaging around 6-8 inches. That’s way taller than the grasses in the ‘tub pasture’, which are showing stress from being repeatedly grazed last year. That grazing affected the size of their root mass and energy reserves, from which it will take them a full year or more to recover. Inside the tub, the grasses were unaffected by that grazing (just low light), so they had more energy for growth this year.
The second reason the grasses inside the tub were so small is due to a term I learned from my wife over the weekend: etiolation. Those of you who follow me on Instagram might have just caught that ‘etiolation’ is the second term I’ve learned from Kim in the last week or so. The other was ‘guttation’, which is when water droplets come out of plant leaves overnight because of a build-up of water pressure as roots continue acquiring water while transpiration has shut down.
I digress. Etiolation, it turns out, is the name for the phenomenon that occurs when plants grow under insufficient light. Those plants are a pale color (sometimes nearly white under extreme circumstances) and tend to grow extra long and skinny in an apparent desperate attempt to reach better light. You’ve probably seen this before – I have an example in our basement right now where a bindweed plant is trying to grow from between the bricks. Anyway, I think the combination of etiolation, early warm temperatures, and grazing exclosure were probably responsible for the crazy difference in height between the grasses inside and outside of the yellow tub.
Now, to really figure this out, I could get 6 or 8 identical yellow tubs and scatter them around the prairie for replication. I could put half of the tubs in areas of recent grazing and the other half where plants are recovered from grazing. If I let them sit between now and next May and then measure grass heights I should have enough statistical power to determine the relative contributions of the ‘hothouse effect’, etiolation, and grazing exclusion toward what I saw under the tub this year.
(Don’t hold your breath. I think I’ll stick with my current observations and educated guesses on this one.)
Look at how much that abandoned tub taught us! Isn’t it a good thing I waited so long to pick it up? Maybe that’s the real lesson here. I wonder what educational value I can find from the clutter in my garage. Most of that has been around much longer than the tub…