Although I was trained in science, I never really made much of a scientist. All that sitting around in the lab, mucking out petri dishes and gathering data, well, I just really couldn’t stand it. What I wanted was to be out in the field, observing nature. And perhaps that’s why I wound up here on the ranch, watching plants and animals and looking at soil every day.
Recently I got to look at an interesting phenomenon involving soil and weather. The photos below are from the back forty at our little ranch. You don’t need to be much of a scientist to see what the effect of extreme heat and drought is on bare ground vs. ground with modest plant cover.
We use small, portable tanks to serve our cow herds; you can see one in the background of the first photo below.
The foreground in the first shot shows a spot where the water tank overflowed and the cows mucked up the wet ground around the tank. The overflow event occurred back in June, at the beginning of our drought. If you look closely, you will see a small oval of plant life in the center (the spot where the tank was), surrounded by a larger circle of bare ground, the area the cows pugged.
The next shots show tremendous cracks in the bare ground at the site, compared to much smaller cracks in the soil directly adjacent, and also in the soil that was directly under the tank.
Apparently, even a modest amount of shade and cover and functional roots can provide enough difference to prevent massive cracking.
Does having cracks big enough to slip your entire hand into mean anything? I don’t know. Is it a good thing or a bad thing? I don’t know. Did it make me wince when I saw it? Yes.
A note to the scientist-types out there: Yes, I know. There may be other factors here that influence the degree of soil cracking. Maybe compaction? Maybe something else? Please respond in the comment section with your own hypothesis.
In looking at background for this piece, Kathy found a May 2012 article from the University of New South Wales. It seems that when we over-saturate soils, and then they dry out, they cracks. They remain open, even after the cracks have visually closed, and they become “preferential pathways” through which water flows away from the surface at a rapid rate, taking with it nutrients and pesticides. Researchers are using this information to develop irrigation guidelines that prevent these cracking in the first place.
John will be speaking with Kathy and two other On Pasture authors, Meg Grzeskiewicz and Jenn Colby, at the upcoming National Grazing Lands conference. We hope you’ll join us! Or visit the On Pasture booth just to say hi!
Some areas of TX have vertisol clay soils (shrink/swell clay type). Crack wide enough for an 8N tire to fit and depths over 10′. These soils are droughty in nature as small steady rain events infiltrate the cracks, but heavy rains swell the clay and close cracks before significant infiltration. The point, some soils have more crack potential than others.
Small areas of bare ground or sparse vegetation are necessary habitat for the lifecycle of some wildlife species. These areas should not be fretted but rather considered as one piece of the mosaic in habitat required by wildlife.
Cracks in the soil are very common in California. They are especially evident during the summer dry season, even with a good cover of litter. I look at the cracks as a way for deep cycling of water and nutrients to occur, especially when they seem to occur regardless of management activities.
In areas where these cracks can be minimized, it is likely better to not have them. As you observed, cool and moist conditions help minimize cracks in the soil.
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