Below the soil surface
October 15, 2009
This past week’s travels took me first to the joint annual meetings of the South Dakota Section of the Society for Range Management with the SD Chapter of the Soil and Water Conservation Society in Mitchell. A major theme of the meeting, both during presentations and the field tour, was soil health. My next stop has been introductory sessions on rangeland systems with aspiring ranchers. We had the benefit during our field session of examining rangeland in very high condition. Both sessions reminded me how frequently I overlook the dynamic interactions and processes that are occurring below the soil surface. I’ve heard it said that, in healthy ecosystems, there is as much or more living biomass below the ground as above.
The annual meeting sessions focused particularly on the rapid adoption of cover crops, especially by no- or minimum- tillage crop producers. A particularly insightful comment by one of the presenters was that progressive crop farmers are attempting to mimic as closely as possible what goes on in natural systems. In the Northern Great Plains, the “natural system” appropriate for reference is our native grasslands. So what are some of the “processes” that crop farmers are attempting to mimic, and what can they help us learn about optimal management of perennial grasslands?
A striking impression on seeing a field of cover crops is the lack of uniformity! When I think of cropland, I think of straight rows and the absence of weeds. Fields we toured included a mixture of six or more different plants growing together: grasses, broadleaves, cool- and warm-season all growing together, most often in wheat stubble. The other striking appearance, in contrast to “conventional” wheat fields, was the quantity of plant materials. Perhaps the most curious plants for me were an assortment of brassicas; turnips, radishes, kale, and the quantity of tuber and root growth these plants had accumulated following wheat harvest. Speakers pointed out the valuable contribution of these root crops as a means of “biological tillage,” capable of introducing root channels capable of penetrating restrictive or compacted layers in the soil. An additional observation was the number of producers who were anticipating using these cover crops for fall and winter grazing.
With these novel images of cropland in mind, it was easier to see a “bigger picture” as I wandered over some high condition rangeland with students. At one site where we stopped to dig some soil to texture it, there was a tremendous diversity of plants; shrubs, broadleaved forbs, cool- and warm-season grasses and sedges. The vegetation cover was extensive and a layer of litter protected the soil surface. In spite of freezing temperatures and a little snow, there were many plants that were still green and alive. Plants varied in stature, from short grasses close to the ground to mid-grasses taller than my knee. Likewise, rooting depth varied from very shallow to deep tap roots. Breadroot scurfpea or wild turnip, grows a fleshy root remarkably similar to the cover crop brassicas. Finally, part of this pasture will be used for winter grazing.
Excellent management of native grasslands, including appropriate grazing, promotes and maintains a great diversity of plant species, some that grow early in the spring, some that grow late in the fall. A variety of rooting shapes and depths provides a continuous supply of food and habitat for soil “critters” that we too often take for granted.
One key to root growth that sustains the soil is a cover of plants that respond rapidly to favorable growing conditions. This fall, at the end of the growing season, provides an important opportunity to evaluate the impact of grazing management during the growing season. Will grassland plants enter the winter with adequate nutrient reserves, able to respond rapidly next spring? Or will pastures that were used hard this summer be slower to respond and need additional time. Making a careful assessment of pasture conditions this fall provides guidance in developing the stocking plans for next year. Providing deferment where it can be most beneficial will maintain plant diversity, promote soil health and ultimately, contribute to an abundant feed supply for livestock.
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Stay warm this “snowy weekend,” but evaluate the outcomes of this year’s grazing decisions and admire the exquisite design and complexity of our native grasslands, especially the part we never see!