John Steinbeck, I believe it was, described the soil of Iowa as being so rich that you didn’t need to process it through vegetables – just eat it with a spoon. Most people wouldn’t go that far, but for someone who grew up on the short grass steppe, where the soil is thin and alkaline, the combination of yard-deep loam and sufficient precipitation is a wonder to behold. But that lovely black stuff didn’t appear out of nowhere. In fact, soil is one of the more fascinating parts of the world of prairies and woodlands.
Without soil you ain’t got life, unless you are a lichen. Bare rock doesn’t hold water, it provides no shelter from the hot sun, and it’s mighty hard to get nutrients from. Lichens and mosses that grow on bare rock work with bacteria and chemicals to break down that rock, assisted by heat and cold, rain and ice. For most plants, only after the rock has been shattered into crumbly bits can their roots start to take advantage of the minerals and water pockets in the rock. Gradually, over very long periods of time, the rock breaks down enough to become soil. Ask anyone who has had the joy of picking rocks out of a field in New England (or old England, or Scandinavia, to name a few) and they can tell you exactly where dirt comes from, probably using some choice words. But with a few exceptions, even powdered rock is not quite soil yet.
For that you need bacteria and plants. And animals that fertilize the soil with their droppings or bodies. The collection of tens of thousands of years worth of rotting plant and animal matter are what makes the lovely black chernozemic soils of the Great Plains and Russian grain belt. You start often with loess (pronounced “luss”), the dust swept off the ends of continental glaciers and drifted into great heaps, like the loess hills of Iowa and Missouri, or in China. Imagine huge sweeps of soft powder drifting with the wind, then piling up around obstacles or along rivers, slowly collecting deeper and deeper. Then the loess spread more evenly as the glaciers retreated until it covered much of the Great Plains, a soft, permeable seedbed. Then add grasses and forbs, and grazers and browsers, and bacteria. Tickle the chemistry a little with different climatic patterns and bacterial groups, and you get the variety of soils that cover the North American grasslands.
Texas has one strip of the rich blackland soils, called the “black waxy,” in the east-central part of the state. Farther west, you get into alkaline limestone and drier places, where the evaporation rate exceeds the rainfall and caliche forms, leaving a thinner but still good soil (unless you want to grow hydrangeas and azaleas and dogwoods). To the east the Piney Woods have acidic soils, often a little poor on nutrients because the rain leaches minerals out, leading to the clays of Georgia and Alabama (and east Texas). For many years, the black waxy was the only area where you could get crop insurance, because farmers stood a prayer of actually making a marketable crop.
Below the A layer, or loamy level, you encounter soil with far less organic matter (the B horizon). If the loam departs through poor land management, or a stream moving, or it is removed for excavation, what remains needs a great deal of amendment and/or time before it becomes productive soil. In the High Plains, a layer of calcium carbonate, called caliche, forms the base of the A layer. Often you can see the difference in color and texture when you excavate a nice trench or archaeological site.
Soils tell a great deal about climate and conditions in the past. Paleo-soils are those which used to be on top and then got buried by later layers. I’ve seen stream gullies and river valleys where you can follow the ancient pattern of erosion and deposition in the striped walls of the arroyo. A layer of “sterile” dust between the remains of campfires at the Lake Lubbock and Blackwater Draw sites told archaeologists about an extended drought that drove humans away from these otherwise favored spots.
But even as rich as the crumbly, loamy soils of Iowa may be, I’d still rather eat it as carrots and corn.