Soil is comprised of sand, silt, and clay, and the combinations are nearly endless. Here in the Heart of the Ozarks – West Plains, Missourah – we have an abundance of red clay and a smattering of alluvial deposits along the creeks and rivers that likely contain small percentages of sand, variable amounts of silt and organic matter, but mostly clay. While the alluvial soils tend to be fertile they also require regular watering or heavy mulch to avoid drying and cracking.
Soil always reflects the properties of its parent material, like sandstone or limestone, and begins its development as the parent material weathers. Mechanical weathering occurs during earthquakes, rock slides, traffic by humans and animals, fracturing by plant roots, wind blown debris, and freezing water within the rock. Rain water, which is slightly acidic, can also dissolve the chemical bonds within the rock.
Sand of course is just very small rocks, primarily quartz and feldspar. While it doesn’t hold water or nutrients, its permeability is desirable in a mix because it allows for drainage, or percolation of water, and its porosity offers space for oxygen which is necessary for root development.
As sand weathers and becomes finer in texture it is classified as silt. Much like flour it has the capacity to bind organic matter and nutrients when wet, yet it retains permability and drains well. When dry however it can be eroded by wind, and easily displaced by water.
Clay is composed of ionic molecules sandwiched together and exhibiting electrostatic charges that attract plant nutrients. While some clay provides a fertile medium for plant roots, the red clay of the Ozarks does not.
Red clays can be found throughout the southern plains of the US and in tropical rain forests. Over centuries, and even thousands of years, water percolating through the soil oxidizes the iron and aluminum molecules in the clay, essentially neutralizing the electrostatic charges and negating the ability of the clay to hold on to plant nutrients. Naturally when iron oxidizes it becomes red and this is the primary visual indicator of a nutrient deprived soil.
The primary nurtients for plant growth are Nitrogen (N), Phosporus (P), and Potassium (K). Because nitrogen is the most mobile of the three, and percolates through the soil, red clay is notably deficient. Phosporus while less mobile is also less available in cold soils, and generally deficient in the spring months. Potassium is generally more available in red clay though easily depleted by intensive cropping.
The most common practice among gardeners is to amend the soil with organic matter, such as compost or manure. The least common practice is to sample the soil and send it to the Missouri Extension Service for analysis. The latter method offers many advantages. A soil test provides information on the relative fertility of the soil, its composition and pH.
Be smart – start with a soil test and follow the recommendations
Howell County MU Extension Center
217 S. Aid Avenue
West Plains, MO 65775
Phone: (417) 256-2391
Fax: (417) 256-8569
Web site: http://extension.missouri.edu/howell