Topsoil is the uppermost 6 to 10 inches of soil. It is the most productive layer of soil and it is where food is grown. Clay soil is an important component of topsoil and can contain an array of minerals important for crop health. “Soils are named and classified on the basis of physical and chemical properties in their horizons (layers),” according to the National Resources Conservation Service.
Soils differ from one another depending on how and when they were formed. Scientists use five determinants to classify soil. The important soil-forming factors are parent material, climate, topography, biological factors and time. Slow-moving water and lakes help form fine-textured clay and silt soils when sediments in water settle out.
Clay is one of the mineral building blocks of soil. Soil structure is the combination or arrangement of mineral particles into larger clusters called aggregates. Air and water occupy the space between aggregates. Soil structure influences its ability to grow plant life. Soil structure is of primary importance to global issues of soil degradation and erosion. Erosion problems cause drought and hunger.
Healthy soil consists of 45 percent minerals, 25 percent each air and water and 2 to 5 percent organic matter. The mineral portion consists of three sizes of mineral particles classified as sand, silt and clay. Sand and silt consist mainly of quartz particles that cannot provide soil nutrients. Clay soil has the smallest particle size of minerals.
Garden loam is considered the ideal planting medium. Clay soil can be made into garden loam by adding organic matter such as compost. Clay soil alone does not contain adequate space for vegetable plant root development. The water content of clay soil can also cause root rot. Organic materials such as compost add oxygen to clay soil. The living organisms in compost ingest clay’s nutrients and transform them into plant nutrients.
Mineral content in clay soil can vary. Seventeen elements have been identified as necessary for plant growth. Clay soil may contain the macronutrients nitrogen, phosphorus and potassium as well as micronutrients calcium, magnesium and sulphur. Trace element micronutrients are boron, manganese, copper, zinc, chlorine, nickel, cobalt and molybdenum. They are present in organic compost as well.