Clay soil is common in river beds and low valleys. It is rich in the nutrients plants need to grow well, but deficient in the sand that makes soil porous and productive. Ideal soil is a combination of the two, with organic matter added for friability (meaning the soil easily crumbles). Clay soil has high water content, but a low oxygen content. Soil texture is an important determinant of its fertility, or its ability to sustain or promote life.
Soil texture is a term that designates the distribution of the different sizes of mineral particles in a soil, according to a report by the University of Florida Extension. Clay soil has small, fine particles of mineral materials that make it sticky to the touch when wet and powdery when dry. It forms into a ribbon when stretched out between the thumb and forefinger. It forms into hard clumps and cracks easily.
USDA Textural Class
Sand, clay and silt determine the soil percentage content, according to the U.S. Department of Agriculture's Soil Textural Class. There are 12 major textural classes. Clay loam is the class of soil that has the most even distribution of sand, silt and clay. It feels as though it has more clay than sand or silt. It is sticky and plastic when wet and forms into a firm ball when held in the hand
Sandy Clay Loam
Sandy clay loam texture is dominated by sand and clay, but still has friability. It has balanced percentages of both particle sizes, which make it a good growing medium for plants. Plants need the nutrient content of clay and the porous qualities of sand to thrive. Plant roots cling to soil aggregates formed by clumps of minerals and organic matter.
Silty Clay and Sandy Clay
Soil analyzed as silty clay and sandy clay is smooth and very plastic when wet. Sandy clay feels slightly grittier to the touch. Silty clay soil forms very hard aggregates when dry. Soils of these textures need organic compost to become productive and fertile. Clay soil has high mineral content, but plant roots cannot spread and absorb the minerals easily.
Backyard composting is one solution to amend dense clay soils. Compost is created from kitchen waste, yard clippings, leaves and newspaper. The materials are put into a compost bin in layers, watered and left to decompose. The decomposed material is ready in one to four months. When compost is added to dense clay soil, it becomes rich, fertile garden loam.