The best soils for vegetable production are found in the left corner of the triangle-those with at least 40 percent sand and less than 20 percent clay. Soil Horizons Soils are not uniform throughout their depth. In general, the surface layer or horizon will be higher in organic matter and lower in clay than the layers beneath it. The fragipan is an example of a special horizon. Soil series are separated by the properties of their subsurface horizons.
Soil types are soil series separated by the texture of the surface horizon.
Soil maps exist for most counties in the United States and are available from the Farm Service Administration. Organic Matter Organic matter is comprised of the remains of once-living tissue such as animals or plant roots, stems, or leaves. Although in Mississippi organic matter normally accounts for less than 1 percent of the soil's volume, it is important. It enables individual soil particles to bind together into aggregates , it contributes to cation exchange capacity, and it provides water-holding ability. Humus is organic matter that is decomposed past recognition.