Sand is very important to vegetable growers, since the sand grains are separated by relatively large voids, which allow movement of air and water. Sand grains also provide a soil that is resistant to compaction because of their large size and toughness. Soil Structure Individual soil particles tend to flocculate into aggregates because of chemical and physical attractions. Limestone is added to acid soils to replace singly charged hydrogen ions on the clay particles. This has a beneficial effect on the soil pH, and the calcium improves soil structure by binding together the clay particles.
Improved structure forms larger voids, which increase air and water movement through the soil.
Soil Names Soil names are based on the amount of sand, silt, and clay found in the surface horizon and on the physical and chemical properties of the subsoil. The textural triangle gives the terms used to describe various mixtures. 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.