Some Facts About Soil Basics-I
This is a brief and simplified introduction to the origins of soils and how they influence capabilities and uses of soils. Importance of Soils: The earth is covered by a thin layer of soil, composed of minerals, organic matter, and living organisms. Within this layer is a record of the area's geological and climactic history, as well as information about the suitability of future use of the soil. Soils affect many areas of our lives; we depend on the soil to grow our food and support the buildings we live and work in. Soils form an essential element in the ecosystem. Human activities that damage soils threaten to disrupt the delicate balance that sustains life. It is important to have a basic understanding of the formation and properties of soils to determine their future uses and to manage soils wisely. Development of Soils: Minerals are the primary component of soils. These minerals are from weathered rock, called parent material. The source of parent material is sometimes the bedrock directly below, and sometimes material transported far from the original bedrock and deposited by ice, water, wind, and gravity. Many soil properties are determined by the type of rock the parent material came from. For example, we have sandstone soils, shale soils, and limestone soils, coming from different parent material and possessing different characteristics. Another component of soils is organic matter—decomposed parts of plants and animals, as well as millions of microscopic soil organisms that help break down minerals and organic residues. Air and water are also found in pores in the soil, tiny spaces between the soil particles. Influence of Topography: It is not surprising that the shape and geology of the landscape contribute to the properties of the soils. Pennsylvania is divided into different physiographic provinces, regions of similar geologic origin and shape. For example, the Ridge and Valley province in central Pennsylvania consists of folded sedimentary beds, which are layers of sandstone, shale, and limestone. Sandstone, the hardest and most chemically resistant layer, forms the ridge caps and is covered with coarse sandy soils. Limestone, however, weathers quickly; the calcium carbonate it contains dissolves in water and is carried away, leaving valleys of fertile limestone soils. The slopes are formed of shale, with intermediate resistance to weathering, or of colluvium, material (in this case sandstone fragments) that has been moved downslope by gravity. The shale soils are shallow, fine-textured, acidic, and low in nutrients. A humid, temperate climate provides adequate amounts of soil moisture to leach soluble substances through soil. Temperature and moisture changes enhance the development of subangular blocky structure. Climate induces many such different soil characteristics. Interacting with climate is vegetation, which also impacts conditions within the soil. Consider two examples. Under grass, soil accumulates organic matter from the dense fibrous, shallow, root system and becomes dark grayish brown to the depth of the roots, 12 to 30 inches. Under deciduous forest, leaves fall to the soil surface, are not incorporated into the soil, and form an organic mat above the mineral soil.