Animals and microorganisms can produce pores and crevices, and plant roots can penetrate into crevices to produce more fragmentation. The presence of living organisms greatly affects soil formation and structure.

Steeps soils are more prone to erosion and may be thinner than soils that are relatively flat or level. Topography affects water runoff, which strips away parent material and affects plant growth. Regional surface features (familiarly called “the lay of the land”) can have a major influence on the characteristics and fertility of a soil. The presence of moisture and nutrients from weathering will also promote biological activity: a key component of a quality soil. Temperature, moisture, and wind cause different patterns of weathering and therefore affect soil characteristics. A fast-moving river could have sediments of rocks and sand, whereas a slow-moving river could have fine-textured material, such as clay.

Sediments in rivers may have different characteristics, depending on whether the stream moves quickly or slowly. Materials located in the depth of the soil are relatively unchanged compared with the deposited material. Other soils form in materials that came from elsewhere, such as sand and glacial drift. Mineral soils form directly from the weathering of bedrock, the solid rock that lies beneath the soil, and therefore, they have a similar composition to the original rock. The organic and inorganic material in which soils form is the parent material. Five factors account for soil formation: parent material, climate, topography, biological factors, and time. A horizon is a soil layer with distinct physical and chemical properties that differ from those of other layers. Within the soil profile, soil scientists define zones called horizons. Soil distribution is not homogenous because its formation results in the production of layers together, the vertical section of a soil is called the soil profile. Most soil microorganisms-bacteria, algae, or fungi-are dormant in dry soil, but become active once moisture is available. The organic component of soil serves as a cementing agent, returns nutrients to the plant, allows soil to store moisture, makes soil tillable for farming, and provides energy for soil microorganisms. About one-half of the pore space should contain water, and the other half should contain air. Soil should ideally contain 50 percent solid material and 50 percent pore space. Soil formation is the consequence of a combination of biological, physical, and chemical processes. A good healthy soil has sufficient air, water, minerals, and organic material to promote and sustain plant life.Įxplore this interactive map from the USDA’s National Cooperative Soil Survey to access soil data for almost any region in the United States. The amount of each of the four major components of soil depends on the amount of vegetation, soil compaction, and water present in the soil. water and air, about 50 percent of the soil volume.organic matter, about 5 percent of the soil volume.inorganic mineral matter, about 40 to 45 percent of the soil volume.Soil consists of these major components ( Figure 31.6): Mineral soils are predominant in terrestrial ecosystems, where soils may be covered by water for part of the year or exposed to the atmosphere. Soils can be divided into two groups: organic soils are those that are formed from sedimentation and primarily composed of organic matter, while those that are formed from the weathering of rocks and are primarily composed of inorganic material are called mineral soils. Soil develops very slowly over long periods of time, and its formation results from natural and environmental forces acting on mineral, rock, and organic compounds. In agriculture, the history of the soil, such as the cultivating practices and previous crops, modify the characteristics and fertility of that soil. Soil quality depends not only on the chemical composition of the soil, but also the topography (regional surface features) and the presence of living organisms.

Soil quality is a major determinant, along with climate, of plant distribution and growth. Soil is the outer loose layer that covers the surface of Earth. Plants obtain inorganic elements from the soil, which serves as a natural medium for land plants. By the end of this section, you will be able to do the following:

Distinct soil horizon definition