CHAPTER 5 2 Soil CHARACTERISTICS OF SOIL Soil

CHAPTER 5. 2 Soil

CHARACTERISTICS OF SOIL • Soil is what is made from weathering and covers most land surfaces. • Weathering produces a layer of rock and mineral fragments called regolith. Soil is an important part of regolith. • Soil characteristics are composition, texture, and structure.

SOIL COMPOSITION • Soil is made of 4 things: mineral matter (brokendown rock); organic matter or humus (decayed remains of organisms); water; and air. • Different soils have different amounts of each of these things. • Good quality soil has 45% mineral matter, 25% air spaces, 25% water, and 5% organic matter. • Organic matter is one of the most important parts of soil and it makes the soil very rich.

SOIL TEXTURE • Most soils have different sizes of particles. Soil texture is the proportions of different particle sizes. • Soil is categorized based on the amount of clay, silt, and sand. • For example: sandy clay has 40% clay, 10% silt, and 50% sand. • Texture is important on whether or not a soil can support plant life. Sandy soils dry out too quickly, clay rich soils drain very slowly.

SOIL STRUCTURE • Soil particles usually form clumps that give it a particular structure. Soil structure determines if the soil can be cultivated and how easily it will erode.

SOIL FORMATION • There are several factors that help form soil. A few of the most important factors are parent material, time, climate, organisms, and slope.

PARENT MATERIAL • Where the mineral matter in the soil comes from is called parent material. • The parent material can be bedrock or unconsolidated deposits. • Soil from bedrock is called residual soil. • Soil from unconsolidated deposits are called transported soil.

• Parent material affects soil 2 ways: • Rate of weathering and soil formation – unconsolidated material are subjected more to chemical weathering. Also, these soils develop more quickly. • Parent material can also affect soil’s fertility – how much plant life the soil can support.

TIME • The longer the soil forms the thicker it becomes.

CLIMATE • This has the greatest effect. Different temperatures and precipitation influence rate, depth, and type of weathering.

ORGANISMS • The type and how many organisms have a major impact on soil. • Plants are the main source of organic matter in soil. Microorganisms, like fungi and bacteria are also important for decomposing dead plant and animals. • Earthworms are very important because they create holes by burrowing this helps water and air into the soil. • Bacteria can be very important for plants in soil.

SLOPE • Steep slopes can have accelerated erosion. • Flat areas will have little erosion and poor drainage. • The way the slope faces also makes a difference – in the Northern Hemisphere, south facing slopes receive more sunlight. In the Southern Hemisphere, north-facing slopes get more sunlight.