topsoil

The amount, intensity, timing, and kind of precipitation influence soil formation. Seasonal and daily changes in temperature affect moisture effectiveness, biological activity, rates of chemical reactions, and kinds of vegetation. Topography. Slope and aspect affect the moisture and temperature of soil.

When parent rock material is exposed to the atmosphere or when organic matter and/or minerals are deposited on the earth’s surface, soil formation begins. The type of parent material and how the soil is formed will greatly influence the properties of the soil. Darker minerals tend to yield more fertile soils.

moist climate

Soil development is facilitated by the downward percolation of water. Soil forms most readily under temperate to tropical conditions (not cold) and where precipitation amounts are moderate (not dry, but not too wet).

Soils develop into layers. These layers, called horizons, are usually seen along road cuts and other areas where a cross section of the soil is exposed.

A soil profile is a vertical section of soil like the diagram above. It allows you to examine the structure of soil. A soil profile is divided into layers called horizons. The main soil horizons are A, B, C and D. Most important for plant growth, the A and B horizons are the top two layers of the soil.

The soil profile is a vertical section of the soil that depicts all of its horizons. The soil profile extends from the soil surface to the parent rock material. The regolith includes all of the weathered material within the profile. The regolith has two components: the solum and the saprolite.

Most soils have three major horizons (A, B, C) and some have an organic horizon (O).

Master Horizons. The A, B, and C horizons are known as master horizons. They are part of a system for naming soil horizons in which each layer is identified by a code: O, A, E, B, C, and R.

The particles that make up soil are categorized into three groups by size – sand, silt, and clay. Sand particles are the largest and clay particles the smallest. Most soils are a combination of the three. The relative percentages of sand, silt, and clay are what give soil its texture.

Pores

infiltration

Water moves by gravity into the open pore spaces in the soil, and the size of the soil particles and their spacing determines how much water can flow in. Wide pore spacing at the soil surface increases the rate of water infiltration, so coarse soils have a higher infiltration rate than fine soils.

Healthy soils are held together by soil glues, or glomalin, that are produced by fungi. Soils rich in soil biota hold together, while soils devoid of soil life fall apart and form a layer of sediment in the bottom of the jar.