Parts of Soil

Minerals

• Soil is full of minerals that are mostly contained in the earth but sometimes are cycled through the atmosphere. Minerals form when magma, or molten rock, cools and solidifies. Ions from this solid rock bond together through electrical attraction to form fixed mineral compositions within the rock. Secondary minerals form when these minerals break apart and form with other solids. Examples of minerals in soil are calcium, aluminum, oxygen, magnesium and potassium.

Organic Matter

• Another physical element of soil is organic matter. This part of soil's composition changes at a more constant rate than minerals do. Animal and plant waste falls to the earth and decomposes in soil. Organic matter is called humus when it has decomposed fully. This decomposed matter is crucial for healthy soil because it holds mineral particles together. Plants thrive on soil with the right types of organic material, since all plants require certain amounts of minerals and waste. Some areas cannot support bountiful plant life due to a lack of decomposing organic waste.

Air

• Voids in soil are partially filled with air. This air is made up of different elemental gasses, such as nitrogen and carbon dioxide. Like air in the atmosphere, nitrogen makes up most of the air in soil; however, carbon dioxide basically replaces oxygen. Air quality changes throughout soil, depending on depth, pore size distribution, aeration, drainage and water vapor. For example, oxygen levels decrease as depth increases, and soil with small pores has poor aeration.

Water

• Water and soil work together constantly. Soil stores and moves water when it is not on the surface of the earth or in the atmosphere. Water exists in soil either as a coating of soil particles or in pore spaces. Plant roots access some of the water in soil while humans tap other water stores for drinking and cleaning purposes. The levels of soil moisture content are field capacity, wilting point, oven dry and saturation.