Teachers TryScience

Soil is a layer on the earth’s crust that provides a combination of resources. These resources
allow the growth of plants and animals. These resources include:
A. Oxygen—needed for adequate root growth.
B. Temperature—soil absorbs heat from the sun. It also loses heat to the atmosphere. This
allows satisfactory temperatures for plant growth and seed germination.
C. Water—utilized for growth of plants.
D. Carbon—utilized in the form of organic matter in the soil.
E. Nutrients—provided as minerals. They are broken down as nitrogen and recycled
through decaying material in the soil.

Moisture-holding capacity is the ability of the soil within a soil profile to retain water.

• Water accounts for about 25% of an average soil.
• It occupies part of the pore space in the soil.
• When it rains, water enters the soil or flows off the soil’s surface.
• The process of water soaking into the soil is known
  as infiltration.
• Once water is in the soil, it moves downward in a
  process known as percolation.

A quality soil allows both kinds of water movement and is said to be permeable. Water in the soil
may be one of three types:

• Gravitational
• Capillary
• Hygroscopic

Capillary moisture is the water held within the pore spaces between soil particles against the forces of gravity.

• It is available to plants.
• It may move upward or sideways by capillary action.
• Clay soils hold more capillary water than sandy soils because they have more pore spaces.