Course: SLF 150 Pasture Management

Reading & Audio Visual

Types of Soil
Types of Soil

Soils are named according to where their sand, silt, and clay composition plots on a soil structure triangle. Three of those are loam, topsoil and humus.

Loam
A kind of soil; an earthy mixture of clay and sand, with organic matter to which its fertility is attributed. A typical loam soil is made up of about a 20:40:40 mixture of clay, silt, and sand. Loam is considered ideal for gardening and agricultural uses because it retains nutrients and water well while still allowing the water to flow freely. This soil is found in a majority of successful farms in regions known for their fertile land. Loam soils generally contain more nutrients and humus than sandy soils, have better infiltration and drainage than silty soils, and are easier to till than clay soils.

Topsoil
The most fertile soil, easiest to start new plants in. Topsoil is formed when mineral particles release due to weathering mixes, living soil organisms, and humus. Topsoil in combination with other distinct soil layers are soil horizons, which can range in depth from millimeters to meters. Topsoil is the most important soil layer for plant growth. Loam is the most fertile of the topsoil, consisting of almost equal amounts of sand, silt, and clay. Fertile topsoil has pores filled with half water and half air, thus maintaining an efficient balance between aeration, drainage, and water storage.

Humus
Is the dark brown or black biochemical substance that gives color to the upper layers of the soil. Humus is difficult to see in isolation, because it binds with larger mineral and organic particles. Humus provides soil with a number of very important benefits:
- It enhances a soil's ability to hold and store moisture.
- It reduces the eluviation of soluble nutrients from the soil profile.
- It is the primary source of carbon and nitrogen required for plant nutrition.
- It improves soil structure.
Humus-rich and Humus-poor Soil

The soil on the left is a highly weathered and without strong humus formation. The soil profile on the right, with its rich, dark brown color, demonstrates good humification.