Model Soil Types

Mineral Grain Size

• One of the most important features of a model soil is its texture. Soil texture is calculated by measuring the percentages of different-sized mineral grains called sand, silt and clay. A soil with roughly equal parts of these three mineral sizes will have a loam texture. A model soil will have a loam texture because it is the most useful. A loam texture can be modified into a firm building surface or used to grow crops. A soil with a loam texture is well drained while at the same time holding enough water for plants to access easily. A soil with too much sand or clay would not be considered model because of the extreme conditions found in these soils. A sand-textured soil will be bone dry most of the time and a soil with more than 60 percent clay can be difficult to build on or use for crops.

Soil Aggregates

• A model soil must be able to both absorb water and allow excess water to drain. Much of this ability depends on a soil's structure and the aggregates that form in the soil. Soil structure is a classification of the type of shape that the sand, silt and clay form into. These structures make cracks, holes and solid spaces in the soil. A well-developed soil structure allows pathways for water to penetrate deep into the ground and be absorbed. A poor soil structure is a dense homogeneous mass of sand, silt and clay.

Organic Matter

• Organic matter acts as a glue that can bind soil particles together. Organic matter comes from decayed plant and animal materials. It can absorb many times its mass in water. Organic matter will make a soil well drained while at the same time absorbing water to be released slowly as plants need it. Organic matter also increases a soil's fertility by holding nutrients in the soil and releasing them. The more organic matter in a soil the more likely it will be a model soil for growing and building on.

Topography

• Soils found on the side of mountains or steep hills tend to be thin and poorly developed. These soils cannot be considered model soil types because they are both difficult to grow and build on. A soil on hilly ground can be modified to be an excellent surface for building on. Moderately hilly ground can actually be ideal for growing on since it will remain well drained even during very wet conditions. Another reason a level soil type is more ideal is because it is less likely to erode. Erosion occurs on sloping surfaces because water that is unable to be absorbed quickly begins to flow downward, carrying soil particles with it.