Characteristics of Soils

Azaleas, which have a pH number lower than 7, do better in acidic soils.
Azaleas, which have a pH number lower than 7, do better in acidic soils. (Image: Jupiterimages/Photos.com/Getty Images)

Soil, which is much more than just dirt, is composed of four basic components in differing proportions. These parts are organic particles, mineral particles, water and air. Different soils have particular colors, textures and even smells. Several characteristics are used in describing soil. Gardeners should understand the various traits of their soils, so they can make changes in their soils to ensure the best possible plant growth.

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Texture

Sandy, silt, clay and loam are among the common terms to describe soil textures. Most of the solid structure of soil is made up of mineral particles. Differences in a particular soil’s particle sizes and proportions help determine the type of soil texture. For example, larger soil particles, including gravel, stones and coarse sands, have different rock fragments than smaller soil particles, which are generally made up of just one mineral.

The most familiar type of mineral particle is sand, which is visible to the naked eye. Silt particles, which are smaller than sand particles, are microscopic and smooth when wet, but they’re not sticky. Clay, the smallest type of particle, is sticky when wet, forming hard clods when dry.

Ease of Soil Tillage

Although heavy and light are common terms for describing soils, they don’t refer to a soil's weight, but to the ease of soil tillage. Heavier soils are usually finer soils that require more strength for tilling, because they have more clay, which makes them stickier. On the other hand, lighter soils have more sand, giving them a coarse texture with less ability to stick together. These soils need less muscle power to be tilled.

Water Infiltration Rate

Water infiltration, or the rate at which soil penetrates water, is a common way to characterize soil. Sandy soils, which are extremely porous, have the greatest penetration depth, absorbing more than two inches of water each hour. Loam soils have a slower water absorption rate, soaking up from .25 to 2 inches an hour. Although loam soil is porous and loose, it still holds water exceptionally well. Clay only absorbs less than .25 inch of water hourly and has just a few air spaces between particles, making it dense. Because clay soil holds water tightly, there’s not much water for plants. Its denseness hinders oxygen from reaching plant roots. Loam has an intermediate infiltration rate.

Soil pH

Soil pH is the amount of acidity or alkalinity found in soil. It’s measured using a pH scale, which consist of 14 numbers, ranging from 1 to 14. Soils that are neither acidic nor alkaline are neutral, falling in the middle of the scale at 7. A soil with a pH number ranging from 7.1 to 14 is considered progressively more alkaline, while a soil pH that's lower than 7 is more acidic. Most soils with a pH of 6 to 7 are considered suitable for growing plants. It's important to have soil tested for its pH, because a soil's degree of acidity or alkalinity can effect plants' ability to absorb nutrients.

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