Soil Texture and Structure

There are three distinct types of soil texture, Clay, Silt and Sand. The biggest difference between the soil textures is particle size. Sand has the biggest particle size ranging from .05mm to 2mm. Silt is next with a particle size ranging from .002mm to .05mm. And lastly clay is the smallest with a particle size less than .002mm. It is difficult or nearly impossible to change the soil texture over a large area. However, one way that this can be accomplished is through container gardening or using raised beds where the gardener can control the type of soil texture.

Why Size Matters

The upper portion of the soil horizon is where plant roots grow. Plant roots need Oxygen and water to survive. The space between the particles is where Oxygen and water exist in the soil. Ideally, there should be 50% pore space between soil particles. The bigger the soil particles the more space there is between them and the more Oxygen and water can infiltrate into the soil. However, the more space the easier it is for water to leach through the soil. Therefore, while sand has greater space between the molecules that allows more air and water to exist, clay holds water better. Sometimes, though the clay molecules can become compacted together so much that it is impossible for water and air to make its way into the soil. This makes it difficult for plants to survive.

Soil Nutrients and Soil Texture

Clay soils contain negatively charged particles called colloids where sandy soils do not. Cations are positively charged ions of many plant nutrients. NH4+. CA2+, K+, Mg2+, Zn2+ are all examples of essential nutrients that are cations. Interestingly, H+ is a cation of an element that is not taken up by plants but does affect plant growth by affecting the pH level in soil. Sandy soil does not contain these negatively charged ions, and thus, require more fertilization than clay soils.

Soil Structure

Soil structure is how close the soil molecules are arranged together. Structure affects the amount of water and air that can make its way into the soil. The types of soil structure include granular, platy, wedged, blocky, prismatic and columnar. While it is next to impossible to control soil type, changing the soil structure is achievable. Adding organic matter to soil can add space between the soil molecules or decrease space if the spaces are too big. Thus, the way to improve the soil structure for both sand or clay is to add organic matter.