Delphinidin

Soil texture refers to the relative proportions of sand, silt, and clay in a given soil. Sands are usually composed of many small particles bound together chemically or by a cementing matrix material. Silt consists of particles that are mostly too small to be seen without a lens or a microscope.

Clay particles are so tiny that they can’t be seen with even a powerful light microscope, although they can be seen with an electron microscope. Individual clay particles are called micelles. Micelles are somewhat sheetlike, negatively charged, and held together by chemical bonds. The negative charges attract, exchange, or retain positively charged ions. Many of the positively charged ions, such as magnesium (Mg++) and potassium (K+), which are needed for normal plant growth, are absorbed with water by the roots. Clay is plastic in nature because the water that adheres tightly to the surface of the particles acts both as a binding agent and a lubricant. Physically, clay is a colloid; that is, a suspension of particles that are larger than molecules but that do not settle out of a fluid medium.

The best agricultural soils are usually loams, which are a mixture of sand, clay, and organic matter. The better loams have about 40% silt, 40% sand, and 20% clay. Light soils have a high sand and low clay content. Heavy soils have high clay content. Coarse soils, which have larger particles, are porous and don’t retain much water, while clay soils have high water content and allow little water to pass through.

Over half the composition by weight of mineral matter is oxygen. Other elements commonly present are hydrogen, silicon, aluminum, iron, potassium, calcium, magnesium, and sodium. However, soil obtains hundreds of different mineral combinations from its parent material.