What Is Loam Soil?

Loam soil is half way between clay and sandy soils. It is the best soil for horticultural and agricultural use, containing enough clay and humus for the retention of water and for the provision of food for plants. It also has sufficient sand to allow the passage of air and the drainage of water, which prevents water logging, and enough lime to prevent acidity.

Loam soil is composed mostly of sand (particle size > 63 µm), silt (particle size > 2 µm), and a smaller amount of clay (particle size < 2 µm). By weight, its mineral composition is about 40–40–20% concentration of sand-silt-clay, respectively. These proportions can vary to a degree, however, and result in different types of loam soils: sandy loam, silty loam, clay loam, sandy clay loam, silty clay loam, and loam. In the USDA textural classification triangle, the only soil that is not predominantly sand, silt, or clay is called “loam”.

Loam soils generally contain more nutrients, moisture, and humus than sandy soils, have better drainage and infiltration of water and air than silt and clay-rich soils, and are easier to till than clay soils. The different types of loam soils each have slightly different characteristics, with some draining liquids more efficiently than others. The soil’s texture, especially its ability to retain nutrients and water are crucial.

Loam soil is suitable for growing most plant varieties. River basins are often covered with a powdery, yellowish-grey loam called loess. This loam has been brought downstream by the river and is derived from glacial deposits of very fine silty, unconsolidated material. Some of the best farming land in the Rhine and Danube basins is composed of this soil. Other loess deposits have no connection with glacial action and are accumulations of fine material picked up by the wind in the world’s arid regions.

When water is introduced into these loess areas by means of irrigation they make unusually fertile soil. There are loess deposits in the plains of south Russia, the Argentine pampas and China, and in Iowa and Illinois in the United States. These are among the richest agricultural regions in the world.

Bricks made of loam, mud, sand, and water, with an added binding material such as rice husks or straw, have been used in construction since ancient times.

Content for this question contributed by Clara Wright, resident of Pomona, Los Angeles County, California, USA