loam, soil composed of sand, silt, clay, and organic matter in evenly mixed particles of various sizes. More fertile than sandy soils, loam is not stiff and tenacious like clay soils. Its porosity allows high moisture retention and air circulation. The popular confusion of loam with humus is probably due to the superior quality of both soils. According to the preponderance of their ingredients, loams are classified as sandy, clay, or silt loams. Most soils of agricultural importance are some type of loam.