As the content of clay in the soil increases, more water is held. If soils contain too much clay, they may not drain well enough to allow enough oxygen in the pore space for good plant growth. These soils drain well, but have little capacity to hold moisture and plant food. Sandy soils have comparatively large particles that permit good aeration, quick passage of water, and quick warming. A clayey soil must contain at least 30 percent clay and is known as a heavy soil.
Heavy soils have relatively poor drainage and aeration capabilities.
Because of this, heavy soils tend to hold more moisture than is good for plants. However, this type of soil also holds fertilizer and plant food well, which can be beneficial to plant growth. This is the most desirable soil for agricultural use. Loam is a mixture of approximately equal parts of sand, silt, and clay. Learning Activities To introduce realistic examples of the differences between clayey, sandy, and loamy soils to youngsters, try the following activity.