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.
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 accumulation 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 lowa and Illinois in the United States. These are among the richest agricultural regions in the world.
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