Since the domestication of the first crop species, farmers have dealt with the problem of soil depletion and declining crop yields. Fallowing of land was the first approach to restoring soil fertility, and is still the most commonly used method among indigenous farmers. Alternatives to fallow, such as crop rotation and green manures, developed in a number of areas. The earliest record of their use is in Chinese writings from ca. 500 B.C. Discussion of these practices is found in European agricultural publications dating from the 16th century. While these ancient techniques have proven value for soil conservation, their use in modern agriculture is quite limited. Renewed interest within the agriculture community in recent decades has resulted in a greater research effort in the areas of green manures, cover crops, and living-mulch cropping systems.
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