ABSTRACT
Green manuring is the tilling of green, growing plants into the ground to improve the condition of the soil. Green manures improve soils in several ways:
1. Addition of organic matter 2. Addition of nitrogen with legumes 3. Conservation of nutrients 4. Protection of soil against erosion 5. Biocontrol of diseases
Increasing the organic matter content of soil is the primary purpose of green manuring. Turning a green manure into the soil adds 1 or 2 tons of dry matter per acre and is the surest method of increasing soil organic matter. Although some effects on soil conditioning, such as aggregation, may last for several years, most of the benefits occur in the growing season following incorporation of the green manures. Green manures decompose rapidly due to their succulence, and about 75% of the organic matter will be rotted in the first season, leaving little residual effects afterward. For maximum benefits, the green manure crop should be in a crop rotation every third year, such as a rotation of corn-oats-green manure or vegetable-vegetable-green manure. Green manures do not have much effect on increasing soil organic matter unless the crop is grown for at least 1 year or growing season. Growing the green manure for more than 1 year usually is undesirable, because this practice takes the land out of production for too long. A winter cover crop (see below) seeded in the fall and turned under in the early spring may not add much organic matter to the soil. Cover crops that are turned under late in the spring after at least 12 inches of growth have occurred may increase organic matter in the soil. The primary purpose of the cover crop is to protect the soil against water and wind erosion during the seasons when the ground otherwise would be bare.
