Green manuring or growing a cover crop for the purpose of cultivating the crop under, as another source of soil humus and a common practice among home gardeners, especially, organic gardeners. Annual and Quick-growing crops, such as winter rye, buckwheat, ryegrass, and mustard, are good for this purpose. They should be cultivated into the soil just before they flower for best results and to avoid seed production.
To solve the problem of temporary nitrogen deficiency after turning these crops under add some balanced fertilizer according to the vendor instructions and or adding some composted animal manure.
Legumes, such as soybeans, vetches, cowpeas, alfalfa, and clovers, have nodules on their roots that house special nitrogen-fixing bacteria. These bacteria take free nitrogen from the air, convert it to forms usable by plants, and hold it. When legumes are used for green manure added nitrogen is not needed.