Green manure refers to plant crops which have been uprooted (and have often already been stuffed under the soil. The dying plants act as fertiliser for other crops. Crops with nitrogen fixing properties are often used as green manure. Green manure can be used to to help replace or reduce the need for chemical fertilisers.
 Plants used as green manure
In the United States, winter cover crops are quite common, such as rye grass.
In the tropics, Sesbania rostrata has been introduced as green manure crop before rainy season rice in the rice soybean system. The legume is broadcasted in mid May and incorporated into soil after 55-60 days. Rice is then transplanted 7-10 days after Sesbania incorporation. The on-station studies and on-farm participatory experimentation show convincing results of increasing rice yield over 20%, which is equivalent to yield obtained by applying 54 kgN/ha. After two years of farmer participation, the area planted to Sesbania rostrata in the test site as green manure crop has been increased three folds.