compost, substance composed mainly of partly decayed organic material that is applied to fertilize the soil and to increase its humus content; it is often used in vegetable farming, home gardens, flower beds, lawns, and greenhouses. Compost usually is made from plant materials (e.g., grass clippings, vegetable tops, garden weeds, hay, tree leaves, sawdust, and peat) together with manure and some soil; lime, superphosphates, and nitrogen fertilizers are often added with manure to reinforce the compost and hasten its decomposition.
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