Composting

Waste from the garden, yard, and table does not have to be thrown away. It may be condensed and reused as a fertilizer through a process called composting. A compost pile may be built by layering different kinds of waste in a bin, leaving space between the layers for air to circulate. Nitrogen is added to the pile in the form of manure, meal, or greenery to generate heat. Heat facilitates rotting and kills all undesirable organisms. Once the pile is slightly dampened, it is covered. As heat and steam build up, the waste decomposes over time into a nutrient-rich substance called compost. The compost is then applied to plants as a fertilizer.

source : encarta