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close this bookOrganic and Compost-Based Growing Media for Tree Seedling Nurseries (World Bank, 1995)
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Increasing organic matter content in potting media is best accomplished through addition of composted organic materials. Use of fresh organic material should generally be avoided because both the growing seedling and the decomposition of the organic matter require nitrogen. As a result, seedling growth is reduced due to competition for nitrogen. It is therefore a good assumption that production of adequate quantities of potting mix will require a composting operation be initiated. A well-managed composting operation can produce a compost with almost all of the properties of a good potting media, i.e. Iightweight, good water-holding capacity, etc. without being prohibitively expensive.

The composting process has some very basic requirements. There must be adequate moisture, oxygen, and the proper balance of carbon to nitrogen (C/N ratio). These requirements can be easily managed to ensure a mature, uniform product. Further discussion of the chemistry and biology of composting are found in Annex II. Other factors will influence composting and the rate at which it occurs, these are: nutrient supply, particle size, structural strength, frequency of turning (for aeration), acidity, and the size of the compost pile or heap. Through management and forward planning, these factors can be optimized. Important points to consider when planning compost production are listed in Box 2.