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COMPOSTING AND MULCHING: A GUIDE TO MANAGING ORGANi-C YARD WASTES Composting is a microbial process that converts plant mate- rials such as grass clippings and leaves to a usable organic soil amendment or mulch. Gardeners have used compost for centuries to increase soil organic marter and supply some of the essential nutrients for plant growth. Mulching refers to the practice of applying a substance such as compost or grass clippings to the soil surface with the purpose of modifying soil temperature and moisture as well as controlling weeds and soil erosion. With the ban on outdoor burning and with laws which soon will lirnitdumping atleaves and grass clippings into landfills, composting and mulching have become attractive alterna- tives for managing yard waste and recycling natural materi- als. Grass clippings and leaves can be hauled to city composting areas as one means of disposal. However, many homeowners may find it more convenient and economical to compost these materials in their own backyards. In either case, the finished compost can be used as a mulch or as a soil amendment to improve most garden soils. This bulletin should help you learn how to build and maintain a compost pile as well as how to use the compost in the yard and gar- den. Why Compost? Composting is an efficient method of breaking down organic materials into an end product that is beneficial to the soil and growing plants. Adding undecomposed materials directly to the soil without first composting may initially have some un- desirable effects. For example, if large quantities of uncom- posted leaves are incorporated into the soil, microbes will compete with plant roots for soil nitrogen during leaf decom- position. This competition for nitrogen can result in nitrogen deficiency and poor plant growth. Adding composted mate- rial reduces the competition for nitrogen. Another benefit of composted material is that it is much easier to handle and mix with soil than uncomposted material. Furthermore, im- provement of soil physical properties, such as infiltration, drainage, and water holding capacity, will usually be faster if composted materials are added. Requirements for Efficient Decomposition Decomposition of organic material in the compost pile is de- pendent on maintaining microbial activity. Any factor which slows or halts microbial growth will also impede the com- posting process. Efficient deromposition will occur if the fol- lowing factors are used to fullest advantage. Aeration: Oxygen is required for microbes to efficiently de. compose the organic wastes. Some decomposition will oc- cur in the absence of oxygen (anaerobic conditions); however, the process is slow and foul odors may develop. Mixing the pile once or twice a month will provide the neces- sary oxygen and significantly hasten the composting pro- cess. A pile that is not mixed may take three to four times longer before it can be used. A well mixed compost pile will also reach higher temperatures which will help destroy weed seeds and pathogens. Moisture: Adequate moisture is essential for microbial activ- ity. A dry compost will not decompose efficiently. If rainfall is limited, it will be necessary to water the pile periodically to maintain a steady decomposition rate. Enough water should be added to completely moisten the pile, but overwatering should be avoided. Excess water can lead to anaerobic con- ditions which slow down the degradation process and cause foul odors. Water the pile so that it is damp, but does not re- main soggy. Particle size: The smaller the size of organic wastes, the faster the compost w!II be ready for use. 5maller par•icles have much more surface area that can be attacked by mi- crobes. A shredder can be used beforeputting material in the pile, and is essential if brush or sticks are to be composted. A low cost met%od of reducing the size of fallen tree leaves is to mow the lawn before raking. If the mower has an appropriate bag attachment, the shredded leaves can be collected di- rectly. In addition to speeding up the composting process, shredding will reduce the initial volume of the compost pile. Fertilizer and lime: Microbial activity is affected by the ca' bon to nitrogen ratio of the organiz waste. Because microlr require a certain amount of nitrogen for their owl, metabolism and growth, a shortage of nitrogen will slow down the composting process considerably. Material high in carbon relative to nitrogen such as straw or sawdust will de- compose very slowly unless nitrogen fertilizer is added. Tree leaves are higher in nitrogen than straw or sawdust but de- composition of leaves would still benefit from an addition of nitrogen fertilizer. Grass clippings are generally high in nitro- gen and when mixed properly with leaves will enhance de- composition. Manure or blood meal can be used as organic sources of nitrogen. Otherwise, a fertilizer with a high nitro- gen content should be used. Other nutrients such as phos- phorus and potassium are usually present in adequate amounts for decomposition. During the initial stages of decomposition organic acids are produced and the pH drops. In the past, small amounts of lime have been suggested for maintaining and enhancing microbial activity at this time. However, high rates of lime will convert ammonium -nitrogen to ammonia sas which will lead to the loss of nitrogen from the pile. Research has shown that although lime additions may hasten decomposi- tion, the loss of nitrogen from the pile often offsets the bene- fits of lime (1). in general, lime is not necessary for degradation of most yard wastes. The pH of finished compost is usually slightly alkaline without the addition of lime. In many areas, the water used to moisten the compost pile i• sufficiently alkaline to increase the pH of the compost. large quantites of pine needles or fruit wastes are composteb,.. some additional limc 'nay be necessary.