- - AGRICULTURE CORE CURRICULUM - - (CLF6000) Advanced Core Cluster: ORNAMENTAL HORTICULTURE (CLF6400) Unit Title: HORTICULTURAL SOILS & PLANTING MEDIA ____________________________________________________________________________ (CLF6405) Topic: COMPOSTING Time Year(s) 1 hour 3 / 4 ____________________________________________________________________________ Topic Objectives: Upon completion of this lesson, the student will be able to: Learning Outcome #: (G-6) - Define compost and discuss its use in gardening. Special Materials and Equipment: References: Cooper, Elmer L. (1990). AGRISCIENCE: FUNDAMENTALS AND APPLICATIONS. Albany, NY: Delmar Publishers. Editors of Sunset Books and Sunset Magazine. (1988). WESTERN GARDEN BOOK. Menlo Park, CA: Lane Publishing Co. Resources: San Francisco League of Urban Gardeners (SLUG), 2540 Newhall St., San Francisco, CA 94124. Evaluation: Unit Exam TOPIC PRESENTATION: COMPOSTING A. Compost Definition and Use: Compost has a double value in that it provides a constructive way of disposing of many plant residues and organic wastes, and at the same time provides a valuable resource for soil improvement. 1. Compost is defined as a mixture of organic residues and soil that has been piled, moistened, and allowed to decompose biologically. The result is a dark, crumbly material high in humus and valuable as a soil amendment. 2. Compost is used for several purposes: a. Soil structure and drainage are improved with the incorporation of compost. Partially decomposed particles are helpful in this regard. b. Water holding capacity, and the ability of soil to hold and release nutrients (cation exchange capacity) are enhanced by compost. Humus acts to improve these features. c. Compost adds some nutrients to the soil. B. Composting Methods 1. Ingredients: The ingredients of compost are basically the same, regardless of the method of composting. a. Organic Materials: Plant and animal residues are the main component of compost. 1) Plant materials (fine or chopped) provide the bulk of most compost piles. a) Leaves, grass clippings, pulled-up weeds, prunings, and dead flowers are typical ingredients for a compost pile. b) Larger materials such as branches should be run through a shredder before being added to a compost pile. Finer materials decompose more readily. 2) Leftover foodstuffs can be added to compost, but this requires extra care in turning the pile and keeping vermin away from rotting food. b. Soil: This is added to hold moisture and interact with decomposing organic matter. It is added in relatively small quantities. c. Nutrient Source: Nitrogen or a complete fertilizer is sometimes added to compost to speed the decomposition process and boost the nutrient content of the final product. d. Moisture: Without moisture, decomposition ceases. 2. Compost Pile Construction: The compost pile should be constructed and managed in such a way to provide the basic requirements for decomposition. a. Basic Requirements: 1. Air: Microbes need oxygen to do the work of decomposing organic material. The compost pile should be open to the air, rather than enclosed or covered. 2. Moisture: Water must be available to organisms in the compost pile or the enzymatic activity which takes place during decomposition will cease. A bowl-shaped top to the compost pile to help water run through, rather than off, is helpful. 3. Heat: Decomposition proceeds more quickly in the warm center of the pile than on the outside where temperatures are cool. (The respiration of microorganisms as they feed on organic material is what generates heat within the pile.) 4. Mixing: The various components of a compost pile need to come into contact with each other to speed decomposition and to form humus. When constructing the pile initially, the various materials should be layered. Later, mixing the pile periodically will enhance decomposition. 5. Nutrients: While, given time, a compost pile will decompose without any added nutrients, the addition of nitrogen, especially, will speed decomposition and improve the nutrient value of the compost. Nutrients MUST be present at some level in order for microorganisms to take action. b. Types of Compost Piles: Below are some of the ways a compost pile can be constructed. The best method depends on the horticulturist's needs and resources. 1. A simple pile with no enclosure. This should stand about 4 feet tall on average, and slump naturally. 2. A long pile: If there are a lot of materials to decompose, a long narrow pile (4 feet tall by 6 feet wide by as long as needed) is easier to manage and turn than a huge broad pile. There is better aeration, too. 3. Wire mesh: Hardware cloth or welded wire, formed into a cylinder, helps fit a compost pile into a smaller space. 4. Compost boxes, installed side by side, allow for mature compost to be aged separately from fresh materials. (Production is staggered.) 5. Garbage can: A very simple, small composter consists of a garbage can with holes cut in it. This is compact enough for a small garden space. __________________________________________________________ ACTIVITY: 1. Have students construct a compost pile consisting of soil, shredded vegetation, and a small amount of nitrogen. 2. Construct an identical pile, only without the nitrogen. 3. Water and mix the piles in an identical fashion. At the end of four weeks, add more nitrogen to the second pile as it is mixed. 4. At the end of eight weeks, compare the contents of the two piles, and discuss the requirements of compost piles. __________________________________________________________ 3. Compost Management: Following are some hints for successful compost management: a. Keep moisture levels adequate. Don't allow pile to dry out. b. Add nitrogen or a complete fertilizer to enhance decomposition and enrich the compost. c. Turn the pile once every two weeks or so. Turning less- decomposed materials into the center of the pile helps to even out decomposition. d. Keep the pile at a reasonable size. Too small a pile loses too much heat and decomposition slows. e. If room allows, maintain different piles at different stages of decomposition. This is better than trying to sift out the compost which is ready for incorporation into the soil from the fresh materials that still need to decompose. f. Depending on conditions, expect a compost pile to take six weeks to six months to produce compost ready for the soil. g. CRITICAL! Keep weed seeds, diseased materials, and undesirable plants (for example, gladiolus cormels) out of the pile. Compost pile temperatures are not high enough to kill undesirable organisms in most cases, and these will be spread around the garden or landscape when the compost is used. In a nursery situation, compost MUST be pasteurized before being added to the growing media. h. WARNING! A compost pile can generate enough heat to cause spontaneous combustion. Be sure to turn the pile often enough to prevent this kind of accident, especially when composting materials high in nitrogen. Also, it is wise to construct and maintain a compost pile away from structures or other burnable materials. 12/14/90 MH/sg #%&C