Building Soils for Better Crops, 2nd Edition

	Making and Using Composts The reason of our thus treating composts of various soils and substances, is not only to dulcify, sweeten, and free them from the noxious qualities they otherwise retain . . . [Before composting, they are] apter to ingender vermin, weeds, and fungous . . . than to produce wholsome [sic] plants, fruits and roots, fit for the table. J. Evelyn, seventeenth century Decomposition of organic materials takes place naturally in forests and fields all around us. Composting is the art and science of combining available organic wastes so that they decompose to form a uniform and stable finished product. Composts are excellent organic amendments for soils. Composting reduces bulk, stabilizes soluble nutrients, and hastens the formation of humus. Most organic materials, such as manures, crop residues, grass clippings, leaves, sawdust, and many kitchen wastes, can be composted. The microorganisms that do much of the work of rapid composting need high temperatures, plenty of oxygen, and moisture. These heat-loving, or thermophilic, organisms work best between about 110 and 130°F. Temperatures above 140°F can develop in compost piles, helping kill off weed seeds and disease organisms, but this overheating usually slows down the process. At temperatures below 110°F, the less active meso-phylic organisms take over and the rate of com-posting again slows down. The com-posting process is slowed by anything that inhibits good aeration or the maintenance of high enough temperatures and sufficient moisture. Composting farm wastes and organic residues from off the farm has become a widespread practice. Accepting and composting lawn and garden wastes provides some income for farmers near cities and towns. They may charge for accepting the wastes and for selling compost. Some farmers, especially those without animals or sod crops, may want to utilize the compost as a source of organic matter for their own soils. Types of "Composting" Some people talk about "low temperature" composting different types are called "sheet," worm (vermicomposting), small pile composting and "high temperature" com-posting. We like to use the term composting only when talking about the rapid decomposition that takes place at high temperatures.   Making Composts Moisture The amount of moisture in a compost pile is important. If the materials mat and rainwater can't drain easily through the pile, it may not stay aerobic in a humid climatic zone. On the other hand, if composting is done inside a barn or under dry climatic conditions, the pile may not be moist enough to allow microorganisms to do their jobs. Moisture is lost during the active phase of composting, so it may be necessary to add water to a pile. In fact, even in a humid region, it is a good idea to moisten the pile at first, if dry materials are used. However, if something like liquid manure is used to provide a high-nitrogen material, sufficient moisture will most likely be present to start the composting process. The ideal moisture content of composting material is about 40 to 60 percent, or about as damp as a wrung-out sponge. If the pile is too dry 35 percent or less ammonia is lost as a gas and beneficial organisms don't repopulate the compost after the temperature moderates. Very dry, dusty composts become populated by molds instead of the beneficial organisms we want. Types of Starting Materials The organic materials used should have lots of carbon and nitrogen available for the microorganisms to use. High-nitrogen materials, such as chicken manure, can be mixed with high-carbon materials like hay, straw, leaves, or sawdust. Compost piles are often built by alternating layers of these materials. Turning the pile mixes the materials together. Manure mixed with sawdust or wood chips used for bedding can be composted as is. Composting occurs most easily if the average C:N ratio of the materials is about 25 to 40 parts carbon for every part nitrogen (see chapter 8 for a discussion of C:N ratios). There are too many different types of materials that you might work with to give blanket recommendations about how much of each to mix to get the moisture content and the C:N into reasonable ranges so the process can get off to a good start. One example is given in the box on the following page. Even Birds Do It? The male brush turkey of Australia gathers leaves, small branches, moss, and other litter and builds a mound about 3 feet high and 5 feet across. It then digs holes into the mound repeatedly and refills them helping to fragment and mix the debris. Finally, the pile is covered with a layer of sticks and twigs. The female lays her eggs in a hole dug into the pile, which heats up to close to 100°F around the eggs while the outside can be around 65°F. The heat of the composting process frees the birds from having to sit on the eggs to incubate them. -- Seymore, 1991   Cornell University's web site for composting issues (http://www.css.cornell.edu/compost/Composting_Homepage.html) features formulas to help you estimate the different proportions of the specific materials you might want to use in the compost pile. Sometimes it will work out that the pile may be too wet, too low in C:N (that means, too high in nitrogen), or too high in C:N (low in nitrogen). To balance your pile, you may need to add other materials, or change the ratios used. The examples given above can be remedied by adding dry sawdust or wood chips in the first two cases and nitrogen fertilizer in the third. If a pile is too dry, you can add water with a hose or sprinkler system. A Sample Compost Recipe Start with: a) grass clippings (71% moisture, 45% C, and 2.4% N) b) leaves (35% moisture, 50% C, and 0.75% N) c) food scraps (80 % moisture, 42% C, and 5.0% N) The ratio of the materials needed to get 60 percent moisture and 30:1 C:N is: d) 100 lbs. of grass, 130 lbs. of leaves, and 80 lbs. of food scraps. -- Richard, Trautmann & Krasny, 1996 One thing to keep in mind is that not all carbon is equally available for microorganisms. Lignin is not easily decomposed (we mentioned this when discussing soil organisms in chapter 3 and again in chapter 8, when we talked about the different effects that various residues have when applied to soil). Although some lignin is decomposed during composting probably depending on factors such as the type of lignin and the moisture content -- high amounts of carbon present as lignin may indicate that not all of carbon will be available for rapid composting. When residues contain high amounts of lignin, it means that the effective C:N can be quite a bit lower than indicated by using total carbon in the calculation (table 12.1). For some materials, there is little difference between the C:N calculated with total carbon versus using only biodegradable carbon. It's a good idea to avoid using certain materials, such as coal ash, wood chips from pressure-treated lumber, manure from pets, and large quantities of fats, oils, and waxes. These types of materials are either difficult to compost or may result in compost containing chemicals that can harm crops. Wood chips or bark are sometimes used as a bulking agent to provide a "skeleton" for good aeration. These materials may be recycled by shaking the finished compost out of the bulking material, which can then be used for a few more composting cycles. Composting Animals It is also possible to compost dead farm animals, which are sometimes a nuisance to get rid of. Chickens and even dead cows have been successfully composted. Cam Tabb, a West Virginia dairy and crop farmer, starts the process for large animals by laying the carcass that's been in the open for one day on a 3 to 4 ft bed of sawdust. Then he covers it with 3 to 4 ft of sawdust/horse manure and then turns the pile in 3 to 4 weeks. After all turning is done, he uses new base material on top. Pile Size A compost pile is a large natural convective structure something like many chimneys all next to each other moving oxygen into the pile as carbon dioxide, moisture, and heat rise from it. The materials need to fit together in a way that allows oxygen from the air to flow in freely. On the other hand, it is also important that not too much heat escape from the center of the pile. If small-sized particles are used, a "bulking agent" may be needed to make sure that enough air can enter the pile. Sawdust, dry leaves, hay, and wood shavings are frequently used as bulking agents. Tree branches need to be "chipped" and hay chopped so that it doesn't mat and slow composting. Composting will take longer when large particles are used, especially those resistant to decay. The pile needs to be large enough to retain much of the heat that develops during compost-ing, but not so large and compacted that air can't easily flow in from the outside. Compost piles should be 3 to 5 feet tall and about 6 to 10 feet across the base after the ingredients have settled (see figure 12.1). (You might want it on the wide side in the winter, to help maintain the warm temperatures, while gardeners can make compost in a 3-feet tall by 3-feet wide pile in the summer.) Easily condensed material should initially be piled higher than 5 feet. It is possible to have long windrows of composting materials, as long as they are not too tall or wide. Minimum Turning Technique Farm-quality composts can be produced by turning the pile only once or twice. To do this you need to carefully construct the pile building it up to reasonable dimensions, using and thoroughly mixing materials that give very good porosity, and making sure the pile stays moist. Turning the Pile Turning the composting residues exposes all the materials to the high-temperature conditions at the center of the pile. Although the materials at the top and on the sides of the pile are barely composting, they do provide insulation for the rest of the pile. Turning the pile rearranges all the materials and creates a new center. If piles are turned every time the interior reaches and stabilizes at about 140°F for a few days, it is possible to complete the composting process within months. On the other hand, if you only turn the pile occasionally, it may take a year or longer to complete. Equipment is now available to quickly turn long compost windrows at large-scale composting facilities. Tractor-powered compost turners designed for composting on farms are also available. Although turning compost frequently speeds up the process, it may also dry out the pile and cause more nitrogen loss. If the pile is too dry you might consider turning it when it's raining to help moisten it. If the pile is very wet, you might want to turn it on a sunny day. Very frequent turning may not be advantageous, because it can cause physical breakdown of important structural materials that aid natural aeration. The right amount of turning depends on a variety of factors, such as aeration, moisture, and temperature. Turn your compost pile to avoid cold, wet centers, break up clumps, and make the compost more uniform later in the process before use or marketing. Figure 12.1 Compost pile dimensions and turning techniques.   The Curing Stage Following high-temperature composting, the pile should be left to cure for about one to three months. Usually this is done once pile temperatures reach 105°F and high temperatures don't reoccur following turning. Curing is especially needed if the active (hot) process is short or poorly managed. There is no need to turn the pile during curing because you are not trying to stimulate maximum decomposition and there is less need for rapid oxygen entry into the pile's center when decomposition rate is slow. [However, the pile may still need turning during the curing stage if it is very large or it didn't really finish composting (determining when compost is finished is sometimes difficult), or if the pile is soaked by rain.] Curing the pile furthers aerobic decomposition of resistant chemicals and larger particles. Common beneficial soil organisms populate the pile during curing, the pH becomes closer to neutral, and ammonium is converted to nitrate. Be sure to maintain water content around 50 percent during curing to ensure that active populations of beneficial organisms develop. It is thought that the processes that occur during the early curing process give compost some of its disease-suppressing qualities. On the other hand, beneficial organisms require sources of food to sustain them. Thus, if composts are allowed to cure for too long depleting all the available food sources disease suppression qualities may decrease and eventually be lost. Disease Suppression by Composts Research by Harry Hoitink and co-workers at Ohio State University shows that composts can suppress root and leaf diseases of plants. This suppression comes about because the plants are generally healthier (microorganisms produce plant hormones as well as chelates that make micronutrients more available) and, therefore, are better able to resist infection. Beneficial organisms compete with disease organisms for nutrients as well as directly consume the disease-causing organisms or produce antibiotics that kill bacteria. Some organisms, such as springtails and mites, "actually search out pathogen propagules in soils and devour them," according to Hoitink. In addition, he found that potting mixes containing composts "rich in biodegradable organic matter support microorganisms that induce systemic resistance in plants. These plants have elevated levels of biochemical activity relative to disease control and are better prepared to defend themselves against diseases." This includes resistance to both root and leaf diseases. Composts rich in available nitrogen may actually stimulate certain diseases, as was found for Phytophthora root rot on soybeans, as well as Fusarium wilts and fire blight on other crops. Applying these composts many months before cropping, allowing the salts to leach away, or blending them with low nitrogen composts prior to application reduces the risk of stimulating diseases. Composting can change certain organic materials used as surface mulches such as bark mulches from stimulating disease to suppressing disease.   Using Composts Finished composts generally provide only low relative amounts of readily available nutrients. During composting, much of the nitrogen is converted into more stable organic forms, although potassium and phosphorus availability remains unchanged. However, it should be kept in mind that composts can vary significantly and some may have high levels of nitrate. Even though most composts don't supply a large amount of available nitrogen per ton, they still supply fair amounts of other nutrients in available forms and greatly help the fertility of your soil by increasing organic matter and by slowly releasing nutrients. Composts can be used on turf, in flower gardens, and for vegetable and agronomic crops. Composts can be spread and left on the surface or incorporated into the soil by plowing or rototilling. Composts also are used to grow greenhouse crops and are the basis of some potting soil mixes. Advantages of Composting Composted material is less bulky than the original material, and easier and more pleasant to handle. During the composting process, carbon dioxide and water are lost to the atmosphere and the size of the pile decreases by 30 to 60 percent. In addition, many weed seeds and disease-causing organisms may be killed by the high temperatures in the pile. Unpleasant odors are eliminated. Flies, a common problem around manures and other organic wastes, are much less of a problem with composts. Composting reduces or eliminates the decline in nitrogen availability that commonly occurs when organic materials, such as sawdust or straw, are added directly to soil. Composting is also very useful for recycling kitchen wastes, leftover crop residues, weeds, and manures. Many types of local organic waste, such as apple pumice, lake weeds, leaves, and grass clippings, can be composted. There is evidence that compost application lowers the incidence of plant root and leaf diseases (see above). In addition, the chelates and the direct hormone-like chemicals present in compost stimulate the growth of healthy plants. Then there are the positive effects on soil physical properties that are derived from improving soil organic matter. All of these factors together may help explain some of the broad benefits to plant growth that are attributed to compost. If you have a large amount of organic waste but not much land, composting may be very helpful. Also, since making compost decreases the solubility of nutrients, composting may help lessen pollution in streams, lakes, and groundwater. On many poultry farms and on beef feedlots, where high animal populations on limited land may make manure application a potential environmental problem, composting may be the best method for handling the wastes. Composted material, with about half the bulk and weight and its higher commercial value than the manure, can be economically transported significant distances to locations where nutrients are needed. Protecting Drinking Water Supplies Composting of manure is of special interest in watersheds that supply drinking water to cities, such as those that serve New York. The parasites Giardia Lamblia (beaver fever) and Cryptosporidium parvum cause illness in humans and are shed through animal manure, especially young stock. These organisms are very resistant in the environment and are not killed by chlorination. Composting of manure, however, is an economical option that kills the pathogen and protects drinking water. Without denying these good reasons to compost, there are frequently very good reasons to just add organic materials directly to the soil, without composting. Compared with fresh residues, composts may not stimulate as much production of the sticky gums that help hold aggregates together. Also, some uncomposted materials have more nutrients that are readily available to feed plants than do composts. If your soil is very deficient in fertility, plants may need readily available nutrients from residues. Routine use of compost as an nitrogen source may cause high soil phosphorus levels to develop, because of the relatively low N:P ratio. Finally, more labor and energy usually are needed to compost residues before applying than to simply apply the uncomposted residues directly. Sources Hoitink, H.A.J., D.Y. Han, A.G. Stone, M.S. Krause, W. Zhang, and W.A. Dick. 1997. Natural Suppression. American Nurseryman. October 1, 1997:90­97. Epstein, E. 1997. The Science of Composting. Technomic Publishing Company. Martin, D. L., and G. Gershuny (eds.). 1992. The Rodale Book of Composting: Easy Methods for Every Gardener. Rodale Press. Emmaus, PA. Richard, T.L., N.M. Traubman, and M.E. Krasny. 1996. Cornell composting website. http://www.css.cornell.edu/compost/Composting_Homepage.html Rothenberger, R.R., and P.L. Sell. Undated. Making and Using Compost. University of Missouri Extension Leaflet (File: Hort 72/76/20M). Columbia, MO. Rynk, R. (ed.). 1992. On Farm Composting. NRAES-54. Northeast Regional Agricultural Engineering Service. Ithaca, N.Y. Seymour, R.S. 1991. The brush turkey. Scientific American. Dec. 1991. Staff of Compost Science. 1981. Composting: Theory and practice for city, industry, and farm. The JG Press. Emmaus, PA. Weil, R.R., D.B. Friedman, J.B. Gruver, K.R. Islam, and M.A. Stine. Soil Quality Research at Maryland: An Integrated Approach to Assessment and Management. Presented in Baltimore, MD at the 1998 ASA/CSSA/SSSA meetings. This is the source of the quote from Cam Tabb. Top