As humans beings, we’ve had such a devastating impact on the Earth’s ecology. We can’t just stop harming. What regeneration means is not just restoring the land to the state that we found it at, but actually making it better”
- Leah Penniman in COMMON GROUND
The following blog post is excerpted from:
Building Soils for Better Crops
Ch 13. Making and Using Composts
Read the entire book for free on the Sustainable Agriculture Research & Education (SARE) website: https://www.sare.org/publications/building-soils-for-better-crops/making-and-using-composts/
Composting helps us use organic waste materials to benefit the soil and increase plant growth.
Made from decomposed organic matter, it adds essential nutrients back into the soil, fostering a rich, fertile environment for organically grown crops.
Critical to good composting is to have 1) a good balance of carbon (brown-dry) and nitrogen (green or colorful-wet), 2) good aeration, 3) moist conditions and 4) a mass of 4–5 cubic feet to reach and maintain high temperatures.
Making Composts
A SAMPLE RECIPE FOR BACKYARD COMPOSTING
Start with the following:
grass clippings (77% moisture, 45% C and 2.4% N)
leaves (35% moisture, 50% C and 0.75% N)
food scraps (80% moisture, 42% C and 5% N)
The ratio of the materials needed to get 60% moisture and a C:N of 30:1 is 100 pounds of grass, 130 pounds of leaves and 80 pounds of food scraps.
—T. Richard (1996b)
Common and Uncommon Feedstock
Composting of wastes and organic residues, both on and off farms, has become a more common practice. Farmers, municipalities and community composters accept many organic residuals, and tipping fees are often charged to offset the cost of managing this waste.
The list of source materials is endless and includes anything, plant or animal, that was alive and is now dead and needs to be managed. Some examples include crop residuals; food processing residuals; livestock carcasses; pet, zoo and human manure; chipped trees; mixed leaf and yard residuals; road kill; egg shells; glucose solutions; brewery waste; paper from document destruction; bakery excess; floral and cut flower production waste; coffee/tea grounds; off-spec human food; residuals from fish canneries and slaughterhouses; poultry feathers; livestock wool; butcher waste; fish from fish kills; aquatic weeds; biochar; whey and other milk products; fats/oils/greases; bagasse (the pulpy residue left from crushing and extracting liquid from sugar cane); drywall; and untreated small pieces of wood.
Feedstock materials cannot just be thrown together randomly; they require a recipe that allows for the appropriate physical conditions (e.g., allowing air flow and the right texture for handling) and lots of carbon and nitrogen available for the microorganisms to feed on. Compost piles are often built by alternating layers of these materials. Turning the pile mixes the materials. Composting occurs most easily if high-nitrogen materials are mixed with high-carbon materials, with the average C:N ratio of the materials being about 25–40 parts carbon for every part nitrogen (see Chapter 9 for a discussion of C:N ratios). Therefore, manure mixed with straw, wood chips or bark can be composted as is, because it has the right C:N balance. Wood chips or bark also provide the coarse structural matrix (skeleton) needed for airflow and handling, and may be recycled by shaking the finished compost out of the bulking material and then used for the next composting cycle. Manure and sawdust would also provide a good C:N mix but the texture of sawdust is too fine to allow for effective air flow.
“A Sample Recipe for Backyard Composting.” There are formulas to help you estimate the proportions of the specific materials you might want to use in the compost pile (see Cornell University’s http://compost.css.cornell.edu).
Backyard composting can be done in piles or vessels. Oxygen moves into the pile while carbon dioxide, moisture and heat rise out of 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 escapes from the center of the pile. If small sizes of organic materials are used, a “bulking agent” may be needed to make sure that enough air can enter the pile. Dry leaves, wood shavings/chips and chopped hay or straw are frequently used as bulking agents, which need to be appropriately cut to size to prevent matting and slow composting. Composting will take longer when large particles are used, especially those resistant to decay like large wood chips, while overly fine particles like sawdust decompose well but cause the pile to become too dense for air flow.
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 job. 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.
The ideal moisture content of composting material is about 40–60%, or about as damp as a wrung-out sponge. If the pile is too dry, 35% 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.
Following high-temperature composting, the pile should be left to cure for about one to three months. Usually, this is done once pile temperatures cool to 105°F and high temperatures don’t recur following turning.
Determining when compost is finished is sometimes difficult, but if it reheats, it is not finished. (The Solvita® test measures carbon dioxide losses from compost as a way to determine compost maturity.) 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, ammonium is converted to nitrate, and soluble salts are leached out if the pile is outside and sufficient precipitation occurs.
Be sure to maintain water content at the moisture-holding capacity (around 50% or less during curing) to ensure that active populations of beneficial organisms develop.
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 soil by increasing organic matter and by slowly releasing nutrients.
In some cases, the repeated use of compost, especially on some organic farms, may result in buildup of certain nutrients. For example, if high amounts of compost are applied to meet a crop’s nitrogen needs (remember, compost is relatively low in available nitrogen), then nutrients like phosphorus and potassium are applied in excessive amounts and can accumulate in the soil. Also, salts may build up if there is not enough rainfall to wash them out of the soil (like under high tunnels and in greenhouses). It is recommended to monitor the soil through regular soil tests
Composting manure -- high temperatures and biological activity during the composting process can help to decrease antibiotic levels in manures, which can be taken up by crops growing on manured land
Without denying the 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. Some uncomposted materials have more nutrients readily available to feed plants than do composts.
Bottom line - keep your kitchen scraps out of the landfill where they're going to produce methane! Feed them to the soil instead. Dig a hole and bury the waste in the ground to feed the soil microbes. Even a rudimentary compost is better than no compost!
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