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Small-Scale Compost Production
By Rekha Banerjee
MOSES Resource Coordinator Rekha Banerjee worked on a mid-scale diversified farm in California before she joined us, and here shares her experience in a simple composting technique suitable for certified organic operations.
Small scale composting is a great way to make high quality fertilizer while recycling resources. With a little attention to details such as volumes of materials, particle size, and moisture and air content, building piles that reach high temperatures can be a breeze. The largest challenge is finding the time to make the piles- but once you’ve the rewards of your own “black gold”- you may find it becomes one of your favorite jobs on the farm!
When I worked in California, building small compost piles was a regular part of our certified organic operations. It would take a couple of people most of the day to build several 4-foot cubed piles. Ideally we timed it for soon after pulling a lot of green waste from the field. Prep work included moving manure and other materials to the compost making area (sometimes this involved mucking the barn), sharpening machetes, spades and hand shears, and setting up the pile site.
Although free-standing piles are possible and better in some ways (more aeration and access to the pile), we liked to make our piles within a wooden box made of palettes. We staked three palettes vertically creating three sides of a cube, leaving the front side open for loading materials and removing the finished compost. The palettes help keep materials in place and also give the right size to shoot for. The piles were anywhere from 3-5 foot cubes. This shape is preferred as it maximizes the ratio of interior to surface area, which helps keep heat in the pile.
A major factor in creating pile heat is chopping or shredding the green waste finely. The smaller the pieces, the more quickly the pile heats up, as heat-generating aerobic bacteria access nutrients from cuts in the greens. The greens do not have to be cut all the way through, just slashed enough to give the microorganisms something to work with. Depending on the thickness and pith of the materials, we would chop them anywhere from 2-10 inches long.
Chopping greens is the most time-consuming part of the compost-making process. We used hand shears, machetes and spade blades to chop the greens. Shredders are also available. Even if we had pulled the greens weeks earlier, we waited until compost-making day to thoroughly chop them, in order to slow decomposition. We piled green waste near the compost-making area and kept it under a tarp.
The key ingredients of the pile are nitrogen (green waste), carbon (browns, like straw, dried leaves or sawdust), water and oxygen. Manure adds both carbon and nitrogen, and also inoculates the pile with aerobic bacteria. The carbon to nitrogen ratio of manures varies widely depending on the animal, its feed and bedding. In my experience, horse manure was always the most effective in heating the pile. It was well worth a trip to the neighbors’ stables for horse manure to mix in with our own sheep and goat manure. Horse manure generally has a C:N ratio of 30:1, which is the ideal initial ratio according to the NOP. The Rodale Book of Composting is a great resource for finding the carbon to nitrogen ratios of various manures, as well as ratios for all sorts of green waste and carbon sources.
The objective of building a pile is to create ideal conditions for aerobic bacteria. They need an environment with water, air, and about a 30:1 carbon to nitrogen ratio to thrive. You can create the right C:N by using ratios of volumes of browns and greens. Because the browns are much more compacted than the greens and have a much higher C:N ratio, we used a very small volume of it compared to the greens. What worked for us was layering about six inches of fluffed-up greens, with about two inches of manure, and then a very thin layer of browns. You should be able to see the manure through the browns layer - only use a half inch or so, even less if using sawdust. If the manure had a whole lot of bedding mixed in, I would skip the browns layer as plenty of carbon would be present in the manure. If there wasn’t much bedding at all, I would double the browns, adding it after greens layers as well as after manure.
The bacteria need access to both nitrogen and carbon, so ideally the pile would be thoroughly mixed from the start. We only layer it as a way to control the volumes of different ingredients. Before or after it is added to the pile, each layer is watered from all angles with a hose spray. Either too much or too little water causes problems- the moisture level should be like a wrung-out sponge: not so much that it is soaking wet and compacts the pile. I add hollow-stemmed greens or husks near the bottom of the pile where compaction tends to be a problem. That way, as the plants decompose, they release more oxygen into the pile. To ensure your pile stays aerated, don’t make it larger than five feet high or put unnecessary weight on it, and fluff it up with a digging fork as you go along. This also helps mix the ingredients a bit.
I also use a digging fork as I layer, to pull materials forward along the front side of the pile. Otherwise, the materials tend to taper back against the palettes, forming a hill shape instead of a cube. Finally, I cover the pile with a tarp to prevent rain from waterlogging the pile or leaching nutrients. Tarping prevents nutrient loss to the atmosphere as well. Keep in mind, every time the pile is turned, it loses nitrogen to the atmosphere. However, turning the pile speeds the decomposition process by adding more oxygen and remixing ingredients. This creates a more homogenous final product. Most important, turning allows you to trouble-shoot in order to reach the temperature range necessary for organic certification.
In my experience with certification agencies in California, this compost is considered a static aerated pile, and follows the NOP requirement of holding a temperature of 131-170 degrees for three consecutive days, as opposed to the windrow 15-day rule. We recorded the temperature of the pile daily until it had passed the three day test- this usually occurred in the first week. Make sure to take a few readings at a time, as temperature varies within the pile. I used a long-stemmed probe thermometer and always checked near the center, as this the hottest part of the pile.
It is helpful to continue checking the temperature of the pile until it is stabilized at ambient temperature, as this is one sign that the compost is finished. Other signs include: the presence of sow bugs, beetles and worms; when the majority of parent materials are unrecognizable; and when the compost has a good forest-floor, earthy smell. Finishing can take up to several months if you do not turn the pile.
Other certification requirements include documenting the source of materials used, and tracking the piles from creation to field application. We did this with a short record page for each pile, naming the pile and listing the sources of materials, the temperatures reached, and to which field or bed it was eventually applied. The paperwork was not time-consuming, and reaching the required temperatures was usually not a problem either. The hardest part was finding the time to make the piles!
I strongly encourage anyone with the time and inclination to try making their own small scale compost piles. It is an incredibly creative process, allowing you time to reflect and to fully appreciate the recycling of farm resources. Also, once you’ve used your own homemade, rich and earthy compost, it’s pretty hard to go back to the store-bought alternative. Even if you only make enough to use in your potting soil, it’s worth a try- you and your farm will be the better for it!
(ed note: Be sure to check with your certifier on your composting process before applying any home-made compost. The law is specific, but may be interpreted differently by different certifiers.)
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