Organic Broadcaster

On-farm composting works best on small-scale farms

By Anne Lupton

At its simplest, composting is gathering plant materials in a large pile or container, letting them decompose, and using the final product to condition soil. In actuality, managing compost to improve soil fertility in something larger than a backyard garden or urban farm plot is much more complex and challenging.

At the recent MOSES Conference, John Jeavons, author of How to Grow More Vegetables, talked about the nitty gritty of compost production in the workshop “Increase Your Compost’s Power.” Talking about carbon-to-nitrogen ratios, pile construction, microbes, soil health, and cold composting, Jeavons explained how composting is done at his Biointensive research farm in California. He went over the methods they’ve worked out over the years to promote soil fertility for maximum vegetable production. Because their research gardens are relatively modest in size, the amount of compost they produce occurs in small batches—1 to 2 cubic yards at a time. The process is nicely laid out in his book.

Composting in small batches speeds up the process, but many organic farmers have found that the challenges outweigh the benefits when it comes to making their own compost.

Claire Strader of Fair Share CSA Coalition found this to be true. She experimented by setting up a half dozen compost bins on the north side of the greenhouse on her farm. After adding all the materials from on-site sources, adequately watering it, covering it with hardware cloth (for rodent protection) and waterproof fabric, the bins took “forever” to make suitable compost. Finding time to turn the piles was the stumbling block. With only hand tools, the job of forking over materials often got put off, effectively making the compost operation a passive one. To make the process easier, Strader said she’d welcome a technology that’s something between a shovel and a front end loader.

“Having a method and tools that work at hand scale, but is less than a windrow would definitely help,” she explained.

Active compost management requires a significant amount of time and attention, requiring frequent temperature monitoring and pile turning. The organic regulations are very specific about the process for creating compost to use in organic production, which is why most organic farmers choose to bring in suitable compost. If composting is done at all it usually comes in the form of “slow roasting” piles of vegetative matter and manures for long, unattended periods of time, often for a year or more.

But, in smaller farming situations (think urban agriculture) active composting is not only feasible but necessary to maintain soil fertility.

Riverview Gardens in Appleton, Wis., once a mid-city golf course, is beginning its fifth year of operation as an urban CSA farm and community space. The farmers there have been in transition to organic for the past three years and have just applied for organic certification. Emily Hoffman, farm operations manager, said compost production is an essential part of their operation.

“We work with a combination of wood chips from the city, field waste from our own operation, and food waste from a local food shelter,” Hoffman explained. With six acres and 16 hoop houses in vegetable production, the flow of compost materials keeps coming all summer. The farm has one employee that is more or less dedicated to managing the mixing of materials, monitoring and recording the temperatures, and turning the piles when appropriate. Along with a small amount of purchased vermicompost, their site-made compost is their sole source of soil fertility inputs.

Cold Composting
In his conference workshop, Jeavons touted the benefits of “cold composting”—building and maintaining a pile that’s slightly higher in carbon with a minimal amount of water to discourage the internal temperature from getting too high. His belief is that this less-warm composting process will leave more undecomposed bits of organic material in the compost that will transfer to the soil and continue the process slowly within the soil itself, which is better for the growing plants. He has found that a carbon-nitrogen ratio of about 45:1 in the initial mix produces the best final product.

He also made a distinction between structural carbon and metabolic carbon, and the balance of each of these in an ideal cold composting pile. Structural carbon includes such things as cellulose and lignin, significant components in mature straw and other fibrous plant material. Metabolic carbon includes sugars and starches, found in immature leaves and stalks. He recommends tending toward more structural carbon than metabolic carbon in cold composting.

Slightly more soil is also used in this approach. A bit of soil in any composting pile is a good way to inoculate the pile with a good mix of native bacteria and fungi that are prone to start decomposing your dead plant material faster. But, in the cold pile it’s beneficial to add a bit more soil—approximately twice as much as in a typical compost pile. In his experience, he said this gets the pile decomposing a little faster.

The whole process should take about three to four weeks (in the warm California climate), with minimal water added over that time. The pile should not be turned, and simply left to do its work in the structure it was initially built in.

It should be noted that there are several things in the cold composting approach that are not allowed under organic standards (205.203). First, the initial carbon-nitrogen ratio should be between 25:1 and 40:1, which means a more nitrogen-rich initial input. Also the temperature of the pile needs to be maintained (and documented) to be between 131°F and 170°F for 3 days “using an in-vessel or static aerated pile system,” or for 15 days if using a windrow system.

Carbon, Nitrogen, Water, Microbes, Air
With managed compost, the process of decomposition can be tightly controlled. Knowing which materials are carbon heavy or nitrogen heavy is the first step in building a pile that really heats up with fast microbial activity or takes its time to break down materials at lower temperatures. The University of Illinois Extension’s “The Science of Composting” provides the following tips.

Generally materials that are higher in carbon are mature and dried (or drying). Straw and wood chips/shavings are the classic examples of carbon-rich plant material. These are sometimes referred to as “browns” as, generally, plant material that is brown has built up more carbon in its structure.

Plant materials high in nitrogen are sometimes referred to as “greens.” And, yes, plants that are green and vigorously growing tend to be much higher in nitrogen. Grass clippings, weeds (before they’ve gone to seed), and most food waste fit this category. The more of these kinds of materials you have in the pile, the more it will heat up.

With the right amount of moisture and air, mesophilic (medium-temperature-loving) microbes start colonizing first. As the temperature creeps up, thermophilic microbes start to take over. Any of the microbes (bacteria, fungi, or actinomycetes) that work on these materials use the carbon in the pile as their energy source and the nitrogen as building blocks for their own proteins. Take away too much air (down to less than 5 percent oxygen) and the conditions start to become anaerobic, producing useless organic acids and unavailable forms of nitrogen, as well as stinky compounds like hydrogen sulfide and putrescine. Turning the pile ensures that an adequate amount of oxygen gets to the good bacteria.

When finished, the final product should have an earthy smell to it with just enough moisture content that you can barely squeeze a drop from a good handful. If there are still larger pieces in the mix, the pile can be sent through a sifter, and the larger pieces sent back through the process in the next pile. This wonderful finished material can either be worked into the soil, spread around as a top dressing, or soaked in water to make a compost tea to spray onto vegetable leaves. The mix of nutrients and active microbial life imparts a considerable health advantage to growing plants.

Outside Sources of Compost
Farms where active compost management isn’t feasible can find plenty of sources of commercially produced compost. Managing your own active compost is definitely a challenge, especially in the context of a certified organic operation. If you’re within easy reach of a commercial, organic composting facility it may just be worth it to outsource it.

Anne Lupton owns Blue Egg Farm in Green Lake, Wis.

From the May | June 2015 Issue

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