The Dirt Issue 33 – Composting

Posted on November 28, 2018
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The Practice and Remarkable Benefits of Composting
Any good cropping system starts with the condition of the soil: its structure, its pH, its nutritional balance and how available those nutrients are when needed. All are critical for a successful yield. Farmers and home gardeners alike have a whole array of methods to enhance the condition of the soil and one of the most beneficial is the use of compost.

Mother Nature is the Original Composter
Let’s start at the beginning: compost is defined as decayed organic matter which, through the chemical interaction of carbon, nitrogen, oxygen and water, creates suitable conditions for biological transformation into a potent, humus-like substance. The process by which it occurs is known as composting and it’s all around us. Leaves fall, decompose, and, given the chance, nourish next year’s growth. It’s natural. It’s sustainable. It’s the circle of life.

On the farm there are many potential sources of compostable material. Referred to as feedstocks, these include crop culls, plant residues after harvest, manure, straw, livestock bedding, and organic byproducts of crop processing. Around here, a common form of animal bedding is sawdust. When combined with manure and given the right conditions for composting, it is one of the most popular forms of organic recycling in Skagit County.

What’s also true is that the benefits from using compost are not restricted to agriculture. Home gardeners with a small, manageable bin or urban dwellers with an earthworm composter, can take food scraps, yard waste, and even shredded newspaper and cardboard and, with a bit of time and attention, convert in to matchless amendment for gardens, flower beds and/or containers.

Right conditions for composting?
There is more than a bit of art in the science of composting and many factors influence the final product. It starts with the feedstocks themselves. Our manure and sawdust combination is a good example. Manure is rich in nitrogen (N) and it’s wet. Sawdust is rich in carbon (C) and it’s dry. When combined in appropriate carbon-to-nitrogen ratios of at least 15:1 to 30:1 and given sufficient quantities of oxygen and water, the compostable materials begin to generate heat. The range of heat produced either attracts or repels an army of biological actors that cause the actual decomposition.  

At moderate heat, the material attracts earthworms, nematodes (microscopic worms) and soil insects such as mites and beetles which breakdown the feedstocks into smaller segments. According to The Art and Science of Composting by Leslie Cooperband, University of Wisconsin-Madison, “Once optimal physical conditions are established, soil bacteria, fungi, and protozoa [one-celled microorganisms] colonize the organic materials and initiate the composting process.”

But that’s just the beginning.
All this activity generates even more heat and once it climbs above 113° F the original cast of biological actors mostly exit and a whole new group takes over. These microorganisms thrive at temperatures ranging from 130 to 150° F or even higher. With proper management, this high heat or active phase can be maintained for a few days up to several weeks. It is a crucial period for the farmer or home gardener because these conditions are what kill weed seeds and soil-borne pathogens, making the finished product safe to introduce into the field, garden or flower bed.

When high heat is no longer generated, it means the process of decomposition is nearly done and temperatures decline to about 100° F. The original cast of biological actors recolonizes the material and the maturing compost is in the curing phase. According to Cooperband, “Compost is considered finished when the raw feedstocks are no longer actively decomposing and are biologically stable.” How long the process takes depends on the feedstocks used and how the process is managed.

Managing the amount of oxygen and water in the compostable material is key. The necessary amount of each varies according to the feedstocks, but their proper balance leads to heat generation and the progression through the phases of decomposition.

Why it matters.
Compost is a wonder. Its first Wow! factor is as a soil conditioner. The Art and Science of Composting explains, “Compost is an organic matter source with a unique ability to improve chemical, physical, and biological characteristics of soils. It improves water retention in sandy soils and promotes soil structure in clayey soils by increasing stability of soil aggregates. Adding compost to soils increases soil fertility and the soil’s ability to hold onto essential nutrients and can reduce fertilizer requirements, potentially up to 50%. Soil becomes microbially active and more suppressive to soil-borne and foliar pathogens.”

But that’s not all. Compost is also a source of nutrients. Not in the same class as a fertilizer, although it does contain significant quantities of micro-nutrients, but in its ability to make nutrients already present in the soil more readily available to plants. According to Planet Natural, “the nutrients contributed by compost far exceed those actually in it.”

Compost is beneficial to all types of farming.
In organic farming, compost is used in combination with crop rotation, cover cropping, green manuring, liming, and a host of natural and biologically friendly fertilizers and amendments (extension.org). While many of those practices are also used in conventional farming, compost can so improve soil fertility that reliance on conventional farming’s synthetic fertilizers may be reduced as much as 50%.

However Skagit County farmland is farmed, compost makes it ever better by increasing soil fertility and plant productivity‑—naturally, sustainably.