From:
MaximumYield.com
By Keith Roberto & Brandon Matthews I CAN REMEMBER the day my family got together to plant our first vegetable garden. We must have bought at least 10 bags of manure, a few cubic yards of peat and many yards of topsoil; we tilled up the mix until it was good and black, light and fluffy, and had a hearty fertile appearance.
A decade or so has passed and the soil isn't as conditioned as it once was. Our garden reverted back to a caked, brown, dusty patch of dirt that didn't produce like it used to. I soon became envious of the black soil of the forest floor just behind my yard. How could untreated soil be perpetually fertile and rich? Consider the Law of Conservation of Mass and Energy. Any raw material introduced to the pile will remain in the pile in some chemical form or another without losing much of its molecular energy, other than heat. I didn't understand at the time, but I used to take buckets of soil from the woods and add it to my garden. These days, composting is my solution to excess yard waste and reconditioning the soil in my garden.
Composting is the process of aerobic decomposition of large macromolecules by soil micro-organisms to produce much smaller, more stable, micro-molecules known as humus. Humus is the final stage of organic decomposition and its active molecule is called humic acid. This molecule is relatively large (molecular weight of 1000+ Daltons) and is highly reactive, with aromatic chains and beneficial side groups that cannot be artificially synthesized in a lab. Humic acid alters the chemical structure of ions and nutrients and organizes them into more usable forms to facilitate their diffusion across plant membranes. By establishing an ionic network, it provides balancing characteristics to soil like good water and air retention, macro and micronutrients to feed plants and beneficial microorganisms, a favourable soil texture and structure, and the rich, black quality that we all know and love.
Luckily, replenishing your garden beds doesn't need to cost anything or include labour-intensive trips to the local gardening centre. All one needs to do is begin piling up valuable wastes and keeping it moist and aerated. Mother nature will do all the work, leaving behind a compost material rich with humus, beneficial microbes, and nutrients. Of course, there are a few concepts to keep in mind in order to generate quality material. That old pile of grass clippings is not the best choice for compost.
Similar to container gardening, a compost pile needs to have certain qualities to guide the decomposition process properly and thoroughly. As previously mentioned, compost is produced through aerobic decomposition by a team of micro-organisms that consume oxygen while digesting organic matter. Bacteria, fungi, and actinomycetes all play their respective role depending on pile temperature, moisture, aeration, material content, and carbon to nitrogen ratio (C:N). Microbial diversity ensures that a windrow can remain active without collapse in a wide range of conditions.
Like a small ecosystem, our micro-organism friends prefer specific conditions, though decomposition does occur over a wide range of environments and raw materials as long as it is periodically maintained. Factors affecting the rate of decomposition include oxygen and aeration, nutrients expressed as C:N, moisture, particle porosity, texture, structure, temperature, and to a small degree, pH. All conditions are easily controlled if the compost pile is properly balanced from the initial recipe of raw material.
One of the most important necessities of a compost pile, or windrow, is oxygen. A slump of compacted material with low oxygen content will promote anaerobic decomposition, a metabolic process known by athletes under extreme exercise when their muscles do not get an adequate supply of oxygen. Everyone knows this builds up lactic acid and causes muscle cramps. In a poorly structured windrow, anaerobic metabolism generates ammonia, contributes to bad odours, does not generate sufficient thermal energy, and progresses at a much slower rate than does traditional aerobic respiration.
To maintain an adequate supply of oxygen, the pile needs to be aerated. This is accomplished by mechanically mixing the pile periodically to redistribute moisture, microbes, heat, and raw materials. Some passive exchange will occur toward the surface but, in some cases, forced aeration by fans is necessary when time is limited or if the pile is too large to turn easily. If the pile temperature begins to fall, it is the first sign of an oxygen deficiency as microbial action slows.
Particle texture also makes a large contribution to oxygenation because smaller particles will pack more tightly and limit passive oxygen exchange. It is, therefore, wise to properly balance the recipe of raw materials. Large particles like straw or wood shavings preserve pore spaces in the pile and increase its oxygen content. Smaller particles like manure or grass clippings provide a greater surface area for microbial action to take place. A compost pile is not to be confused with a waste dump. The goal of composting is to produce a quality balanced soil conditioner from the proper ratio of raw materials. Don't get scared - it is much easier than it sounds.
In full swing, microorganisms generate a lot of metabolic heat. Optimal decomposition occurs when the internal temperature is between 120ºF and 140ºF (~49 and 60ºC). Regulations set the critical temperature for killing human pathogens at 131ºF (55ºC), and in this range, most soil-bound and plant pathogens will be killed, leaving the composted humus safe for use. Temperatures below this level will limit microbial activity, lessen oxygen and moisture exchange, and ultimately slow decomposition. Prolonged temperatures above 140ºF (60ºC) will harm soil micro-organisms, making them dormant or less active, or they may even kill them. But for short periods of time, high temperatures will kill most contaminating seeds.
Fortunately, a compost pile is well insulated and even low external temperatures will not affect the warm, cozy 120ºF (~49ºC) interior as long as the pile is periodically mixed to ensure even decomposition. A compost thermometer is a wise investment and will take out a lot of the guesswork. Near completion, the pile temperature will fall to approximately 100ºF (~38ºC), when soil microbes have little substrate left to consume. The curing process can now begin.
It is possible for the windrow to become overheated and very dry during summer months. Like humans, microorganisms need water for all metabolic processes. In addition, adequate moisture levels are important to maintain good heat dissipation and to establish a medium of chemical exchange, usually in the range of 40 to 60 per cent H 2 O. There is no need to measure water content; just pretend you are watering a container garden. Before it becomes dry to the touch, simply water it, turn it over, break it up, and water it again evenly, trying to avoid puddles and oversaturation. As a general rule, the pile is too wet if water can be squeezed from a handful.
The main factor of any compost pile is microbial activity. Microorganisms feed off the organic material and in turn reduce this material into a more useable, uniform, nutrient-rich humus. A compost pile is made of mostly plant matter: leaves, grass, crop remains, wood chips, food remains, or manure. Thus, a complete array of carbon, nitrogen, phosphorous, and potassium should be present in adequate supply. It is important to maintain a favourable C:N of approximately 30:1. Since microbes consume carbon while decomposing, a low C:N will deplete all available carbon without using all available nitrogen, contributing to nitrogen loss by ammonia or nitrous oxide and causing bad odours. A high C:N of 50:1 will require a longer composting time because nitrogen is depleted before all available carbon is assimilated into microbial cell mass.
Initial decomposition can be improved with the addition of a soil microbe inoculant. It is always best, however, to start a new compost pile with old material of similar composition and its own supply of microbes. Bacteria reproduce quickly and even a small amount of old material will catch on quickly in a new compost heap. It should be noted, however, that not all materials decompose at the same rate. For example, spoiled fruit will release its carbon much faster than straw, and straw much faster than wood shavings. In these instances particle size is important because smaller particles have a greater surface area per unit mass for microbial action and will decompose faster. Egg shells should be broken, wood and cardboard should be ground or shredded and mixed with material of opposite texture and size to balance porosity. Sand is a great medium for preserving aeration and porosity, though it is primarily biologically inert.
Under favourable conditions a complete compost can be produced in less than two months, with an additional curing period of one to two months. Mechanical methods are available as drums or bins, which can compost matter in two or so weeks because they retain a lot of heat and moisture and are easily rotated to provide maximum aeration. By the time composting is complete, the internal temperature will stabilize around 100ºF (~38ºC), moisture fluctuation will decrease, and the mix will become more uniform and less biologically active. In general, compost time is dependent on the type of raw material used and the desired application. For industrial purposes, compost can be left in the field over time to finish; for home garden use, a longer curing time for a more readily useable result.
After the compost has reached a uniform characteristic, let the curing stage begin. Curing compost allows microbial action to gradually decrease while they continue to consume oxygen. Application of uncured compost will decrease the availability of oxygen to plants' roots. In addition, curing helps eliminate and stabilize any unwanted byproducts, like ammonia or organic acids, that were produced in the initial compost, possibly because of low levels of anaerobic respiration, pesticides, or other contaminants.
Composting is probably the cheapest and most highly effective way to recondition a garden bed. It is also a good way to eliminate excess organic waste and reduce household trash. In some instances, depending on the scale of an operation, removal of other people's trash may even generate extra revenue for a farm. Either way, small scale composting sure beats buying someone else's waste at the home garden centre and guarantees a never-ending supply of fertile organic humus. |