To continue our information about compost, let’s talk more about using un-composted material. Although in time un-composted materials will eventually decompose, adding organic matter directly to the soil without first composting it may have some undesirable effects. For example, if large quantities of un-composted leaves are incorporated into the soil, microbes will compete with plants’ roots for soil nitrogen during leaf decomposition. This competition for nitrogen can result in nitrogen deficiency and poor plant growth. The composting process breaks down organic materials into an end use product that increases the availability of essential minerals, such as potassium and phosphorous, to growing plants and reduces the competition for nitrogen. The addition of composted materials to soils also improves physical properties, such as tilth, infiltration, drainage, and water-holding capacity. Composted material is much easier to handle and mix with soil than un-composted material.
Carbon Nitrogen Ratios
The microorganisms in compost use carbon for an energy source and nitrogen to make proteins. The proportion of these two elements used by the microorganisms should be about 30 parts carbon to 1-part nitrogen by weight. Given a steady diet at this 30:1 ratio, microorganisms can decompose organic materials quickly. For instance, sawdust has a high C:N ratio (100-500:1) and decomposes slowly unless some additional nitrogen is supplied. Grass clippings have a relatively low C:N ratio (12-25:1) that matches our requirements and decompose relatively quickly.
A general rule of thumb for a good C:N balance is to mix roughly equal weights of fresh green material (grass clippings, weeds) and dried brown wastes (leaves, straw, wood chips, dead plants, manure) or use a 2:1 ratio of dried brown wastes to fresh green material. Blending of materials to achieve a workable C:N ratio is part of the art of composting.
A compost pile with a good moisture content will benefit from being covered with plastic or carpet scraps. Covering helps to keep piles moist in summer and prevents them from getting too soggy in winter. However, if a pile is too dry or soggy to start with, covering may make the problem worse. Too wet can cause mold and too dry stops the compost heat process.
Carbon-rich woody wastes will not compete with plants for nitrogen if they are placed on the soil surface around plants. However, these materials should not be mixed into soil without extra nitrogen fertilizer. Use wood chips and sawdust to mulch trees and shrubs where the soil is not tilled, and the mulch stays on the surface. Sawdust is safest to use as a mulch if it is not fresh and has had six months to a year to age.
What Makes a Compost Pile Work Right?
Components of good compost: Aeration, small particle size, moisture, temperature. An actively decomposing pile will reach temperatures of 130° to 160°F in the middle in just a few days. At this time, you’ll notice the pile “settling,” a good sign that your heap is working, If the pile does not heat up, the cause may be one or more of the following: too small a pile, not enough nitrogen, lack of oxygen, too much moisture, or not enough moisture. Turn the pile with a spading fork or shovel when the temperature in the center begins to cool. Turning will introduce oxygen and undecomposed material into the center and subsequently regenerate heating. The composting process is essentially complete when mixing no longer produces heat in the pile.
Over time, yearly additions of compost create a desirable soil structure, making the soil much easier to work. For improving soil physical properties, add and incorporate one to two inches of well-decomposed compost in the top six to eight inches of soil. Use the lower rate for sandy soils and the higher rate for clay soils.