Organic Matters (cont)
By: Carrie Chalmers
Temperature and Moisture
Depending on your region, the difficulty of increasing your soil's organic matter level varies. In northern climates where temperatures drop for long periods, biological activity and decomposition decrease during those times. Tropical climates rarely accumulate organic matter because the warmer temperatures and high rainfall promote rapid decomposition of the organic matter.
In arid climates, humus may decay more slowly, but the soil's ability to accumulate and replace lost organic matter is hampered because dehydration also hinders the decay process. However, mulching can conserve moisture and enhance biological activity.
Tilling in the spring and fall helps minimize the loss of humus reserves because soil temperatures in some regions aren't high enough for vigorous biological activity. Fresh residues may pose a problem in cool or arid conditions because they decompose slowly and tie up nutrients. Composting, at least partially, may be prudent unless you can time your application appropriately for your region.
Unwanted Effects of Adding Amendments
To avoid nitrogen loss, weed growth, and plant diseases, add the right amendments at the right time. Microorganisms use nitrogen, and rapid microbial activity can also consume the soil's oxygen, leading to nitrogen loss: As soil organisms dismantle nitrates in their search for oxygen, nitrogen is left in a gaseous form that readily escapes. Wait at least two weeks between amending with immature residues and planting to allow nutrient excesses to stabilize, making nitrogen available.
Leaves, manure, grass clippings, and herbaceous and woody plants in various stages of decomposition are the raw materials to add to soil. Decomposition, however, requires specific conditions. The best conditions for decomposition are: soil temperatures above 55° F., adequate oxygen and moisture, and a pH level near 7 (neither acid nor alkaline).
Because decomposition in soil occurs without a compost pile's high temperatures (up to 145° F), plant diseases and weed seeds aren't killed. Carefully monitor the compost pile's temperature (using a temperature gauge) to raise the temperatures, then stop the decay process by spreading the compost and drying it out, or incorporating it into the soil at that point. Decomposition resumes in the garden soil. Good amendments that don't require sterilizing temperatures include straw, leaves, healthy lawn clippings, alfalfa pellets, and cocoa hulls.