By: Carrie Chalmers
While most gardeners understand that organic matter is a "good thing," knowing exactly when and how much to use is elusive. Adding them to clay soils increases aeration and drainage; in sandy soils, it holds moisture and nutrients. Of course, other factors such as pH, soil texture, and cultivation timing greatly affect soil structure and nutrient availability, so you have to consider them also. Specific crops' nutrient requirements may also determine which soil treatments you should use.
However, effective use of organic soil amendments can improve soil texture; produce large, healthy yields; and save you money. Here's an explanation of what they are, how they work, and what you can do to maximize their benefits.
Two Key Stages
The decomposition process begins when microorganisms (bacteria, fungi, and molds) in partially decayed organic residues in the soil and compost feed on the fresh organic matter. Half old material to half new material is a good ratio.
In the first stage, fresh organic residues serve as food for soil microorganisms; when residues are plentiful, biological activity increases quickly. The microorganisms feed on the residues' carbon, nitrogen, and proteins. The kind of residue, the absence or abundance of microorganisms, moisture, temperature, and carbon-to-nitrogen ratio (C:N ratio) all determine the extent and speed of decomposition. The more microorganisms, for example, the faster it happens.
In the second stage, as microorganisms consume the organic material, biological activity slows. Some of them die, and others that can consume any woody plant materials increase in number. Then, the C:N ratio falls, and the organic-matter decomposition slows. At this mature stage, humus results from the residues that microorganisms didn't consume during the first stage. Different microorganisms then digest the stable compounds and excrete the indigestible residues. Nutrients remain but are only available slowly because they've been incorporated into the organic matter.
Make the Most of Soil Conditioning
By allowing some or all of the decomposition phases to occur in your soil (rather than in the compost pile), you'll improve soil structure. As microorganisms digest fresh organic material, they stabilize clumps of minerals and organic matter, called soil aggregates. High rates of biological activity create the good soil structure that allows root penetration, enhances drainage and oxygen flow, and distributes nutrients.
A Surprising Tip From an Expert
Dr. Will Brinton of Woods End Research Laboratory in Mount Vernon, Maine, emphasizes that adding compost that's reached the humus stage won't have the same effect. The interaction and blending of the soil particles, active microorganisms, and partially decayed organic matter help condition your soil. So, if you need to improve soil drainage, texture, and water-retention, introduce immature organic material into your soil. For increasing primarily the nutrient reserves, add humus.