Roots Down, June 2012As I mentioned yesterday, soil structure is incredibly important in maintaining healthy soil. Soil with a healthy structure will allow for proper water movement, heat transfer, and aeration. It has will absorb moisture that would otherwise run off, causing erosion and a loss of nutrients. Without proper drainage or aeration, too much water is retained causing root rot.

Soils are made up of four different components: minerals, organic matter, air, and water. Soils that contain 90 percent mineral and around 10 percent organic matter are called “humus” and are able to support plant growth well. Soils that contain small amounts of organic materials have a difficult time sustaining plant life.

Organic matter in the soil also ensures a continuous food source for soil organisms. These organisms help decompose the organic materials.  The decomposition process improves the soil structure by developing compounds that bring small soil particles together into aggregates, allowing for both increased drainage and moisture retention. Decomposition also changes the organic matter into inorganic nutrients that can be used by growing plants.

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Adding organic matter aids in sustaining the structure of the soil. However, organic matter cannot be built up permanently in the soil because it continually decomposes and disappears; soil building must be a continual process in the garden.To improve the soil structure, or “tilth,” add organic matter in the form of compost, cover crops, or shredded leaves. Shredded leaves, crop residues, straw, and similar materials should be mixed into the soil in the fall to allow decomposition through the fall and winter. At the same time, grass clippings, manure, or fertilizer should be incorporated to provide the extra nitrogen required to help break down the dry organic materials. This material can be composted in a traditional compost pile  and added to the garden in the spring if your prefer.

This is part 4 of a 5 part series on compost and healthy soil. Read the other articles here:
Part 1: “Building Healthy Soil with Compost
Part 2: “Vermiculture: Let the Worms do the Sorting!

Part 3: “Fertile Soil