How Compost Helps Your Soil

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How Compost Helps Your Soil
Excerpt from Let it Rot!, by Stu Campbell

Compost contains nutrients that your plants need for optimum growth, such as nitrogen, phosphorus, and potassium. And it's an especially good supplier of micronutrients that are needed in small quantities and are sometimes overlooked by gardeners, such as boron, cobalt, copper, iodine, iron, manganese, molybdenum, and zinc. The more varied the materials used to make the compost, the greater the variety of nutrients your compost will provide. In some situations, you may not even need to fertilize soil enriched with compost.

Nutrients are released at the rate your plants need them. In early spring, as your plants are slowly starting their growth, the microorganisms in compost are slowly releasing nutrients. As the weather warms up and your plants begin rapid growth, the microorganisms also work faster, releasing more food for your plants. Isn't nature wonderful?

The organic matter in compost binds with soil particles (sand, silt, and clay) to form small aggregates, or crumbs. Crumbly soil is said to have good structure, as opposed to sand, which has poor structure because it's too coarse to form aggregates, or clay, which can act like cement when wet. These aggregates hold water on their surfaces, making it available to your plants as they need it. As aggregates form, more spaces are created for oxygen, an essential for good root growth. At the same time, the soil spaces form channels for excess water to percolate through the soil, improving drainage.

Increases water-holding capacity of soil. Compost can hold an amount of water equal to 200 percent of its dry weight, compared to 20 percent for a low-humus soil.

Acts as an inoculant to your soil, adding microorganisms and larger creatures such as earthworms and insects, which are nature's soil builders. The compost environment is teeming with life, and all soils can benefit from such a rejuvenation.

Neutralizes various soil toxins and metals, such as cadmium and lead, by bonding with them so they can't be taken up by plants.

Acts as a pH buffer so plants are less dependent on a specific soil pH. The earthworms in the compost help in this process, because in passing organic matter through their bodies they modify the pH of the soil. And you can lower the pH of your soil by adding compost made from acidic raw materials, such as oak or beech leaves, sawdust, and pine needles.

Can be used in a variety of ways in your lawn or garden - as a seed-starting medium, as a soil enhancer, as a side-dressing.