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Soil Building

• How Soil Works
• Soil Food Web
• Measuring Soil Health
• Improving Soil Health

Human activities as diverse as constructing homes and overusing fertilizers and pesticides affect the ground beneath our feet – the soil. Regular use of pesticides and fertilizers take a toll on soil because these actions can suffocate essential soil life.

Did you know that...

• Soil provides air, water and nutrients for plants and also serves as nature's environmental protector?
• In the Puget Sound region, sand or clay form the basis for most soils and that the soil is most likely a thin layer of glacial till, not very rich in organics?
• Adding compost and mulch to soil is the best ways to improve soil health?
• Improving the soil can actually help Hood Canal chum and Puget Sound Chinook salmon, which are protected under the Endangered Species Act?

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How Soil Works

Soil Works to Keep Plants and People Healthy

Did you know that there are over four billion micro-organisms in a teaspoon of healthy soil? That's more than the populations of 220 countries combined!

We depend on soil and the soil food web for more than just growing plants. Healthy soil not only provides air, water and nutrients for plants but also serves as nature's environmental protector.

Soil Performs Many Functions

It can serve as a:

• Sponge, soaking up excess rainwater and slowing down excess runoff
• Spigot, turning water flow on and off by storing and releasing water for plants
• Snare, trapping urban pollutants such as oil, metals, and pesticides
• Strainer, filtering and purifying the air and water that percolate through it
• Supermarket, supplying valuable nutrients and antioxidants to plants.

If left undisturbed, native soil can easily perform these functions; but if native soil has been disturbed by construction or the development of roads, houses or shopping malls, it can no longer function properly. The result will be problems with run-off and erosion. Enhancing the quality of poor soil greatly improves our air and water and creates a healthier environment.

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Soil Food Web

The structure of soil is similar to that of a house made of bricks. To form bricks, straw and sand must stick together. Then the bricks are held together with mortar to form walls. The house has structure when the walls are arranged in certain patterns (Dr. Elaine Ingham of Soil Foodweb, Inc.).

In the soil food web, various organism groups perform the same function for soil structure. Bacteria glue the clays, silts and sands together into micro-aggregates – the bricks. The micro-aggregates are bound together by underground fungal vegetative growth, root hairs and roots – the mortar. Insects and earthworms make the structure of the rooms – the house. When all the organisms are present and active, roots and water move into and through the soil with ease.

A spoonful of healthy soil contains millions of different organisms, including bacteria, fungi, nematodes and protozoa, which:

• Keep disease-causing organisms in check
• Recycle and store nutrients and make them available to plants
• Provide a pathway through which air and water can pass

This intricate food web not only provides nutrients but also serves as a pollution control system. The many pathways created in the soil food web allow it to:

• Break down pesticide and hydrocarbon pollutants
• Bind heavy metals into immobile forms
• Convert soluble fertilizers into complex stored organic forms

This is known as biofiltration or bioremediation and is what keeps these pollutants from entering ground and surface waters. In healthy soil, this happens naturally. We can help the soil in our yards to do this by adding organic amendments, or compost, to the soil.

Additional information on soil biology and soil function can be obtained from the U.S. Department of Agriculture NRCS Soil Quality Institute (external).

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Measuring Soil Health

In the Puget Sound region, sand or clay forms the basis for most soils, and the soil is likely a thin layer of glacial till, not very rich in organics. Knowing what type of soil you have will help you to determine how to care for your lawn and garden.

• Sandy soil: Water flows right through the large particles carrying nutrients with it.
• Clayey soil: Water and nutrients have a hard time moving through the tightly packed particles and become stuck.

A quick way to test soil is to dig up a small sample of moist soil from where it has been least disturbed.

• Clayey soil will form a ribbon up to two inches long.
• Sandy soil will not form a ribbon, but will fall apart easily.
• Loamy soil, which is considered the ideal soil condition, will form a ribbon about one inch long.

You can also take a "plug" of your soil. Use a soil core sampler to pull a four to six inch plug or use a shovel to cut a thin section of soil (you can replace it like a divot), and examine the soil yourself. From the sample, you can observe how your soil and plants interact, how deep roots grow, and how dark brown, moist and crumbly the topsoil is.

For a list of local laboratories that can test the amount of sand, silt and clay in your soil, call the Washington State University/King County Extension at 206-205-3100 and ask for fact sheet No. 508.

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Improving Soil Health

To improve soil health, feed your soil with compost, as follows:

• Spread 1 to 2 inches over garden beds in the spring and fall
• Sprinkle 1/2 to 3/4 inch on lawns in the spring or fall
• Till 1 to 4 inches into new garden beds and lawns.

Recycle your yard waste by turning it into compost:

• Leaves, chopped stalks, flowers, and grass all make great compost, either in a bin or a pile.
• Add water, keep it moist and wait six months.

Mulch it!

Add a layer of organic material such as leaves, wood chips, compost or grass clippings around your plants (keeping it about an inch away from stems) in the spring or fall. Mulch feeds the soil, conserves water and prevents weeds.

Fertilize with Organic!

Look for the words "slow-release" or "organic" on the bag. Chemical fertilizers are quick-release fertilizers and can wash off quickly into streams.

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