Reading the Layers

As the different soil-forming factors interact over thousands of years, soil matures and forms distinct horizon layers, The thickness and nature of the layers will vary in different soils. In certain soils, some layers are har see or aren't even there. You have to dig 2 to 3 feet deep to see the layer-cake effect. ^^^

If you run into bedrock when you dig, your soil is very shallow. Its hard to change the overall depth of SOj| at least within a single lifetime. Within garden areas or in raised beds, you'll need to bring in good-quality top soil. Or you can make lots of compost to add to your existing soil to thicken it.

If you were to dig a hole deep enough, you might encounter groundwater — the water table - before vr reached underlying bedrock. If the water table is near the surface for much of the year, it can stop root growtfM as effectively as a layer of solid rock. '

Organic layer. A thin layer of plant material in vofM

r\- ous stages of decomposition. Absent if the soil has been —I bulldozed or cultivated..

- Topsail. The top layer of soil, darker and more crumbly than deeper layers, where most nutrients, roots, and soil organisms exist. The deeper this layer, the better.

Subsoil. Usually lighter than topsoil because it contains less humus. Much of the water plants need is stored here, plus some nutrients. Often contains two or more distinct layers. Nutrients, minute specks of humus, and tiny ciay particles may be washed into a deeper, darker subsoil layer where they're harder for roots to reach.

Parent material. Rubble that hasn't yet weathered enough to look like soil.

for down | find^^ layer of sdid rock, usually foo


What Your Subsoil Says

Though digging a deep hole takes much effort in most soils, examining subsoil am tell you a lot. J Afferent colors show how well the subsoil drains, which in turn affects the drainage of the overlying topsoil.

What You See What It Tells You

Red or yellow subsoil Indicates lots of iron oxides from weathering of parent materials usually indi cates good drainage: often indicates acidic soil; common in warm climates.

Blue or blue-gray subsoil Indicates lack of oxygen and therefore poor drainage; common in thick layers of clay.

White to ash gray subsoil Indicates that nutrients and humus have been leached away; usually sits above a darker layer where the leached nutrients and humus have deposited; often indicates acidic and/or sandy soil; common under pines and similar trees.

Even, medium brown subsoil Adequate drainage.

Pale subsoil with little difference Very young or poorly developed soil; original topsoil may have eroded or been from topsoil removed (as by bulldozing during house construction).

Dark brown subsoil Indicates abundant (usually decomposed) organic matter; usually occurs only with peat or muck soils, or where former wetlands have been drained.

Patches or streaks of different Indicates pockets of poor drainage or different soils (see specific colors); plant colors roots may have trouble moving from one pocket into the next.

Roots all end at same depth Indicates layer of compacted soil (hardpan) or — in dry climates — a cemented layer (caliche); usually causes poor drainage and hampers plant growth.

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Master Gardening Tips

Some soils are naturally well suited for gardening; they require the least effort to be tuned into super soil To see if you have such soil, check the list below. The more your soil differs, the more work it will take to get super soil.

► Adequate soil moisture. Enough water is available (from rain or irrigation) to support a variety of plants.

Adequate drainage. The water table stays below the depth to which most roots grow, and the area isn't flooded more than once every two years.

* Adequate soil depth. There's enough topsoil over bedrock, hardpan. or gravel to allow for root growth and moisture storage.

Lack of rocks. Gravel, stones, or boulders aren't so plentiful that they interfere with tilling or plowing,

I'Mse of water infiltration. The soil should be able to absorb at legist inch (.15 cm) of rain or irrigation water per hour in the upper 19.7 inches (50 cm).

> Balanced chemistry. The soil shouldn't be extremely acidic, alkaline, saline, or sodic.

> Even topography. Any slopes should be gentle so that the soil doesn't erode easily and so that it s easy to move loaded garden carts or lawn mowers

N across it

> Moderate temperature. The average annual soil temperature should be higher than 32T (()' C). and the average summer soil temperature should be higher than 46T (8T).

The finest soil particles, those smaller than 0001 inch and too small to see, are the day particles Nex largest are silt particles, larger than clay but smaller than .002 inch and still tea small Ze ore cay or silt feels mastly smooth between yOUr angers Son, particles range in size from 002 o •08 .nc . They re usually large enough to see ond feel gritty between your fingers An 1 larger than sand is considered gravel^ ^

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