Soil Science
For a better understanding of what kind of soil you've got,
what it's made of, what kind of texture it has and how well it drains, read on.
You'll also learn how to use old soil to rid your soil of weeds, pests and diseases.
Undercover Test
One of the best ways of gaining an understanding of your
soil is to perform an undercover test. The test requires a fair amount of
digging, so you might want to wait until you're ready to plant a new tree or
shrub. Dig a hole 18 to 24 inches deep and wide, piling the excavated soil
nearby. Get down on the ground and look closely at the sides of the hole.What
you'll likely discover is a series of soil layers. The first layer is topsoil,
and it should be at least 6 inches thick and fairly fluffy. The
remaining layers, whose thickness and densities may vary considerably, are generally
referred to as subsoil. Now look at the roots in the soil. In healthy soils, they
grow straight down, but in poor soils, roots tend to grow horizontally due to a thin
layer of topsoil or compactionin the subsoil, or both.
The different colors of the layers are probably the best
indicators of soil health, and generally speaking, the darker the color, the better the
soil. For instance, dark browns, reds and tans suggest soils with a high humus content. Soils
with a blue or gray tint are indicators of poor drainage, usually a result of compaction.
Now look at the excavated soil for signs of life. It should
contain a fair number of earthworms as well as other critters. If it doesn't, the
soil either lacks sufficient organic matter or has been maintained far too long on a diet
of harsh, synthetic fertilizers. Actually, the undercover test isn't so much a
test as it is an observation. It can reveal all sorts of problems related to a lack of
organic matter, compaction, poor drainage and the like.
If you use a rototiller a lot, the top 8 to 10 inches of
your soil may be nice and fluffy, but below that, hard as a rock. That's because excessive
tilling can lead to the creation of something called hardpan, a layer of subsoil below the
reach of the tiller's tines. You can drive a pitchfork deep into the subsoil each time
you till, to loosen the hardpan layer.
The Watering Test
Start by watering your lawn or garden thoroughly. Two days
later, dig a 6-inch hole and check the moisture content of the soil. If the hole is dry
at the bottom, your soil is draining too quickly for most plants to grow properly. If
the hole is soggy, your soil isn't draining fast enough. So how do you deal with soil
problems? Whether your soil has too much sand or too much clay, drains too slowly or too
quickly, or lacks sufficient nutrients and soil organisms, the solution is the same in
every case: organic matter.
Compost is the best source of organic matter. If you've got
good soil, but each year you have problems with weeds, pests and diseases of one form
or another, use a technique known as soil solarization, which is best done during the
summer months.
Soil Solarization
First, rake the problem area smooth, getting rid of any
clods along the way, and level it. Then water the area, soaking it more than usual. The next
day, cover the area with 3- to 3-millimeter clear plastic, covering the edges with soil to
hold it in place. Within four to six weeks, the greenhouse effect caused by the sun
hitting the plastic will cause soil temperatures beneath the plastic to reach between
140 and 160 degrees Fahrenheit, which is hot enough to kill almost everything in
the soil. At that point, you can remove the plastic and plant away.
Squeeze Test
To literally get a feel for the content and texture of your
soil, perform a squeeze test, for which you need a handful of soil from your lawn or
garden. First, roll the soil in your hand until it's about the size of a golf ball. Then
gently squeeze the soil between your thumb and index finger. Sand feels gritty, silt feels
more like talcum powder and clay feels slippery. Now squeeze the ball in your hand. If
it crumbles, it has a well-balanced texture. If it holds its shape, it has a fair
amount of clay. And if you can roll it into a snake, it has more clay than you want.
Perc Test
Drainage problems account for an incredible number of
problems in the lawn and garden. If the soil drains too quickly, plants may never have a
chance to absorb enough water to adequately sustain their growth, no matter how often you
water. And if the soil drains too slowly, plants may actually suffocate or rot.
That's why it's a good idea to perform a perc test.
Dig a hole 6 inches wide and 1 foot deep using a shovel or
post-hole digger. Then fill the hole with water and let it drain. When the water has
drained completely, fill the hole again, and this time keep track of how long it takes
for the water to drain completely from the hole. If the water drains completely
within 3 hours or less, you have a drainage problem, probably due to sandy soil. If
water is still standing in the hole after 8 hours, you have a drainage problem due to too
much clay in the soil, and if the water drains within 4 to 6 hours, you don't have a
drainage problem.