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AR Gardener Magazine Articles
Soil Sampling
Soil is an important part of growing a garden, yet it is often
taken for granted. People spend thousands of dollars planning a landscape,
buying the plants, but without a decent soil to grow in, the results, may not be
what you had in mind. So lets get to the root of the problem.
Traditionally, Arkansans complain about the lack of soil, and
the abundance of rocks. Or they may have "gumbo"–i.e., heavy clay, pure sand, or
it’s so acidic, you could make vinegar from it. Fortunately, there isn’t a soil
or planting site out there, that can’t be amended or corrected. It just may take
a while. Learning your problems before planting, will make solving them much
simpler.
Your first step should be to have a soil sample tested. This is
a very simple process. Take a shovel and go six to ten places in the area you
are planning to plant in. Dig down six inches --which may require a pick axe,
but we do need a full soil profile. Then take a slice of the full six inch
profile and place it in a bucket. Repeat this process six to ten times. By now,
you have probably worked up a sweat, and gotten a great exercise workout. Mix
this soil together, to get a good representation of what you will be growing in,
and take a pint of it to your local county extension office. It should be
relatively dry, since it will be shipped in a cardboard box, so let it air dry
first.
If you will be growing distinctly different plants–such as
lawns, vegetable gardens, perennials, etc, you can have several different soil
samples tested. Simply repeat the same process for each one. A full pint of soil
is needed for each sample you want tested. If you have a problem area in the
yard, you may want an isolated sample from it to compare with the rest of the
yard. Don’t divide your yard into too many samples, unless you plan to fertilize
each area separately.
When you take your samples to the county extension office, they
will ask you some routine questions to fill out the accompanying soil sampling
form. In addition to the pertinent personal information, such as name and
address, you will also be asked what you will be growing. If you are having more
than one soil sample tested, you will also need an identifying name for each
sample. Vegetable, lawn and flowers would suffice, just make sure you know what
the name corresponds to, should you use something like 1, 2 or 3. Now all you
have to do is wait on your report, which should be mailed to you within a week
or two.
At this time, there is no fee associated with the routine soil
testing process in Arkansas. Fees associated with fertilizer sales pay for this
service.
When you receive your soil report, it may look a bit confusing.
There are a lot of numbers and nutrients listed. There will also be a
recommendation for the plants you are growing, as to fertilizer and liming
needs. A fact sheet entitled "Understanding the Numbers on Your Soil Test
Report" should accompany each soil test report. This should help to explain the
level of the nutrients in your soil—what is high, and what is low, and even what
some of the terms mean. Some people prefer to just follow the recommendations,
and ignore all the numbers.
Some key items to look for include the pH of the soil. The pH of
the soil is a measure of acidity or alkalinity, often referred to as a sweet or
sour soil. Many soils in Arkansas are acidic, but knowing how acidic can
determine your liming needs, if any. Many garden plants like slightly acidic
soils, and some even prefer it–azaleas, gardenias and blueberries in particular.
An optimum soil pH range for most plants is 5.8 to 6.3. Slightly lower or
slightly higher isn’t a big deal, but some plants will suffer in soils with
strongly acidic soils, while acid lovers struggle when it is higher than 6.5. If
it has been determined that your soil sample is too acidic, there will be a
recommendation of how much lime should be applied to get your soil in the proper
range. Lime does not move quickly in a soil, so applying it prior to planting,
where it can be tilled into the soil is ideal. If by chance, your soil is too
alkaline, elemental sulfur or aluminum sulfate will be recommended to lower the
pH.
Nutrients needed for plant growth are all listed in the soil
report. They include phosphorous, potassium, calcium, magnesium, iron,
manganese, copper and zinc. Nitrate-nitrogen and sulfate-sulfur are also there.
On the soil report there will be a listing of each of these nutrients and a rate
or level that they have been extracted from the soil, usually in pounds per
acre. An example, for phosphorous: values below 20 are low, 20- 40 is moderately
low, 40- 60 is medium, 60-80 moderately high, with 80- 100 being high. Again,
the fact sheet will give you a comparison level.
Salinity or E.C. is another important consideration. Remember
that all fertilizers are basically salts, and too much salt in the soil can
cause injury to plants. This is also included on the report, and includes all
soluble salts. If the readings are too high, there will be no fertilizer
recommendations or fertilizer reductions until these levels go down.
There are other numbers and terms listed, which are important to
soil scientists, and may stand out if there is a problem, but should not be of a
huge interest to the home gardener. Knowing your soil pH is important, and
getting your nutrient levels in line is also needed for good plant growth. If
you have specific questions, call and visit with your local county extension
agent.
If there are problems to your soil site, amending is important. But do
remember, if you alter your soil with lots of organic matter or other
amendments, it will change all your nutrient and pH levels, and it is important
to test your soil again. Fall is an ideal time to test your soil, since often
plants are nearing the end of their growing cycle, fertilization is ending, and
you can prepare for next year in advance. Plus, you beat the spring rush, when
everyone else is thinking about it.
This story first appeared in the
AR
Gardener Magazine.
By: Janet Carson
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