If you’re a long-time reader of Whitetail News, then you’ll have read
these statements before: Having a qualified soil-testing laboratory test your
soil anytime you’re considering buying lime and/or fertilizer is the best tool
available to you for ensuring optimum forage growth, and saving money in the
process. It can be the difference between having the best food plot you can
imagine and total failure.
The first time you
see a laboratory soil-test report, though, you may not know exactly how to use
the information it provides. That’s especially true of reports that, unlike the
Whitetail Institute soil-test report, are structured primarily for commercial
farmers. The Whitetail Institute soil-test kit and report are specifically
designed for food plotters and can be much easier to read. Even so, it helps to
know what information in the report is useful to you, and why. Hopefully, this
article will help you easily understand any laboratory soil-test report so that
you can quickly take from it the information you need to optimize soil
conditions for forage growth.
The first thing to know is that the information
in all laboratory soil test reports can be divided into two main categories,
which are often referred to in conversation as “Readings” and “Recommendations.”
In short, the Readings tell you what the soil pH, soil-nutrient levels and soil
structure of the sampled soil are, based on the laboratory’s analysis; and the
Recommendations tell you what to do about the Readings to assure optimum forage
growth for the specific forage you’ll be planting or maintaining.
The most
important category from the grower’s perspective are the laboratory’s Recommendations,
since they tell you what action you need to take to get certain Readings into
optimum range. Even so, you also need to know why the laboratory takes the
Readings it does and what they mean if you want to understand why the following
statement is true:
Only a soil test performed by a qualified soil-testing
laboratory can assure you that you buy the correct amount of lime, and the
exact amount and blend of fertilizer, to assure optimum forage growth and allow
you to eliminate wasted lime and fertilizer expenditures!
READINGS
(Soil pH,
Soil Fertility, and Soil Structure)
As previously mentioned, the
Readings in a soil-test report are the results of the laboratory’s analysis of
your soil, and they’re used by the laboratory to arrive at its Recommendations.
But, what is it that the lab is “reading” in the soil, and why?
SOIL PH
Just
as humans need to take in food to survive and grow, plants must take nutrients
such as nitrogen, phosphorus and potassium from the soil. In each case, two
situations must exist: the food (soil nutrients) must be there, and they must
be freely available for intake by the plants.
The first Reading you should look
for when you receive your soil-test report is the Soil pH Reading (also
sometimes stated as “Water pH”), since it immediately tells you whether or not
nutrients in your soil may be inaccessible to your forage plants. Unless soil
pH is within the optimum range for the forage being planted or maintained, the
forage plants will not be able to freely uptake nutrients from the soil. That
makes the soil pH Reading (and when soil pH is low then also the attendant lime
Recommendation we’ll discuss later) the most important information on your
soil-test report. Put simply, soil pH is a measurement of the alkalinity or
acidity of soil, and that measurement is represented by a number, most commonly
from about 4 to about 8. A number from 6.5 – 7.5 defines “neutral” soil pH. Numbers
below that range indicate “acidic” soil, and higher numbers define soil that is
“alkaline”. Most fallow soils are acidic. And since we often find fallow sites
covered with grass and other weeds, it stands to reason that many naturally
occurring grasses and weeds can freely uptake nutrients from soils within a
fairly wide soil pH range, including neutral and acidic soils. And that’s the
reason for the common misconception that a site will sustain forage plantings
well just because grass and other weeds flourish there. Most high-quality
forage plantings can freely uptake soil nutrients only in soils with neutral
soil pH — a much narrower range. Why is that important to understand? Because
plants growing in the site cannot freely uptake nutrients from the soil unless
soil pH is within the range in which they can do so. Still not convinced? Okay,
let’s put it in terms your wallet can understand. High-quality forages planted
in a site with a soil pH of 5.0 can only access about 46 percent of the
nutrients in the soil. That means if you spend $100 on fertilizer for the
plants in that plot, you just wasted $54!
SOIL FERTILITY INDEX
(Soil-Nutrient
Levels)
Most laboratory soil-test reports list soil nutrient Readings
in parts per million (ppm). “Optimum level” doesn’t mean the same thing for all
crops; some require higher levels of specific nutrients than others, so if your
soil test report only lists these levels in ppm, then you’ll need to find out
what the optimum level of that specific nutrient is for the specific forage
you’ll be planting or maintaining.
Some reports such as the Whitetail
Institute’s soil-test report, though, also provide this information in a format
that’s much easier for food-plotters to understand. For example, the Whitetail
Institute report’s Readings are also expressed in lbs./acre, which is more
familiar to many folks, and even provides an easy-to-read bar graph that tells
you in an instant whether the level of a particular nutrient in your soil is
low, sufficient for the coming year, high, or even too high.
Specific nutrient
levels specified in most soil-test Readings include nitrogen, phosphorous,
potassium, calcium, magnesium, boron, copper, iron, manganese, sulfer and zinc.
Nitrogen, Phosphorous and Potassium. The most important nutrients by far
to most food plotters are nitrogen (N), phosphorous (P) and potassium (K).
Focus on these. They’re the “Big Three”.
Calcium, magnesium, boron, copper,
iron, manganese, sulfur and zinc. Other nutrient Readings you may find on
your soil-test report may include calcium, magnesium, boron, copper, iron,
manganese, sulfur and zinc. When the crop being planted is intended as a food
plot to attract and hold deer rather than for harvest, these Readings can be
largely ignored. While that’s not true in all cases, it’s true in such a
majority that the role of these nutrients and the effect of their levels won’t
be covered within the scope of this article. Also, as previously mentioned,
calcium and/or magnesium, if low, will be addressed if the vastly more common
dolomitic type of lime is used to raise soil pH.
SOIL STRUCTURE
So
far, we’ve covered why soil pH and soil nutrient levels must be at (or brought
up to) certain levels for the forage plants to have access to all the nutrient
levels they need.
Why, then, isn’t there a chart out there that says exactly
how many pounds of lime should be added in all cases to raise the soil pH of
all soils with the same starting soil pH to the same target soil pH? The answer
reveals why when it comes to having your soil tested, a laboratory soil test is
the only way to go; and it will make sense to anyone who has ever noticed that
dark, bottomland soil doesn’t look like the soil in a sandy ridgetop: all soils
aren’t the same. And just as they don’t look the same, not all soil types hold
lime activity and nutrients as long or as well as others. For example, “heavy”
soils such as clays or soils with lots of organic matter tend to hold lime
activity and nutrients better than soils that are “lighter” or have a higher sand
content. That’s why only a laboratory soil test can precisely tell you exactly
how much lime and/or fertilizer you need. If the lab’s nutrient and soil pH
Readings are below optimum, then the lab will consider what levels of nutrients
are already in the soil, apply its findings as to how well (or poorly) your
soil can hold lime and fertilizer activity, and develop its Recommendations
accordingly — based on the unique physical characteristics of the soil in your
sample.
Since the laboratory’s soil structure Readings are simply
sub-calculations the laboratory used in arriving at its final Recommendations,
they are things you can ignore as a practical matter. If you’re still
interested, though, here’s what they mean:
Buffer pH. On some soil test
reports, you may see “Buffer pH” listed. Buffer pH really tells you nothing.
It’s simply the result of a test done at the laboratory to help it form its final
Recommendations for how much lime to be added to soils with low soil pH. A
liming material called a buffer solution is added to the soil sample, and the
increase in soil pH is then measured and used by the laboratory in reaching its
final lime Recommendation. A big jump in soil pH suggests that the soil pH of
the sample is easily changed, and vice versa if the change is small. The
laboratory then uses this calculation in reaching its final lime
Recommendation.
Organic Matter and CEC: The “Organic Matter” Reading
indicates the amount of organic matter in your soil. “CEC” (Cation Exchange
Capacity) is a measurement of the soil’s ability to release positively charged
nutrients, or “Cations.” Together, Organic Matter and CEC tell the laboratory how
well (or poorly) the soil can hold nutrients. The lab uses the Organic Matter
and CEC Readings together as part of its final calculations for its Recommendations.
RECOMMENDATIONS
(Lime and Fertilizer)
Recommendations are the
most important things on a laboratory soil test report, since they tell you
what action you need to take (what you need to add to the soil) to bring it
into optimum condition if planting, or to maintain optimum condition if
maintaining an established forage stand.
LIME
If your soil pH
Reading is below optimum for the forage being planted or maintained, then the
soil-test report will also make a Recommendation as to how much lime to add to
the soil to raise it. This is one of — if not the most — critical
Recommendations your soil-test report will make. That’s because high-quality
forages that grow best in soils with a neutral soil pH won’t be able to freely
uptake soil nutrients if soil pH is low, so lime should be added to raise soil
pH in such cases, if possible several months in advance of planting.
Most
laboratory soil-test reports will provide Recommendations for the amount of
lime that needs to be added when the soil pH reading is low. Don’t be surprised
if you see the lime recommendation expressed in tons per acre. (The good news
is that lime is relatively inexpensive, especially when purchased in bulk.) The
reason it takes so much lime to raise soil pH is that lime does its work by
acting in particle to particle contact with the soil. In other words, a
particle of lime needs to touch a particle of dirt to neutralize its pH. The
fact that tons of lime are usually required makes more sense when you
understand that and consider how many particles of dirt are in the top few
inches of a one-acre seedbed.
The recommended liming material to raise soil pH
is crushed limestone rock. There are two types of limestone rock that are mined
and then crushed for use in raising soil pH: dolomitic and calcitic. How
quickly they can raise soil pH depends on whether it’s dolomitic or calcitic
limestone, how finely it’s crushed, and how thoroughly it is incorporated into
the soil.
While both dolomitic and calcitic limestone are used as liming
materials to raise soil pH, dolomitic is far more common. In fact, if you buy
lime for your food plot, chances are extremely high that it will be dolomitic
limestone. In most cases, dolomitic is preferable for several reasons: (A)
calcitic acts more quickly, but it carries an attendant risk of over-liming,
which is not presented with dolomitic; (B) dolomitic already has magnesium in
it; and (C) dolomotic’s liming effect lasts longer. Whether the lime is dolomitic
or calcitic, it can’t work overnight. That’s why for best results, you should
try to plan ahead and, if possible, incorporate lime at least several months in
advance of planting.
FERTILIZER
Most soils already have some
nutrients in them, although most fallow soils usually don’t have sufficient
levels for high-quality forage plants to really thrive, so we add fertilizer to
the seedbed to bring those levels up.
As we mentioned earlier, the “Big Three”
nutrients addressed with blended fertilizers are nitrogen, phosphorous and
potassium. When you review the fertilizer Recommendations in your soil-test
report, though, you may notice that those terms don’t appear. Instead, you’ll
see similar sounding titles such as “nitrate” and “phosphate.” Don’t let that
confuse you. For our purposes, just remember that nutrient Readings are shown
by the names of their natural forms, and the Recommendations are for those same
elements, but in compounds used in fertilizers to make those elements available
to plants. Here’s how you’ll see the Big Three listed:
Element Compound
(Fertilizer Form)
Nitrogen (N) Nitrate
Phosphorous (P) Phosphate
Potassium
(K) Potash*
* The commonly used name for potassium-compound fertilizers.
Calculating
fertilizer rates. Most, if not all, laboratory soil-test reports make
fertilizer Recommendations in two formats: pounds per acre, and for smaller
plots, pounds per 1,000 square feet.
Blended fertilizers in bags are labeled
with a series of three numbers separated by dashes, for example 13-13-13 and
6-24-24. In order from left to right, those numbers tell you the percentage of
N, P and K in the package.
The Whitetail Institute soil-test report provides a
chart (Table 2) that suggests different combinations and amounts of readily
available bagged fertilizers common to many areas that will satisfy the
nutrient Recommendations in the report. Each block may suggest one, two or
three different fertilizers. It’s important to understand that each block (and everything
in it) is a single option, and that all the other blocks (and everything in
them) are alternatives.
For example, take a look at Table 2 in this article. In
the first block (highlighted in red), you can see that 10-10-10, 0-20-20 and
0-46-0 are recommended. If you can find all three of these fertilizer blends in
your area, then apply all three, each in the amount (lbs./ac or lbs./1,000 sq.
feet) as recommended in Table 2. If you aren’t able to locate all three of the
fertilizers recommended in the first block, then go to the second block
(highlighted in blue), which recommends 15-15-15, 0-20-20 and 0-46-0. Not all
soil-test reports have more than one recommendation. If you can’t locate
fertilizers in your area that satisfy at least one of the Table 2 blocks, then
call the Whitetail Institute for additional advice.
FINAL THOUGHTS
Preparing
And Sending the Soil Sample to the Laboratory
Most, if not all,
laboratory soil-test kits come with at least two items: a submission form,
which asks you for specific information the lab will need to process the sample
and prepare a precise report for you, and a container for sending in the soil
you want to have tested.
Submission Form. Most, if not all, submission
forms ask for the same basic information, such as your name and address. Be
sure to write legibly so the lab can correctly label the report for mailing.
Two
more things: it’s very important to tell the lab (A) whether you will be
planting or maintaining a forage in the site, and (B) what that forage is. The
reason is that soil pH and fertilizer requirements differ among plant types,
and among those, some differ with regard to planting and maintenance. The
Whitetail Institute soil-test kit also makes this step very easy. All you have
to do is check a block beside either “Establishing New Field” or “Maintaining
Existing Field,” and another block beside the name of the Whitetail Institute
forage product you’ve chosen. Or, you can choose “other” if you have decided to
plant something other than a Whitetail Institute forage product. If you haven’t
completely decided on what forage you’ll be planting, you can even check up to
two forage-product blocks, and the lab will provide Recommendations for both at
no additional charge.
Preparing the Soil Sample: Keep in mind that you’ll
be sending in a relatively small amount of soil (about a pint), and that sample
must be representative of all the soil in the top few inches of the entire
seedbed. If you’re planning on plowing the seedbed with a moldboard plow, which
inverts dirt in a column, try to do your plowing before you take your samples if
possible. That way, you’ll be testing the soil in which the plants will actually
be growing.
Take samples one to six inches deep in 10 to 20 locations within
the seedbed after scraping away plant residue from each sample location. Mix all
the samples together thoroughly in a clean, plastic container. If the soil is
wet, then allow it to air dry to a workable condition before packaging it. Then,
put the representative sample into the soil-sample container provided in the
kit.
Sending the sample to the laboratory. Be sure to package the
soil-sample container and the submission form together. Do not mail them
separately. If you have more than one sample, it can also be a good idea to
seal each sample container and its accompanying submission form in a separate shipping
envelope, and then put all the sealed envelopes into one box to ship. That way,
you can be sure all the samples arrived at the same time, and you can track the
shipment.
If you need assistance interpreting your Whitetail Institute
soil-test report, or a soil-test report from any other laboratory, call the
Whitetail Institute’s in-house consultants at (800) 688-3030. The call and
advice are free.
