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Dial in Soil pH
From
Farm Journal Media
By
Darrell Smith, Farm Journal Conservation & Machinery Editor |
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This document is available as a
PDF (portable document file) -
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Calculate Your Correction Factor
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here to view chart |
Every farmer knows lime is a cornerstone of high, efficient crop
yields. Keeping soil pH at 6.0 to 7.0 makes nutrients and
micronutrients more available, boosts herbicide effectiveness,
promotes populations of soil microorganisms and improves soil
structure.
That impressive list of advantages makes it important to ensure you
maximize lime applications—and dial in pH. A poor choice of
product can waste money, and sloppy application can create a
patchwork pH pattern that can take years to correct. Here’s how
to make sure you get your money’s worth when you apply lime. |
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Understanding Lime and Lab Recommendations |
Agricultural lime is ground-up limestone bedrock. It contains
calcium carbonate and magnesium carbonate, which neutralize
acidity in soil. Calcitic lime is mainly calcium carbonate.
Dolomitic lime contains both calcium carbonate and magnesium
carbonate. Soils become acidic because of excessive hydrogen
ions in the soil solution and attached to soil particles.
Calcium and magnesium ions in lime displace some of the hydrogen
ions—and take their place on soil particles. Then the carbonates
neutralize the hydrogen ions.
Some soil test laboratories make recommendations in terms of
calcium carbonate others make recommendations in tons of
lime—meaning tons of lime product with a typical CCE for that
state or region. If a lime product varies from that standard,
you must apply a correction factor to determine how many tons
you need to apply. “I recently encountered a dealer who
discovered he had been under applying because he misinterpreted
tons of CCE as tons of lime,” says Farm Journal Field Agronomist
Ken Ferrie.
Be sure you and your dealer or lime applicator understand whether
your recommendation is for tons of CCE or tons of a standard
lime, as well as how to compare products.
Finally, adjust your rate for incorporation depth. Most
recommendations are based on 9" moldboard plowing. If you till
shallower, reduce the application proportionately. If you
no-till, apply only one-third as much (as if you were
incorporating 3" deep). |
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What’s the Best Lime Quality? |
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All lime products are not equal in value because they are not
equal in neutralizing power. “There are no national or regional
standards for lime quality,” explains Randall Warden, director
of client services, A & L Great Lakes Laboratories.
Even so, lime quality determines how many tons to apply to achieve
the necessary pH change. The quality is influenced by the
calcium carbonate and magnesium carbonate content, which is
determined by laboratory analysis and expressed as CCE. The CCE
figure represents the neutralizing power of the lime product
compared with pure calcium carbonate.
The coarseness or fineness of the ground lime product also impacts
the quality. The fineness of the grind is expressed as the
percentage of particles passing through several standardized
sizes of mesh screens.
The finest particles provide the quickest reaction with acidic
soil. Particles that pass a 60-mesh screen are effective the
first year. Bigger particles need more time. If you have doubts
about the grind, ask your crop consultant to run a test just for
you. “People understand the purity [CCE] factor, but I think
they often overlook fineness,” Warden explains.
In most cases, he notes, lime quarries grind their product for
customers other than farmers, such as road builders. Those
clients want a coarser product, and the fine particles, of
various sizes, which are left over are what is sold to farmers
for ag use.
Editor’s Note: Most Indiana lime quarries specifically produce
aglime.
When you’re buying lime, your supplier should be able to tell you
the CCE and the fineness of the grind. For Indiana suppliers,
check the Aglime Council Quality Report at
www.aglime.org |
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What’s the Best Buy? |
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Using CCE and fineness, you can calculate a correction factor
for different lime products. (See page 31). The correction
factor lets you determine which one is the best buy.
The lower the correction factor, the higher the quality of the lime
and the less required. Say one quarry is selling higher-quality
lime with a correction factor of 0.53 for $8 per ton and another
quarry is selling lower-quality lime with a correction factor of
1.52 for $5 per ton. (These prices do not include delivery and
application charges, which often equal the cost of the lime.)
If your recommendation calls for 3 tons of lime per acre, you’ll
need to apply only 1.59 tons of the higher quality material,
costing $12.72 per acre. You’ll need to apply 4.56 tons of the
cheaper material, costing $22.80 per acre. So the cheaper lime
is no bargain. |
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The Ideal Grind for Lime |
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The finest-ground lime is the hardest to spread, requiring great
attention to detail during calibration and avoiding spreading on
windy days. That’s why you need a mixture of small and large
particles (besides the fact that small particles neutralize
acidity immediately, and larger particles continue neutralizing
over several years).
For ideal spreadability, Warden suggests a product meeting the
follow criteria: 95% of particles passing an 8-mesh sieve, 70%
passing a 20-mesh sieve, 50% passing a 60-mesh sieve and 40%
passing a 100-mesh sieve.
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Getting Uniform Coverage |
Improved hydraulics on today’s applicators allow wider spread
patterns, and rate controllers make delivery very accurate. “But
they make calibration even more important than it was before,”
says Lynn Dolan, Linco Equipment, a New Leader dealer, El Paso,
Ill.
Your applicator owner’s manual will contain calibration
instructions, but here are a few general tips:
• Calibrate for the type of lime you will be spreading. With a
coarser product, you can cover a wider swath—maybe 50' compared
with 30' or 35' with a finer grind. To check the uniformity of
your spread, set several large, flat pans on the ground across
the width of your swath and make a pass over them.
• Remember to take the density of the lime into account as you
calculate the flow rate, says Gary Cooper of The Andersons Farm
Center in Litchfield, Mich. It can vary from about
70 lb. to about 90 lb. per cubic foot. Your supplier can tell
you the density or provide a density scale.
• Calibrate your groundspeed radar, as well as your applicator.
• If you tow an applicator behind your tractor, Dolan recommends
investing in a lightbar swather for guidance. “If a field has
been tilled across the rows, it’s very easy for the driver of
the applicator to switch from following the old rows to
following the tillage passes,” he says.
•
Consider dealer support when you buy an applicator, Dolan
suggests. Ask if the company provides a service team to
calibrate your machine. If you buy a used spreader, consider
hiring a service team to calibrate it. |
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Fluid Lime Suspensions |
Fluid lime contains lime recycled from municipal water systems
and industries—very fine particles suspended in water.
University of Illinois research indicates the rate of reaction
and neutralizing power are the same as for dry lime of the same
particle size. To get the product applied evenly, there are some
procedures you need to keep in mind, Ferrie says. Your goal with
any lime product is to apply it as uniformly as you would paint
on a wall.
Buy from a dealer with a sound reputation and who pays attention to
detail. A good dealer will mark each semi load with its
solid-lime content. That can vary from 14% to 25%, depending on
whether the material was drawn from the top, middle or bottom of
the lagoon. A skilled floater operator will adjust his
application rate to reflect the solid content.
If the truck hauls suspended lime a long distance, it may settle
out and need to be agitated, Ferrie says. A well-trained
operator will run the load through the applicator and back onto
the truck to mix it uniformly.
“After application, you can tell if no one paid attention,” Ferrie
says. “The limed field will have a quilt-like appearance, with
dark and light spots.”
If you’re offered a partially dried suspended lime product with a
semi-solid consistency—sometimes free from municipalities—you’d
be wise to reject it, Ferrie says. “Usually, farmers try to
apply it with a manure spreader, and they wind up with clods of
all sizes,” he explains. “To be useable, the semi-solid product
needs to be dried and pulverized or pelletized.” |
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“Dial in Soil pH” © 2008
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