As a 10-year-old, piano lessons were obligatory
and torture. Part of this inhumane rite of passage were the warm-up lessons “Dozen
a Day” — repetitious monotony. I
hope readers do not judge repeated discussions of soil acidity and the
importance of liming with the same degree of contempt. The fact is, soil
acidity is a universally persistent problem in food plots and limits
productivity. Further, soil acidity is easily corrected with limestone, making
the continual problem even more perplexing.
What
is Soil Acidity, and Why is it Relevant?
Soil acidity is the quantity of
hydrogen ions in the soil. In the eastern and central United States, soils tend
to be acidic, even in a natural and undisturbed state. The problem comes with
our land-use patterns, which exacerbate the natural acidic tendency. The
mineral structure of most soils has limited buffering capacity, and any form of
soil disturbance — such as fire, timber harvest or long-term tillage — removes the
limited buffering capacity. As a result, soils quickly become more acidic. Acidity
is expressed as pH, with values ranging from 0 (very acidic) to 14 (very
alkaline). The pH value is a negative logarithm, which mathematically means
that soil acidity differs by a power of 10. The target soil pH varies slightly
among soil types and crops but is about 6.5-7.0. A soil with a pH value of 4.5
is 100 times more acidic than a soil with the ideal pH of 6.5. Acidic soils are
an indication of soil infertility. Chemically, acidic conditions alter the
chemical form of important soil nutrients, making those elements unavailable to
crops; that is, nutrient starvation. Acidic soils also alter other naturally
occurring elements in the soil, making them toxic to crops, with aluminum being
the major culprit. I distinctly remember a classmate asking an instructor about
the major reason why acidic soils affect crop growth, and he quickly responded that
aluminum toxicity was the major reason — that is, poisoning. Soil acidity has
an additional insidious effect on forage legumes such as clover and alfalfa.
Legumes have the unique ability to capture and use nitrogen from the atmosphere
(actually in air spaces in the soil) for plant growth. This is done with a
symbiotic relationship between nitrogen-fixing bacteria in the soil and legume
roots. Acidic soils inhibit the survival and efficiency of the symbiotic
bacteria, affecting growth of forage legumes. How much growth reduction? I have
seen in the agricultural scientific literature a report of a 28-time yield
increase in limed alfalfa compared to alfalfa grown in a non-limed, highly
acidic soil. This is why properly limed soils are essential for food plots
planted to forage legumes such as Imperial Whitetail Clover and Alfa-Rack Plus.
Correcting
Soil Acidity
Neutralizing soil acidity is fairly
straightforward. Common neutralizing soil amendments are carbonates
(limestone), oxides and hydroxides. These materials are combined with calcium
or magnesium, which are often incorrectly thought to neutralize soil acidity.
Calcium and magnesium are essential
elements for plant growth, but do not directly neutralize soil acidity.
Carbonates, oxides and hydroxides are the chemical agents that neutralize soil
acidity. Consider calcium and magnesium to be carriers of the actual
neutralizing agent. Which is best to neutralize soil acidity in food plots:
carbonates, oxides or hydroxides? Carbonates offer the best combination of
cost, chemical reactivity, widespread availability and ease of use. Carbonates include
calcitic limestone (calcium carbonate) and dolomitic limestone (a mixture of
calcium carbonate and magnesium carbonate). In the context of neutralizing soil
acidity, there is no real difference between calcitic limestone and dolomitic
limestone. Both are naturally occurring, and the material locally available is
often based on which type is mined in the closest limestone quarry. In
commercial agricultural regions, limestone is sold in bulk and stored at
dealers in massive outdoor piles. Bulk limestone is sold as a blend of
particles of varying size. Smaller particles quickly react to neutralize soil
acidity. Larger particles take longer to react, extending the length of
neutralization. Consider the particle size blend to be an ad-hoc form of time
release. This is why farmers typically lime about every three years. Limestone
is also sold in bags at home-improvement stores, mainly for use in home
gardens, lawns or landscape areas. Bagged products contain finely ground
limestone that has been pelleted for ease of homeowner application. The coating
is water soluble, releasing the finely ground limestone that quickly
neutralizes acidic soils. This sounds good at face value, but the uniform fine
texture equates to short-term neutralization, and bagged limestone costs
significantly more than bulk limestone. However, I can think of food plot
scenarios where bagged, pelleted limestone is a wise choice, assuming the user is
willing to accept the higher cost. Pound for pound, oxides and hydroxides are
the most efficient and quick-acting materials to neutralize soil acidity.
However, they are potential irritants to handlers and overall difficult to
apply. Further, their quick-acting properties mean very short-term neutralization.
These disadvantages largely outweigh the advantages of neutralization
efficiency, but perhaps oxides and hydroxides are viable options in some extreme
situations. From time to time, I’m included in discussions on using liquid or sprayable
formulations of limestone on food plots. Sprayable limestone is a slurry of
ultra-fine limestone particles in water. It will neutralize acidic soils
quickly but no quicker than applying dry limestone of the same particle size.
Because of uniform small particle size, the benefits of sprayable limestone are
short-lived, just like dry fine limestone. However, I do not recommend
sprayable limestone because of limitations of commonly used sprayers. Sprayable
limestone is often used for hydromulching/seeding operations that have trash
pumps to spray dense slurries of solids (seeds, fertilizer, mulching materials)
in large volumes of water (thousands of gallons per acre) with aggressive mechanical
agitation in the tank. A typical ATV- or tractor-mounted sprayer cannot generate
the necessary output for sprayable limestone and does not have adequate
agitation to maintain suspension in the spray tank. Additionally, spraying
heavy slurries using an ATV sprayer can destroy the pump.
