Soil Test Every Four Years To Monitor Limestone
URBANA, ILL.
Proper use of limestone is one of the most
important management strategies in crop
production. Limestone should be the first
soil amendment considered in cropping systems.
Don’t try to guess what your soil lime needs
are. A soil test every 4 years is the best way to
monitor the need for limestone. The measurement
of soil pH tells if limestone is needed, but
not how much.
In a cash-grain system a pH of at least 6.0 is
recommended. With alfalfa and clover in the rotation,
the pH needs to be at least 6.5, preferably
closer to 7.0.
Remember the pH scale is in logarithmic
terms, so each unit change in pH means a tenfold
change in acidity or alkalinity. Thus, lime
needs increase rapidly as pH drops.
The benefits of a liming program are many.
Limestone can lower the soil solution concentration
of aluminum and manganese, which can
be toxic to plants. An increase in soil microbial
activity is noted as soil acidity is decreased. Liming
enhances nitrogen fixation and may improve
soil structure and tilth. The availability of mineral
elements (for example phosphorus and
molybdenum) to plants can be increased by
proper liming.
Several factors determine the type of liming
program, with the crop to be grown probably the
most important. Soil texture, organic matter,
and method and depth of tillage are other critical
items. The timing and frequency of lime applications
are also important. For example, with
leguminous crops, lime should be applied at
least 6 months before seeding on acid soils. If
applied just before seeding, the lime will not
have adequate time to react with the soil.
Limestone quality is measured by two factors the
effective neutralizing value and the degree of
fineness. The acid-neutralizing ability of the material
is indicated by the calcium carbonate
equivalent (CCE). The higher the CCE value, the
greater the limestone's ability to neutralize soil
acidity. Pure calcium carbonate (CCE of 100) is
the standard against which all liming materials
are measured. The CCE level is inherent in the
material, it can not be changed.
The second factor is particle size or fineness of
grind. The rate of reaction depends on the surface
area of the liming material in contact with
the soil. The finer the limestone is ground, the
faster it will neutralize soil acidity. Limestone too
coarsely ground will be very slow in raising the
soil pH. Lime particle size is based on the percentage
of materials that pass through 8-, 30-,
and 60-mesh screens.
Those applying limestone are encouraged to
obtain a copy of the “Illinois Voluntary Limestone
Program Producer Information” booklet.
The booklet, produced every August by the Illinois
Department of Agriculture and Department
of Transportation, indexes limestone samples
from quarries that wish to participate in the Illinois
Voluntary Limestone Program. Analyses of
CCE, fineness scores, magnesium percent, and
correction factors are included. It's available at
University of Illinois Extension Offices and at
http://www.agr.state.il.us/news/pub/2008LimeBook.pdf . Δ