Soil Test Note – No. L001
Dr. Stanley L. Chapman, Extension Soils Specialist
LIMING CLAY SOILS
Introduction
Where lime is recommended
for row and forage crops on delta clays such as alligator and Perry or Blackland
Prairie clays such as Oktibbeha and Sumter, the probability of crop response
is less than on more coarse textured lighter soils. Such clay soils usually have soil test calcium levels greater than
8,000 pounds per acre. Lime application
has shown little to no increase in yields of soybeans, cotton or forages at
soil pH levels in the low 5’s. Physical
problems that limit crop yields often mask soil fertility limitations.
Oxygen during wet periods and water during dry periods are the main
deficiencies.
Objectives of Liming
The
main objectives of liming are (1) avoidance of excessive manganese and aluminum
solubility, (2) increased phosphorus and molybdenum availability, and (3)
increased calcium as a plant nutrient. Toxicities
of manganese and aluminum have not been demonstrated in alluvial clay soils.
They contain liberal amounts of calcium for plant nutrient needs and
a good supply of organic matter which serves as a reservoir of available phosphorus. The organic matter and high calcium buffer
against a rapid change in pH when nitrogen fertilizer is added.
Any deficiency of molybdenum
for legumes may be overcome by applying molybdenum as a seed treatment.
Molybdenum is recommended for soybeans and forage legumes on all soils
testing below pH 7.0.
Where irrigation is used,
lime content of the water should be considered along with the soil pH in making
final decisions on liming.
Conclusions
Where lime is recommended
for row crops, forages, and small grains on clay soils, it should not be considered
as a high return investment for short-term purposes. It should be considered as a long-term investment and then only
after all other proven technology, including land forming and good drainage,
is employed.
Where
lime is recommended, preference should first be given to fields testing near
pH 5.0 and last to those testing near pH 6.0.
For
alfalfa and certain pasture legumes, recommended lime on clayey soils can
be a good investment for legume establishment and long-term maintenance.
April,
1995
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