Gypsum is a common soil amendment and has historically been applied
for several different purposes. Gypsum provides a source of
calcium and sulfur for plants; it is commonly applied to peanut crops
in the Southeast US as a source of calcium at rates of 600 to 800
pounds per acre. Many vegetables, including potatoes and corn,
have been shown to benefit from gypsum
application. Unlike lime, gypsum does not raise the pH of soils
and
it is thus preferred for crops that require calcium but where the soils
are
already alkaline (and can not accommodate pH adjustment). Gypsum
has
also been found to be useful for reclaiming very salty soils; the
calcium in the gypsum substitutes for the sodium in the soils, allowing
the sodium to leach away. Gypsum has the ability to flocculate
clayey soils that have drainage problems.
The processing requirements for gypsum drywall that is applied to soil
may differ somewhat from industrial markets.
While foreign materials such as nails and corner beads should be
removed, agricultural uses can tolerate some ground paper in the
mixture. The presence of trace components (such as lead from lead
based paint) might be of greater concern when land applied (relative to
the industrial uses) because of the potential for human contact and
soil or groundwater contamination.
The method of gypsum application will control the size of the material
and
the degree of processing needed. With some application
techniques,
larger pieces of drywall may cause damage to plants when thrown from
the
spreader
at high velocities. If the drywall is being tilled into the soil,
large
sizes may be permissible as size reduction will also occur during the
application
process and plant damage from application is not a concern. While
some
recyclers have marketed bagged gypsum products for soil and plant
application,
the largest uses are the bulk applications by farmers. |
Gypsum
from processed drywall being land applied as part of plant growth
impact research study in Florida
Processed gypsum from drywall ready for
shipment to agricultural market in California
|
