Fertilizers are responsible for over half of global food production, but there are areas in world with nutrient deficiency and other areas of nutrient excess.
Managing mineral plant nutrients requires careful application of science and skill to meet production, environmental, and social goals.
Wednesday, September 26, 2012
Gypsum... What is it?
Gypsum is a
common mineral obtained from surface and underground deposits. It can be a
valuable source of both calcium (Ca) and sulfur (S) for plants and may provide
benefits for soil properties in specific conditions.
Gypsum mining, Utah
psum is found in
both crystal and rock forms. It generally results from the evaporation of
saline water and is one of the more common minerals in sedimentary conditions.
The white or gray-colored rocks are mined from open-pit or underground
deposits, then crushed, screened, and used for a variety of purposes without
further processing. Agricultural gypsum generally consists of CaSO4·2H2O (dihydrate). Under geological conditions of high temperature and
pressure, gypsum is converted to anhydrite (CaSO4 with no water).
gypsum comes from fossil-fuel power stations where S is scrubbed from exhaust
gas. Gypsum is also a byproduct from processing phosphate rock into phosphoric
acid. Gypsum from recycled wallboard is finely ground and used for soil application.
Chemical Properties:Calcium sulfate
NameFormula & CompositionWater Solubility
Dihydrate (Gypsum) CaSO4·2H2O 2.05
[23% Ca, 18% S, 21% water] [5,570 lb/acre foot]
Anhydrite CaSO4 [29% Ca, 23% S] 2.05
Hemi-hydrate CaSO4·1/2H2O [Reverts
water is added]
called landplaster) is generally added to soils either as a source of nutrients
or to modify and improve soil properties. Gypsum is somewhat soluble in water,
but more than 100 times more soluble than limestone in neutral pH soils. When
applied to soil, its solubility depends on several factors, including particle
size, soil moisture, and soil properties. Gypsum dissolves in water to release
Ca2+ and SO42-,
with no significant direct impact on soil pH. In contrast, limestone will neutralize
acidity in low pH soils. In regions with acid subsoils, gypsum is sometimes
used as a relatively soluble source of Ca for alleviation of aluminum toxicity.
Some soils benefit
from application of gypsum as a source of Ca. In soils with excess sodium (Na),
the Ca released from gypsum will tend to bind with greater affinity than Na on
soil exchange sites, thus releasing the Na to be leached from the rootzone.
Where gypsum is used in the remediation of high Na soils, it generally results
in the enhancement of soil physical properties – such as reducing bulk density,
increasing permeability and water infiltration, and decreasing soil crusting.
In most conditions, adding gypsum by itself will not loosen compacted or heavy
Gypsum piles before spreading
A well-known use of
gypsum is to supply Ca for peanuts, which have a unique growth pattern. Gypsum
is most commonly spread on the soil surface and mixed in the rootzone.
Equipment exists that allows finely ground gypsum to be distributed through an
irrigation system. Gypsum is sometimes prilled to make application more
convenient for home and turf use.
Non Agricultural Uses
use of gypsum is for building materials (such as plaster and wallboard). For
construction purposes, gypsum is ground and heated (calcined) to remove most of
the bound water, resulting in hemi-hydrate plaster (plaster of Paris). When
water is later added, the powder reverts to gypsum and dries in a rock-hard
state. Gypsum is extensively used in many other applications, such as for water
conditioning, in the food and pharmaceutical industries, and as a setting
retardant in cement.