Gypsum Is Almost A Universal Soil Amendment
Arthur Wallace and Garn A. Wallace
Wallace Laboratories, 365 Coral Circle, El Segundo, CA 90245
Abstract: Agriculture has
failed to be sustainable several times in the history of the
world because of soil failure (Rush, 1987).
Irrigated land eventually leads to sodicity and salinity unless
extreme care is taken. Gypsum is a key ingredient for the
maintenance of agriculture on many types of soils and over
a wide pH range including sodicity. Waste-product gypsum is
available in a large number of locations at very little or
no cost. Advantages of gypsum in addition to prevention and
correction of sodicity include greater stability of soil organic
matter, more stable soil aggregates., improved water penetration
into soil, and more rapid seed emergence.
The need for gypsum in amounts varying from small to large
is almost universal. Gypsum and water-soluble polymers magnify
the value of each other. Together they have an important role
in making a better environment, especially for growing plants..
Introduction
Regular use of gypsum is essential to the
sustainability of most irrigated soils. It has been used as
a soil amendment and fertilizer for over 200 years. Benjamin
Franklin was said to have successfully spelled out the sentence
on one of his field with the response from gypsum, “
This land has been plastered. ” Plaster of Paris is
a from of gypsum.
Gypsum is calcium sulfate. The most common
form of it is the dihydrate– which means that each molecule
of calcium sulfate has two water molecules associated with
it. It is expressed as CaSO4 2H2O.
The plaster of Paris used commercially has only one-half water
and another form called gypsum anhydrite has no water. Much
of the gypsum used in agriculture is mined and the has no
water. Much of the gypsum used in agriculture is mined and
then pulverized to desirable particle sizes. The smaller sizes
go into solution more rapidly than do large sizes. Gypsum
is also a by-product of various manufacturing operations.
For many reasons, gypsum can be considered
to be a farmer’s friend.
Almost 40 benefits from its use on land have been documented.
Some of the reasons are multiple and interrelated.
Some Reasons For Using Gypsum
Gypsum Improves
Soil Structure
Gypsum provides calcium which is needed
to flocculate clays in acid and alkaline soil (Shainberg et
al. 1989, Sumner 1993, Sumner and Miller 1992). It is the
process in which many individual small clay particles are
bound together to give much fewer but larger particles.
Such flocculation is needed to give favorable soil structure
for root growth and air and water movement.
Gypsum Helps Reclaim Sodic Soils
Gypsum is used in the reclamation of sodic
soils (Aldrich and Schoonover 1951). Where the exchangeable
sodium percentage (ESP) of sodic soils is too high, it must
be decreased for soil improvement and better crop growth.
The most economical way is to add gypsum which supplies calcium.
The calcium replaces the sodium held on the clay-bind sites.
The sodium can then be leached from the soil as sodium sulfate
to an appropriate sink. The sulfate is the residue from the
gypsum. Without Gypsum, the soil would not be leachable.
Sometimes and ESP of three is too high, but sometimes up to
ten or more can be tolerated. The range is partly the result
of concentration of soluble salts.
Gypsum Prevents Crusting of Soil and
Aids Seed Emergence
Gypsum can decrease and prevent the crust
formation on soil surfaces which result from rain drops or
from sprinkler irrigation on unstable soil (Shainberg et al.
1989; Sumner and Miller 1992). It can even prevent crusting
that results when acid soils are limed (Summer 1993)–
the gypsum is co-applied with the lime. The gypsum is either
surface applied or put on in the irrigation system. Prevention
of crust formation means more seed emergence, more rapid seed
emergence, and easily a few days sooner to harvest and market.
Seed emergence has been increased often by 50 to 100 percent.
The prevention of crusting in dispersive soils is a flocculation
reaction.
Gypsum Improves Low-Solute
Irrigation Water.
Gypsum is used to increase the solute concentration
of lwo-solute water used for irrigation (Traynor 1980). Irrigation
water from rivers that no longer have sources of leachable
salts either penetrates poorly into soil or causes soil particles
to degrade which results in low-water penetration. Rain water
can behave the same way and result in soil compaction. The
problem can be corrected with surface-applied gypsum or application
to the irrigation water.
Gypsum Improves
Compacted Soil
Gypsums can help break up compacted soil
(Shainberg et al. 1989) and decrease penetrometer resistance
(Hall et al. 1994a). Soil compaction can be prevented by not
plowing or driving machinery on soil when it is too wet. The
compaction in many ( but not all soils) can be decreased with
gypsum, especially when combined with deep tillage to break
up the compaction. Combination with organic amendments also
helps, especially in preventing return of the compaction.
Gypsum Makes Slightly Wet Soils Easier
to Till
Soils that have been treated with gypsum
have a wider range of soil moisture levels where it is safe
to till without danger of compaction or deflocculation (Shainberg
et al. 1989). This accompanied with greater ease of tillage
and more effective seedbed preparation and weed control. Less
energy is need for the tillage.
Gypsum Stops Water Run-off And Erosion
Gypsum improves water infiltration rates
into soils and also hydraulic conductivity of the soil ( Shainberg
et al. 1989). It is protection against excess water run-off
from especially large storms that are accompanied with erosion.
Gypsum Decrease
pH of Sodic Soils
Gypsum immediately decreases the pH of sodic
soils or near sodic soils from values over 9 but usually over
8 to values from 7.5 to 7.8. hydrolysis values are in the
range of acceptability for growth of most crop plants. Probably
more than one mechanism is involved.
According to Lindsay (1979), Ca++ reacts with bicarbonate
to precipitate CaCO3 and release protons which decrease the
pH. Also, the level of exchangeable sodium is decreased which
lessens the hydrolysis of clay to form hydroxides. organic
reactions can decrease the incidence of lime and bicarbonate-induced
iron deficiency.
Gypsum Increases
the pH of Acidic Soils
One mechanism in which gypsum can increase
soil pH enough in some acid soils to sufficiently decrease
the level of soluble aluminum to grow crops satisfactorily
is replacement of hydroxyl ions from some clay lattices by
sulfate ions (Sumner 1994).
Gypsum Improves Swelling
Clays
Gypsum can decrease the swelling and cracking
associated with high
levels of exchangeable sodium on the montmorillonite-type
clays
(Aldrich and Schoonover 1951). As sodium is replaced by calcium
on hydrolysis clays, they swell less and therefore do not
easily clog the pore spaces through which air, water and roots
move.
Gypsum Prevents Waterlogging of Soil
Gypsum improves the ability of soil to drain
and not become waterlogged due to a combination of high sodium,
swelling clay, and excess water (Aldrich ad Schoonover 1951).
Improvements of infiltration rate and hydraulic conductivity
with use of gypsum add to the ability of soils to have adequate
drainage.
Gypsum Can Help Remove Excess Boron from Sodic Soil More Boron
was leached from sodic soils when gypsum was applied than
when the soil was leached without gypsum (Bajwa and Sharma
1990).
Gypsum Increases the
Stability of Soil Organic Matter
Gypsum is a source of calcium which ;gives
stability to soil aggregates (Muneer and Oades 1989). The
value of organic matter applied to soil is increased when
it is applied with gypsum.
Gypsum Makes Water-Soluble
Polymer Soil Conditioners More Effective
Gypsum complements or even magnifies the
beneficial effects of water- soluble polymers used as amendments
to improve soil structure (Wallace and Nelson 1986). Like
for organic matter, calcium, which comes from gypsum, is the
mechanism for binding of the water-soluble polymers to the
clay in soil.
Gypsum Makes Excess
Magnesium Non-Toxic
In soils having unfavorable calcium: magnesium
ratios, such as serpentine soils, gypsum can create a more
favorable ratio (Jones et al. 1976).
Gypsum
Corrects Subsoil Acidity
Gypsum can improve some acid soils even
beyond what lime can do for them. Surface crusting an be prevented
(Shainberg et al. 1989, Smyth and Cravo 1992). The effect
of toxic soluble aluminum can be decreased, including in the
subsoil where lime will not penetrate. It is then possible
to have deeper rooting with resulting benefits to the crops.
The mechanism is more than replacement of acidic hydrogen
ions which can be leached from the soil to give higher pH.
Hydrogen ions don't migrate rapidly in soils containing clay.
It is suggested that sulfate from gypsum forms a complex (AISO4+)
with aluminum which renders the aluminum non-toxic (Shainberg
et al. 1989). AI(OH)2+ and A (OH)3 are also nontoxic to plants
(Menzies et al. 1994). Also suggested is that sulfate ions
react with iron hydroxides to release hydroxyl ions which
give a lime effect to increase soil pH. Gypsum is now being
widely used on acid soils.
Gypsum Can Enhance The
Values of Liming
Addition to soil together with lime increased
crop yields (McLay et al. 1994ab, Shkel 1991). The combination
also decreased leaching losses of potassium and magnesium
(Nogueira and Mozeto 1990).
Gypsum Improves Water-Use
Efficiency
Gypsum increases water-use efficiency of
crops. In areas and times of drought, this is extremely important.
Improved water infiltration rates (Wildman et al. 1988), improved
hydraulic conductivity of soil, better water storage in the
soil all lead to deeper rooting and better water-use efficiency
(Shainberg et al. 1989; Hall et al.
1994b). From 25 to 100 percent more water is available in
gypsum- treated soils than in non-treated soils.
Gypsum Creates Favorable
Soil EC
Gypsum, being readily soluble, results in
a proper buffered solute concentration (EC) in soil to maintain
soil in a flocculated state (Handbook, 1985). It is better
environmentally and cost-wise to maintain the needed EC with
gypsum than with excess application of fertilizers. Regular
annual applications of gypsum are needed for this purpose.
Many highly weathered soils throughout the world have surface
crusting because of low electrolyte content (Sumner 1993).
This can be corrected with gypsum.
Gypsum Makes It Possible
to Efficiently Use Low-Quality Irrigation Water
Gypsum is essential when low-quality irrigation
water must be used (Traynor 1980). The effective sodium absorption
ration SAR) of irrigation water should be less than 6 for
some crops and less than 6 for some crops and less than 9
for others. When it exceeds hydrolysis limits, gypsum should
be applied to the soil or to the water. Use of reclaimed municipal
waste water is important for conservation of natural resources.
Reclaimed water can be satisfactorily used if amendments,
such as gypsum and water-soluble polymers, are also used.
Care must be taken, however, to avoid sodium build-up in the
lower horizons of soil because of excessive leaching when
swelling clays are present (Nader and Margaritz 1986).
Gypsum Decreases Dust Erosion
Use of gypsum can decease wind and water
erosion of soil (Shainberg et al. 1989). Severe dust problems
can be decreased, especially when combined with uses of water-soluble
polymers. Less pesticide and nutrient residues will escape
from the surface of land to reach lakes and rivers when appropriate
amendment are used to stabilize soil.
Gypsum has several environmental values.
Gypsum
Helps Plants Absorb Plant Nutrients
Calcium, which is supplied in gypsum, is
essential to the biochemical mechanisms by which most plant
nutrients are absorbed by roots (Epstein 1961). Without adequate
calcium, uptake mechanisms would fail.
Gypsum Decrease Heavy-Metal
Toxicity
Calcium also acts as a regulator of the
balance of particularly the micro-nutrients, such as iron,
zinc, manganese and copper, in plants (Alva et al. 1993; Wallace
et al. 1980). It also regulates non- essential trace elements.
Calcium prevents excess uptake of many of them; and once they
are in the plant, calcium keeps them from having adverse effects
when their levels get high. Calcium in liberal quantities
helps to maintain a healthy balance of nutrients and non-
nutrients within plants. Gypsum contains calcium.
Gypsum Increases Value
Of Organics
Gypsum adds to the value of organic amendments.
Blends of gypsum and organics increase the value of the other
as soil amendments, especially for improvement of soil structure.
High levels of soil organic matter are always associated with
liberal amounts of calcium which is part of gypsum (Muneer
and oades 1989). Calcium decreases burn-out of soil organic
matter when soils are cultivated by bridging the organic matter
to clay.
Gypsum Improves Fruit
Quality and Prevents Some Plant Diseases
Calcium is nearly always only marginally
sufficient and often deficient in developing fruits (Shear
1979). Good fruit quality requires and adequate amount of
calcium. Calcium moves very slowly, if at all, from one plant
part to another and fruits at the end of the transport system
get too little. Calcium must be constantly available to the
roots. In very high pH soils, calcium is not available enough;
therefore, gypsum helps. Gypsum is used for peanuts, which
develop below the ground, to keep them disease-free.
Gypsum helps prevent blossom-end root of watermelons (Scott
et al.
1993) and tomatoes, and bitter pit in apples. Gypsum is preferred
over lime for potatoes grown in acidic soils so that scab
may be controlled. Root rot of avocado trees caused by Phytothora
is partially corrected by gypsum and organics (Borst 1986).
Gypsum
Is A Source Of Sulfur
Gypsum is a source of fertilizer sulfur.
Due to the trend to production of high-analysis fertilizers
and due to the need of removing sulfur dioxide emission in
industrial operations to give cleaner air, more and more sulfur
deficiencies are present in agriculture (Tabatabai 1986).
Gypsum Helps Prepare
Soil For No-Till Management
A liberal application gypsum is a good procedure
for starting a piece of land into no-till management or pasture.
Improved soil aggregation and permeability will persist for
years and surface-applied fertilizers will more easily penetrate
as result of the gypsum (Shainberg et al. 1989).
Gypsum Decreases Bulk Density
of Soil
Gypsum-treated soil has a lower bulk density
compared with untreated soil (Shainberg et al. 1989). Organics
can even decrease it more when both are used. The softer soil
is easier to till, and crops like it better.
Gypsum Decreases the Toxic
Effect of NaCl Salinity
Calcium from gypsum has a physiological
role inhibiting the uptake of sodium by plants (Akhavan-Kharazian
et al. 1991). For species of plants not tolerant to sodium,
calcium protects from toxicity of sodium but not chloride.
Calcium overcomes toxic effects of sodium chloride salinity
on seed germinations and plant growth (Cachorro 1994).
Gypsum Can Decrease
pH of Rhizosphere
Increased calcium uptake by roots when gypsum
is applied can decrease the pH of the rhizosphere (Wallace
1963; Wallace and Wallace 1992).
In high pH soils, the added availability of iron and zinc
is very important to some plant species.
Gypsum Keeps Clay
off Tuber and Root Crops
Gypsum can help keep clay particles from
adhering to roots, bulbs and tubers of crops like potatoes,
carrots, garlic and beets. In combination with water-soluble
polymers, it is even more beneficial (Wallace and Nelson 1986).
Gypsum Decreases
loss of Fertilizer Nitrogen to the Air
Calcium from gypsum can help decrease volatilization
loss of ammonium nitrogen from applications of ammonia, ammonium
nitrate, UAN, urea, ammonium sulfate, or any of the ammonium
phosphates (Fenn et al.
1991, Bayrakli 1991). Calcium can decrease the effective pH
by precipitating carbonates and also by forming a complex
calcium salt with ammonium hydroxide which prevents ammonia
less to the atmosphere (Evangelou and Lumbanraja 1989). Actually,
calcium improves the uptake of nitrogen by plant roots, especially
when the plants are young (Fenn et al. 1993).
Gypsum Can Be A
Source Of Oxygen for Plants
The sulfate that is taken up by plants and
metabolized releases the associated oxygen which is a source
of oxygen to plant roots- although a limited source. Nitrate
nitrogen does the same except it is a larger source of oxygen
than is sulfate. Under adverse conditions, the oxygen coming
from sulfate can be important such as with root rot in avocado.
Gypsum helps
Earthworms to Flourish
A continuous supply of calcium with organics
is essential to earthworms that improve soil aeration, improve
soil aggregation, and mix the soil ( Sinnes 1979). Earthworms
can do the plowing for no- till agriculture.
Gypsum Can Increase Water Retention in
Soil
Gypsum when applied to sodic soil decreased
levels of exchangeable sodium resulting in a large increase
in water retention at a given tension compared with controls
(Tiwara et al. 1993). Dry matter and seed yield were increased
as a result.
Gypsum Can Increase Crop Yields
Gypsum for various combinations of the above
effects can substantially increase crop yields from 10 to
50 percent (Handbook 1985).
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