Gypsum Improves Soil Structure

Gypsum provides calcium which is needed to flocculate clays in acid and alkaline soil. Gypsum is a good source of soluble Ca and can improve soil physical properties by promoting aggregation, especially in high clay soils. Surface-applied gypsum increases the electrolyte concentration of infiltrating water and compresses the electric double layer around clay particles. It also provides Ca2+ to the soil exchange complex where it has selectivity over more dispersive Mg2+ and Na+. 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

Where the exchangeable sodium percentage (ESP) of sodic soils is high, it must be decreased for soil improvement and better crop growth. Sodic soils, also known as very poor agricultural soils. The presence of excessive Na ions adversely affects soil structure and disturbs the availability of some nutrients in the soil for plants. Gypsum is by far the most commonly used form, it is widely available, and it is moderately soluble, which allows available Ca to be released over time in sufficient solubilized quantities to displace Na on the CEC sites. The Ca ions present in gypsum can exchange with Na ions on clay particles and reduce the dispersion of soil particles by promoting clay particles to bind together.  The sodium can then be leached from the soil as sodium sulfate to an appropriate sink. In sodic soils without using gypsum, the soil would not be leachable.

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 crusting is dependent on soil moisture content and, due to the potential for gypsum treatment to slow the rate of surface drying, the crust development rate and final strength will be affected. Surface crust strength effects have often been reported in terms of marked improvements in plant emergence and establishment, and reductions in penetration resistance. 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.

Gypsum Decreased pH of Sodic Soils

Gypsum immediately decreases the pH of sodic soils or near sodic soils from values often over 9 but usually over 8 to values of from 7.5 to 7.8. These values are in the range of acceptability for growth of most crop plants. Application of gypsum to sodium-affected soils in the pH range from 8.3 to 10 raises soluble Ca2+ and lead to the precipitation of calcite with release of protons (H+):

In this condition the soil pH then drops into the range of 7.5 to 8.

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

Gypsum Improves Compacted Soil

Gypsum can help break up compacted soil and decrease penetrometer resistance. 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 decreased Water Runoff and Erosion

Gypsum improves water infiltration rates into soils and also the hydraulic conductivity of the soil. It is protection against excess water runoff from especially large storms that are accompanied with erosion. Also gypsum reduced surface sealing and increased infiltration and improving internal soil drainage is attributed to its ability to release electrolytes that enhance aggregation of soil clay particles in both sodic and non-sodic soils.

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, improved hydraulic conductivity of soil, better water storage in the soil all lead to deeper rooting and better water-use efficiency. Gypsum had a significant effect on soil water retention curve (WRC). Gypsum made WRC with higher water retention at near saturation conditions. Thus plant available water is increased using gypsum.

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. This is accompanied with greater ease of tillage and more effective seedbed preparation and weed control. Less energy is needed for the tillage.

Gypsum Makes it Possible to Efficiently Use Low Quality Irrigation Water

Shortage of fresh water is becoming a main constraint to irrigated agriculture thought the world. In the past years, over exploitation of ground water for agricultural irrigation is leads to declining in ground water level, increasing soil salinity and decreasing water quantity. However, continuous irrigation with saline water often leads to adverse effects on crop growth, because salts may gradually accumulate in the rootzone, resulting in soil salinization. Also under salinity stress, salty ions (e.g. Na+ and Cl) may accumulate in plant tissues and finally induce ion toxicity and imbalance in cells, further restricting crop growth. Application of gypsum is an efficient agricultural practice used to reduce salt stress and improve crop growth in salt-affected areas.

The effective sodium adsorption ratio (SAR) of irrigation water should be less than 6 for most of the crops. When it exceeds these limits, gypsum should be applied to the soil or 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.

Gypsum Decreased wind Erosion

Use of gypsum can used as mulch for decreasing the wind and water erosion of soil. Mulching is known as a common traditional practice for stabilization the soils. Among the most practical mulches including vegetative residues, biological geotextiles, gravels etc., oil mulch is discarded due to risky environmental impacts. Recently, the application of naturally accessible materials as affordable mulches has attracted more attention. These materials including clay, gypsum and others with cementitious properties are very important in arid and semiarid areas due to the abundance of natural resources. Gypsum as a soil amendment containing calcium is very important in improvement of soil physical properties and the enhancement of the stable particles.  It adheres the soil particles and protects them against degradation by wind erosive forces. Increasing the soil mechanical resistance and decreasing the erodibility of soil particles requires the use of stabilizers with cementitious properties.

Gypsum Corrects Subsoil Acidity

Because of the high mobility of gypsum dissolution products, gypsum is often superior to limestone-based materials with regard to alleviating subsoil acidity issues. This would be especially important in no-till systems where liming material cannot be incorporated. In addition, since the solubility of lime is reduced at neutral soil pH, a neutral surface soil overlying an acid subsoil is unlikely to be alleviated through application of lime. In contrast, gypsum solubility is less influenced by pH. Although the gypsum dissolution products cannot directly neutralize acidity as carbonate does, it can alleviate Al toxicity by shifting soluble Al to less toxic forms and decrease Al activity. Decreased subsoil acidity has potential for improving root growth and increasing water and nitrogen use efficiency. In contrast, Ca2+ added to soils through gypsum applications is more mobile because sulfate is a relatively mobile anion. According to some studies, gypsum applied to the surface of an acid soils allowed deeper penetration of Ca2+ than applied CaCO3.

Gypsum as Source of Plant Nutrients

Gypsum has been applied to agricultural soils for more than 250 years in those crops which have high Ca requirements, or to areas that have Ca poor soils since it is an excellent source of soluble Ca and S. Root and field crops such as peanut, potato, tomato, corn, wheat, etc. seem to especially respond to Ca, and application of gypsum can improve both yield and quality of products. Similarly, S fertilization is required for many crops, such as alfalfa, soybean, canola, etc., and application of gypsum can be an effective source of S.  In general, crops grown on soil with low organic matter and coarse-textured can respond to S application. In addition to Ca and S, gypsum also provides some essential micronutrients to plants.

Gypsum Improving Nutrient Availability

The application of gypsum in soils, increases the sorption activity of Ca2+ and (SO42–) by plants, and results in improvement of nitrogen (N) uptake. This may reduce the need to apply more N to the plants, as well as diminish the potential for nitrate (NO3) contamination of surface and ground waters. Some researchers conducted field experiments to study the interaction effects of N and S fertilization on corn growth and yield. They found that application of gypsum (33 kg S ha–1) with N (0-233 kg N ha–1) promoted corn growth and uptake of N.

Gypsum Reducing Soil and Nutrient Loss

Soil-applied gypsum releases electrolytes that prevent soil surface sealing, thereby preventing a leading cause of soil erosion. It increases ionic strength and Ca2+ concentration in the soil solution. Thus, adsorption of phosphate (PO43–) becomes stronger, and it reduces the dispersion of soil particles by promoting flocculation and aggregation of clay particles. Converting readily soluble reactive P into insoluble Ca phosphate complex, gypsum can reduce nutrient runoff, mainly P, into receiving adjacent streams, lakes or groundwater. Some studies reported that gypsum application reduced water runoff by 17%, soil loss by 60% and P losses by 67% when compared to the control.

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 with is part of gypsum. Calcium decreases burn out of soil organic matter when soils are cultivated by bridging the organic matter to clay. Gypsum is a source of calcium which is a major mechanism that binds soil organic matter to clay in soil which gives stability to soil aggregates. The value of organic matter applied to soil is increased when it is applied with gypsum.

Gypsum Improves Low-Solute Irrigation Water

Gypsum is used to increase the solute concentration of low-solute water used for irrigation. Irrigation water from rivers that no longer have sources of leachable salts wither 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 Fruit Quality and Prevents Some Plant Diseases

Calcium is nearly always only marginally sufficient and often deficient in developing fruits. Good fruit quality requires an 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, calcium is not available enough; therefore, gypsum helps to provide Ca2+ for plant. Gypsum is used for peanuts, which develop below ground, to keep them disease free. Gypsum helps prevent blossom-end root of watermelon and tomatoes and bitter pit in apples. Gypsum is preferred over lime for potatoes grown in acid soils so that scab may be controlled. Root rot of avocado trees caused by Phytophthora is partially corrected by gypsum and organics.

Gypsum Can Increase Crop Yields

Photosynthesis rate is significantly influenced and increased by gypsum application under irrigation with saline water compared to the control. Application of compost combined with gypsum increases ChlorophylI when saline water uses for irrigation. Gypsum increases plant biomass and plant height as a result of increased plant photosynthesis.

Gypsum Makes Excess Magnesium Non-Toxic

In soils having unfavorable calcium: magnesium ratios, such as serpentine soils, gypsum can create a more favorable ratio.

Gypsum Decrease Bulk Density of Soil

Gypsum-treated soil has a lower bulk density compared with untreated soil. Gypsum increase water stable aggregates, and the volume of soil pores. For these reason it decrease the soil bulk density.   The softer soil is easier to till, and crops like it better.

Gypsum Improves Swelling Clays

Gypsum can decrease the swelling and cracking associated with high levels of exchangeable sodium on the montmorillonite-type clays. As sodium is replaced by calcium on these 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. Improvements of infiltration rate and hydraulic conductivity with use of gypsum add to the ability of soils to have adequate drainage.

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. 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 Helps Prepare Soul for No-Till Management

A liberal application of gypsum is a good procedure for starting a piece of land into no-till soil 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.

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 the sulfate can be important such as with root rot in avocado.