20). This observation suggests that the addition of gypsum for erosion-control and soil-stabilization purposes may be more effective during some phases of the soils' evolution compared to others. In this regard, the Australian Soil Health Knowledge Bank adds that, "Soil slaking or dispersion is evident in soils with a high content of fine sand and/or silt (loamy soil) and low organic matter levels, with crusting and hardsetting most common in soils with 10 to 35% clay" (Soil stability, 2011, para. 3). In addition, the crusting and hardsetting processes can in turn affect the infiltration rate that determines a soil's composition, and infiltration rates are highly affected by the concentrations of saline that exist near the surface (Cochrane et al., 2005). Although soils with high concentrations of saline may be responsive to gypsum applications, the gypsum will likely be required to be reapplied from time to time in order to remain effective (Soil stability, 2011). According to these authorities, "Gypsum (calcium sulfate) contains calcium which stops clay from dispersing when wet. Gypsum can be spread to manage surface soil problems, with more recent methods (injection into subsoils) used to counteract subsoil sodicity - often in combination with ripping" (Soil stability, 2011, para. 3). The effectiveness of gypsum in these applications, though, is only short-term and does not contribute significant improvements to the overall stability of soils that are not heavily salinated (Soil stability, 2011).

Some of the potential disadvantages of the application of gypsum for erosion-control purposes include the following:

1. Gypsum sold as an industrial by-product may contain heavy metals (cadmium) and other contaminants (fluoride).

2. Mined (lakebed) gypsum tends to have very little heavy metal impurity, but can contain substantial amounts of lime, sodium chloride, sand and/or clay.

3. Financial returns can be highly variable

4. Application of calcium may cause...

4).
Some companies have introduced gypsum formulations that are specifically designed to control both wind and water-based erosion that specifically take these foregoing strengths and constraints into account (Product roundup, 2007). For instance, United States Gypsum Company developed its Enviro-Shield product as "an innovative erosion defense system that prevents both water and wind erosion while promoting plant growth. Safe and non-toxic, the product is designed to be spray-applied in a variety of applications" (Product roundup, 2007, p. 68). This gypsum formulation is also applied using conventional hydraulic seeding equipment, making its use more economical and faster to install compared to erosion control blankets or sod (Product roundup, 2007). Moreover, the application of gypsum has even been shown to reduce erosion from overhead sprinkler systems (Cochrane et al., 2005). In sum, the research was consistent in shown that gypsum increases the sediment concentration for sandy and loamy types of soil under saline conditions in ways that help contribute to erosion control and soil integrity.