Location: Water Quality and Ecology Research
Title: Erodibility of a sodic soil amended with FGD gypsum Author
Submitted to: Soil Science
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: January 24, 2011
Publication Date: N/A
Interpretive Summary: Soils with high sodium contents (sodic soils) occur extensively in the lower Mississippi River Valley states of Arkansas, Louisiana, Mississippi, and Tennessee where they create management problems due to their high erodibility and dispersive nature, and salt toxicities that restrict plant growth. The historical approach to the remediation of such problem soils is through the use of a high calcium content material, such as mined gypsum from the western U.S., to leach excess sodium from the plowlayer. The use of mined gypsum is too costly to use on large acreages. Instead, a synthetic material, fluidized gas desulfurized (FGD) gypsum produced by coal-fired power plants was evaluated as a replacement. We amended a sodic soil from Mississippi with FGD gypsum at rates of 0, 1.5, 3.0, and 6.0 tons/acre, and then applied simulated rainfall to determine the ability of synthetic gypsum to reduce dispersion rates and erodibility. The data show that the addition of FGD gypsum, at rates as low as 1.5 tons/acre, will substantially increase the stability of the surface soil and infiltration rates which result in lower surface runoff and erosion losses. We conclude that FGD gypsum is at least as effective as mined gypsum for sodium-affected, dispersive soils.
Technical Abstract: Soils with high sodium concentrations are a serious management problem in the coastal plain regions of the lower Mississippi River valley due to salt toxicity and their dispersive nature. The primary method of remediation of sodic soils in arid regions is naturally occurring gypsum, however, due to its relatively high cost this material is not considered a primary amendment in the southeastern region. The use of FGD gypsum, produced by coal-fired power plants, is potentially a more cost effective alternative for managing the dispersive characteristics of these soils. This study was conducted to determine the effectiveness of FGD gypsum at reducing the erodibility and dispersive nature of sodic soils. The fine earth fraction (< 2mm) of samples collected from the A-horizon of a sodic soil was characterized for a range of basic physical and chemical properties. Additional sub-samples (< 8 mm) were amended with FGD gypsum at rates equivalent to 0, 3.36, 6.72, and 13.44 Mg ha-1, packed to a depth of 7.6 cm in plexiglass cylinders, and subjected to simulated rainfall at an intensity of 64 mm h-1 for 1 h. The erodibility data indicated that as the FGD gypsum rates were increased above the 0 Mg ha-1 treatment level, significant (P < 0.05) increases were recorded for all aggregation/dispersion parameters (% aggregation, aggregation index, % transmission). These improvements in soil structural stability, attributed to Ca displacement of Na, produced a 71% increase in total infiltration, a 36% decrease in total runoff, and a 77% decrease in soil loss at the 13.44 Mg ha-1 rate relative to the 0 treatment. Sediment size distributions between 53 and 500µm increased an average of 38%, and the fractions < 5 µm decreased by 21%. The results indicate that FGD gypsum can be used effectively to remediate sodic soils, and that statistically significant improvements can be expected in the form of increased infiltration, and lower runoff and soil loss rates. The gypsum-induced increases in the larger sediment size distributions indicate that the quality of surface waters as the proportion of finer sediment in the runoff is diminished.