The application of gypsum to sodic soils is a commonly used agricultural practice to improve soil structure and water infiltration rates. The gypsum provides a major source of calcium, which replaces exchangeable sodium present in soils, and consequently minimises dispersive and swelling effects in sodic soils. Of all amendments, gypsum is the most widely used because of its availability and low cost. Sources of gypsum include mined deposits as well as nongeologic sources, which stem from industrial processes producing gypsum as a byproduct. An attractive source is Flue Gas Desulphurisation (FGD) gypsum, produced as a byproduct from coal fired power stations.
The current investigation is part of a wider project to demonstrate the feasibility of establishing carbon sinks using FGD gypsum produced from Japanese power stations. It aimed to determine the effect of various mined and industrial gypsum sources (in particular FGD) on sodic soils.
Experiments investigating the dissolution of gypsum with and without the presence of soil were conducted using gypsum powder placed in a 50 ml centrifuge tube with dam water. In addition a permeameter device was constructed in which the hydraulic conductivity of a sodic soil before and after gypsum addition was analysed.
Major findings from this work are:
· A mined gypsum source from Queensland and FGD gypsum from Japan both displayed higher rates of dissolution than other sources
· All gypsum sources were found to improve the hydraulic conductivity, however the hydraulic conductivity appeared to decrease over time
· The industrial FGD gypsum was not as effective in improving the hydraulic conductivity as the mined gypsum
It appears that the use of FGD gypsum does have advantages in the short term improvement of sodic soil, however additional experiments are required to be run for a longer period of time to determine the longer term benefits of FGD.