Amelioration of sodic soils is commonly achieved by applying gypsum, which increases soil hydraulic conductivity by altering soil chemistry. The magnitude of hydraulic conductivity increases expected in response to gypsum applications depends on soil properties including clay content, clay mineralogy, and bulk density.
The soil analyzed in this study was a kaolinite rich sodic clay soil from an irrigated area of the Lower Burdekin coastal floodplain in tropical North Queensland, Australia. The impact of gypsum amelioration was investigated by continuously leaching soil columns with a saturated gypsum solution, until the hydraulic conductivity and leachate chemistry stabilized. Extended leaching enabled the full impacts of electrolyte effects and cation exchange to be determined.
For the columns packed to 1.4 g/cm3, exchangeable sodium concentrations were reduced from 5.0 ± 0.5 mEq/100 g to 0.41 ± 0.06 mEq/100 g, exchangeable magnesium concentrations were reduced from 13.9 ± 0.3 mEq/100 g to 4.3 ± 2.12 mEq/100 g, and hydraulic conductivity increased to 0.15 ± 0.04 cm/d. For the columns packed to 1.3 g/cm3, exchangeable sodium concentrations were reduced from 5.0 ± 0.5 mEq/100 g to 0.51 ± 0.03 mEq/100 g, exchangeable magnesium concentrations were reduced from 13.9 ± 0.3 mEq/100 g to 0.55 ± 0.36 mEq/100 g, and hydraulic conductivity increased to 0.96 ± 0.53 cm/d.
The results of this study highlight that both sodium and magnesium need to be taken into account when determining the suitability of water quality for irrigation of sodic soils and that soil bulk density plays a major role in controlling the extent of reclamation that can be achieved using gypsum applications.
1University of Queensland, St. Lucia, Queensland, Australia.
2CRC for Irrigation Futures, St. Lucia, Queensland, Australia.
3Department of Environment and Resource Management, Queensland, Australia.
4CSIRO Water for a Healthy Country National Research Flagship and CRC for Irrigation Futures, PMB Aitkenvale, Queensland, Australia.
Address for correspondence: Lucy P. Reading, Department of Environment and Resource Management, GPO Box 2454, Brisbane, Queensland 4001, Australia. E-mail: firstname.lastname@example.org
Received March 27, 2011.
Accepted for publication November 4, 2011.
Financial Disclosures/Conflicts of Interest: This work was supported in part by the CRC for Irrigation Futures, the Queensland Department of Environment and Resource Management, the University of Queensland, and CSIRO Water for a Healthy Country National Research Flagship. The senior author acknowledges in particular the PhD scholarship provided by the CRC for Irrigation Futures.