The effect of soil salinity and sodicity on soil erodibility, sediment transport and downstream water quality
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There is an abundance of literature on many aspects of soil salinity and sodicity, and the impact of increased salt and sodium on properties, behaviour, management and productivity of soils. However the impact of salinity and sodicity on erosion and soil erodibity has received little attention. The effects of runoff originating from saline lands and delivering soluble, sorbed, and suspended salts, ions, sediment and other chemical pollutants to low lying areas and water bodies, is also in need of further investigation. This project's aim is to investigate the effects of soil and water salinity and sodicity on soil erodibility and erosion rate as well as the off-site effects of runoff generated from saline/sodic lands. Changes in the saturated hydraulic conductivities and dispersion coefficients of three selected Queensland soils were studied under laboratory conditions. Results show that hydraulic conductivity remains high in non-expanding clay soils for all SAR values tested as long as the EC of leaching solutions remain high. Flushing the soil columns with distilled water resulted in rapid reduction in hydraulic conductivity. The main body of experiments has been carried out in the 1 x 6 m flume of Griffith University's large rainfall simulation facility (GUTSR). A bed of soil is put in the flume, levelled, saturated with water of known EC and SAR and rained on using town water after adjusting the flume to the required slope. Early results show that sediment concentration in runoff varies with ESP and the duration of rainfall event. Runoff sediment concentration was low under high salinity-low ESP condition, but increased as the salinity was reduced or ESP increased. This effect was more pronounced in the sandy loam and Vertisol than in Oxisol. Mean particle size of the eroded sediment also decreased with increasing ESP and reducing salinity. High ESP contributed to the weakening of soil aggregates and their dispersion under the raindrop impact. Further experiments have been planned to study the effects of soil salinity/sodicity and their interactions on soil erodibility and sediment transport. Surface water quality impact of runoff generated from saline/sodic soils is also being studied.
Proceedings of the13th International Soil Conservation Organisation Conference, 4-9th July, Brisbane, Qld., Australia, Eds. S.R. Raine, A.J.W. Biggs, N.W.