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United States Department of Agriculture

Agricultural Research Service

Title: Occurrence and Measurement of Salinity Stratification in the Shallow Ground Water in the Murrumbidgee Irrigation Area, South Eastern Australia.

Authors
item Northey, Jessica - CSIRO
item Christen, Evan - CSIRO
item Ayars, James
item Jankowski, J - UNIV OF SYDNEY, AUSTRALIA

Submitted to: Agricultural Water Management
Publication Type: Trade Journal
Publication Acceptance Date: June 28, 2005
Publication Date: August 15, 2005
Citation: Northey, J., Christen, E., Ayars, J.E., Jankowski, J. 2005. Occurrence and measurement of salinity stratification in the shallow ground water in the murrumbidgee irrigation area, south eastern Australia. Agricultural Water Management, Vol 81 (2006) 23-40.

Interpretive Summary: Capillary upflow from shallow saline ground water is a significant contributor of soil salinisation in irrigated areas and is highly dependent on the water table depth and ground water salinity. Lysimeters have traditionally been used to quantify capillary upflow from shallow water tables and the potential salinisation risk. However, water table depth and salinity generally remain constant in lysimeters, while short-term variations in these parameters exist under surface irrigated agriculture. Consequently, the extrapolation of calculated crop water uptake and potential soil salinisation from lysimeters to field conditions may be misleading. A multilevel sampler was designed and used to collect depth specific water samples to investigate changes in the height and salinity of a shallow fluctuating water table under furrow irrigated areas in the Murrumbidgee Irrigation Area, in south-western New South Wales, Australia. The water table was within 2m of the ground surface at all sites. Salinity stratification was found to exist within the shallow ground water with low salinity irrigation water overlying the more saline groundwater with a zone of variable salinity extending to 2.5m. Short-term variations in the depth and salinity of shallow water tables under field conditions would affect capillary upflow and salt movement into the root zone. These parameters should therefore be measured at the field scale where possible, to obtain accurate measurements of crop water uptake and potential soil salinisation. The stratification has implications with regard to the potential for in-situ use of water by crops that can't be explained when bulk ground water samples are taken. There is the potential for higher use than would be expected because of the lower average EC in the region just below the water table.

Technical Abstract: Capillary upflow from shallow saline ground water is a significant contributor of soil salinisation in irrigated areas and is highly dependent on the water table depth and ground water salinity. A multilevel sampler was designed to collect depth specific water samples to investigate changes in the height and salinity of a shallow fluctuating water table under furrow irrigated areas. Water samples were taken from the top of the shallow ground water as it rose and fell following irrigation events at three farms in the Murrumbidgee Irrigation Area, in south-western New South Wales, Australia. The water table was within 2m of the ground surface at all sites. Salinity stratification was found to exist within the shallow ground water with low salinity irrigation water overlying the more saline groundwater with a zone of variable salinity extending to 2.5m. The salinity generally increased with depth. In addition to changes in groundwater salinity with depth, fluctuations in salinity occurred at individual depths over the irrigation season. The salinity of the top of the shallow groundwater also varied with changes in water table depth. Following an irrigation event, the rise in water table height was associated with a decrease in the salinity at the top of the ground water and a water table decline corresponded to an increase in salinity in the upper layers of the ground water. The water table position is an important determinant of salinity risk since this is the foundation for capillary upflow. Consequently, short-term variations in the depth and salinity of shallow water tables under field conditions would affect capillary upflow and salt movement into the root zone. These parameters should therefore be measured at the field scale where possible, to obtain accurate measurements of crop water uptake and potential soil salinisation.

Last Modified: 10/20/2014
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