Using Saline Groundwater in the Shepparton Irrigation Region
Note Number: GW0027
Published: November 2002.
Reviewed: May 2008
Introduction
In the Shepparton Irrigation Region, groundwater is pumped to reduce soil salinity and lower watertables. Groundwater is also seen as a valuable water resource used to supplement channel water supplies for irrigation. In addition groundwater is used for stock drinking water and dairy wash-down in the winter months when fresh water supplies are low.
Due to the varying quality of groundwater found in the Region and the problems associated with using saline water, the challenge becomes how to match the quality of groundwater with a suitable end-use. Users of groundwater need to consider the long-term impacts on pasture productivity, soil structure, animal health, as well as dairy and irrigation equipment.
This Groundwater Note deals specifically with salty groundwater and the potential problems arising from its use.
Saline groundwater
Salinity is defined as the total concentration of salts dissolved in water or soil. The salt content is determined by the water’s ability to conduct an electric current, referred to as electrical conductivity (EC). The higher the salt concentration, the larger the current that can be conducted and the higher the EC of the water.
Electrical conductivity is measured in microsiemens per centimeter (µS/cm) or more commonly EC units. One thousand µS/cm is equivalent to 640 parts per million (ppm) or 1 decisiemens per meter (dS/m) ie 1000 EC units = 640 ppm = 1 (dS/m)Effect on pasture
When saline water is used as an irrigation source, soil salinity problems can develop as salts accumulate in the root zone of the pasture. Excessive accumulation of salts limits a pasture’s ability to extract enough water from the soil, resulting in water stress.
Reduced water uptake by the pasture can result in slow or reduced growth and a wilting appearance even though soil moisture content may be high. Each species of pasture has its own salinity tolerance.
A maximum salinity of 800 EC is recommended in the Shepparton Irrigation Region for irrigation of white clover/ryegrass pastures on a Lemnos loam. Studies carried out at the Institute of Sustainable Irrigated Agriculture, NRE Tatura and on several farm trials show pasture irrigated with 1 700 EC will result in a 15% productivity decrease.
Saline groundwater may also have a toxic effect on pasture. Sodium and chloride, the main salts in groundwater are absorbed by plants and accumulate in the leaves. This may result in reduced plant growth and yields.
High concentrations of sodium and chloride may also interfere with a pasture’s ability to uptake nutrients such as potassium, magnesium, nitrogen or phosphorus, all of which are essential for healthy growth.
Effect on cattle
Saline groundwater is frequently provided to cattle for drinking water. Tolerance to saline groundwater depends on the age and physical condition of the cow, as well as feed composition and climate.
Mature cows in good condition exhibit a greater tolerance to saline drinking water than calves and pregnant or lactating cows.
Hot dry conditions can affect the quality of groundwater supplied for drinking water. High evaporation from troughs results in salts becoming concentrated and water temperature increasing. As a result, stock may require larger quantities of water and have a lower tolerance to salty water.
Saline water can reduce milk production and animal condition and health. In general, dry dairy and beef cattle can tolerate saline water up to 11 000 EC if introduced slowly to the water source. For pregnant or lactating cattle, drinking water should be kept below 5 000 EC.
Effect on irrigation and dairy equipment
Salinity may be used as a general indicator of the corrosive potential of groundwater. Waters with high EC are likely to be more corrosive than lower salinity waters, however pH, hardness, dissolved oxygen and carbon dioxide levels also influence the corrosive nature of groundwater. Care should therefore be taken when using saline water in dairy wash down and cooling of plates to prevent corrosion of equipment. Consultation with the equipmentmanufacturers is recommended to determine the most appropriate water quality.
Determining the effects of saline groundwater on pasture productivity
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| Figure 1: Estimated soil salinities (µS/m) resulting from irrigating different soil types in the SIR with a range of irrigation water salinities. Efsl - East shepparton fine sandy loam, Sfsl – Shepparton fine sandy loam, Ll – Lemnos loam, Gl – Goulburn loam, Gcl – Goulburn clay loam (Noble, 1987). |
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| Figure 2: The effect of soil salinity (µS/m) on the growth of pasture species commonly grown in the SIR. LUC = lucerne, WC = white clover, SUB = sub-clover, WC+SC = white and strawberry clover, AP = annual pasture, PP-WC = perennial pasture (white clover based), PP-WC+SC = perennial pasture (white and strawberry clover based) (Noble, 1987). |
The effects of irrigating pasture with saline water are dependent on a number of site specific factors such as soil and pasture type, drainage, climate as well the resulting salinity of the soil. Here, soil salinity is expressed as ECse, the EC of an extract from a saturated soil.
A simple way of estimating the effects of saline water on productivity is to first calculate the expected soil salinity (Figure 1). For example, irrigation of an East Shepparton fine sandy loam (Efsl) with 1 700 EC will result in a soil salinity of approximately 2 100 EC within 3 to 4 years ofirrigation.
On a heavier soil type such as a Goulburn clay loam (Gcl), salt concentrates more rapidly within the soil profile resulting in a soil salinity of 3 800 EC in the example provided. Having a watertable less than 2 m from the soil surface will result in slightly higher soil salinity.
The impact of soil salinity on pasture productivity is determined by referring to Figure 2. Using the previous example 2 100 EC, relative yield equals 74 % for white clover (WC), ie. a 26% decline in yield. Similarly, on a Gcl with soil salinity of 3 800 EC there is little or no white clover growth and a 20 % decrease in a white and strawberry clover based perennial pasture (PP-WC+SE).
Using water for irrigation at 800 EC (the recommended maximum salinity for irrigation waters), will result in little or no decline in pasture productivity on a Lemnos loam. However, on a Gcl soil a 24 % decline in WC production and a 5 per cent decline in PP-WC+SE production can be expected.
When determining the impact of saline irrigation on pasture productivity, it is important to consider the type of soil and pasture being irrigated. Visual inspection of pasture or soil is unlikely to show a decline in productivity. Therefore, it is recommended a complete soil and pasture analysis is undertaken by a reputable consultant to determine the most appropriate management strategy for your property. For more information contact Terry Batey, Groundwater Extension Officer, NRE Tatura. Phone: 5833 5222
References
Noble, C (1987), Plant salt tolerance and water use in relation to accessions and groundwater use in the SIR. Working paper for the Shepparton Irrigation Region Land and Water Salinity Management Plan.
Acknowledgements
This Information Note was developed by Terry Batey, Tatura
Thanks to the Natural Heritage Trust, Goulburn Broken Catchment Management Authority and the Department of Natural Resources and Environment for providing funding for this project.
