Over recent years there has been a major drive for the turf industry to become less reliant on potable (drinking) water for irrigation and to use alternative water sources (often of lower quality) such as recycled and bore water.
Recycled water can contain salts, harmful concentrations of Sodium, Chloride and Bicarbonate as well as nutrients and other contaminants. Its quality will vary depending on the source (eg. sewage treatment plants, stormwater run-off, industry wastewater etc.) and often on the time of year (seasonal fluctuations). Bore water can contain salts and high levels of sodium and iron.
Irrigation water quality can impact various aspects of turf management, including turf vigour, soil structure, fertiliser requirements, and irrigation scheduling. Therefore, it is essential that comprehensive testing is routinely undertaken to determine the water’s suitability and to understand any management implications for its use.
Some of the important test parameters include:
Salinity: Salinity is measured as Electrical Conductivity (EC) which is directly related to the concentration of Total Soluble Salts (TSS).
Salinity is the most common problem with using alternate water sources and has both direct and indirect effects on turf growth. Growth can be directly affected through foliar damage due to sodium and chloride phytotoxicity. The long-term use of saline water can result in a build-up of soluble salts in the rootzone which can adversely affect growth by the osmotic inhibition of water uptake (physiological drought).
When high salinity water is the main or only source of water available, various management practices can assist, including deep irrigation beyond the rootzone, not allowing the soil to dry out excessively, maintaining adequate drainage through the profile (surface & subsurface aeration) and irrigating with good quality water whenever possible to aid leaching.
Sodium: The Sodium Adsorption Ratio (SAR) is the ratio of Sodium ions to Calcium and Magnesium ions and indicates the potential sodic effects that the water may have on soil structure primarily in fine textured soils.
Irrigating with water high in Sodium can lead to soil structural problems including the formation of a hard-impermeable surface crusts, reduced soil permeability, aeration & root penetration and poor soil workability. Sodium can also have a direct toxic effect on the plant as it is readily available for uptake.
High Sodium levels in the soil may be managed by using calcium amendments (eg. gypsum, lime etc.) which displace the sodium ions causing the soil particles to aggregate thereby improving soil structure. Calcium can also be applied through the irrigation system as a liquid alternative on a more frequent basis.
Bicarbonate & Carbonate: The sodium hazard can be increased if the water contains a significant concentration of Bicarbonate and Carbonate ions. These ions combine with Calcium and Magnesium and cause them to precipitate out as insoluble carbonates (Calcium Carbonate or Magnesium Carbonate). This has the effect of increasing the relative proportion of Sodium to other cations and therefore increasing the SAR. The effects of Bicarbonate and Carbonate in water are measured by the Residual Sodium Carbonate (RSC) or the adjusted SAR.
Bicarbonate is considered the more important of these two ions as Carbonate is generally not found in water with a pH below 8.3. High levels of Bicarbonate in irrigation water can also increase the soil pH over time.
The effectiveness of Gypsum applications is reduced when using water high in Bicarbonates. High Bicarbonate water can be treated by acidification and there are several systems available in Australia which injects acid directly into the irrigation system. The acid breaks down the Bicarbonate and releases soluble Calcium (and Magnesium) back into the soil solution so they can assist with displacing Sodium from the soil.
Chloride: Chloride not only contributes to the salinity of the water but is directly toxic to plants. Irrigating with water high in Chloride can result in leaf burn especially under hot windy conditions. Like Sodium, Chloride is taken up by plant roots and translocated to the leaves where it accumulates, and this can lead to leaf scorch and in extreme cases leaf kill.
pH: The pH of water is seldom directly detrimental to turf growth and is often a good indicator of more harmful constituents such as Bicarbonate and Carbonate. Depending on the soil’s buffering capacity and volume of water used, the pH of the soil can adopt the pH of the water and may become more acid or alkaline over time and this can restrict nutrient availability.
Pesticide instability (chemical breakdown) can be a problem with high pH water and lead to poor pest control. The use of better-quality water (eg. town water) or adding a buffer to the spray mix is recommended in this situation.
Nitrogen & Phosphorus: Treated effluent can be high in Nitrogen and Phosphorus (as well as Potassium). Fertiliser programs need to be adjusted when irrigating with water high in Nitrogen as excessive Nitrogen applications will produce a weak, thatchy turf susceptible to disease and wear.
Irrigation management needs to be precise when using water high in Nitrogen and Phosphorus as over watering can result in run-off and leaching of these dissolved nutrients into surface and ground water respectively. This can result in the eutrophication of water bodies (proliferation of aquatic plants such as algal blooms and decreased water clarity).
Iron, Sulphur & Water Hardness: The blocking of irrigation pipes and sprinkler nozzles with Iron sediment can occur when using water containing high levels of Iron (eg. bore water). Reddish brown deposits of Iron Oxide may also be visible on plant leaves and in extreme cases photosynthesis can be reduced. Water high in Iron will also stain and discolour wetted surfaces such as concrete cart paths.
High levels of Sulphur in water tend to be more of an inconvenience causing metal corrosion rather than any turf related problems. However, the application of large volumes of water high in Sulphur can lower the pH of the soil over time.
Water Hardness is dependent on the concentration of Calcium and Magnesium in water and the greater their concentration the harder the water. Irrigating with very or extremely hard water can result in the formation of scale (deposits of Calcium and Magnesium carbonate) in pipes and nozzles of the irrigation system. Hard water may also cause problems with mixing certain pesticide formulations.
Using Low Quality Water
It is highly likely that following testing of your irrigation water, some of the chemical constituents will fall outside the ideal range for use. With careful management, lower quality water can generally be used to irrigate turf areas in all but the extreme cases (for example an excessively high salinity or an extreme Sodium hazard etc.)
Various strategies can assist with minimizing the negative effects of using low quality water;
- Blending (diluting) with good quality water
- Alternating irrigations with better quality water
- Regular surface and subsurface aeration to improve soil drainage
- Frequent heavy irrigations to flush the rootzone of harmful salts (leaching)
- Using soil penetrants to aid leaching
- Avoiding irrigating during the daytime when evaporation is high
- Applying Gypsum to assist in reducing the Sodium hazard (often only a temporary fix)
- Installing water treatment systems (acid & calcium injection, nano filtration systems etc.) for long term improvement of water quality
- Regular soil testing to monitor salt, Sodium levels etc.
- Using more tolerant turfgrass species and varieties
Regular testing of your irrigation water during the season is essential as its quality may vary. You may need to carry out a comprehensive analysis several times during the season and the general rule is that the poorer the water quality the more frequent the testing required. Regular testing of pH and salinity is also recommended to warn you of any deviations from the norm which could indicate a major change in quality.
STRI Australia offers irrigation suitability testing as well as microbiological testing and algal scans. Contact us on 03 9558 6514 or email us at info@striaustralia.com.au.
