The quality of irrigation water can influence plant growth, the structure and condition of the soil and the effectiveness of water application through irrigation. For instance, bore water from a shale or quartz-based aquifer can have a low pH, which can lead to nutrient leaching and nutrient deficiencies. Bore water from a dolomite or limestone aquifer can have a high pH, plus high calcium or magnesium content which can clog up irrigation lines and sprinkler heads and reduce the water flow to your crop.
Water quality tests can help to identify any issues and allow the grower to manage their irrigation more effectively. Growers must match their nutrition to their water quality parameters, soil and leaf nutrient testing will provide appropriate recommendations for both water types.
A general physical and chemical analysis of water quality generally requires:
Although there is little published research to define the limits to water quality parameters for mango production, a general guide for salt content, pH, alkalinity and hardness of irrigation water is provided below.
Table 3. Primary irrigation water quality parameters (Adapted from WA AGRIC, 2019. Water salinity and plant irrigation).
Salts in irrigation water are mainly common salt (sodium chloride), calcium and magnesium bicarbonates, chlorides and sulphates. The salinity of water is usually estimated from its electrical conductivity (EC), which can be converted to total dissolved solids (TDS).
The EC does not identify the salts present but gives a fairly reliable indication of salinity problems.
EC is measured in milliSiemens per metre (mS m-1).
|<1000 mgL-1 TDS|
The test for pH measures the balance between positive hydrogen ions and negative hydroxyl ions.
This test indicates if water is alkaline (pH >7), neutral (7) or acid (<7).
Alkalinity is a measure of the total or hydroxyl ions. It is mainly caused by the presence of bicarbonates and carbonates in the water, and should not be confused with the measurement of pH.
It is measured as mg/L CaCO3 equivalent.
Hardness means the concentration of all the metallic cations in water. It is a measure of the dissolved calcium and magnesium salts and is expressed as mg/L CaCO3.
Over time, hard water can block hot water systems, metal pipes and irrigation fittings, and can reduce soil structure.
Water with less than 100 mgL-1 CaCO3 is generally regarded as suitable for most uses.
Suggested hardness limits are:
Read more Physical and chemical parameters of irrigation water can impact soil health and structure.
Farm water quality and treatment factsheet from NSW DPI.
Read more The pH level of water can accrue in the soil over time, changing the soil pH, and the nutrients available to the plant.
Read more about pH ranges and the effect on soil on the Queensland Government webpage.
The physical structure of soil can be altered by irrigation of water with high sodium content, causing the development of sodic soil. The three main problems caused by sodium-induced dispersion are:
Irrigation water in Carnarvon can contain moderate to high levels of boron (0.2 to 1 mgL-1). Water with a boron concentration over 0.5 mgL-1 is considered marginal for sensitive crops such as avocados, grapes and stone fruit, but no information is available for mangoes. Irrigation water high in boron can result in the accumulation of boron in the trees root zone. A symptom of boron toxicity in mangoes is a wavy burn pattern along the margins of older leaves starting at the leaf tip.
Water with high concentrations of calcium salts can calcify over time, blocking irrigation equipment including sprinkler heads, irrigation lines etc. This reduces the water flow through the system.
The efficacy of irrigation can be altered by water quality through the deterioration of irrigation infrastructure. Water with high concentrations of particles or solids will require filtration to ensure irrigation infrastructure does not block over time.