Water Quality in Agriculture

The Importance of Water Quality

The final evaluation of water quality is its effect on sustainable crop production. In fruit production, it is measured by the yield of quality fruit according to the demands of local and export markets. Water quality has a direct and indirect influence on fruit production.

Direct Effects

The direct effects of water quality include:

The concentration of salts dissolved in the water has a direct effect on the water available to the tree or any other crop. The higher the salt content, the more energy is required by the crop to utilise the water. Remember that dissolved fertilisers add to the salt content of the water.

• Magnesium (Mg) is a plant nutrient but can cause imbalances at high concentrations. A high concentration of magnesium interferes with the utilisation of potassium (K).
• The high pH of water is caused by bicarbonates. In water with low total dissolved solids, a little bicarbonate can cause a high pH. Too high pH reduces the availability of nutrients, especially the micro-nutrient elements.
• High concentrations of chlorides in water used for foliar sprays can cause scorching of the leaves.
• Although boron (B) is an essential nutrient element for plants, it is required in low concentration and can easily be over-supplied by water containing more than 1mg boron per litre.

Indirect Effects

The indirect effects of water quality include those factors that have a detrimental effect on soil properties, the efficacy of foliar sprays and blocking of the emitters (micro-sprayers and drippers).

• Sodium adsorption ratio (SAR) is a measurement of the potential hazard posed by the sodium in the water to the soil. Water with high sodium content will gradually reduce the stability of the soil structure. A stable structure of the soil is required to promote water penetration and root development.
• The efficiency of foliar sprays to supplement nutrients depends on the pH and buffer capacity of the water used to mix the chemical. The optimal pH for the uptake of nutrients from foliar sprays is 5 to 6.
• The half-life of some insecticides and pesticides depends on the pH of the water used in the spray solution.
• Blocked emitters will discharge less water than intended or none at all. The distribution of the water will also not be optimal. Therefore, some trees will receive too little water and production will be reduced.

Half-Life: The half-life of a chemical is the time taken for it to lose half its strength or the period of time that must elapse for an agro-chemical to lose half of its original toxicity.