Water Quality Parameters
Irrigation water contains impurities in varying concentration. The suitability of irrigation water mainly depends up on the amount and type of salts present in the water. The main soluble constituents are calcium, magnesium, sodium as cations and chloride, sulphate, bicarbonates as anions. The other ions present in minute quantities are boron, selenium, molybdenum and fluorine which are harmful to animals fed on plants grown with excess of these ions. Quality of irrigation water is judged with three parameters
1. Total salt concentration
2. Sodium absorption
3. Bicarbonate and boron content.
1. Total Salt Concentration:
Salt content of irrigation water is measured as electrical conductivity (EC). Conventionally, water containing total dissolved salts to the extent of more than 1.5 m mhos / cm has been classified as saline. Saline waters are those which have sodium chloride as predominant salt. Brackish water is one that is contaminated with acid, bases, salts or organic matter, where as saline water contains mainly dissolved salts, Based on EC irrigation water is classified as below.
Soil for which suitable
1.5 to 3.0
Light and Medium Soils
3.0 to 5.0
Light and Medium Textured Soils for Semi tolerant crops
5.0 to 10.0
Light medium textured soils for Tolerant crops
2. Sodium absorption ratio (SAR) and boron content:
In addition to EC which has been used as a main criterion to determine the quality of irrigation water, sodium absorption ratio (SAR), residual sodium carbonate (RSC) and boron content are also used to find suitability of irrigation water.
Irrigation water which contains more than 3 ppm boron is harmful to crops, especially on light soils.