Water Quality Guidelines for Irrigation

The use of marginal quality waters impacts plant growth with the development of salinity, sodicity, and toxicity hazards. Thus, their suitability should be appropriately diagnosed before using as an irrigation source. Irrigation water quality standards and guidelines have been formulated periodically worldwide, especially in countries where saline water irrigation is more prevalent. However, in developed countries, such guidelines are more conservative, as the objective is to support only the environmentally safer irrigation of marginal waters. The guidelines in developing countries, where irrigation practices are usually unplanned and unregulated, further aim at enhancing livelihood opportunities. The FAO-1985 guidelines are the most prevalent. Considering the new water quality concepts, more realistic water quality guidelines later emerged where soil and factors were given due consideration. However, these remained more pertinent to regions of their emergence. Updated versions are now available which are based upon more diversified conditions of saline water use and are adjustable to for site-specific conditions. For rating both saline and alkali waters, these include the chemical composition of irrigation waters, soil type (texture, clay mineralogy), salt tolerance rating of crops, and rainfall for broader adaptability. As modified by soil texture and rainfall, crop salt tolerance is the decisive factor for fixing upper salinity limits in hyper-arid, arid, semi-arid, and semi-humid regions. The customized recommendations included conjunctive use, leaching/rainfall management, irrigation methods, ionic ratios, fertilizers, and manures. Guidelines for sodic/alkali waters are based on both crop responses and sodicity-induced water infiltration problems. The amendment requirements stand defined.