Irrigation Water Quality Sampling Guide Burdette Barker, Utah State University (USU) Extension Irrigation Specialist Matt Yost, USU Extension Agroclimate Specialist Erin Rivers, USU Extension Water Quality Specialist Rhonda Miller, USU Extension Agricultural Environmental Quality Specialist Kalen Taylor, USU Extension Assistant Professor, Millard County Tiffany Evans, USU Analytical Laboratories Manager
Why Sample?
The suitability of a water source for irrigation depends on the water quality, and some sources may be altogether unsuitable for practical use. Additional considerations include the plant species being irrigated, the end use of the plants, the irrigation system type, the texture and chemical quality of the soil, and the quantity of precipitation. Some water may require treatment or special management before using it for irrigation. Assessing irrigation water quality includes testing for chemical and biological constituents, which begins with proper water sampling.
What to Sample/Test? Salinity
In Utah, the most common concerns for irrigation water quality relate to salinity. Excessive salt concentrations from irrigation water can build up in the soil and impair the ability of plants to extract water. Excessive salt can also be toxic to plants when in the soil or on plant leaves (Hoffman & Shalhevet, 2007). The total salt concentration is measured in terms of electrical conductivity (EC) because salts are electrolytes (they conduct electricity when dissolved in water). There are many kinds of salt ions in the soil, and EC does not differentiate among these. In some cases, salt accumulation can be managed by leaching by applying additional irrigation water. Most samples of irrigation water processed by the Utah State University Analytical Laboratories (USUAL) in the past several years have had relatively low EC (2 dS/m or less), though some have been 20 dS/m or greater (Figure 1).
Sodium
Excessive sodium in relation to other positive ions can reduce water infiltration into the soil. This is measured using the sodium adsorption ratio (SAR), which is the ratio of sodium relative to calcium and magnesium. The impact of sodium on water infiltration also depends upon irrigation water EC and pH (Suarez, 2012). Most of 1 of 11