A New Index for Sodicity Risk Assessment of Irrigation Water.

Pressure on potable water resources is rising, and golf courses and other turfgrass areas are increasingly choosing or being required to use low quality water for irrigation. Salinity and sodicity risk are two major problems associated with poor quality water. Salinity risk is caused by elevated salts in irrigation water which reduce plant water uptake. Sodicity risk is caused by irrigation water with low salinity but high sodium concentrations whereby the soil clays become dispersed and drainage is reduced. It is fairly well established that salinity risk increases with evaporative concentration in the soil. However, sodicity risk may also be affected by this process as evaporative concentration of soil water can lead to calcium precipitation, thus increasing the percentage of sodium on cation exchange sites. Existing methods attempt to estimate the evaporation-adjusted SAR (Sodium Adsorption Ration) to account for calcite precipitation; however, these indexes are either unreliable or unnecessarily complex. Irrigation water sources differ substantially in their sodicity potential and their latent sodicity risk only becomes apparent at moderate to high salinity. Therefore, rather than seeking an accurate adjusted SAR estimate, which unavoidably requires very complex calculations, the proposed sodicity index projects SAR models as a result of calcium carbonates precipitation and evaporation water loss from irrigation water. The new approach sets upper and lower boundaries on the SAR range as evaporation increases salinity to derive a simple method designed to identify the potential risk of water. This new sodicity index is utilizes irrigation water chemistry and soil alkalinity release during irrigation as soil minerals weather. It has important implications for the management of turfgrass areas using low quality irrigation water.