A new index for sodicity risk assessment of irrigation water

Salinity and sodicity can cause major problems on golf courses. A better way to predict potential problems will lead to improved salt management.

Golf courses with poor quality irrigation water must worry about sodium accumulation in soil. Sodium adsorption ratio (SAR) is the primary criterion of estimating sodium hazard of irrigation waters. However, SAR has been shown to underestimate the risk of sodium hazard because it doesn’t account for calcite precipitation. There are a few adjusted SAR equations that attempt to correct for this, but they are either too complicated (and therefore not used by water testing labs) or overpredict sodium hazard of irrigation water. The purpose of the study was to propose a new sodicity index to provide a simpler and more accurate sodicity risk assessment of irrigation water on golf courses.

We analyzed eight irrigation waters and their drainage water from a lysimeter study in the greenhouse with a coarse-loamy soil. We periodically collected and analyzed rain water. Based on just sodium (Na), magnesium (Mg), calcium (Ca) and electrical conductivity (EC) of irrigation water, we are able to project two boundaries for each water — where all the calcium in the water precipitates (which increases the sodium hazard), and where none of the calcium in the water precipitates in soil. The upper boundary (worst-case scenario) is built using the following equation:

and the lower boundary (best-case scenario) is determined by:

(units in mmol/l, dS/m).

The results demonstrate that as the irrigation water concentrates in soil (caused by evapotranspiration) the drainage water was most often found between the two boundaries (LSAR and ESAR), and the drainage water tended to migrate to the upper limit as time went on. These results suggest that soil water composition is controlled by evapotranspiration and calcite precipitation after irrigation water is applied to soil. This method can provide a simple, accurate sodicity assessment of irrigation water, and it can help turf managers better understand when sodium management practices are required.


Qiyu Zhou, Doug Soldat, Ph.D. and William Bleam, Ph.D., University of Wisconsin–Madison. You may reach Doug Soldat at djsoldat@wisc.edu for more information.

Photo: Brian Whitlark

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