Soil Salinity Assessment by Electro-Magnetic Induction in Irrigated Turf Field.

Increasingly marginal quality saline waters are being used to irrigate turf and golf courses in the southwest U.S. Long-term irrigation with saline water can lead to serious soil salinity problems. Appraisal of salinity and sodicity distribution in turf field soils is the necessary first step for developing appropriate salinity management practices. Traditional method of determining saturated paste extract electrical conductivity (EC_e) to measure salinity and sodium adsorption ratio (SAR) to measure sodicity distribution within a field at a high resolution is labor intensive, time consuming and expensive. Electromagnetic induction (EMI) method of measuring apparent electrical conductivity (EC_a) can be an effective alternative to wet chemistry methods to delineate salinity/sodicity distribution within the affected area. This study evaluated the effects of two years of saline water irrigation using drip and sprinkler systems on soil salinity and sodicity by EMI technique in a turf field. Simple correlation analyses between EC_a and select soil properties suggested that EC_a was significantly positively influenced by soil clay content. Calibration equations to convert EC_a values to EC_e and SAR were derived using multiple linear regression (MLR) model included in the ESAP program developed by US Salinity Laboratory. R²s for MLRs to estimate EC_e and SAR from EC_a data were highly significant ranging from 0.821 to 0.982. The R²s between saturated paste EC_e and SAR and that estimated by model for 18 verification sites were significant, thus validating the calibration. Similar to wet chemistry methods, EMI data indicated that salinity and sodicity values was greater in soils irrigated with saline water by drip system compared to that irrigated by sprinkler system as well as soils irrigated with freshwater either by drip or sprinkler systems. Salinity in the top 30 cm of study site ranged from <1 dS m^-1 in freshwater irrigated plots to 6.5 dS m^-1 in soils irrigated with saline water by drip system. Similarly, SAR ranged from <1 mmol^1/2 L^-1/2 in freshwater irrigated soils to >7 mmol^1/2 L^-1/2 in soils irrigated with saline water using drip system.  Study results indicated that EMI technique can provide accurate information on spatial distribution of both salinity and sodicity in less time and using less labor from a relatively smaller number of soil samples.