Abstract:
Salinity is the primary water quality concern in irrigated agriculture. An Electrical
Conductivity (EC) meter and a hydrometer are two possible methods for measurement of
irrigation water salinity. The conductivity meter method is based on measuring the
amount of electrical current that a fluid will support. Although it is the most widely used
method, the instrumentation is rather expensive and in some instances may require
sample dilution. The hydrometer method is based on measuring the density of the fluid.
The main objectives of this study were to compare these two methods and, based on
hydrometer method, develop empirical models for prediction of EC, sodium adsorption
ratio (SAR), and the principle ion concentrations in the irrigation waters of Yazd
Province, Iran. The electrical conductivity, temperature, and density of 206 water samples
from wells across Yazd Province were measured. Temperature correction factors for
adjusting the hydrometer reading to 25 oC were determined. The correlation between EC
and hydrometer readings was high (R2 = 0.97). Although the empirical model developed
for prediction of EC slightly underpredicted the measured values, it is still accurate
enough for practical purposes. Hydrometer readings were also highly correlated with the
principle ions and SAR. The salt type also affected the hydrometer readings. Magnesium
sulfate solution had the highest density among the major salt types present in irrigation
waters. Finally, a chart was developed for rough estimations of EC, sodium and chlorine
concentrations in irrigation waters of Yazd Province, Iran.
