Soil salinity assessment by some destructive and non destructive methods in calcareous soils

Salinity is a major problem limiting plant growth throughout the world. Various methods have been used to measure soil salinity. The destructive (standard) method involves soil sampling followed by laboratory measurement of electrical conductivity (EC) in saturated paste extracts, 1 : 1, and 1 : 5 soil and water suspensions. Whereas, a non destructive (Sigma probe) method give a direct measurement of soil pore water salinity. Various methods for measuring salinity are commonly correlated in similar soils. The objective of this study was to determine the relationships between salinity readings obtained from standard methods and Sigma probe in calcareous soils of different texture and salinity. Results from the laboratory methods (saturated paste extracts, 1 : 1, and 1 : 5 soil/water ratios) were generally highly correlated (RE2=0.98). Moreover, present of many salts in the soil were affecting linearity of the relationship between saturated paste extracts and 1 : 5 ratio in which the best correlation was found when the EC of saturated paste extract was less than 20 dS msup(-1). Sigma probe was successfully correlated with standard methods. Its readings were relatively affected by soil salts and water content, in which the best correlation was found between Sigma probe reading and EC measured at saturated paste extracts values, at low water content with EC less than 10 dS msup(-1). Many salts (ex. Nasup(+), Casup(2+, Mgsup(2+) ...etc.) were interfering the correlation equations between methods and as soil water increased more salts were dissolved and gave weak correlation factor (RE2). Using Sigma probe removes the need for soil sampling prior to salinity measurements and should allow in situ soil salinity measurements to be taken that could be related to standard methods. Moreover, readings of Sigma probe at low water content, which is around field capacity considered as the best measuring conditions. However, more researches with gradient increase in soil salinity and water content need to be done. Finally, soil properties and measuring conditions should be considered before applying any published method or equation for soil and water salinity evaluation. However, if the equations found in this study are suitable for certain soils, salinity measurements could be done in short time by Sigma probe and related to the standard methods.