Effects of salinity and sodicity of water on friability of two texturally-different soils at different matric potentials

Abstract

Soil salinisation and sodification are two principal processes in arid and semi-arid regions which have been irrigated with poor-quality waters. A laboratory experiment was carried out to study the effect of soil texture, salinity (EC) and sodicity (SAR) of irrigation water and matric potential on soil friability. Intact soil aggregates/clods with different size ranges of 4–8, 8–15, 15–20, and 20–40 mm were collected from two texturally-different soils of sandy loam (SL) and clay loam (CL). Undisturbed soil samples were also taken for determination of soil water contents at matric potentials (h) of –30, –100, –200, and −400 kPa. All of the soil samples were subjected to five wetting/drying cycles using twelve different water quality treatments, combinations of four levels of EC (0.2, 1, 6, and 10 dS m−1) and three levels of SAR [1, 5 and 12 (meq L−1)1/2]. The tensile strength of aggregates/clods was determined by the indirect Brazilian test. Then, the soil friability was calculated by employing three methods of coefficient of variation (F1), ranking order (F2), and volume-dependence (F3). The results showed that the F values varied considerably depending on the friability calculation method and matric potential. Soil friability was not affected by the treatments at the wet range because of the dominant effect of high water content on soil mechanical behavior; whereas soil aggregates/clods of 4–8, 8–15 and 15–20 mm at h of −400 kPa showed the highest friability. Soil friability decreased with an increase in SAR and increased with an increment in EC at low matric potentials (i.e., –200 and −400 kPa) due to the negative and positive effects of sodium and soluble ions on soil microstructure, respectively. The effects of SAR on soil stability, dispersion clay and tensile strength and as a consequence on soil friability was more pronounced at low EC values. Results showed more influence of water quality (EC and SAR) in clay loam than sandy loam soil due to its higher clay content. Comparison of the F values with well-known classification revealed that F1 and F2 were about 2–4 orders of magnitude higher than F3, especially for aggregates size ranges of 4–8 and 8–15 mm at h of –200 and −400 kPa and air-dry condition; and the coefficient of variation and ranking order methods were more acceptable and reliable than the volume-dependence method for characterizing the soil friability.