Effects of Irrigation Water Quality on Some Soil Physical Indicatorsdispersion, penetration resistance, macroporosity, flocculation, diffuse double layer

Soil structural properties which are influenced by pore size distribution are important physical indicators of soil that affect plant and root growth. Irrigation water quality by affecting salt concentration and sodicity of soil solution alters the soil structure. This study was carried out to investigate the effects of different water qualities on pore size distribution, aeration porosity, soil water characteristic and mechanical resistance curves of a clay loam soil, irrigated with different water qualities. A combination of three levels of EC (1, 6 and 10 dS m-1) and SAR (1, 5 and 12 (meq L-1) 0. 5) values were used to simulate the different types of irrigation water. The undisturbed soil samples (45 mm length and 51 mm inner diameter) were treated with solutions for 5 cycles of saturation and drying. The result showed that at each SAR, as water EC increased, the salinity enhanced the soil macroporosity and aeration porosity as a result of flocculation that is effective in development of stable structure. Due to increasing the micoporosity and water holding capacity, the amount of retained water in filed capacity was increased. Saturated water content was increased due to the effects of salinity on pore alteration, as a result of contraction of diffuse double layer and particle’s flocculation. It is also seen that penetration resistance decreased probably due to development of macro pore. At each EC level, as the sodicity of irrigation water (SAR) increased, the moisture content at field capacity and retained water were increased due to structural disruption, clay swelling and dispersion which lead to increased adsorptive and interlayer surfaces. It was also observed increasing in miroporosity and penetration resistance and decreasing in macroporosity and aeration porosity with increasing SAR.