The impact of rain water on soil pore networks following irrigation with saline-sodic water

The soil pore network is an important factor affecting soil hydraulic conductivity (Ksat). In this study we examine the effect on the soil pore network of a Red Ferrosol caused by irrigation with good quality irrigation water (GQW), as well as saline-sodic water with varying sodium absorption ratios (SAR; 10, 50 and 120) and constant electrical conductivity (EC; 2 dS m-1), followed by application of distilled water (simulating rain water). The Ksat was measured for the different waters before and after applying the rain water to the soil. Soil samples were taken from different depths (1, 4 and 8 cm) for exchangeable cations measurement and the changes in ESP of the soil. Soil horizontal cross-sections were taken from the first 2 cm of the soil cores after drying with acetone and impregnation with polyester resin mixed with green fluorescent dye catalyst and hardener. These sections were polished and visualized under a microscope to investigate the changes in the soil pore network. By increasing the SAR of the water applied from 0.11 (GQW) to SAR 50 and 120, a significant reduction in Ksat was found, alongside a significant increase in the ESP of the soil from 3 to 10 and 11, respectively; this was most evident near the soil surface. After applying rain water, the Ksat reduced significantly approaching 0 mm h-1 where soil was treated with water of SAR 120. Visualisation of the soil pore network of the treated soils following the application of deionised water clearly showed a reduction in soil macroporosity where water quality of SAR ≥10 was applied, even where soils were non-sodic. Where irrigation occurred with good quality, low SAR water, this reduction was not evident

Influence of porosity and permeate suspended clay concentration on clay entrainment within a red ferrosol

Soil pore size is an essential factor affecting pore blockage and subsequently saturated hydraulic conductivity (K sat). In this study we examined the effect of soil bulk density on suspend clay movement in a Red Ferrosol soil. Water with varying suspended clay concentrations (0, 5, 10 and 20 g L-1) was allowed to infiltrate cylindrical soil cores of a Red Ferrosol packed at two bulk densities (1.0 and 1.2 g cm-3). The Ksat was measured at both bulk densities and at all suspension concentrations. The outflow suspension concentration was measured as a function of pore volumes of drainage ~ 10 pore volumes. Following measurement, 2-cm long portions of undisturbed, drained soil cores were sampled from the top and bottom to measure water retention. Soil with low bulk density (1.0 g cm-3) allowed easier passage of suspended clay than the soil at high bulk density (1.2 g cm-3), even at a high suspension concentration (20 g L-1) with little occurrence of pore blockage. At both bulk densities, significant increases in water retention occurred near soil surface (top of soil core) than subsurface (bottom of soil core). This suggests that accumulation of clay sediment may have lead to pore blockage in the soil surface segments