Towards predicting the soil-specific threshold electrolyte concentration of soil as a reduction in saturated hydraulic conductivity: The role of clay net negative charge

Effects of interactions between soil particles and electrolytes on saturated hydraulic conductivity

“…Practitioners and industry use government C TH guidelines (e.g., ANZECC, ) to make practical irrigation implementation decisions. The industry C TH guidelines are typically based on a generalized equation for the C TH , which is contradictory to the fact that C TH is soil specific and is only linearly correlated with SAR (Bennett et al, ; Dang et al, ). It seems that the P max is a better indicator for soil structural management, because P max is not only soil specific, but also includes the combined contributions of electrolyte concentration, SAR and EIP according to the theoretical calculations of P EDL .…”

A pH‐Based Pedotransfer Function for Scaling Saturated Hydraulic Conductivity Reduction: Improved Estimation of Hydraulic Dynamics in HYDRUS

“…We propose that the better performance of the nonlinear equation suggests that soil‐specific attributes of soils will be important in explaining the reduction in hydraulic dynamics. This result is not surprising, given the literature indicating that soil hydraulic reduction is soil specific (Bennett et al, 2019; Marchuk and Rengasamy, 2011), but it does reinforce the need to update such parameters within soil‐water models.…”

“…While beyond the scope of this study, it is noted here that the McNeal (1968) model was modified by Ezlit et al (2013) to function on a soil‐specific basis via a semiempirical disaggregation approach. Dang et al (2018c) validated the specificity and the disaggregation model for field soils, while Bennett et al (2019) demonstrated the magnitude of soil variability, even for the same soil orders. Therefore, in seeking to improve the soil‐water dynamics of HYDRUS, it is prudent to utilize the semiempirical approach of Ezlit et al (2013) as well as to seek to improve the incorporation of pH effects.…”

“…The scaling factor r is a function of the soil solution pH, SAR, and EC, and the relative hydraulic conductivity K r is a function of the hydraulic pressure head: where K is the hydraulic conductivity (cm d −1 ), h is the pressure head (cm), pH is the solution pH (−log[H + ]), SAR is the sodium adsorption ratio, EC is the total electrolyte concentration of the solution (mmol c L −1 ), and r is a scaling factor (a function of pH, SAR, and EC). Subsequently, the scaling parameter, r , is divided into two sub‐factors: where r 1 is a function of SAR and EC, providing the disaggregation (inter‐ and intra‐crystalline swelling) and dispersion effects on the hydraulic conductivity, as described by Quirk and Schofield (1955), Dang et al (2018b), and Bennett et al (2019), while r 2 represents the effects of solution pH on the hydraulic conductivity (Suarez et al, 1984). The assumption is that the scaling parameters r 1 and r 2 can be applied for the entire range of pressure heads under unsaturated conditions.…”

“…Soil hydraulic conductivity is strongly dependent on soil structural status and stability and the geometry of pore spaces in the soil (Assouline and Narkis, 2011). The use of marginal quality irrigation water is likely to cause deterioration in the soil structure; a change in the ratio of solids, water, and air within the soil; and reduced hydraulic conductivity due to clay disaggregation and dispersion processes (Bennett et al, 2019; Quirk and Schofield, 1955; Rengasamy and Olsson, 1991). A reduction in hydraulic conductivity often occurs as a result of excess Na within the soil solution (measured as the sodium adsorption ratio, SAR), which can result in both intra‐ and inter‐crystalline swelling, leading to clay dispersion (Dang et al, 2018b; Ezlit et al, 2013).…”