Targeting Subsoil Constraints in Southern Queensland: Concept Proof of Spraying Polyacrylamide for Subsoil Stabilisation during Tillage

Deep ripping, in conjunction with gypsum and/or organic amendment, is known to be useful for removing physical constraints and improving crop yields in dispersive subsoils. However, the benefits are short-lived due to lateral movement of Na into soil between the rip lines, and slumping following the wetting of loosened soil, leaving low pore volume for air and water movement. This study evaluated the effect of high concentration polyacrylamide (PAM) solutions on stabilising soil structure, with a focus on PAM application on dispersive aggregates theoretically dislodged by ripping, as part of the subsoil decompaction. Three distinct soils (Vertosol, Kandosol, and Dermosol) from southern Queensland were treated to be sodic. These aggregates were further applied with PAM solutions under three scenarios, including: immersion, coating, and no application. In general, PAM stabilised soil aggregates with a concentration above 1.5 g L–1 when immersed into PAM solution or coated with PAM product, as compared to non-PAM-treated samples. The efficacy depended on PAM concentration, viscosity, soil type, and mechanical force. The concept of spraying PAM for stabilising the subsoil during tillage was proposed, as there is feasible potential for PAM to prolong the benefits of subsoil decompaction long enough through stabilising aggregate structure.