Physical and chemical ameliorations of a heavy soil constrained by sodicity and alkalinity for improving productivity in the low rainfall regions of Western Australia

Heavy soil can be compacted and poorly structured with dense sodic and alkaline (high pH) clay in the B-horizon, which prevents root exploration in the subsoil layer, potentially restricting grain yield in the low rainfall regions of Western Australia (WA) and globally. This study investigated whether loosening of compacted soil layers through deep ripping with or without phosphorus (P) and gypsum addition can increase barley ( Hordeum vulgare L.) crop productivity in a 3-year-long field experiment. Soil loosening significantly increased barley root exploration and yield immediately after deep ripping in 2021 and showed no significant difference in 2022 and 2023. The surface application of P also did not have any impact on barley root exploration and yield in any growing season. The subsoil of the soil profile (below 20 cm) was highly alkaline and sodic, which might have restricted crop root exploration. The surface addition of gypsum resulted in the lowest yield in 2021 and showed no difference in 2022 and 2023 compared to the control. A significant negative correlation (r = -0.64, P <0.05) was observed between soil strength and grain yield in 2021. We concluded that soil loosening through deep ripping had short-term benefits in this poorly structured and compacted heavy soil with non-sodic topsoil, but constrained subsoil with sodicity and alkalinity for increasing crop productivity. Therefore, future research should focus on soil amelioration approaches that are effective in decreasing the subsoil pH and sodicity and/or effective in soil moisture conservation to increase crop root exploration and yield.