Impacts of Amelioration on Sodic Soil Hydraulic Conductivity and Potential Consequences for Deep Drainage in the Lower Burdekin, North Queensland

摘要: Groundwater tables are rising beneath irrigated fields in the Lower Burdekin North Queensland, Australia. The soils where this occurs predominantly sodic clay with low hydraulic conductivities. Many of these have been treated by applying gypsum or increasing salinity irrigation water mixing saline groundwater fresh river water. While purpose treatments is to increase infiltration into surface and improve productivity root zone, it thought that may altered soil properties well below zone leading increased recharge tables. objective thesis assess potential for amelioration conductivity hence rates. This research focuses on impacts chemistry, deep drainage To determine current local soils, previous surveys were reviewed field work was conducted collect samples. From analysis determined sodicity levels remain high at some locations even under extend typically sampled “root zone” Using samples collected experiments measure changes response selected treatments. results column showed applications can lead increases an order magnitude when compared maximum a surrogate good quality Hydraulic occurred leached continuously saturated solution least three weeks. These positively correlated decreases exchangeable sodium magnesium concentrations. salt concentration applied found significant influence conductivity; however continued leaching mixed cation waters caused rapid followed gradual decrease. vi Numerical modelling used study expected depth timing amelioration, compare different large amounts rain during relatively short wet season drainage. When ten metre profiles clays simulated using HYDRUS-1D, only close but rates still increased. season, following times greater than no applied. Gypsum overall impact depends initial active crop frequency duration treatments, rainfall, materials deeper unsaturated zone.