Field prediction of sodicity in dryland agriculture in Central Queensland, Australia

Abstract

Field classification of Vertosols and Sodosols in Australia involves the calculation of an exchangeable sodium percentage (ESP) of the subsoil to estimate sodicity. ESP has historically been determined by laboratory measurement of the cation exchange capacity (CEC) and exchangeable sodium. This often leads to a delay in field classification and mapping and missed extension opportunities with landholders. Recently, ion-specific electrode field meters have been developed that allow the determination of the sodium ion concentration within a soil solution. If field tests and/or calculation can estimate clay percentage and sodium concentration, there is potential for rapid field assessment of ESP. The field meter accurately predicted exchangeable sodium (R2 = 0.83). In addition CEC was related to clay percentage (R2 = 0.79). The estimated ESP calculated by the field tests compared favourably with the actual ESP measurement (R2 = 0.85).