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

Field classification of Vertosols and Sodosols in Australia involves the ca lculation of an exchangeable sodium percentage (ESP) of the subsoil to esti mate sodicity. ESP has historically been determined by laboratory measureme nt of the cation exchange capacity (CEC) and exchangeable sodium. This ofte n leads to a delay in field classification and mapping and missed extension opportunities with landholders. Recently, ion-specific electrode field met ers have been developed that allow the determination of the sodium ion conc entration within a soil solution. If field tests and/or calculation can est imate clay percentage and sodium concentration, there is potential for rapi d field assessment of ESP. The field meter accurately predicted exchangeabl e sodium (R-2=0.83). In addition CEC was related to clay percentage (R-2=0. 79). The estimated ESP calculated by the field tests compared favourably wi th the actual ESP measurement (R-2=0.85).