Measuring K+ in Rice Basal Stem Sap with a Cardy Meter

A rice (Oryza sativa) experiment was conducted to determine the accuracy of a fast tissue testing method using a Horiba Cardy K+ meter. Rice was field-grown in three soil potassium regimes. At three early reproductive growth stages (R0, R1, and R2), stem samples from the basal six inches of rice plants were collected and analyzed for K content. Basal stem samples were tested with extracted sap analyzed by a Cardy K+ meter and digested stem tissue analyzed with an Atomic Absorption Flame Spectrophotometer (AAS). Regression correlations between basal stem sap K and total K ranged from r2 = 0.57 to 0.89 for the three growth stages. Both methods of measuring lower stem K content at the R1 growth stage were equivalent in their ability to predict grain yield response to potassium fertilization.