Calibration of cardy-ion meters to measure nutrient concentrations in soil solution and in plant sap

Fertigation management requires rapid and accurate methods to determine nutrient concentrations in soil solution and in plant sap. This study was developed to evaluate the performance of cardy-ion meters (CIM) for the determinations of NO3-, K+ and Na+ concentrations in soil solution and tomato plant sap, for fertigation management purposes. Tomato was cultivated in a greenhouse with different levels of N, K and Na in the irrigation water. Soil solution was collected by suction at the 15 cm depth with porous ceramic cups and the concentrations of NO3-, K+ and Na+ were determined by CIM and also in the laboratory by standard methods. At the end of the cropping season, 50 leaf samples were also collected and concentrations of the nutrients in the petiole sap were analyzed by CIM and compared to the amounts of total-N, K and Na in the dry matter of the leaves. Concentrations in soil solution and plant sap determined by CIM presented good correlations with measurements in soil solution and in leaf dry matter, respectively, analysed by standard methods. The use of CIM is advantageous due to the quickness of the analyses and the low cost.