Introduction Plants take nutrients from soil for their growth. Nutrient levels in soil and plant tissues give an indication of the nutrient requirements of crop. Folegatti et al (2005) developed a study to evaluate the performance of Cardy ion meters on the determination of nitrate (NO 3 - ), potassium (K + ), and sodium (Na + ) ion concentrations in soil solution and tomato plant sap for fertigation management purposes. The sodium ion (Na + ) is not an important ion for tomato, but its concentration in soil solution and plant sap gives valuable information when using saline irrigation water. Cardy ion meters were superseded by LAQUAtwin B-700 series ion pocket meters, which have replaceable sensors, upgraded software, and enhanced user interface. The LAQUAtwin B-722,

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