Fertigation is a technique that is increasingly expanding in the citriculture, but this technique is usually performed using predetermined doses without monitoring the nutritional status of plant and soil. The mismanagement of fertigation can cause imbalances in the conditions of soil and plant nutritional status over time. Traditional techniques for monitoring the condition of the soil and the plant do not allow the provision of data quickly, wasting this great potential of fertigation. This research project was aimed at evaluating the effect of five Potassium rates in the soil solution and sap, observing the sensitivity of this method. For this, an experimental work was conducted in the city of Reginópolis-SP/Brazil, using ‘Hamlin’ trees, grafted on citrumelo Swingle rootstock. The treatments consisted of five K₂O rates, applied through fertigation: T1 - control (no nutrient), T2 - 25%, T3 - 50%, T4 - 100% and T5 - 200% of K₂O. The 100% rate, officially recommended, was established based on historical of soil and leaf analysis and also in accordance with the expected productivity. The remaining rates were calculated from it. To monitor the potassium status on the plants, sap analyses were performed and the nutrient dynamic in the soil was evaluated by soil solution analysis, with the help of porous covering soil solution extractors. The K concentrations in the sap and in the soil solution correlated significantly with the K rates applied, what means that soil solution and sap analysis can be an efficient technique to recommend the Potassium fertilization. The K concentrations in the sap also correlated significantly with the K concentration in the soil solution (0,98), what means that the K concentration in the sap is directly related with the K concentraton in the the soil solution.