Nutritional assessment of potassium in tomato (Lycopersicon esculentum Mill.) by direct reading of fruit sap

Analysis of content made available to the plants and their relationship with what is present in plant tissue, are great alternative for proper handling of fertilizer, but the methods currently used, are expensive and require time. This study aimed to implement a new methodology for its determination and thus develop a correlation with the conventional method. It also evaluated the influence of the increase of K doses in production, plant development and relationship with the other nutrients. For the study we used two experiments with fertirrigated tomato having five different doses of potassium, grown in a greenhouse and analyzed according to the methodology developed. In the experiments were evaluated productivity, illuviated electrical conductivity and nutritional content in the fruit and leaf immediately above each bunch. Potassium was analyzed by conventional methodology and for comparison purposes. The values were submitted to polynomial regression analysis to the second degree and correlation. The results showed that increased potassium levels significantly influenced the productivity, illuviated electrical conductivity and K contents. After comparing the two methods was reached a relationship where reading by the conventional method is 20.085 times higher than the values presented by reading without digestion if the sap of the fruit and 9.6857 in the sap of the leaf petiole. The new methodology has proved capable of replacing the conventional of quick, cheap and effective form. Increased potassium levels had significantly influence in the illuviated electrical conductivity, productivity and nutritional content of the plant tissue.   Key words: Plant tissue, methodology, analysis, nitric perchloric acid digestion.