NUTRIENTS IN THE SAP OF FERTIGATED CITRUS PLANTS

The analysis of nutrients in the sap has been gaining attention as a sensitive tool for the study of the nutritional state of perennial plants, being also useful in assessing the availability of nutrients for the plants in the soil. This study was conducted with the purpose of evaluating the concentration of nutrients in the sap of two varieties of sweet orange trees, when supplied with five rates of N, P2O5 and K2O via fertigation. The sap was monthly extracted from stems of new shoots with ethyl ether during two consecutive growth seasons. In order to understand the dynamics of the nutrients in the sap, analyses of leaf and soil solution were also made at the same time. The pH in the sap remained constant at around 5.5, regardless the treatments. The sap analysis showed to be very sensitive to variations in the fertilization regime, because the concentrations of N and K in the sap increased with the applied rates of nutrients, and also because it had a positive correlation with the values of these nutrients in leaf and soil solution. A high concentration of K was observed in the sap, at about 4.0 g L-1, being higher than the concentration of all the other nutrients. There were significant differences in the N-NO3 level between the two studied varieties: the Hamlin variety, with early maturity, showed N-NO3 concentration in the sap at about 20% higher than the Valencia variety, which is late maturity. The results suggest that the sap analysis can be used as tool in assessing the nutritional status of citrus plants.