Boundary line method to update critical soil phosphorus and potassium levels in banana plantations in Santa Catarina

- The rational use of correctives and fertilizers in banana orchards depends on reliable standards for interpreting soil fertility. The study aimed to establish critical levels (CL) for phosphorus (P) and potassium (K) in the soil of banana plantations in Santa Catarina, using the Boundary Line (BL) method. A database with information of soil chemical analysis and fruit yield obtained from orchards in producing regions was used. Scatter plots were obtained relating P and K concentration in the soil extracted by the Mehlich-1 method with the relative productivity of fruits and then the pairs of data in the upper border were selected and used to establish a mathematical model. The model was derived and obtained the concentrations of P and K in the soil that provided the maximum physical productivity (100 %) and maximum economic productivity (90% of the maximum production), corresponding to the CL in the soil. It is proposed that the update of critical levels of P and K for banana cultivation in Santa Catarina to be 85 and 229 mg/dm3, respectively. The banana grower will be able to suppress the P and K doses in a punctual and temporary way in areas of built fertility with the proper monitoring of productivity, soil and leaf analysis.