Factors influencing the efficiency of foliar sprays of monopotassium phosphate in the olive

Olive trees have been traditionally cultivated in dry conditions as it is a crop very well adapted to Mediterranean dry lands. Foliar fertilization is a widespread application method used by olive growers to correct frequent deficient levels of potassium in olive trees under rainfed conditions. Monopotassium Phosphate (MKP) is an economic and easily available fertilizer and a fast source of P and K when it is applied as a foliar spray. The influence of environmental and formulation factors on the efficiency of MKP foliar application has never been evaluated. In this study the different responses of five MKP foliar treatments (control-untreated, MKP3% at dayligh, MKP3% overnight, MKP3% plus urea and MKP3% plus surfactant) on olive trees under field conditions were evaluated during three different application times (April, July, and November). In all cases, MKP3% plus urea and MKP3% plus surfactant increased P contents with July being the most effective treatment month. All treatments, except MKP3% at dayligh, improved the K nutritional state of olive in July, but not in November or April. In general, the addition of urea and surfactant to the MKP3% solution and its application in July improved its efficiency on olive trees, most likely due to the higher proportion of young leaves present during this period.