Determination of the Electrical Conductivity, pH and Fertilizer Concentration of Insecticide-Nematicide Solutions and Nutritional Cocktails Applied to Pineapple (Ananas comosus MD-2)

In commercial pineapple farms, the electrical conductivity (EC), pH, and fertilizer concentration of the insecticide-nematicide and nutrient solutions that are applied commercially were determined to analyze if they are related with the presence of toxicity symptoms in the pineapple foliage. Insecticide-nematicide and nutrient solutions were evaluated at one thousandth of the solution used commercially per hectare and correspondingly using one thousandth of the rate indicated per hectare of the product or of each fertilizer source. The EC of the solution was measured with a SevenGo DuoTM SG23 Mettler Toledo conductivity meter and the pH with a Hanna® Instruments model HI9811-5 electronic pH meter and in each fertilizer solution the concentration of macronutrients (N-P-K-Ca- Mg), micronutrients (Zn, Fe, B, Mn, Cu) and total fertilizer was estimated. The EC of the insecticide-nematicide solutions fluctuated between 0.14 and 0.43 mS cm-1 and the pH between 3.6 and 7.3. On farms that added citric acid to the insecticide-nematicide solutions, their pH was reduced to a very acidic condition that can favor the mineralization of the product and its corresponding loss of efficacy. In the nutrient solutions, the EC varied between 40.5 and 111.8 mS cm-1, the pH between 2.7 and 4.7, and the fertilizer concentration between 2.6 and 13.09%. The fertilizer sources that most contributed to the EC were UAN (31-0-0), YaraMilaTM ComplexTM, potassium chloride and potassium sulfate given their amounts included in the nutritional cocktails. Four independent factors or some of them together or a combination of all of them, could be associated or explain the phytotoxicity in the crop: nutritive solutions with EC greater than 40 mS cm-1, very low pH of the solutions less than 4.7, fertilizer concentrations greater than 4, 5 and 9%, and over-application of the solutions. Although some nutrient solutions did not exceed 5% concentration, their EC exceeded 40 mS cm-1. It seems then that to avoid leaf crop damage it would be more accurate to use the EC instead of the fertilizer concentration. To prevent foliage toxicity or burning due to foliar fertilization, it is suggested to apply low EC fertilizer cocktails of less than 40 mS cm-1. This can be achieved by adding smaller amounts of the products that most contribute to EC. Another possibility is to incorporate sources that lead to a reduction in the EC of the fertilizer cocktails, for example, using potassium citrate (Greenplants® K) as a source of K. The pH of the solutions must be adjusted to the optimal range (5.5 to 6.5) of absorption suggested for the crops and over-application of the solutions must be eliminated. Therefore, the pressurization of the equipment must be carried out with the arms outside the terraces, in terraces that do not have the total number of beds, the arms of the boom must not be tilted and in the curves of the roads when it is necessary to go back to align the equipment and continue with the application, the nozzles should be closed to prevent over application of the nutrient solutions.