Fertilização foliar com zinco e cobre no desempenho de mudas de coqueiro anão-verde.

Abstract

Zinc (Zn) and copper (Cu) are not part of the coconut fertilization program because the soil generally supplies the levels considered sufficient for the crop (15 mg kg-1 for Zn and 5 mg kg-1 for Cu ). However, studies show that Zn and Cu fertilization improved the performance of crops, including coconut trees. In view of this, this study sought to analyze the influence of Zn and Cu fertilization on the nutritional status, growth and physiological parameters of green dwarf coconut tree seedlings. The study was carried out by conducting two experiments, one with doses of Zn and the other with doses of Cu, conducted in a greenhouse at the Federal Rural University of the Amazon. The first experiment was conducted between September 2021 and April 2022, the treatments consisted of five doses of Zn (5, 10, 15, 20 and 25 g per plant) and a control treatment (without Zn), and were applied via leaf. The results showed that increasing Zn doses reduced iron by 45% and manganese by 38%, and increased Zn to values above 100% with the 25 g dose compared to the control treatment. Regarding growth and gas exchange, the greatest increases were observed in seedlings that received around 16 g of Zn per plant and that had a Zn content of around 82 mg kg-1, increases of 40% in leaf area (LA), 7% in height (H), 29% in shoot dry mass (SDM), 22% in total dry mass (TDM), 38% in photosynthesis (A), 67% in transpiration (E), 83% in stomatal conductance (gs) and 52% in internal CO2 concentration (Ci), when compared to plants that did not receive Zn. The second experiment was conducted between the months of October 2022 and April 2023, the treatments consisted of five doses of Cu (4, 8, 12, 16 and 20 g per plant) and a control treatment. The results showed that doses of 4 and 8 g of Cu provided higher nitrogen and phosphorus contents. Regarding growth, gas exchange and chlorophyll a fluorescence, 8 g of Cu provided the best results in most variables, with increases of 12% in H, 26% in LA, 27% in SDM, 23% in TDM, 14 % in A, 24% in E, 24% in gs, 7% in Fv/Fm and 8% in ETR. However, the calculation of the dose for maximum technical efficiency showed that 5 g of Cu per plant is sufficient to obtain improvements in seedling performance. Thus, in a pioneering way, the best dose of Zn and the best dose of Cu were identified to obtain maximum technical efficiency in green dwarf coconut seedlings, important information that can contribute to the improvement of the fertilization program for coconut trees cultivated in the state from Pará.