Influência dos horários de aplicação na eficácia de formulações de glufosinato sal de amônio na dessecação pré-colheita da soja

Abstract

The soybean’s pre-harvest desiccation is a process that aims to anticipate and uniformize the crop’s maturation. In this context, the ammonium glufosinate – available in different formulations – is a possibility for this practice. However, its efficacy can vary according to the hour of application. Thus, this work aimed to evaluate the best positioning of two different ammonium glufosinate formulations (Finale® and Trunfo®) under different hours of application in soybean’s pre-harvest desiccation. For this purpose, it was conducted two experiments in experimental design of casualized blocks with four repetitions. The application occurred at the phenological stage of R7.3, in a dose of 400g a.i.ha-1, for both formulations, and the experiments were constituted by 6 treatments with different times of light exposure. For that, the treatments were applied in distinct hours: 12 Hours Light (06:20), 8 Hours of Light (10:20), 4 Hours of Light (14:20), 12 Hours of Dark (18:20), 8 Hours of Dark (22:20) and 4 Hours of Dark (04:20) besides a witness. Defoliation and desiccation evaluations were conducted visually at 3, 5, 7 and 10 days after the application (DAA) and taken pictures of the experimental unities for green pixels quantification through sotware ImageJ®. Daily, it was collect pods samples for grains maturation evaluation through moisture analysis in stove and green pixels quantification. At 24 hours after the application, it was collected leaves for membrane disruption analysis in condutivimeter, besides initial fluorescence (F0) and maximum fluorescence (Fm) and estimated the electron transport rate (ETR) evaluations. By the end, after the period of experimental conduction, the experimental unities were harvested manually and evaluated yield and 1000 grains weight. For statistical analysis, the data was submitted to R’s software, where it was applied the F test, and when significant at 5%, applied the Tukey’s test and built the regression analysis. For defoliation, in relation to Finale®, 12 and 8 Hours of Light reached values superior to 90%, and were the only ones to differ from the witness. For Trunfo®, all treatments with light exposure presented similar values (next to 90%) and differed from the witness other ones. For desiccation, the levels were proportional to the quantity of hours of light exposure for the first formulation and indifferent for the second one, which pattern, was also observed for the green pixel’s quantification in the experimental unities. For grain’s maturation, the first formulation showed sharp drop for 12 and 8 hours of light, while the second one, showed no statistical difference among treatments. For membrane disruption, 8 hours of light presented the highest values for both formulations. For F0, all treatments with glufosinate showed values superior to the witness with levels between 30 and 45. For Fm, the highest values were observed for 4 hours of dark, and the lowest ones, for 12 and 8 hours of light for both formulations. In relation to electron transport rate (ETR), for Finale®, only 4 hours of dark, while for the second formulation, only 12 hours of light differed from the witness. Therefore, it’s concluded that although both formulations are photo-dependent, Finale®, showed higher efficacy in a shorter period of time. However, Trunfo® showed less photo-dependency although it needs a longer period for its correct efficacy. Therefore, the formulation choosing must vary according to the climatic conditions in the moment of application and availability of days between the application and harvest.