Restrição luminosa e o manejo químico com glyphosate sob a resposta fisiológica de Urochloa brizantha

Abstract

The action of glyphosate on the physiology and control of Urochloa brizanthacultivated under light restriction is little known. We sought to evaluate the influence of light restriction and the application of glyphosate on the physiology of U. brizanthaand its relationship with herbicide control. The experiment was conducted in the field in a randomized block design, with 5 replications, in a split-plot scheme. Three types of environments were allocated to the plots, being full sun, intermittent shading with three hours of direct light exposure and continuous shading, and in the subplots doses of 0, 480, 960 and 1440 g. It is. The. ha-1 of glyphosate. At 14 days after application, glyphosate control, photosynthetic rate, stomatal conductance, transpiration rate, quantum efficiency of photosystem II, electron transport rate, the ratio between variable and maximum fluorescence (Fv/Fm) and (EUA) was determined. Control was above 80% in the environment with continuous shading from the dose of 995 g ha-1while in full sun the controldid not reach 60% at the highest dose tested. Urochloa brizantha had a reduction in photosynthetic rate according to the increase in the doses of glyphosate tested. Glyphosate doses caused a reduction in AUS with quadratic adjustment of the adjusted regression. Continuous shading had US 36% lower than other environments, however this variable did not differ between full sun and intermittent shading. Urochloa brizantha had its photosynthetic apparatus compromised at the lowest dose tested (480 g ha-1) and this was aggravated by exposing the plants to shading, with reductions in the electron transport rate of up to 70%. The plants did not show variation in the Fv/Fm ratio between environments. It is concluded that glyphosate negatively alters the physiology of U. brizantha regardless of light restriction. The action of glyphosate is more efficient in plants under light restriction, with greater data on the physiological variables analyzed.