Hormesis de 2,4-d sal colina na cultura da soja de hábito de crescimento determinado

Abstract

The stimulant effect of resulting from application of low rates of one substance considered toxic when the same substance is applied in larger quantity is called hormesis. This objective of this trial was to use doses-response curves to evaluate the of hormesis caused by 2,4-D coline salt herbicide on biometric variables of soybean with determinate growth habit at different phenology stages. It was adopted the entirely randomized experimental design, with seven repetitions and the treatments composed by six fractions established as a function of 2,4-D coline salt recommended in label, as following: 0; 0.068, 0.684, 6.84, 68.4, 684.0 g ae ha-1 . The rates were applied at V2 or V5 soybean phenology stages. Visual injuries symptoms were evaluated as 3, 7, 14,0 21 and 33 days after application (DAA) and the kinetics of maximum fluorescence emission of chlorophyll “α” was obtained at 3, 7 and 21 DAA. The characterization of soybean plants submitted to sub-doses of 2,4-D coline salt it was done at 30 DAA by determining plant height, stem diameter, leaves number and dry matter of shoots, roots and total dry matter. The results were submitted to variance analysis and, when significative, it was proceeded the hormesis test. Visual symptoms of injury in soybean plants at phenological stages of V2 and V5 were representative at rates of 68.4 and 684.0 g ae ha-1 , being that at V5 stage this last rate provided 100% of soybean death. The rates of 68.4 and 684.0 g ae ha-1 prejudicated the photosynthetic II quantic efficiency at 14 DAA when applied at V2 stage; and at 3, 7 and 14 DAA when applied at V5 stage. Maximum hormesis effects to height, dry matter of shoots, roots and total were estimated at rates of 0.20, 0.60, 0.41 and 0.44 g ae ha-1 , respectively, when applied at V2 stage.