Efeito hormético na cultura da soja em função à aplicação de 2,4-d sal colina

Abstract

The action of herbicides on sensitive plants, depending on the dose, can have a beneficial effect. This stimulating effect caused by low doses of a substance considered toxic is known as hormesis. Thus, the aim of this research was to evaluate the effect of hormesis provided by 2,4-D choline salt doses on biometric and productive variables of non-tolerant soybean at different phenological stages. A randomized block design was used with four replications. The treatments were arranged in a 6 x 5 factorial scheme, with six fractions of the average dose at the leaflet of the herbicide 2,4-D formulation choline salt (0 (control); 0.068; 0.684, 6.84, 68.4 and 684.0 g e.a. ha-1 ) associated with five application times during the phenological stage of soybean, V2, V5 and R2 and two sequential: V2 and R2; V5 and R2. The soybean plants were evaluated considering the main biometric and productive parameters. The results were submitted to analysis of variance and, when significant, the hormesis regression model was tested in order to describe the dose-response curves with stimulus in low doses. It was observed that the effects of 2,4-D choline salt on soybeans are influenced by the age of the plant and that at all stages in which 2,4-D choline salt applications were made, including the sequential ones, at least one variable presented hormesis. In general, the sub-doses of the herbicide 2,4-D salt choline promoted, in some cases, positive effects for some variables in the development of the soybean crop, such as grain yield, insertion of the first, shoot dry matter, height, weight of thousand grains and the total number of pods, providing the expected hormetic effect for the crop. The effects of 2,4-D choline salt in soybeans are influenced by the age of the plant, however, in contradiction, the visual effects of injury were lower in the early stages of development, with emphasis on the V5 and sequential stages V5 and R2, in which there was no significant increment in any productive variable. For the other stages V2, R2 and in the sequential V2 and R2, in which doses of 2,4-D choline salt were applied, more than two variables presented hormesis.