Nodulação da soja sob diferentes tratamentos químicos de sementes

Abstract

Soy is distinguished by the high concentration of oil and protein in its grains, also, it is known that it is high demand of Nitrogen by the crop, this element is only economically viable to be supplied through the symbiosis that occurs naturally between soybean plants and nitrogenfixing bacteria, such as those of the genus Bradyrhizobium, that can be inoculated to the seeds of the crop. In this sense, a trial was conducted with the objective of evaluating the impacts of seed treatment on nodulation and its efficiency in soybean using Bradyrhizobium inoculation. The experiment was conducted in a completely randomized design with four replicates. The soybean was sown in pots with 8 dm-3 of soil, and 4 plants per pot were carried out, at a depth of 3 cm. The treatments were composed by inoculation of nitrogen fixing bacteria and seed treatments, as follows: control (bare seed); inoculant; fipronil + pyraclostrobin + methyl thiophanate + inoculant; fipronil + carboxin + thiram + inoculant; fipronil +, metalaxyl-m + fludioxinil + inoculant; fipronil + carboxin + thiram + metalaxyl-m + fludioxinil + inoculant. The test was conducted until the plants reached the phenological stage of V3. The variables analyzed were number of nodules per plant, leaf area, dry shoot mass, root dry mass, and leaf nitrogen content, the results were submitted to analysis of variance and the means were compared by the Scott Knott test (p ≤0.05). The highest nodulation efficiency occurred when inoculation was carried out via seeds without association with pesticides, demonstrating the toxic effect of the association with fungicides and insecticides. Root dry mass presented higher values when treated with carboxin and thiram, as well as fludioxinil and metalaxyl - m, possibly by positive physiological stimuli. Dry shoot mass and leaf nitrogen content were not influenced by the treatments. It is concluded that the association of agrochemicals with inoculant via seeds causes damage to the number of nodules, however, the reduction of nodulation does not have significant effects on other aspects of soybean plants in this phase.