Desempenho de soja transgênica ao glifosato e seu efeito na nodulação e produtividade da cultura

Abstract

The increasing intensification of the use of herbicides generates discussion on the technical and economic advantages, disadvantages on this form of control in the presence of weeds. The objective of this work is to evaluate the effect of the application of doses of glyphosate on nodulation of Bradyrhizobium, under greenhouse and field. The works were carried out in a greenhouse, in the experimental field of Embrapa Agropecuária Oeste in Dourados-MS and in commercial farming in the municipality of Rinópolis-SP, in 2011/2012 agricultural year. The experimental design used in the greenhouse was entirely at random, being the treatments corresponding to six doses of glyphosate (0; 0.96; 1.92; 2.88; 3.84 and 4.8 kg a.e. ha-1), with five repetitions. In the adopted design in randomized blocks, with the eight doses of glyphosate (0; 0.96; 1.92; 2.88; 3.84 and 4.8; 5.76; 6.72 kg ha-1 a.e.), with six repetitions in Embrapa and six doses (0; 0.96; 1.92; 2.88; 3.84 and 4.8 kg a.e. ha-1), with four repetitions in Rinópolis-SP in herbicide application was used a sprayer pressurized with costal CO2. At the stage of full flowering (R2), the plants were collected, washed with distilled water, counted the number of nodules of plants, dried in an oven with forced air circulation at 65° C, until constant weight and then the materials were weighed to determine the dry mass of the shoot, and root nodules. The visible symptoms of injury were observed in plants, the day after the application, in the greenhouse, with yellowing of new leaves followed by necrosis. The application of glyphosate at doses studied reduced, significantly, the number of nodules, nodule dry mass, root, shoot and shoot N of the plant in the greenhouse. This reduction is due to interference in nodulation, because the toxicity affected the survival of diazotrophs. In the field, there was significant for dry weight of nodules in both places and dry weight of shoot, only differences in commercial farming. Based on the results observed can be concluded that the dosages of glyphosate used in the test were sufficient to reduce the number of root nodules, shoot dry mass, root portion and total N content of the shoot, causing injury to plants . In the field, even some characteristics with significant differences were not sufficient to cause loss in productivity of soybean in both locations.