Detrimental effects of glyphosate on plant mineral nutrition have been reported in the literature, particularly on Mn uptake and redistribution. However, in most of the experiments conducted so far glyphosate-susceptible plants were used. Effects of glyphosate on Mn absorption kinetics, accumulation, and distribution within the plant, as well as soybean response to Mn as affected by glyphosate were studied in three experiments. In the first experiment, in nutrient solution, the effect of glyphosate on soybean Mn uptake kinetic parameters (Imax, Km and Cmin) was determined. In a second experiment, also in nutrient solution, differential Mn accumulation and distribution were studied for a conventional soybean cultivar and its near-isogenic glyphosate-resistant counterpart as affected by glyphosate. In a third experiment, response of glyphosate-resistant soybean cultivars to Mn application was studied in the presence of glyphosate, in pots with Mn-deficient soil. Maximum Mn influx (Imax) was higher in the herbicide-resistant (GR) cultivar than in its conventional counterpart. Glyphosate applied to nutrient solution at low rates decreased Km and Cmin. A few days after herbicide treatment, RR soybean plants developed yellowish leaves, a symptom which, in the field, could be misinterpreted as Mn deficiency, but herbicide application had no effect on Mn uptake or distribution within the plant. In the soil experiment, soybean Mn uptake was increased by Mn application, with no effect of glyphosate. Under greenhouse conditions, there was no evidence of deleterious effects of glyphosate on Mn absorption, accumulation and distribution in the plant and on soybean cultivars response to Mn application.

SUMMARYNitrification can lead to substantial losses of the applied N through nitrate leaching and N 2 O emission. The regulation of nitrification may be a strategy to improve fertilizer N recovery and increase its agronomic efficiency. The objective of this study was to evaluate the inhibiting capacity of nitrification in soil by Brachiaria species. The greenhouse experiment was conducted using pots with 10 dm 3 of a Red Latosol sample. The treatments consisted of the cultivation of three forage species (Brachiaria brizantha, B. ruziziensis and B. decumbens) and four N rates (0, 100, 200, and 300 mg/pot), and the control (without plants). In the absence of the forage plants, all N fertilization levels raised the N-NO 3 -soil levels, as a result of nitrification. The mineralization of organic matter supplied much of the N requirement of the forage plants and nitrification was influenced in the rhizosphere of B. brizantha; however, this effect was not high enough to alter the N-NH 4 + level in the total soil volume of the pot.

Palavras-chave: Glycine max, herbicida, inibidores da EPSPs, nutrição, seletividade.ABSTRACT -The study of selectivity and secondary effects of herbicides on crops is extremely important to successful agriculture. This research aimed to evaluate the effect of glyphosate formulations on nutrient accumulation and dry matter production on the shoot of two glyphosateresistant (GR) soybean cultivars. The assay was carried out in a greenhouse and arranged in a randomized complete block design, replicated six times. The treatments were in a factorial arrangement including six glyphosate formulations (Roundup Original , plus a control treatment, and two soybean cultivars (CD 225 RR and V Max RR). The herbicide applications were performed when the plants were at the V3 growth stage, using a dose of 960 g a.e. ha -1 . The macronutrient and micronutrient accumulation and dry matter production in the shoot of the soybean plants were greater in V Max RR cultivar than in CD 225 RR cultivar. The formulations Roundup Ready ® and Roundup Ultra ® did not promote nutrient accumulation reduction in the shoot of the cultivars. In addition, the formulations Roundup Original ® , Roundup Transorb ® and Roundup WG ® caused the greatest damage to nutrient accumulation and dry matter production. It was concluded that nutrient accumulation and dry matter production in the shoots of the soybean plants are affected by glyphosate application, even for GR cultivars.

Foi levantada a hipótese de que o glifosate aplicado à soja resistente ao herbicida poderia alterar a eficiência de absorção e translocação do nutriente na planta. Com o objetivo de estudar o acúmulo e distribuição do Mn, assim como a cinética de absorção de Mn pela soja geneticamente modificada sob efeito da aplicação de glifosate, foram conduzidos dois experimentos. No primeiro, os tratamentos foram constituídos por duas cultivares de soja quase isogênicas cultivadas em solução nutritiva (Conquista e Valiosa RR com aplicação ou não do herbicida). As concentrações de Mn empregadas na solução nutritiva foram: 0; 0,085; 0,125; 0,250; e 0,500 mg L-1. Após 25 dias de cultivo, parte do total de plantas de soja transgênica foi pulverizada com o herbicida. No segundo experimento, para avaliação da cinética de absorção do Mn da cultivar Valiosa RR, as plantas foram pulverizadas com glifosate aos 26 dias de cultivo nas doses de 0, 15 e 960 g ha-1 e.a. Constatou-se que a transgenia para resistência ao herbicida não altera a nutrição mangânica na cultivar de soja Valiosa RR. Mesmo reduzindo a massa de matéria seca de raiz, o glifosate não interfere na absorção e no transporte de Mn na planta de soja transgênica. Quanto à absorção do Mn pela cultivar transgênica, os parâmetros cinéticos Km, Vmáx. e Cmín. não são alterados pelo herbicida aplicado via foliar.