Coexistence of soybean plants and Urochloa spp. under glyphosate and water deficit effects

In the insertion of forage plants of the genus Urochloa P. Beauv. (Poaceae) coexisting with annual crops, proper management of the intercropping becomes necessary to avoid economic losses. Among management measures, the chemical inhibition of forage plants with herbicide subdoses is highlighted. Therefore, this study evaluates the morphophysiological responses of soybean ( Glycine max (L.) Merr.) genetically modified to tolerate glyphosate (RR soybean), in coexistence with Urochloa spp., treated or not with glyphosate subdoses and subjected to water deficit. Two tests were carried out in pots with forage species Urochloa ruziziensis (R.Germ & Evrard) Crins and Urochloa brizantha (Hochst. Ex A. Rich.) R. D. Webster cv. Marandu coexisting with soybean, in randomized blocks with five replicates. The tests were arranged in a 2x2x2 factorial arrangement: the first factor was repre­sented by the absence and presence of forage; the second by the absence and use of glyphosate subdoses; and the third factor by 50% and 100% field capacity in the pots. The use of glyphosate suppressed the competitive capacity of forages, benefiting the soybean in coexistence. In the absence of suppression from glyphosate, the competition exerted by the forage promoted lower values for the physiological and morphological variables of soybean plants. Among the forages, U. ruziziensis was the most competitive with soybean plants. The root system of forages was not affected by water deficit, only the physiological and morphological characteristics of soybean, mainly rootdry mass. Glyphosate affected forage growth.