RESIDUAL ENTRE APLICAÇÕES DE NICOSULFURON E A SEMEADURA DE VARIEDADES DE SOJA

Abstract

The herbicide nicosulfuron is widely recommended for the control of invasive grasses in corn crops, especially when applied post-emergence. However, this product also shows potential for use in pre-planting applications in other crops, such as soybean. In this context, the objective of this study was to evaluate the tolerance of soybean variedades to the herbicide nicosulfuron applied at different pre-sowing intervals. Two experiments were conducted: one in a greenhouse and the other in the field. The first experiment was carried out in a greenhouse located in Rio Verde, Goiás. The experimental design was completely randomized with five replications, arranged in a 3x6 factorial scheme. Factor 1 consisted consisted of two application times of nicosulfuron, 28 and 7 days before sowing (DAS), plus a control without application. The second factor consisted of six soybean varieties: Olimpo IPRO, Iguaçu IPRO, Guepardo IPRO, M7601 i2x, Tormenta CE, and ST700 i2x.Throughout the experiment, phytotoxicity evaluations were performed, as well as biometric measurements of plant height and stem diameter. At 21 days after emergence (DAE), chlorophyll fluorescence was assessed, and at 28 DAE, shoot and root dry mass were evaluated. The application of nicosulfuron prior to soybean sowing had varying impacts on the early development of the evaluated varieties, revealing differences in varietal sensitivity to herbicide residues in the soil. The varieties Guepardo IPRO, ST700 i2x, and Tormenta CE stood out for their greater tolerance. The second experiment was conducted under field conditions during the 2023/2024 growing season in Rio Verde, Goiás. The experimental design used was a randomized complete block design with six replications and a 2×4+1 factorial scheme. Factor 1 consisted of the soybean varieties Olimpo IPRO and Iguaçu IPRO; factor 2 consisted of four application timings: 7, 14, 21, and 28 days before sowing (DBS), plus a control treatment with no nicosulfuron application. Throughout the experiment, plant stand, plant height, and stem diameter were evaluated, followed by analysis of chlorophyll a and b indices during flowering. Yield was assessed at the end of the crop cycle, with measurements of plant height, number of pods per plant, number of seeds per pod, and thousand-seed weight. No significant interaction was observed between varieties and application timing. Only varieties effects were significant, with Olimpo IPRO showing higher chlorophyll a and b indices, number of pods and seeds per plant, thousand-seed weight, and grain yield.