EFEITO RESIDUAL DE HERBICIDAS EM SOLO ARENOSO E ARGILOSO COM A SUCESSÃO SOJA-SORGO

Abstract

Four experiments were conducted in different soil types (sandy and clay). The purposes of these trials were to study the herbicides pre-emergent control to weeds (Commelina benghalensis, Cenchrus echinatus - CCHEC, Eleusine indica - ELEIN) and understand about the selectivity for soybean, sowed in summer period and sorghum, sowed in the second season during 2018-2019. The treatments sprayed at soybean pre-emergence were: diclosulam (35.3 g ia ha-1), chlorimuron (20 g ia ha-1), flumioxazin (50 g ia ha-1), sulfentrazone (200 g ia ha-1) and s-metolachlor (1728 g ia ha-1). The treatments sprayed at sorgum pre-emergence were: s-metolachlor + atrazine (576 + 1250 g a.i. ha-1) and atrazine (1250 g a.i. ha-1). The weed control was evaluated using the EWRC scale (1964) at 7, 14, 21 and 28 days after planting (DAP) for both crops. Selectivity was analyzed as a visual evaluation (% visual). Vegetation indexes MPRI, VARI and PRI, obtained after flying over trials at 35 DAP using an unmanned aerial vehicle (UAV) were evaluated. In addition, the bands of visible spectrum were captured with the aid of a low-cost RGB sensor. Plant stand and plant height were performed at 14 DAP, as well the distance between canopies and indirect measurement of chlorophyll content at 35 DAP. The leaves tissues were evaluated about the nutrient contents at 35 DAP. The yield was collected in the end of trials. None of the herbicides applied in the pre-emergence of soybean affected soybean or sorghum productivity. The complementation of radiometric evaluations with other assessments conducted in the field reinforced this selectivity. Herbicides were effective to control weeds until 28 DAP. In sorghum, at 21 DAP, in sandy soil, for CCHEC, the control provided by sulfentrazone sprayed at soybean pre-emergence was 97%, while atrazine sprayed at sorghum pre-emergence provided 86%. About ELEIN control, in the same evaluation period, sulfentrazone, diclosulam and chlorimuron also had better control than atrazine (97.3%; 96%; 95.8% and 85.8% respectively). The conclusion was that pre-emergent herbicides are excellent tools to be used in the soybean-sorghum succession, helping growers with weeds management. It is recommended that they should be used within the technical recommendations and with plant monitoring through field evaluations (biometrics analysis and injury) and through of digital agriculture tools (vegetation indexes and leaf analysis).