Retenção de herbicidas pré-emergentes pela palhada sob diferentes condições de irrigação

Abstract

Brazil is the largest producer of soy in the world, and it has great representation in the country's economy. However, production is reduced when there are adverse factors, such as competition with weeds. Thus, it is necessary to look for alternatives so that there is efficient control of them, in order to reduce the producer's costs and increase the productivity of the crop. An alternative is the application of herbicides during the pre-emergence of weeds. However, the straw adopted in the no-tillage system (NT) can be an adverse factor for the pre-emergent herbicides to have maximum efficiency, since it prevents some herbicides from reaching the soil completely, being retained next to it. Therefore, the objective was to simulate the interference of rain in the retention of different herbicides by the straw, applied in the pre-emergence of soybeans and Brachiaria decumbens, at different time intervals after application. The experiment was conducted in a greenhouse, in 8-liter pots. A completely randomized design (DIC) was adopted, in a 4x4 bifactorial scheme, where the first factor consisted of the application of different pre-emergent herbicides (Control without product, Smetolachlor, Imazethapyr and Cletodim). The second factor consisted of irrigation of the treatments after application (No irrigation, 1 hour after application (HAA), 24 HAA and 48 HAA). At 7, 14, 21 and 28 DAA, the number of emerged plants for soybean and brachiaria was counted. At 28 DAA, the height of soybeans and brachiaria was measured, as well as trefoil counts and stem thickness measurements for soybeans and leaf counts for brachiaria. It was observed that the herbicide s-metolachlor had better efficiency in the control of Brachiaria decumbens and had less interference in the development of soybean, when irrigation 1 and 24 HAA were performed. The herbicide clethodim, on the other hand, had better efficiency in all situations when there was irrigation after application. For the herbicide Imazethapyr, no significant difference was noted in any of the situations. However, it is understood that when there is rain after application, the efficiency of some pre-emergent herbicides can be increased.