Efeito residual de herbicidas aplicados em pré- emergência na cultura da soja sobre o milho e o algodão cultivados em sucessão

Abstract

The importance of soybean (Glycine max (L.) Merrill) to the country is undeniable, being the largest cultivated area in Brazil and a major source of foreign exchange through the export of grains and derivatives. In Brazil, the succession of crops is widely used, taking advantage of the tropical conditions of the country, which allows successive crops with high yields of productivity. Two crops stand out in the national scenario as options of cultivation in succession to the soybean: the corn and the cotton. The search for economy and productivity is opposed to weed interference, where control tends to increase production costs, reducing profit margins and decreasing product quality. In this context, herbicides appeared as a tool to control weeds and among the types of herbicides used, the pre-emergent ones have important characteristics, among them the long residual period. However, when the bioactivity of the herbicide exceeds the cycle of the target crop, persisting in the soil by the harvest of the next crop, the so-called carryover phenomenon occurs. Given the importance of succession/rotation of crops to the country's economy and the need for rational use of herbicides, it is necessary to conduct studies to understand the behavior of herbicides in soil and plants to avoid the potential risk of phytotoxicity caused by carryover. The objective of this work was to evaluate the residual activity of chlorimuron-ethyl, diclosulam, flumioxazin, imazapyr+imazapic and metribuzim herbicides applied in pre-emergence on soybean cultivation on maize and cotton grown in succession, identifying the potential risk in cause carryover. Three simultaneous experiments were conducted in areas of the Federal Rural University of Rio de Janeiro - Seropédica/RJ, during the period from September 2016 to March 2017, in a crop succession scheme, with an experimental design of randomization by block, with four replications , in factorial scheme 5x4+1 each, where factor A was composed of the herbicides chlorimuron-ethyl, diclosulam, imazapyr+imazapic, flumioxazin and metribuzim, and factor B, the four doses of the herbicides (½D, D, D + ½ and 2D) - in grams of active ingredient per hectare (g ia ha-1), plus the control treatment for each trial: maize, cotton and watermelon. The variables analyzed were chlorophyll a fluorescence; plant height, root length, root volume, dry shoot mass, root dry mass and antioxidant enzyme activity. The data generated in the experiment were submitted to analysis of variance (p≤0.05) and submitted to the Tukey test, at 5% probability. For corn and cotton crops, the carryover effect was not verified when cultivated 120 days after the pre-emergence of chlorimuron-ethyl, diclosulam, imazapyr+imazapic, flumioxazin and metribuzim herbicides. However, this persistence was not able to cause phytotoxicity in maize and cotton crops grown in succession to the soybean within the range tested in this study.