Respostas morfofisiológicas e nutricionais de soja a aplicação de herbicidas e a competição com plantas daninhas

Abstract

The loss of soybean grain productivity due to weed competition can exceed 50% if no control method is adopted. Among the control methods most used by soybean producers, chemical control with herbicides stands out, one of the reasons being its practicality, efficiency, and lower cost compared to other management methods. Therefore, the objective of this study was to evaluate the effect of herbicides and weed competition on the morphophysiological and nutritional characteristics of the soybean cultivar Vênus 57K58RSF CE. The experiments were conducted in a greenhouse using a completely randomized design with four repetitions, repeated during the 2022/23 and 2023/24 agricultural seasons. Soybeans competed with the weeds horseweed (Conyza bonariensis), Alexandergrass (Urochloa plantaginea), pigweed (Amaranthus hybridus), and morning glory (Ipomoea indivisa). The herbicides applied were 2,4-D choline (971 g ha-1), ammonium glufosinate (400 g ha-1) + mineral oil (0.5% v/v), and glyphosate (1231.62 g ha-1), applied either individually or in tank mixtures when the soybeans were at the V3 to V4 growth stages. The evaluated variables were: a) phytotoxicity at 7, 14, and 21 days after treatment application, b) morphological variables including leaf area (LA) and shoot dry mass (SDM), c) physiological variables including sub-stomatal CO2 concentration, stomatal conductance to water vapor, photosynthetic rate, transpiration rate, carboxylation efficiency, and water use efficiency, and d) nutrient concentration, specifically nitrogen, phosphorus, and potassium (N, P, and K) in the leaf tissues.The herbicides applied individually or in tank mixtures demonstrated selectivity for the crop, exhibiting low symptoms of phytotoxicity and no negative effects on the morphophysiology of the soybean. Soybeans in the presence of Alexandergrass, morning glory, pigweed, and the combination of horseweed+Alexandergrass+morning glory+pigweed showed reduced leaf area (LA) and shoot dry mass (SDM) production. When infested with horseweed, soybeans exhibited better physiological performance compared to the other weeds. Soybeans in the presence of pigweed showed greater nutrient accumulation (N, P, and K). The herbicides 2,4-D choline, ammonium glufosinate, and glyphosate applied individually or in tank mixtures did not affect the morphophysiological and nutritional characteristics of the soybean.