Vegetative characteristics of soybean (Glycine max L.) as bioindicator parameter of herbicide in the soil

Abstract

The objective of the present study was to evaluate the presence of the herbicide 2,4-D in the Neosol. We conducted the experiment in a greenhouse using the soybean crop as a bioindicator. A randomized block design with 5 × 3 factorial scheme composed of five application periods before sowing (0, 3, 6, 9, and 12 days) and three simulated rain (0 mm, 20 mm, and 30 mm), with four repetitions was conducted. The herbicide dose was 1500 g a.i. ha-1, the rainfall was simulated one hour after pulverization. Twelve hours after the last rain simulation, Cv. TMG® ANTA 82 RR was sown, and pot moisture remained at 80% of pot capacity throughout the experiment. Herbicide in the soil was evaluated by visual plant phyto-intoxication, plant height, shoot fresh mass and root fresh mass, and shoot dry mass and root dry mass at 26 days after sowing. Statistical analysis was performed according to the polynomial regression model. The application of herbicides in dry soils that remained without rain during the first hours resulted in greater residual effect on the soil (0 mm of rain). The occurrence of higher humidity accelerated the degradation of the herbicide in the soil (30 mm of rain). Longer periods between application and sowing provided more significant increments. The herbicide's toxic effects reduced linearly as started from 12 days before sowing. The 2,4-D showed low persistence in the soil, and 12 days was observed to represent a safe time length between spraying and sowing, regardless of the occurrence of rainfall. The soybean was a good indicator of 2,4-D.