Abstract
Scarce research has been published concerning the effect of soil pH on the leaching potential of herbicides in tropical soils. Thus, we designed this study to evaluate the influence of soil liming on the leaching of trifloxysulfuron-sodium and pyrithiobac-sodium after simulated rainfall depths in soil columns. In the study, two trials were conducted simultaneously; the first experiment evaluated trifloxysulfuron-sodium (7.5 g ha-1), while the second experiment evaluated pyrithiobac-sodium (70 g ha-1). Both experiments were conducted in a randomized block design with a 2 x 4 x 5 factorial scheme and four replications. The design’s factors corresponded to 2 soil liming conditions (with or without liming), 4 simulated rainfall depths (0, 15, 30, and 45 mm) and 5 depths in the soil column (0-5, 5-10, 10-15, 15-20, and 20-25 cm). The trials were repeated, and only the source for the soil neutralization was changed, i.e., dolomitic limestone in Experiment 1 and calcium oxide in Experiment 2. Compared to trifloxysulfuron-sodium, the herbicide pyrithiobac-sodium indicated a greater potential for leaching. With more acidic soils, the leaching potential in limed soils was greater for both herbicides. Only the liming that used calcium oxide provided a significant leaching of trifloxysulfuron-sodium for depths greater than 20 cm. Simulated rainfall ≥ 15 mm provided leaching of pyrithiobac-sodium to a depth of 25 cm at near-neutral soil pH values.
Highlights
An herbicide’s fate is affected by the processes related to its retention, transformation and transport in the soil
Related to the inhibition of shoot fresh biomass, there was a significant interaction between soil liming, simulated rainfall and the depth range of herbicide leaching for both herbicides and experiments
The rainfall depths of 0 and 15 mm did not cause the displacement of this herbicide in depths exceeding 10 cm
Summary
An herbicide’s fate is affected by the processes related to its retention, transformation and transport in the soil. The mobility of a particular herbicide has a major influence on the herbicide’s effectiveness in weed control and its dissipation into the environment. Leaching is the major transport pathway for nonvolatile, water-soluble molecules. After the movement of water, these molecules shift in the soil. Leaching is a fundamental process in most herbicides’ incorporation into the soil. This incorporation is necessary if the herbicides are to reach either the germinating seeds or emerging seedlings. Over leaching might drive these particles into deeper layers of the soil, thereby limiting the herbicide’s activity and increasing its potential to become a groundwater contaminant as well
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