Effects of Liming and Urochloa brizantha Management on Leaching Potential of Picloram

Abstract

In pastures, the application of limestone is often performed after removal of the animals for proper development and establishment of regrowth. Together with this practice, the use of picloram in high concentrations for dicotyledonous weeds is common. Therefore, the evaluation of the behavior of this herbicide in these conditions is critical. The objective of this study was to determine the leaching of the picloram, in the soil with different pH and cultivated with Urochloa brizantha (signalgrass) trimmed or not. The experiment was plotted in a subdivided plot with four repetitions, where the plots were constituted by factors pH (5.3 and 6.4) and Urochloa brizantha managements (trimmed and no trimmed). The subplots were composed by depths (0 to 50 cm). The picloram was applied to the top of the columns after 65 days after emergency. A rain of intensity of 60 mm was simulated 12 h after the herbicide application. Picloram concentration was quantified by the high-performance liquid chromatography. Besides that, a control treatment was added without the presence of the signalgrass, for each substrate. The picloram was not detected in the percolated water through the columns. Picloram leached to deeper layers in the soil with pH 6.4, independently of the signalgrass management. The signalgrass reduced the leaching of the picloram, and those no-trimmed demonstrate a higher capacity to retain the herbicide in superficial layers. The liming of the soil increases the pH and reduces the amount of organic matter in the soil, which favors the leaching of picloram to the layer of 30–35 cm. Trimming of Urochloa brizantha reduces the capacity of this forage to reduce the leaching of picloram.

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