Reactivity of the Plant Growth Regulator Paclobutrazol (Cultar) with Two Tropical Soils of the Northeast Semiarid Region of Brazil

Abstract

The reactivity of paclobutrazol (PBZ, a plant growth retardant) with a Yellow Ultisol and a Vertisol from the semiarid northeast region of Brazil was evaluated through batch sorption experiments and modeling. Although not instantaneous, the sorption kinetic of PBZ (pure and formulated) was fast (a few hours) in both soils. The sorption kinetics were well described by a second-order (dS(t)/dt=k(2)(S(e2)-S(t))(2)) but not by a first-order model. The sorption isotherms were found to be linear and the calculated K(D) values were 8.8 +/- 0.11 and 7.4 +/- 0.2 L kg(-1) for pure PBZ in the Ultisol and the Vertisol, respectively. The corresponding K(OC) values were 1275 +/- 34 (logK(OC) = 3.11) and 1156 +/- 49 (logK(OC) = 3.06) L kg(-1), respectively. Considering the very different texture of the two soils and the similar K(OC) values determined, these results showed that in both soils, the sorption of PBZ is dominantly controlled by organic matter, although some interactions of PBZ with iron oxides (goethite) were observed in the Ultisol. Based on these sorption parameters a low leachability potential of PBZ in soils is anticipated, as they correspond to a groundwater ubiquity score (GUS) ranging from 2.0 to 2.7, i.e., moderately to not mobile, in contradiction with the actual groundwater situation in Brazil. This work stresses the need to evaluate and predict the risk associated with aquifer contamination by this widely used plant growth regulator.

Plant growth regulator and nitrogen fertilizer effects on soil organic carbon sequestration in creeping bentgrass fairway turf

“…However, some studies have pointed out the peculiarity of paclobutrazol in the soil in relation to the organic matter. Milfont et al (2008) reported that its fate and toxicity is still unclear and poorly documented. According to these authors, paclobutrazol absorption is predominantly controlled by the organic matter, probably through hydrophobic bonding.…”

Small‐Scale Spatial Variability of Atrazine and Dinoseb Adsorption Parameters in an Alluvial Soil

“…Soil samples were sieved to a size fraction <2 mm. Adsorption isotherms were determined according to an experimental procedure similar to the one used in previous studies (Martins and Mermoud, 1998, 1999; Milfont et al, 2008). Three grams of dry soil were mixed with 6 mL of dinoseb or atrazine solutions at different concentrations into 9‐mL polypropylene centrifuge tubes (Sarstedt, Nümbrecht, Germany).…”

Can the productivity of mango orchards be increased by using high-density plantings?

“…Paclobutrazol persists in soils due to its interaction with organic matter and iron oxides (Milfont et al, 2007(Milfont et al, , 2008. It is mobile in some soils and can be leached below the root-zone (Costa et al, 2008;Milfont et al, 2008).…”

“…It is mobile in some soils and can be leached below the root-zone (Costa et al, 2008;Milfont et al, 2008). Residues persist in the soil after frequent or heavy applications of the chemical (Subhadrabandhu et al, 1999;Sharma and Awasthi, 2005a;Sharma et al, 2008;Bhattacherjee and Singh, 2015).…”