Variation of the bioavailability of metsulfuron-methyl herbicides and triasulfuron under different liming conditions in two volcanic soils of southern Chile

Abstract

The use of sulfonylurea herbicides together with calcareous amendments is a common practice in acid soils derived from volcanic ash, especially in cereal crops. The objective of this study was to determine, through bioassays, the bioavailability of metsulfuron-methyl and triasulfuron herbicides by liming in two soils derived from volcanic ash. The soils used were a Hapludand series Malihue and a Paleohumult series Fresia. The indicator species was pea (Pisum sativum L.), planted in pots with both soils and under four levels of liming (equivalent to 0, 1.9, 3.7 and 7.4 t ha^-1 of Ca (OH)₂) and 11 concentrations of herbicides. In each bioassay a control treatment with non-adsorptive substrate with non-limestone quartz was included. After 8 days of herbicide application, the radical length of the indicator species was measured and the values obtained were adjusted to a non-linear model, the dose that inhibited 50% of the radical development (ID₅₀) in each treatment was determined. The bioavailability of each herbicide corresponded to the quotient between the ID₅₀ obtained in the quartz substrate and the ID₅₀ obtained in each treatment. The results showed that the adsorption of metsulfuron-methyl and triasulfuron decreased as the liming dose increased, increasing their relative bioavailability in both soils. The adsorption of triasulfuron with increasing lime applications was lower than that of metsulfuron-methyl in quantitative terms, but higher in relative terms. These results were corroborated when examining the adsorption coefficients (Kd).