EVAPORATIVE EFFECTS ON MOBILITY OF 14C-LABELED TRIASULFURON AND CHLORSULFURON IN SOILS.

Abstract

A laboratory soil column experiment was conducted to determine the mobility of 14 C-triasulfuron in A horizon material of Farnum loam, fine-loamy, mixed, thermic Pachic Argiustoll from Kansas, Norfolk loamy sand, fine-loamy, siliceous, thermic Typic Hapludult, and Rion sandy loam, fine-loamy, mixed, thermic Typic Hapludult from North Carolina, and Webster silt loam, fine-loamy, mixed, mesic Typic Haplaquoll from Iowa as well as 14 C-chlorsulfuron in Rion sandy loam and to measure the effects of evaporation on capillary transport of the leached herbicides upward when soil columns were in contact with free water and not over free water. Triasulfuron mobility was in the order Norfolk (R f = 0.52) = Rion (R f = 0.48) > Farnum (R f = 0.40) > Webster (R f = 0.26), and R f was inversely related to the organic and humic matter contents of the soils. Evaporation of water from the soil surface of leached triasulfuron-treated Rion and Norfolk soils over a 2-week period had pronounced effects on herbicide transported upward, particularly when soil columns were in contact with free water simulating a shallow water table. Evaporation had no effects on capillary transport upward in Farnum and Webster soils, probably because of their higher contents of organic and humic matter. Chlorsulfuron was 18% more mobile than triasulfuron in Rion sandy loam, and both herbicides were distributed in a similar pattern in the soil when water was applied to the surface and leached or applied to the base of the columns and transported upward by capillary action. Redistribution of the herbicides upward in capillary water will likely influence persistence of the chemicals, particularly in soils over shallow water tables.