VOLATILIZATION OF FONOFOS, CHLORPYRIFOS, AND ATRAZINE FROM CONVENTIONAL AND NO-TILL SURFACE SOILS IN THE FIELD

We measured the effect of no-till on pesticide volatilization in a side-by-side comparison of volatilization rates from no-till (NT) and conventionally tilled (CT) fields. Volatilization rates were determined using the theoretical profile shape method for 10 of the 26 d following application. Soil and mulch residues were also measured. Volatilization losses of fonofos (O-ethyl S-phenyl ethylphosphonodithioate) and chlorpyrifos [O,O-diethyl O-(3,5,6-trichloro-2-pyridyl) phosphorothioate] from the NT field were two to four times volatilization losses from the CT field. As much as one-half of the application volatilized during 26 d. Volatilization of atrazine [6-chloro-N-ethyl-N'-(1-meth-ylethyl)-1,3,5-triazine-2,4-diamine] was also greater from NT, but only 1 to 2% of the application volatilized. Maximum volatilization rates were usually measured at midday, indicating that volatilization was not limited by soil dryness. Over the 26 d of the experiment, volatilization decreased faster than pesticide residue was depleted, suggesting residues were becoming more strongly sorbed to soil and/or mulch, or were becoming less accessible to the surface.