Herbicide Movement in Conventional and Reduced Tillage Soils

Abstract

Reduced tillage systems, in which the previous crop's residue is left at the soil surface at planting, are becoming increasingly popular. The USDA Office of Planning and Evaluation (1975) has estimated that by 2010, 95% of the U.S. cropland will be planted using reduced tillage. One of the main advantages of these systems is the conservation of soil water due to greater infiltration and less evaporation. Concern has arisen that the higher soil water contents in reduced tillage systems may lead to more deep drainage and movement of herbicides into groundwater (Hinkle, 1983). Metribuzin, 4-amino 6-(1,1-dimethylethyl)-3-(methylthio)-1,2,4trizain- 5(4H)-one and alachlor, 2-chloro-N-(2,6-diethylphenyl)-N(methoxymethyl) acetamide are two commonly used soil applied herbicides. Metribuzin is more soluble in water than alachlor and has been shown to be more mobile in soil than alachlor (Savage, 1976; Wu, 1980). Under reduced tillage, over half the applied metribuzin and alachlor may be intercepted by the crop residue at the soil surface (Banks and Robinson, 1982; Banks and Robinson, 1986). The effect of reduced tillage on the movement of these herbicides in the soil has not been shown. The objective of this study was to determine the effect of tillage, straw cover, and irrigation on movement of metribuzin and alachlor in a field soil.