Soil Sample Variation and Herbicide Incorporation Uniformity

Copper sulfate (CuSO 4 · 5H 2 0) was used as a tracer to determine soil sample variation and the effects of incorporation and seedbed preparation practices on the horizontal distribution of broadcast herbicide sprays. A Dubbs very fine sandy loam soil was sprayed with 14.1 kg/ha copper (as CuSO 4 solution) and 19 mm diameter soil core samples were taken to a depth of 15 cm after spraying, after single or double disk-harrow incorporation, and after incorporation followed by bedding and row leveling. Cores were systematically located along and across the center two rows of the plots and numbered according to position. Soil cores were weighed, extracted with 0.05 M Na 2 EDTA and the extract was analyzed by atomic absorption spectrophotometry. For all samples, cores had a range of copper between 50 and 1000 μg, with a coefficient of variation of 47%. Disk-harrow incorporation decreased the copper found in the center of the harrow path by nearly 50%. Bedding followed by row leveling did not change the tracer content of cores but decreased soil core densities. Disk-harrow incorporation may redistribute a herbicide that is initially applied evenly, producing areas of poor weed control and/or crop damage. This observation was confirmed in a field bioassay using trifluralin (α,α,α-trifluoro-2,6-dinitro- N,N -dipropyl- p -toluidine) and wheat ( Triticum aestivum L. ‘Coker 6815′).