Effects of injection systems and plastic mulches on distribution and emissions of cis- and trans-1,3-dichloropropene and chloropicrin.

The concentration and distribution of a soil fumigant in the subsurface of field plots are two key factors in the determination of the fumigant efficacy. Subsurface concentrations of the biologically active compounds cis- and trans-1,3-dichloropropene (1,3-D) and chloropicrin (CP) were determined in soil at two adjacent injection traces and midpoint between the two traces in plastic-covered field beds after injection of the fumigant Telone C35 by conventional chisels or by a coulter rig (Avenger coulters). Two of the four beds were covered with metallic polyethylene film (MPE) and the remaining two were covered with virtually impermeable film (VIF). Three hours after chisel injection, concentrations of the three compounds at the two adjacent injection traces in the two beds were highly variable. Large concentrations of the compounds were detected at the side traces, whereas the compounds were not detected at the middle traces (bed centers) in the two chisel-injected beds covered with MPE or VIF. Initial concentrations of the three compounds at the two adjacent injection traces in the two Avenger-coulter-injected beds were more uniform than in the chisel-injected beds but still variable. Also, the three compounds had diffused horizontally to midpoint between the two injection traces in all four beds, generally in smaller concentrations. Concentrations of the three compounds in the shallow subsurface soil layer (0.5-30 cm) in the beds became progressively more uniform and then declined slowly. Volatilization losses from the two Avenger-coulter-injected beds and the chisel-injected bed covered with VIF were low. Combination of Avenger coulter injection and VIF provided better retention of the compounds in this soil layer and, thus, likely would provide better fumigant efficacy and crop yield.