| The efficacy of inter-row vegetative filter strips (VFS) for controlling runoff of the commonly used organo-phosphate insecticide (diazinon) from dormant-sprayed orchards was investigated through physical (microecosystem) and numerical models.; The microecosystem consisted of a pesticide sprayer, rainfall simulator and orchard floor model with and without VFS. Diazinon was sprayed at a rate of 2.8 kg/ha within 24 hours prior to rainfall simulation. Rainfall, at an intensity of 50 mm/hr, was simulated for 60 minutes. Experiments were conducted for 0%, 50%, and 100% soil coverage by VFS. Diazinon concentrations in overland flow, interflow and infiltration outflow, and also in soil and vegetation samples were measured.; Total diazinon losses from the orchard floor model at the end of rainfall-runoff simulation as applied pesticide mass were 8.6%, 5.8% and 2.3%, respectively for the 0%, 50%, and 100% VFS cover treatments. The microecosystem study indicated that inter-row VFS has potential for reducing diazinon runoff from dormant-sprayed orchards. The principle mechanism of diazinon runoff control in VFS was the diversion of runoff water, the primary pesticide carrier, into interflow and vertical infiltration. Most of the diazinon was trapped on the surface of the VFS and its root zone.; A numerical simulation model of Pesticide Runoff through Vegetative Filer Strips (PRVFS) was developed as a tool for investigating effects of the pesticide transport mechanisms on VFS design in the field. The PRVFS model satisfactorily predicted the micro-ecosystem simulated diazinon transport for the 0%, 50% and 100% VFS cover conditions. Model sensitivity analyses indicated that pesticide transfer from surface soil to overland flow and the pesticide washoff from VFS were important mechanisms affecting diazinon transport. The combination of rainfall intensity and VFS coverage are important design factors. However, at small rainfall intensities, increasing VFS coverage may provide little additional diazinon runoff control. For a 35 mm/hr rainfall intensity, even 25% VFS coverage significantly reduced diazinon losses in runoff. The PRVFS model is shown to be a beneficial tool for evaluating and analyzing possible Best Management Practices for controlling offsite runoff of pesticides applied in orchard production. |
