Soil Fumigation Applied through Deep Drip Tapes in Totally Impermeable Film Mulched Raised-bed Systems for Strawberry Production

California strawberry production is highly dependent on soil fumigation through drip tapes buried at shallow depth in polyethylene (PE) mulched raised-beds. However, the high fumigant emission loss is being regulated stringently by government due to human safety and air pollution concerns. Using totally impermeable film (TIF) and applying fumigants deeper may reduce the fumigant emission and improve pest control efficacy, but little information is available regarding the effects of these application strategies in the raised-bed production system. A trial was conducted in a strawberry field at Camarillo, CA to evaluate the distribution, emission, and fate of the fumigants in Pic-Clor 60 EC [a mixture of 56.7% chloropicrin (CP), 37.1% 1,3-dichloropropene (1,3-D), and 6.2% inert ingredients] as affected by application depth, application rate, and film type. The treatments included applying fumigant with full rate (25 gallon/ac) or half rate at shallow depth or at shallow plus deep depths under TIF (TIF/shallow/full; TIF/shallow/half; TIF/deep/full; TIF/deep/half), and a full rate at shallow depth under PE (PE/shallow/full).  A non-fumigated control with shallow irrigation and TIF (TIF/shallow/CK) was included for comparison. Results showed that fumigant emissions are primarily through the TIF covered beds and very little fumigant escaped from the furrows between beds. Comparing to past results on fumigant emissions in PE tarped raised-beds, TIF reduced fumigant emission dramatically. In the TIF/shallow/full treatment, the emission peak fluxes were 41.4 and 24.0 ug m^-2 s^-1 for 1,3-D and CP respectively, while in the TIF/deep/full treatment, they were only 17.3 and 5.8 ug m^-2 s^-1, suggesting that deeper applications can further reduce fumigant emission. At the same application depth, the fumigant concentration under TIF with half rate was found even higher than that under PE with full rate, implying that the use of TIF may allow reduced fumigant rates to achieve pest control comparable to conventional applications. Field observations on the strawberry growth during early stage did not show significant differences among fumigation treatments.  However, there is modest yield improvement with the deep drip lines, possibly due to the improved pest control results. The on-going field evaluation is expected to further show the advantage of using deep drip fumigation, especially during the later season as pest reinfestation may occur.