Dispersion of Reactive Fumigant Gases in Soil.

Soil fumigation is often used for control of soilborne diseases and plant pathogens in perennial nursery and orchard/vineyard crops.  Because perennial crops have relatively deeper rooting depth than annual crops and, in replant situations, may be in close proximity to existing growing plants, there is a need to develop fumigation practices that enhance vertical dispersion of fumigant gases without creating significant horizontal gas movement to adjacent areas.  Field studies were conducted to evaluate soil distribution of reactive fumigant gases under six treatments with different initial and boundary conditions.  The treatments were designated as “Buessing Shank”, “Straight Shank”, “Shank Tarp”, “Shank Bare”, “Shank Spot”, and “Drip Spot”.  Vertical fumigant gas movement was compared between the “Buessing Shank” and the “Straight Shank” treatments.  Horizontal fumigant gas movement was compared between the “Shank Tarp”, “Shank Bare”, “Shank Spot”, and “Drip Spot” treatments.  Soil air was sampled at various depths up to 90 cm at several time-points after fumigant application, and analyzed for fumigant concentrations.  Because of the additional nozzle at 66 cm depth on the “Buessing Shank”, compared to the single nozzle at 46 cm on the “Straight Shank”, there was some increased fumigant gas concentrations at the 66 cm depth zone but the increase was not significant.  Compared to the “Shank Bare” treatment, the “Shank Tarp” boundary condition greatly enhanced horizontal gas movement.  The “Shank Spot” treatment showed some horizontal gas movement between the treated areas, and significant quantities of fumigant gases were found within 50 cm from the subsurface emitters of the “Drip Spot” treatment.  These results showed that current and new fumigation methods are unlikely to cause significant horizontal off-site gas movement and additional techniques are needed to enhance vertical penetration of fumigant gases.