Dissipation of soil fumigants from soil following repeated applications.

BACKGROUND

The dissipation of pesticides in soil and the occurrence of accelerated degradation following repeated applications are well-known phenomena with many pesticides, but much less so with soil fumigants. The fate of various soil fumigants was studied in different agricultural soils following repeated applications of chloropicrin.

RESULTS

Fumigant dissipation reflected by Σconcentration × time (ΣC × T) and half-life values varied widely among the tested soils. Methyl iodide (MI) had the slowest dissipation rate compared with other fumigants in all tested soils. Elimination of biotic agents by soil sterilization prior to MI application did not affect MI concentration in Oxnard soil. Clay content and fumigant dose (ΣC × T values) of chloropicrin, 1,3-dichloropropene and MI were significantly correlated. No significant correlations were found between soil properties and ΣC × T values following metam sodium and methyl bromide (MBr) application.

CONCLUSION

The fate of the tested soil fumigants is highly dependent on and specific to the fumigant, previous fumigant application and soil type. This study suggests that biotic factors are more essential in the dissipation of metam sodium and MBr than abiotic factors. By contrast, MI dissipation from the tested soils is affected more by abiotic factors than by biotic activities.