| Abstract
| - To reduce volatilization of the fumigant methyl bromide(MeBr) from soil into the atmosphere, attempts were madeto enhance microbial degradation of MeBr in soil bystimulating the activity of soil nitrifiers. DisappearanceofMeBr in limed Arredondo soil (pH 7.70) treated with anammonia-based nitrogen fertilizer,(NH4)2SO4, wasinitiallymore rapid than in unlimed Arredondo soil (pH 5.5−5.7).Disappearance of MeBr in limed soil with or withouttreatmentof (NH4)2SO4 that received 20μg/g MeBr was more rapidthan in the corresponding soil samples that received ahigher rate of MeBr (50 μg/g). Due to highernitrificationactivity in limed surface soil (0−15 cm depth) than inlimed subsurface soil (15−30 cm depth), disappearance ofMeBr in the surface soil with or without(NH4)2SO4treatmentwas also more rapid than in the corresponding subsurfacesoil. Both microbial and chemical degradation wereinvolved in the MeBr degradation in soil, with chemicaldegradation possibly being the major factor.Contributionfrom microbial degradation was greater in soil treatedwith (NH4)2SO4 than inuntreated soil, and up to 57% of MeBrdegradation was attributed to microbial degradation,mainlyby the activity of nitrifiers during the oxidation ofammonia. Inoculation of an ammonia oxidationbacterium,Nitrosomonas europaea ATCC 19718, to soilgreatlystimulated the initial degradation of MeBr. Inconclusion,stimulation of MeBr degradation in soil can be achievedthrough liming and application of an ammonia fertilizer aswell as through inoculation of an ammonia oxidationbacterium. Consequently, the rate of MeBr flux intotheatmosphere may be reduced after fumigation is completed.
|
