Residual effects of soil fumigation on soil respiration and mineralization

Soils were taken from fields that had been fumigated with formalin or methyl bromide 6 months to 5 years previously. Fumigated and unfumigated soil respired at similar rates when incubated in the laboratory. By contrast, after they had been exposed to chloroform vapour, the fumigated respired less rapidly and mineralized less nitrogen than the unfumigated. Irradiation (2.5 Mrad) was broadly similar to chloroform vapour in its effects on soil respiration and mineralization. These results are attributed to the elimination of a section of the soil biomass during field fumigation: recovery was not complete even after several years.

Field experiments sometimes show a declining crop response to repeated fumigation. Our results show that less nitrogen is mineralized after a second fumigation than after the first. Thus, when nitrogen is limiting growth, a second fumigation will be less effective than the first, quite apart from any effect on plant pathogens.