The effects of liquefied petroleum gas (LPG) flaming on soil microbial biom
ass and soil temperature were studied in a laboratory trial. The trial was
arranged to imitate the most common weed flaming practice, non-selective fl
aming pre-emergence of the crop. Soil samples were taken, without disturbin
g the soil surface, before the germination of the crop from a field cultiva
ted and sown in the spring. The microbial biomass in the 0-5 mm depth, meas
ured by substrate induced respiration (SIR), was decreased by 19% when the
soils were flamed with open flame burners using a flaming intensity of 4600
MJ ha(-1). The treatment was quite extreme, corresponding to a propane dos
e of 100 kg ha(-1), while the usual dose in practice is 20-80 kg ha(-1). Fl
aming had little effect on microbial biomass deeper in the soil (5-10 mm).
The soil temperature at 5 mm depth was raised by 4.0 degrees C and at 10 mm
by 1.2 degrees C. It is concluded that the threat that flaming poses to so
il microorganisms is small.