The effects of flame weeding on soil microbial biomass

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.