Comparison of Heat Transfer and Soil Impacts of Air Curtain Burner Burning and Slash Pile Burning

We measured soil heating and subsequent changes in soil properties between two forest residue disposal methods: slash pile burning (SPB) and air curtain burner (ACB). The ACB consumes fuels more efficiently and safely via blowing air into a burning container. Five burning trials with different fuel sizes were implemented in northern California, USA. Soil temperature was measured at 1, 2, 3, 4, 6, and 8 cm depth. Immediately after burning, soil samples from two depths (0-10 and 10-20 cm) and ash samples were collected for analyzing organic matter; carbon and nitrogen content; and calcium, magnesium, and potassium concentrations. The highest temperature observed was 389 degrees C at 1 cm depth under the SPB. Mean peak temperatures were 133.2 degrees C and 162.2 degrees C for ACB and SPB, respectively. However, there were no significant differences in peak temperatures and duration of lethal soil temperatures (total minutes over 60 degrees C) between ACB and SPB. Heat transfer decreased rapidly as the soil depth increased. There is little evidence that any subsequent changes in soil chemical properties occurred, concluding that these small-scale burns had few negative impacts at our study site. Therefore, given the lack of extreme soil heating and more efficient and safer woody residue reduction, the ACB may be more effective than open SPB, especially where fire escape or long-term fire damage to soils are of concern.