Wednesday, November 7, 2007
285-9
Changes in Temperature Profile and Properties of Organic Soils of Different Initial Moisture Conditions Under External Thermal Impact.
Atsuko Obuchi, Taku Nishimura, Masaru Mizoguchi, Hiromi Imoto, and Tsuyoshi Miyazaki. Graduate School of Agricultural and Life Sciences, University of Tokyo, Yayoi 1-1-1, Bunkyo-ku, Tokyo, 113-8657, Japan
Forest fires occur throughout the world and their effect on soil needs to be studied to assess the potential for vegetation restoration. In this research we simulated forest fires by exerting thermal impacts on soil columns consisting of either andisol, toyoura sand or a peat-sand mixture which contained total carbon of 4.8%, 0%, 3.9% respectively. The soil samples were packed into stacked unglazed cylinders, 18 cm in diameter and 5 cm in length, to form 30 cm soil columns. Bulk density and initial water content were controlled for each soil sample. Charcoal was burned on the soil surface to heat the surface to 500-700 ℃ for 6 hours. Temperature profiles were monitored with thermocouples at 0, 1, 2, 4, 6, 8, 10, 15, 20 and 25 cm below the soil surface. After burning, volumetric water content, carbon and nitrogen contents of the soils were measured at different depths. Soil water repellency was determined using the Water Drop Penetration Time (WDPT) method. At the end of the experiment the drying front induced by the fire was observed at about 6 to 8 cm depth. The drying front was deeper when the initial water content was lower. The temperature was higher than 100 ℃ in the soil behind the drying front, and loss of organic matter was observed in the surface 5 cm layer both of the andisol and peat-sand mixture columns. In addition, the Carbon-Nitrogen ratio became higher than 20 in the same layer. These results mean that the soil was inappropriate for plant growth immediately after burning. Soil water repellency, which was different according to depth and initial water content, was observed only in peat-sand mixture. The repellency appeared when the soil temperature was raised to between 100 and 500 ℃, but became less above 500 ℃.