Briggs Breiner Graham Pinus Ponderosa Charcoal 9 May 2005 Contributions of Pinus Ponderosa Charcoal to Soil Chemical and Physical Properties Christopher M Briggs Abstract Charcoal results from the incomplete burning of plant material and is found in most soil surface horizons but little is known about its effects on soil properties The objectives of this study were 1 to determine the chemical and physical properties of ponderosa pine charcoal produced under controlled conditions 2 to compare the properties of the laboratory produced charcoal to those of wildfire produced charcoal after it had resided in the soil for a number of years and 3 to determine how charcoal additions to soil affect soil properties We collected our samples from a pine forest in the San Bernardino Mountains of southern California We found that laboratory produced ponderosa pine charcoal has a cation exchange capacity on the order of 20 30 cmol kg 1 and field collected samples accumulate native cations on their exchange sites Field collected charcoal samples from immediately below the litter layer were much less water repellent water drop penetration time 10 s than all other field collected and laboratoryproduced samples water drop penetration time 2 h The laboratory produced charcoal C N ratio 644 was about three times larger than the field collected charcoal ratio 196 263 Addition of finely divided charcoal to mineral soil significantly increased the available water capacity and darkened the soil We conclude that charcoal is not simply an inert compound in soils It may play an important role in determining the properties and behavior of some surface soil horizons p 1 Briggs Breiner Graham Pinus Ponderosa Charcoal 9 May 2005 Introduction Charcoal results from the incomplete burning of plant material and is also called char or wood char Charcoal is produced by wildfires in natural environments and is found in the surface horizons of soils across the globe It can persist in the soil environment for thousands of years Teixeira et al 2002 Wood charcoal has historically been used in filtration and purification due to its large specific surface area Bansal et al 1988 suggesting that it may impart unique physical and chemical properties to soils Early research on charcoal addressed its properties as an amendment to agricultural soils Charcoal additions were found to soil increase water content Retan 1915 and retention Tryon 1948 Charcoal was also shown to increase soil cation exchange capacity Swenson 1939 an important aspect of soil fertility Tryon 1948 conducted extensive experiments on other chemical and biological effects of charcoal in soils and found that conifer charcoal increased soil pH and limited the growth of pine seedlings Early studies showed charcoal effects at high concentrations up to 450 g charcoal kg soil 1 but it has been suggested that charcoal amendments could be beneficial at concentrations closer to those occurring naturally in soils Glaser et al 2002 which generally do not exceed 10 g kg soil 1 Skjemstad et al 1996 Schmidt et al 1999 Research related to the preparation of charcoal for industrial purposes has shown that the temperature of charcoal formation burn time and gaseous environment are influential in determining charcoal properties such as pH Chang et al 1982 and carbon to nitrogen ratio Glaser et al 1998 Charcoal pH may vary along a gradient from acidic to basic as the temperature at its exposure to oxygen increases Oxides form during complete combustion and are transformed to carbonates and hydroxides Etiegni and Campbell 1991 and these transformed oxides may raise charcoal pH Nitrogen in plant material is easily volatilized at high temperatures White et al 1973 and the C N ratio of pine wood charcoal produced at 300 C has been found to increase with longer burn times Glaser et al 1998 It is clear then that charcoal properties are dependent on burn length temperature and oxygen availability Despite the ubiquity of charcoal in soil surface horizons particularly in forest soils few studies have addressed how charcoal might influence soil properties Early studies that did address this topic did not report the methods of producing charcoal used in the studies e g Tryon 1948 The objectives of this study were 1 to determine the chemical and physical p 2 Briggs Breiner Graham Pinus Ponderosa Charcoal 9 May 2005 properties of ponderosa pine charcoal produced under controlled conditions 2 to compare the properties of the laboratory produced charcoal to those of wildfire produced charcoal The wildfire produced charcoal was collected from the field after it had resided in the soil for a number of years and in this paper is referred to as field collected charcoal We assumed that the addition of charcoal to a soil shifts the properties of the soil toward the properties of the charcoal proportionate to the charcoal concentration in the soil By testing properties of pure charcoal we allow the calculation of soil chemical mixture properties Due to the dark color of and difficulty in wetting the pure charcoal samples we tested soil charcoal mixtures to 3 determine how charcoal additions to soil material affect water holding capacity and soil color Methods In this study we focused on charcoal from ponderosa pine Pinus ponderosa because it is a dominant conifer species in many of forests of the western United States where fires are common We collected freshly cut ponderosa pine wood at the Skyforest Ranger Station in the San Bernardino Mountains of southern California We also collected charcoal samples from ponderosa pine logs near Jenks Lake in the San Bernardino Mountains These logs had burned in a prescribed fire 7 years prior to sample collection We took charcoal only from logs we could identify as ponderosa pine to ensure uniformity of wood species between laboratory and field samples Some charcoal was collected from the surface of the litter some below the litter layer and above the soil and some within the top 10 cm of mineral soil The pieces of charcoal were 0 5 to 15 cm3 in size Some soil material adhered to the charcoal so we used a small dry brush to clean each piece The soil material used in the laboratory part of this study was a sandy loam coarse loamy mixed superactive mesic Typic Dystroxerept derived from granitic rock similar to soils of many ponderosa pine habitats Burns and Honkala 1990 It is from the C horizon of a soil in the Sequoia National Forest California and it is more
View Full Document
Unlocking...