Briggs, Breiner, Graham Pinus Ponderosa Charcoal 9 May 2005p. 1Contributions of Pinus Ponderosa Charcoal to Soil Chemical and Physical PropertiesChristopher M. BriggsAbstract Charcoal results from the incomplete burning of plant material and is found in mostsoil surface horizons, but little is known about its effects on soil properties. The objectives of thisstudy were (1) to determine the chemical and physical properties of ponderosa pine charcoalproduced under controlled conditions, (2) to compare the properties of the laboratory-producedcharcoal to those of wildfire-produced charcoal after it had resided in the soil for a number ofyears, and (3) to determine how charcoal additions to soil affect soil properties. We collected oursamples from a pine forest in the San Bernardino Mountains of southern California. We foundthat laboratory-produced ponderosa pine charcoal has a cation exchange capacity on the order of20-30 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 waterrepellent (water drop penetration time <10 s) than all other field-collected and laboratory-produced samples (water drop penetration time >2 h). The laboratory-produced charcoal C/Nratio (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 watercapacity and darkened the soil. We conclude that charcoal is not simply an inert compound insoils. It may play an important role in determining the properties and behavior of some surfacesoil horizons.Briggs, Breiner, Graham Pinus Ponderosa Charcoal 9 May 2005p. 2IntroductionCharcoal results from the incomplete burning of plant material, and is also called char orwood char. Charcoal is produced by wildfires in natural environments and is found in thesurface horizons of soils across the globe. It can persist in the soil environment for thousands ofyears (Teixeira et al., 2002). Wood charcoal has historically been used in filtration andpurification, due to its large specific surface area (Bansal et al., 1988), suggesting that it mayimpart 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), animportant aspect of soil fertility. Tryon (1948) conducted extensive experiments on otherchemical and biological effects of charcoal in soils, and found that conifer charcoal increasedsoil pH and limited the growth of pine seedlings. Early studies showed charcoal effects at highconcentrations (up to 450 g charcoal kg soil-1), but it has been suggested that charcoalamendments 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 thetemperature of charcoal formation, burn time, and gaseous environment are influential indetermining 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 thetemperature at its exposure to oxygen increases. Oxides form during complete combustion andare transformed to carbonates and hydroxides (Etiegni and Campbell, 1991), and thesetransformed oxides may raise charcoal pH. Nitrogen in plant material is easily volatilized at hightemperatures (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, thatcharcoal properties are dependent on burn length, temperature, and oxygen availability.Despite the ubiquity of charcoal in soil surface horizons, particularly in forest soils, fewstudies have addressed how charcoal might influence soil properties. Early studies that didaddress 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 physicalBriggs, Breiner, Graham Pinus Ponderosa Charcoal 9 May 2005p. 3properties of ponderosa pine charcoal produced under controlled conditions, (2) to compare theproperties of the laboratory-produced charcoal to those of wildfire-produced charcoal. Thewildfire-produced charcoal was collected from the field after it had resided in the soil for anumber of years, and in this paper is referred to as field-collected charcoal. We assumed that theaddition 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, weallow the calculation of soil-chemical mixture properties. Due to the dark color of and difficultyin wetting the pure charcoal samples, we tested soil-charcoal mixtures to (3) determine howcharcoal additions to soil material affect water-holding capacity and soil color.MethodsIn this study we focused on charcoal from ponderosa pine (Pinus ponderosa) because it is adominant conifer species in many of forests of the western United States, where fires arecommon. We collected freshly cut ponderosa pine wood at the Skyforest Ranger Station in theSan Bernardino Mountains of southern California. We also collected charcoal samples fromponderosa pine logs near Jenks Lake in the San Bernardino Mountains. These logs had burnedin a prescribed fire ~ 7 years prior to sample collection. We took charcoal only from logs wecould identify as ponderosa pine to ensure uniformity of wood species between laboratory andfield samples. Some charcoal was collected from the surface of the litter, some below the litterlayer and above the soil, and some within the top 10 cm of mineral soil. The pieces of charcoalwere 0.5 to 15 cm3 in size. Some soil material adhered to the charcoal, so we used a small drybrush 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 ofmany
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