Characterization of Char for Agricultural Use in the Soils of the Southeastern United States

Char produced from the pyrolysis of biomass has potential as an agricultural amendment in low fertility soils. Much of the interest in its use as an agricultural amendment has been stimulated by research discussed in this book and the previous volumes on the role of charcoal in terra preta soils. Results from studies conducted in South American and African tropics on acidic, highly-weathered Oxisols with low organic carbon (C), cation exchange capacity (CEC), and base saturation indicate that addition of charcoal has significantly influenced nutrient cycling, soil biology, and crop productivity (Glaser et al. 2002; Lehmann and Rondon 2006; Oguntunde et al. 2004). Increased yields and biomass have been reported for various legumes (Iswaran et al. 1980; Lehmann et al. 2003; Topoliantz et al. 2005) and for corn (Lehmann and Rondon 2006; Oguntunde et al. 2004). Increased productivity may be related to available nutrients (Glaser et al. 2002; Lehmann et al. 2003; Steiner et al. 2007), or increases in pH (Topoliantz et al. 2005; Steiner et al. 2007), and CEC (Steiner et al. 2007; Liang et al. 2006), as well as changes in water relations and soil biology (Glaser et al. 2002; Steiner et al. 2004). Although most studies report increased plant productivity with charcoal addition, plant biomass decreases have been observed, particularly at high application rates (Glaser et al. 2002). These responses could be related to nitrogen immobilization through high C:N ratios and sorption of NH₄ and NO₃ (Lehmann and Rondon 2006).

The southeastern United States is an important agricultural area. The state of Georgia alone has approximately 4.3 million hectares of corn (Zea mays), soybean (Glycine max), cotton (Gossypium hirsutum), and peanuts (Arachis hypogaea) in production and 9.6 million hectares of forestland largely in loblolly pine (Pinus taeda) production (USDA 2002; Georgia Forestry Commission 2007). The growing interest in biofuels is increasing demands on row crop production and may also increase demand on forestlands. The Ultisols of the southeastern United States are similar to tropical Oxisols with low organic C concentrations of less than 1%, low CECs of approximately 5 cmol kg⁻¹, and low base saturation of usually less than 30% (Perkins 1987). Char from energy production through pyrolysis may provide an opportunity to increase the productivity of southeastern soils, similar to the way charcoal functions in terra preta. However, because char characteristics vary with feedstock and pyrolysis conditions (Harris et al. 2006; Antal and Gronli 2003), a better understanding of the influence of these factors on char characteristics and the effect of different chars on soil processes in the southeastern United States is needed.