Carbon Mineralization in a Charcoal Amended Forest Soil: Effect of Tree Species.

Charcoal application to forested soils has the potential to moderate nutrient leaching as well act as a carbon increment that counts toward carbon credits in a sequestration market. The function of charcoal as a soil amendment depends on its nutrient sorptive capacity and its recalcitrance. The objective of this research was to (1) investigate the phosphorus sorption characteristics of charcoal made pioneer species of the Central Amazon, and (2) investigate the recalcitrance of the charcoal when added to a sandy forested soil. The four tree species were Inga, Imbauba, Bamboo and Lacre. Charcoal was produced from their wood at 400, 500 and 600 degree Centigrade by pyrolysis. Charcoal from Inga, Imbauba and Lacre sorbed added P. All four species were more stable in a soil environment than was native soil organic matter. Carbon mineralization rates were initially 10 times slower. Imbauba, however, exhibited much higher rates of mineralization from charcoal formed at 400 and 500 degrees than that formed at 600 degrees. On average carbon mineralization rates of Imbauba were significantly higher than the other three species; and while Inga, Lacre and Bamboo carbon mineralization stabilized to near zero rates of carbon mineralization after 50 days, Imbauba continued to mineralize at constant rates to at least day 100.  Carbon sequestration potential of charcoal additions to forest soils can provide stable forms of carbon that mineralize much slower than native soil organic carbon, increasing the sequestered carbon stock of soils; however, the degree of sequestration can be related to the temperature of pyrolysis in the formation of the charcoal and the species from which the wood originated. Once in the soil, the charcoal is an efficient phosphorus absorber than has potential for moderating leaching of phosphorus in the very sandy soils characteristic of the lower coastal plain of the U.S.