Title: Carbon mineralization in two ultisols amended with different sources and particle sizes of pyrolyzed biochar Authors
Submitted to: Chemosphere
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: December 6, 2013
Publication Date: March 18, 2014
Citation: Sigua, G.C., Novak, J.M., Watts, D.W., Cantrell, K.B., Shumaker, P.D., Szogi, A.A., Johnson, M.G. 2014. Carbon mineralization in two ultisols amended with different sources and particle sizes of pyrolyzed biochar. Chemosphere. 103:313-321. Interpretive Summary: Intensive crop production depletes nutrients and reduces soil organic matter from soils. A potential solution is the use of biochar as a soil amendment to enhance soil fertility and offset expenses for fertilizer and lime. An increase in soil fertility is the most frequently reported benefit linked to adding biochar to soils. However, the relationship between biochar properties and its potential to enhance agricultural soils is still unclear and does not allow the establishment of appropriate process conditions to produce a biochar with desired characteristics. The objective of this study was to compare carbon (C) mineralization in two Ultisols (Norfolk and Coxville) soils amended with different sources and particle sizes of biochars. Results of this study strongly support our hypothesis that feedstock processed into pellets will have lower rate of C mineralization in soils compared with smaller-size (dust) biochar particles produced from the same feedstock. Hence, biochar processing into pellets and dust-sized materials had significant effect on its mineralization under laboratory conditions in two Ultisols. Our results further suggest that different sizes and forms of biochar as well as soil type can influence biochar mineralization. For the purposes of enhancing soil fertility, dust-sized manure-based biochars (poultry litters and swine solids) could be the ideal choice, whereas pelletized lignocellulosic-based biochars like pine chips or switch grass would be beneficial for a long-term stability of carbon source in the soil. Our study represents an initial step, but further efforts are needed to perform soil test in order to establish some appropriate formulations of desired biochar properties based on sources and particle size.
Technical Abstract: Biochar produced during pyrolysis has the potential to enhance soil fertility and reduce greenhouse gas emissions. The influence of biochar properties (e.g. particle size) on both short- and long-term carbon (C) mineralization of biochar remains unclear. There is minimal information on the potential effects of biochar particle sizes on their breakdown by soil microorganisms, so it is unknown if the particle size of biochar influences C mineralization rate and/or stability in soils. In order to evaluate the effect of different sources and particle sizes of biochar on C loss and/or stability in soils, an incubation study on C mineralization of different biochar sources and particle sizes was established using two soils: Norfolk soil (fine loamy, kaolinitic, thermic, typic Kandiudults) and Coxville soil (fine loamy kaolinitic, thermic, Paleaquults). In separate incubation vessels, these soils were amended with one of two manure-based biochars (poultry litters, PL; swine solids, SS) or one of two lignocellulosic-based biochars (switchgrass, SG; pine chips, PC), which were processed into two particle sizes (dust, <0.42 mm; pellet, >2 mm). The amount of carbon dioxide (CO2) evolved varied significantly between soils; particle sizes and the interactions of biochar source and sizes of biochars with soil types. Averaged across soils and sources of biochar, CO2 evolved from dust-sized biochar (281.3 mg/kg) was significantly higher than pellet-sized biochar (226.2 mg/kg). Coxville soil with SS biochar produced the greatest average CO2 of 427.5 mg/kg and Norfolk soil with PC had the lowest CO2 production (93 mg/kg). Measured rates of carbon mineralization also varied with soils and sources of biochar (Norfolk: PL>SS>SG=PC; Coxville: PC>SG>SS>PL). The average net CO2 evolved from the Coxville soils (385.2 mg/kg) was about three-fold more than the CO2 evolved from the Norfolk soils (123.4 mg/kg). Our results suggest different particle size and sources of biochar as well as soil type can influence biochar stability.