Soil Organic Carbon Measurement Protocols: A USA and Brazilian Comparison and Recommendation

Soil organic carbon measurement protocols: A USA and Brazilian comparison and recommendation

Maggie R. Davis 1, Dana Abulebdeh2, Bruno Alves 3, Marcelo Galdos 4, Douglas L. Karlen5, Keith L. Kline1

1 Oak Ridge National Laboratory, Oak Ridge Tennessee, USA

2 University of North Carolina at Charlotte, Charlotte NC, USA

3 The Brazilian Agricultural Research Corporation (EMBRAPA), Brasília, DF – Brazil

4 Brazilian Bioethanol Science and Technology (CTBE), Campinas, Sao Paulo - Brazil

5 National Laboratory for Agriculture and the Environment (NLAE), Ames Iowa, USA

Key words: standards, greenhouse gas, bioenergy, sugarcane, maize

Abstract:

Measuring changes in soil organic carbon (SOC) has received significant attention not only from researchers and policy makers striving to develop climate change mitigation strategies, but also by those focused on the increasing global demand for food, feed, fiber, and most recently feedstocks for bioenergy and bio-product industries. Both efforts have intensified concerns regarding SOC depletion, but there is a lack of consensus on sampling strategies, measurement techniques, and verification methods. This has created an urgent need for standardized, practical measurement protocols for SOC (Post et al. 2001, Jandl et al. 2014) that will provide a consistent assessment and a comparable product regardless of where studies are conducted (Panagos 2012). Even with a documented lack of consensus on the protocols for measuring, processing, and estimating SOC, this parameter is being used to estimate CO2 flux from agricultural practices and has become a component of lifecycle analyses (LCA) for bioenergy systems (Doran and Jones 1996; Reeves, 1997; USDA, 2006; McBride et al. 2011; Jandl et al. 2014). Bioenergy producers that can show a GHG offset for their fuel could have an advantage in the increasingly competitive global bioenergy market (Cerri et al., 2013). Therefore, LCA results are extremely important to biofuel producers and end-users seeking the most sustainable bioenergy options.

This presentation focuses on SOC studies conducted in two major bioenergy producing countries with the two primary ethanol feedstock crops – corn (Zea mays L.) in the U.S. and sugarcane (Saccharum officinarum) in Brazil. We conducted a literature review and have provided a comparison of sampling protocols for measuring SOC to identify and address inconsistencies in SOC assessment between the two countries. In this comparison, we draw significantly on research by Cerri et al. (2013) which identified appropriate methodologies for determining SOC for sugarcane, the US Department of Agriculture’s (USDA) Greenhouse gas Reduction through Agricultural Carbon Enhancement network (GRACENet) protocols for soil sampling (Liebig et al. 2010), and the closely aligned Resilient Economic Agricultural Practices (formerly the Renewable Energy Assessment Project) (REAP) protocols (Karlen 2010, Karlen et al. 2011) for assessing sustainability of corn stover production and harvest. We identify sources of significant variance due to methods and discuss options to build consensus for a common SOC assessment approach that could be implemented for future studies.

Financial Support: CTBE, Grant 2012/06933-6 São Paulo Research Foundation (FAPESP), NLAE, ORNL, UT-Battelle LLC, U.S. Department of Agriculture - Agricultural Research Service, U.S. Department of Energy

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