Soil carbon sequestration potential of US croplands and grasslands: Implementing the 4 per Thousand Initiative

SOIL CARBON SEQUESTRATION Scientific interest in managing soil organic carbon (SOC) stocks in the United States dates back more than a century because of its importance to soil fertility (Allison 1973), and the importance of the soil-climate nexus was advanced early on by Jenny through his iconic book Factors of Soil Formation (Jenny 1941, 1980). However, intensive research on SOC and climate change mitigation really started during the 1990s (Barnwell et al. 1992; Lal et al. 1998c; Paustian et al. 1997). Since then, rates of SOC sequestration through adoption of best management practices have been assessed for diverse land uses and eco-regions throughout the country, including for a wide variety of management practices on cropland (Paustian et al. 1997; Lal et al. 2004; Johnson et al. 2005; Franzluebbers 2005; Ogle et al. 2005; Causarano et al. 2006; Balkcom et al. 2013; Lal et al. 1998c; Martens et al. 2005), such as the inclusion of cover crops (Causarano et al. 2006; Olson 2013; Lal 2015a, 2015b, 2015c; Poeplau and Don 2015; Sainju et al. 2006, 2008); for conversions to perennial grass biofuel plantations (Liebig et al. 2008; Follett et al. 2012); and for improved management on grazing lands (Conant et al.