“…Klimanek and Greilick (1981) found CO 2 concentrations in soil air of up to 2.9% in field experiments while examining the influence of bulk density on soil aeration for the same soil (a Chernozem at Bad Lauchstädt). A large number of field studies and field experiments have reported similar concentration ranges with maxima in the range of 1 to 5% (e.g., Pumpanen et al, 2003a, 2003b; Doff Sotta et al, 2004; Riveros‐Iregui et al, 2007; DeSutter et al, 2008; Koehler et al, 2010; Ek and Godissart, 2014; Han et al, 2014; Roland et al, 2015; Fan et al, 2016). Others have observed soil respiration processes at CO 2 concentrations below 1% (Risk et al, 2002; Jochheim et al, 2018), while concentrations of up to 10% have also been reported (Oh et al, 2005; Taneva et al, 2006; Bekele et al, 2007; Jaakkola and Simojoki, 2008; Wiaux et al, 2015).…”