Fig. 3. Model II regressions between incubation labile carbon (C_l) and other techniques for measuring labile soil organic C pool sizes: (a) light fraction C (P < 0.2), (b) hydrolyzable C (P < 0.001), (c) microbial biomass C (P < 0.1), and (d) Day 12 labile C (P < 0.00001). The C_l is determined with a two-pool model using constrained nonlinear curve fitting to respiration data from a 360-d laboratory incubation. All measurements were made on samples from the 0- to 10-cm soil depth.