Fig. 2. Relationship between severity of damping-off (DO) of cucumber and (a) free particulate organic matter, (b) FDA activity, (c) microbial biomass C, and (d) water-stable aggregates. Regressions are across three sample times, 2 mo after the first amendment (), 12 mo after the first amendment (•), and 2 mo after the second amendment (). Each solid line represents a statistically derived "suppressive threshold": the level of disease severity significantly different from the control (P < 0.05).