Fig. 1. The correlation between the amount of N mineralized from the mobile humic acid (MHA) fraction or the calcium humate (CaHA) fraction that were extracted from seven tropical lowland rice soils and incubated in the IRRI soil versus Tanhoi soil under anaerobic conditions at 30°C for (a) 3 and (b) 6 wk. ** and *** indicate significance at 1 and 0.1% levels, respectively; ns is not significant.