Results and discussion
Plant residue quality
Carbon contents of some materials were higher than previously reported values, i.e., S. saman, L. leucocephala, and S. grandiflora, of 543, 533, and 523 g kg–1, respectively Tawinteung et al. 1996, and in D. tuberculatus, I. malayana and T. indica of 447, 468, and 460 g kg–1, respectively Adulprasertsuk et al. 1997. However, C contents of some other native species, S. obtusa and X. xylocarpa, were lower than those of Adulprasertsuk et al. 1997 of 531 and 475g kg–1, respectively Table 3. Seasonal and stand variations in C contents have been found in some native forest species of the Northeast, for examples 440 511 g kg–1 in X. xylocarpa, and 431 526 g kg–1 in P. macrocarpus Toda, T. pers. comm. Dec 2003. Our C contents of rice straw and S. rostrata were lower than those of Vityakon et al. 2000 of 390 and 420 g kg–1, respectively.