When leaf litter exhibited net N immobilization, immobilization increased until week 2-4 but then decreased until week 16 Figure 3, Figure 4 a, b, suggesting that the treatments were entering the net N mineralization phase after this period. S. saman and P. macrocarpus exhibited lower N immobilization than the other residues. Both had higher N 14-18 g kg–1 and lower PBC approx. 100 g BSA mg–1 than the other residues Table 3. Handayanto et al. 1997, in their work on mixing residues of different quality i.e., Gliricidia and Peltophorum, found a critical value of approximately 100 g BSA mg–1 above which N mineralization is strongly reduced.