NITROGEN MINERALIZATION FROM LEAVES AND LITTER OF TROPICAL PLANTS - RELATIONSHIP TO NITROGEN, LIGNIN AND SOLUBLE POLYPHENOL CONCENTRATIONS

Rates and patterns of nitrogen mineralization from decomposing plant m aterials are known to be affected by initial concentrations of N, lign in and soluble polyphenols, but published results show differences in which properties correlated best with N release. We incubated soil wit h fresh leaves and litter from 12 species commonly used in tropical ag roforestry systems, including both legumes and non-legumes, to estimat e how release of mineral N was affected by chemical composition. After 16 weeks, net accumulation of mineral N in incubations ranged from 81 % of initial N in fresh Sesbania sesban to net depletion equivalent to 70% of initial N in Casuarina equisetifolia litter. Fresh legume leav es generally had net N accumulation, whereas legume litter and non-leg ume fresh leaves and litter had net depletion. At all sampling dates, the percent of leaf N accumulated was most highly correlated with init ial N concentration. Phosphorus and the ratios lignin:N and (lignin polyphenol):N also strongly correlated with N accumulation, although t hese indices themselves were correlated with N. We conclude that diffe rences among previous studies in best chemical predictors of mineraliz ation rates arose from relatively small ranges in chemical composition of materials used. Over our wide range of materials, initial soluble polyphenols were secondary to initial N, which explained most of the v ariation in N accumulation or depletion.