NITROGEN RELEASE FROM PRUNINGS OF LEGUME HEDGEROW TREES IN RELATION TO QUALITY OF THE PRUNINGS AND INCUBATION METHOD

Three methods: litterbags, incubation of materials in pots and incubation in leaching-tubes, were compared to determine the effects of N, lignin and polyphenols of legume tree prunings on their decomposition and N release rates in a Red-yellow Podzolic soil (Ultisol). A protein-binding capacity assay was used to measure the content of active polyphenols in pruning materials in relation to their effect on decomposition. Prunings of Calliandra calothyrsus, Peltophorum pterocarpa, Gliricidia sepium, Leucaena leucocephala, and a mixture of Peltophorum and Gliricidia from an alley cropping experiment in Lampung, Indonesia, were used for the study. Decomposition and N release rates of the prunings were in the order Gliricidia > Leucaena > Calliandra > Peltophorum in all three incubation methods, however, the patterns of N release varied between incubation methods and species. The (lignin + polyphenol):N ratio was consistently among the best quality descriptions to predict weight losses and N released from the prunings in the litterbag and leaching-tube experiments but not in the pot experiment. In the latter the lack of a good correlation with quality factors maybe due to the presence of soluble polyphenols with a greater capacity to bind protein under non-leaching conditions.