Soil Organic Matter Management: The Roles of Residue Quality in C Sequestration and N Supply - Sustainable Management of Soil Organic Matter - page 91

Fig. 3.1. CO 2 evolution of incubated leaves and roots of the tropical grass B.humidicolaand
tropical legume D. ovalifolium. Verticals bars are ± 1 SEM .
attack due to its entrapment within the cell walls (Chesson, 1997). Thus
the lignin : N ratio is widely known to govern residue decomposition of
many plant materials and is also used to allocate residue fractions to the
slow decomposing structural pool in many models such as CENTURY
(Parton et al ., 1987).
Condensed Tannins-Protein Complexes: A Direct Route
to Soil Organic Matter?
Tropical legumes are well known as a source of a wide variety of poly-
phenols and of other secondary metabolites (Waterman and Mole, 1994).
The importance of polyphenols in decomposition and nitrogen release from
the leaves and litters of tropical legumes has been demonstrated in both
herbaceous forage species (e.g. Desmodium intortum , Vallis and Jones, 1973)
and legume trees (e.g. Acacia , Calliandra , Inga and Peltophorum , Palm and
Sanchez, 1991; Constantinides and Fownes, 1994; Handayanto et al ., 1994)
and summarized by Giller et al . (1998). The combined (lignin +
polyphenol) : N ratio is now widely recognized as a useful predictor of
decomposition and N release for many plant materials (Constantinides and
Fownes, 1994; Handayanto et al ., 1994). However, the total amount of
extractable polyphenols does not necessarily reflect the activity and
recalcitrance of these organic residues. The ability of polyphenols to bind
protein has been established as a better indicator of short-term N release of
tropical legume pruning materials (Handayanto et al ., 1995). Longer term
implications of polyphenol-protein interactions have been investigated by