DECOMPOSITION AND NUTRIENT RELEASE PATTERNS OF THE LEAVES OF 3 TROPICAL LEGUMES

Information on decomposition and nitrogen release patterns of tropical legumes is scarce despite the important role of legumes in agroforestry systems. Decomposition patterns of the leaves of three tropical legumes Inga edulis Mart., Cajanus cajan (1.) Millsp., and Erythrina sp. were determined by a litterbag study in an alley cropping experiment conducted in the Peruvian Amazon. The leaflets of the three species had similar nitrogen concentrations but different lignin and soluble polyphenolic concentrations. Inga and Cajanus decomposed at similar rates (k = 0.91 and 1.72 yr-1, respectively) and had similar polyphenolic concentrations but differed in lignin. Erythrina had the lowest concentration of polyphenolics and decomposed the fastest (k = 3.45 yr-1). Polyphenolics appeared to influence rates of decomposition more than percent nitrogen or percent lignin. It is proposed that the polyphenolics bind to N in the leaves forming compounds resistant to decomposition. These compounds may be precursors to stable forms of nitrogen in soil organic matter. Rates of nutrient loss followed the general trend potassium > phosphorus, nitrogen, and magnesium > calcium. It is apparent from this study that not all leguminous leaves decompose and release nitrogen quickly, despite high nitrogen concentrations in the leaves. Nitrogen release by legumes with high polyphenolic concentrations will be slower than that by legumes with low polyphenolic concentrations and has important implications to nitrogen cycling and the selection of legumes for agroforestry systems.