Above-ground nitrogen dynamics following the complete pruning of a nodulated woody legume in humid tropical field conditions
1995
Nygren, P.
Above-ground nitrogen fluxes following a complete pruning of the neotropical agroforestry tree Erythrina poeppigiana (Walpers) O.F. Cook (Leguminosae: Phaseoleae) were studied during pruning intervals of 26 and 23 weeks in the humid tropics of Costa Rica. The experiment included four clones and a half-sib family of the species. The leaf-level N fluxes were modelled as a function of leaf age, and were scaled to the canopy level on the basis of the leaf age distribution. The N content of young leaves increased exponentially, followed by relatively small changes at maturity. Slight net N retranslocation started at the middle of leaf life span, but a major N efflux occurred only a few days before leaf shedding. It was estimated that, depending on the tree source, 29-44% of the total N accumulation in the above-ground biomass occurred during 11 weeks after pruning (WAP), before initiation of nodulation. The nodule biomass peaked at the time leaf shedding started (15-17 WAP). Considerable rapid N efflux from the foliage was observed at this time, suggesting regulation of nodulation by a feedback from the foliage. The implications of the N economy of E. poeppigiana on its management in agroforestry systems are discussed.
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