Allometric relationships in Bactris gasipaes for heart-of-palm production agroecosystems in Costa Rica

Abstract

Peach palm (Bactris gasipaes Kunth) agroecosystems for hearts-of-palm constitute a productive and sustainable land use for the humid tropics. Allometric models allow to predict biomass non-destructively at any time, and subsequently, to determine the span of growth phases, biomass and nutrient pools, and economic yields. The overall goals of this study were to obtain and validate predictive functions of above-ground dry biomass of peach palm shoots, and to relate standing biomass with heart-of-palm yields as well. Towards this purpose, peach palm shoots were harvested and separated into components (foliage, petiole and stem) in the Atlantic region of Costa Rica. Basal diameter (BD) was a more effective predictor of biomass than height to the fork between the spear leaf and the first fully expanded leaf, total height and number of leaves. Regression models explained 70–89% of the variance in component (foliage, petiole and stem) or total shoot biomass. Nonlinear regression, which independently calculates equation coefficients for biomass components and total shoot biomass, was compared with a nonlinear seemingly unrelated regression (NSUR) procedure, which simultaneously fits the component equations that predict leaf, petiole and stem in order to assure biomass additivity. Equation coefficients for NSUR fitted-regressions that also model unequal variances, were substantially different from those for individual regressions; e.g. Biomass_leaf = 11·4739 BD^1·8042, Residual mean square (RMS) = 69·9 for the individual equation, versus Biomass_leaf = 6·841 BD^2·086, RMS = 72·4 for the NSUR fitted-equation. NSUR equations had slightly less precision in estimating biomass than individual equations but consistently less bias. In separate harvests of peach palm plants within four stands ranging in age from 1·9 to 21 years, estimates of component and total above-ground shoot biomass were similar to observed values except for the youngest stand in which biomass was overestimated. In another harvest, yield of heart-of-palm per plant was linearly related to total above-ground biomass in two peach palm stands of age 5 and 9 years. The non-destructive estimation of above-ground biomass from easily measured plant dimensions will permit any-time, less expensive and reasonable precise biomass estimates in peach palm. Biomass data can be incorporated to decision support aids for nutrient management in heart-of-palm agroecosystems and serve other purposes such as for carbon sequestration calculations.