Eloy Molina

Soil aluminum and iron fractions and their relationships with P immobilization and other soil properties in andisols of costa rica and panama

Abstract The immobilization of P is a significant fertility limitation of Andisols in Central America. It is believed that soil Al and Fe fractions have an important influence on P availability. This study was conducted to obtain information on the various forms of Al and Fe in ten pedons derived from volcanic ash in Panama and Costa Rica. Correlations between these Al and Fe fractions and P immobilization were measured by different methods. The Al and Fe fractions, extracted by acid ammonium oxalate, 4M KOH, sodium pyrophosphate and dithionite‐citrate, were determined, and the correlations between these fractions, P immobilization, and other soil properties made. It was observed that oxalate extractable Al correlated significantly with P immobilization, which had values of over 85% by the New Zealand method and 96% by the isotherm method. The Al concentration corresponding to this immobilization was over 2%. The difference between oxalate extractable Al and pyrophosphate extractable Al (inorganic Al frac...

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

SUMMARY 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 nondestructively 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 114739 BD, Residual mean square (RMS) 699 for the individual equation, versus Biomass leaf 6841 BD, RMS 724 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 19 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 heartof-palm agroecosystems and serve other purposes such as for carbon sequestration calculations.

Lime response of tanier in an Ultisol of Costa Rica

Abstract Root crops constitute an important part in the diet of millions of people throughout the Tropics. These crops are produced by subsistence farmers in poor soils where acidity is the most common problem and liming materials, such as limestone, are scarce and expensive. Few experimental data are available on the fertility requirements and liming response of tanier (Xanthosoma sagittifolium). This study was conducted to determine the effect on yield of limestone application. Rates of 0, 1, 2, 3, and 4 t/ha of calcitic and dolomitic limestome, respectively, were applied in an Ultisol. Tanier shows tolerance to soil acidity with yields 58% a of maximum with 64% aluminum (Al) saturation. The limestone additions of 4 t/ha resulted in a pH of 4.38 and 4.68 with calcitic and dolomitic limestone, respectively, which produced the highest yield.

Calibration of the time‐domain reflectometer and determination of the volumetric water content of the soil profile in an ultisol of Costa Rica

Abstract An experiment was conducted to determine if time‐domain reflectometry (TDR) could be used to measure the water content at different depths in the O‐to‐75 cm soil layer. Probes of three wires (1/8 inch diameter and 30 cm exposed length) were installed in field plots differing in current crop‐fertilization history. Measurements of volumetric water content using bulk density and gravimetric water content were made to calibrate the TDR method. Comparison of water contents determined by TDR with those from gravimetric samples showed that there is a linear relationship (small offset but same slope) of water content with depth, indicating that there is little difference in volumetric water content from the 0 to 75 depth. However, the TDR method gives consistently lower water content values as compared with values obtained by gravimetric determination. Continuous measurements of profile soil water content with TDR in wet and dry periods during the year indicated that the mayor differences in volumetric w...