Coastal Tableland is a landscape unit in the North East of Brazil in which the main soils are Ultisols. In these soils, a compacted layer denominated "cohesive horizon" occurs and root growth is limited by it. An experiment with five treatments and six replications was set up in order to study how liming and gypsum could improve root depth of orange (Citrus sinensis L. Osbeck) crop in an Ultisol in which a compacted layer was found at 0.3 m. Treatments were: A - No liming and no gypsum; B - Liming to achieve 60% base saturation; C - B + 1 t of gypsum ha-1 ; D - B + 2 t of gypsum ha-1 and E - B + 3 t of gypsum ha-1. Gypsum increased calcium and sulfate in the cohesive horizon. Surface application of lime and gypsum did not cause changes in soil density and total porosity in the cohesive horizon. An improvement of root length was observed at the cohesive horizon.

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 l 11n4739 BD" n )!%#, Residual mean square (RMS) l 69n9 for the individual equation, versus Biomass leaf l 6n841 BD# n !)', RMS l 72n4 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 1n9 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.

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Do sis óp ti ma para la fer ti li za ción ni tro ge na da del arroz, en la Re gión Cen tral de Pa na má. El es tu dio se reali zó en los años 2003 y 2004 en las Es ta cio nes Ex pe ri menta les de Ca la ba ci to y Gua ru mal y en fin cas de pro duc to res de Ma ria to, Pro vin cia de Ve ra guas y To no sí, Pro vin cia de Los San tos. Se apli ca ron dosis de 0; 40; 80; 120; 160 y 200 kg de N/ha, con urea co mo fuen te de N. Adi cio nal men te se apli caron 100 kg de P 2 O 5 /ha y 50 kg de K 2 O /ha, se empleó co mo fuen tes su per fos fa to tri ple y clo ru ro de po ta sio, res pecti va men te. Se uti li za ron las va rie da des IDIAP 2503 y CHI 3-30 en Ca la ba ci to y Gua ru mal; IDIAP 2503 y CR 5272 en To no sí, Co lom bia XXI en Ma ria to. El di se ño ex pe ri men tal fue de blo ques com ple tos al azar en un arre glo fac to rial con seis tra ta mien tos y cua tro ré pli cas. Hu bo res pues ta sig ni fi ca ti va a la apli ca ción de N en to dos los si tios. Los ren di mien tos ob te ni dos variaron des de 3,3 t/ha en Ma ria to a 5,7 t/ha en To no sí, en el 2003. En To no sí se ob tu vie ron do sis óp ti mas de 44 kg /ha pa ra IDIAP-2503 y 84 kg /ha pa ra CR-5272. En Ma ria to 71 kg /ha fue la do sis más efectiva pa ra la va rie dad Co lom bia XXI. En 2004 en Ca la ba ci to se de ter minó que pa ra CHI-330 no hubo res pues ta a más de 55 kg /ha apli ca do y se es ti mó una efi cien cia de uso de N de 35%, sin em bar go pa ra IDIAP-2503 el ni vel óp ti mo fue de 155 kg de N/ha y la efi cien cia de uti li za ción de N fue de 25%. El ni vel crí ti co fo liar de N fue de 3,06% pa ra am bas va rie da des. En Gua ru mal se de ter mi nó que la dosis óptima de N pa ra IDIAP-2503 fue de 119 kg /ha y pa ra CHI-330 de 105 kg /ha. El ni vel crí ti co de N fue de 2,9 y 2,57, res pec ti va men te.Palabras clave: Arroz, dosis óptima de N, fertilización nitrogenada, nivel crítico, eficiencia de N. and 200 kg/ha were applied as urea. All plots received 100 kg P 2 O 5 /ha as triple superphosphate and 50 kg K 2 O/ha as potassium chloride. Rice varieties IDIAP 2503 and CHI 0330 were compared at Calabacito and Guarumal; varieties IDIAP 2503 and CR 5272 were compared at Tonosi, and variety Colombia XXI was used at Mariato. A randomized complete block design with four replications was used in all experiments. There was a significant yield response to applied N in all experiments. Maximum grain yields in 2003 ranged from 3.3 t/ha at Mariato to 5.7 t/ha at Tonosi. Optimum N rates were 44 kg/ha for IDIAP 2503 and 84 kg/ ha for CR 5272, both at Tonosi, and 71 kg/ha for Colombia XXI at Mariato. For the experiment at Calabacito in 2004, there was no yield response by variety CHI 0330 above 55kg applied N/ha and fertilizer N use efficiency was estimated to be 35%; optimum fertilizer N for IDIAP 2503 was 155 kg/ha with a 25% use efficiency. Critical foliar N at flowering for both varieties at Calabacito was 3.06%. Optimum fertilizer N levels at Guarumal were 119 kg/ha for IDIAP 2503 and 105 kg/ha for CHI 0330, with critical foliar N levels...