Water requirements for growth and survival of Swietenia macrophylla and Tabebuia heterophylla juvenile trees in relation to water production capacity of dew condensers1

Drought mortality of juvenile trees is a major cause for failure of reforestation projects. Portable devices such as passive radiative dew condensers can often provide 0.15 L/day of water in situ, possibly sufficient for tree survival until roots can access groundwater, allowing self-sustainability. To evaluate growth and survivability of juvenile trees of Tabebuia heterophylla Britton and Swietenia macrophylla King under such low water amounts, juvenile trees received approximately 0.033, 0.067, 0.134, 0.201 and 0.268 L/tree/day, representing fractions (relative evapotranspiration or RET) of 0.125, 0.25, 0.50, 0.75 and 1.00 of the evapotranspiration demand (ETo). The experiment lasted 60 days for S. macrophylla and 90 days for T. heterophylla. All T. heterophylla juvenile trees survived even at the lowest irrigation rate. However, S. macrophylla juvenile trees began dying at RET \u3c 0.5, with only 60 percent surviving at RET = 0.25 (0.067 L/day) and 100 percent mortality occurring at RET = 0.125 (0.033 L/day). Water requirements of 0.134 L/day, necessary for full survival of both species, were within the typical production capacity of 1-m2 dew condensers. However, a greater safetyfactor is obtained using drought tolerant species such as T. heterophylla, which can survive under water application rates as low as 0.03 L/day

Evaluación preliminar de condensadores de rocío y su utilización para riego de plántulas de árboles en Puerto Rico

Dew condensers have been proposed as a means to reduce drought mortality of tree seedlings in early stages of reforestation projects. We investigated the amount of dew condensate produced by locally constructed dew condensers, constructed with three different infrared emitting surfaces: standard polyethylene/ TiO2 / BaSO4 foil, thermoplastic polyolefin (TPO), and plastic coated with locally available Lanco UrethanizerTM8 roofing paint. All surfaces produced similar amounts of total dew condensate, typically ranging between 0.05 and 0.25 L/m2/night. However, the materials differed in the fraction of dew running off the surfaces, which represents the water available for tree seedlings. Highest runoff fractions were obtained with painted surfaces, followed by polyethylene and polyolefin surfaces, respectively. Considerably greater amounts of nightly dew condensate were observed during the winter than in summer, attributed to differences in night length and cloud cover. A commercially available dew condenser, the Groasis WaterboxxTM, did not generate more than 0.04 L per night of runoff dew, due primarily to a small condenser surface area of < 0.2 m2. A field study showed that 1 m2 dew condensers maintained the root zone of mahogany seedlings at matric potentials > -60 kPa during dry spells. Overall, results indicated that passive dew condensers with condenser areas of 1 m2 are capable of producing sufficient water for survival of small tree seedlings during drought periods.Los condensadores de rocío se han propuesto como mecanismo para proveer agua a plántulas de árboles en etapas iniciales de reforestación. Se investigó el potencial de condensadores de fabricación local para producir agua. Se compararon condensadores construidos con tres diferentes superficies emisoras en infrarrojo: lámina estándar de polietileno impregnado con TiO2 y BaSO4, poli-olefina termoplástica (TPO), y plástico recubierto con pintura Lanco UrethanizerTM disponible en ferreterías locales. Todas las superficies produjeron cantidades similares de condensado total de rocío, por lo general entre 0.05 y 0.25 L /m2/noche. Sin embargo, los materiales variaron en la fracción del condensado escurrido desde las superficies, lo cual representa el agua disponible para las plántulas. Las fracciones de escorrentía más altas se obtuvieron con las superficies pintadas, seguido por las superficies de polietileno y de poli-olefina, respectivamente. Las cantidades de condensado durante el invierno fueron mayores que en verano, probablemente debido a noches más largas y menor nubosidad en invierno. Se evaluó el volumen de rocío (escorrentía) producido por un modelo comercial de condensador de rocío, el Groasis WaterboxxTM. Este nunca superó 0.04 L por noche, atribuido principalmente a la pequeña área de superficie (< 0.2 m2) del condensador. Un experimento de campo mostró que condensadores de rocío de 1 m2 mantuvieron el potencial matricial de agua en la zona de raíces de plántulas de caoba en valores > -60 kPa durante periodos de sequía. En general, los resultados indicaron que los condensadores de rocío con áreas superficiales de 1 m2 producen suficiente agua para la supervivencia de pequeñas plántulas de árboles