Preliminary evaluation of dew condensers and their use for tree seedling irrigation in Puerto Rico

Abstract

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 Urethanizer^TM8 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 Waterboxx^TM, 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.