FIELD AGING OF TRANSPARENT POLYETHYLENE MULCHES: I. PHOTOMETRIC PROPERTIES.

Field observation of the temperature regime of irrigated plots mulched with new and old (previously used during one solarization season) transparent polyethylene sheets, has shown that higher temperatures prevail under the old sheets. In order to explain this unexpected phenomenon, we measured the photometric properties (absorbance, transmittance, and reflectance in the ultraviolet-visible and infrared regions of the radiation spectrum) of polyethylene mulches at four aging states encountered during prolonged field utilization. The measurements, carried out both in the field (with pyranometers) and in the laboratory (with spectrophotometers), show that the photometric properties change significantly during the aging process.