An Investigation of Reflective Mulches for Use Over Capillary Mat Systems for Winter-time Greenhouse Strawberry Production

Photosynthethically active radiation (PAR) is a principle environmental variable used by horticultural specialists, agronomists, and ecosystem modelers to characterize the quantity and quality of light conducive to plant growth and development. Spatial distribution of PAR in a greenhouse can be quite variable and diffuse throughout the daytime photoperiod, especially at low sun angles in northern regions of the United States. Four colors of reflective plastic mulches (white, red, olive, and black) were evaluated for winter-time strawberry (Fragaria x ananassa Duch.) production based on their reflectance and transmittance properties in a double-polyethylene, plastic-glazed Quonset greenhouse in Nebraska. The spectral properties of the plastic film mulches were investigated in the laboratory using a spectral radiometer and integrating sphere. For greenhouse spectral studies, a modified field of view set of LiCOR PAR sensors and infrared thermocouple sensors (IRT/c) were mounted over the greenhouse gravel floor and the strips of plastic films of four different colors. Both incident and reflected PAR and plastic mulch temperatures were recorded during the day using a wireless, LabVIEW-based data logger system. The red mulch reflected less than half the amount of PAR than that from the white mulch and the olive and black mulches reflected even less. The white 6-mil reflective mulch was then selected to cover a capillary mat (CapMatII) irrigation system in a greenhouse strawberry production study. A three-month production study using the white reflective mulch under 312 strawberry pots resulted in the production of over 1700 saleable berries with a mass of over 19 kg. Plastic mulches could enhance the PAR environment of greenhouses and thus translate to more consistent plant production during winter months.