Stacy A. Adams

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 × 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.

Improved Instrumentation and Controls for Biomass Heating and Impact on Greenhouse Profitability

An adaptive real time crop and greenhouse model was implemented in a Nebraska commercial double-poly greenhouse during 2008 and 2009. Biomass heating using a pellet-burning furnace was alternated with a traditional propane heating system. Data collected included three spatial measurement zones within the greenhouse, including air and furnace temperatures, plant temperature, floor temperature, potting soil temperature, and inside roof glazing temperature using low-cost IRT/c sensors. Humidity, total and photosynthetically Humidity, total short wave radiation and photosynthetically active radiation (PAR) and the outside conditions were also measured. Ventilation fan, unit heater, and biomass burner operations were monitored with split core current sensors attached to the electric supply and control wires. National Instruments LabVIEW® software was developed to collect data and to report energy usage, moisture condensation potential, and production performance of the greenhouse. The zone loggers communicated using wireless technology with a master computer located at one end of the house. Moisture condensation potential on the leaves, floor, and inside glazing was continuously monitored throughout each day. Night time heat loss over the growing periods ranged from 25,000 to 160,000 BTU per hour. Greenhouse moisture condensation was found generally less for biomass than with the propane heating operation. Furnace performance was reported and a fuzzy logic control system is still being tested. Biofuel energy content was measured using an adiabatic bomb calorimeter. Considerable fuel savings were found possible with the system providing feedback to the grower.

Use of Reflective PAR Mulches to Enhance Winter-time Greenhouse Strawberry Production

Photosynthethically-active-radiation (PAR) has long been used by horticultural specialists and crop modelers to characterize the quantity and quality of light conducive to plant growth and development. The spatial distribution of light within a double-polyethylene glazed plastic Quonset greenhouse can be quite variable and diffuse throughout the photoperiod, especially at low sun angles in the northern regions of the United States. Previous literature has reported 10-35% increase in canopy lighting using reflective plastics under various plants. A study was undertaken to evaluate the productivity of fourteen strawberry cultivars in a campus Quonset house during the winter months. Modified field of view LiCOR™ PAR reflectance sensors, full hemispherical PAR incident sensors, and infrared thermocouple sensors (IRT/c) were mounted over gravel and five different color plastic backgrounds. PAR and mulch temperatures were recorded for several months using a wireless LabVIEW™-based sensor network within the greenhouse. Weather and the greenhouse environment were also monitored. The use of background reflective plastics or so-called reflective mulches to increase PAR and to capture heat within cap-mats was also studied. It was experimentally found that several of these cultivars will bear significant fruit and could be economically productive during winter.