Utilizing the Soil-Plant-Atmosphere-Research (SPAR) Facility for Turfgrass Physiology Research.

The SPAR facility comprises ten outdoor, naturally-lit chambers that minimize many confounding factors associated with field trials.  The units are optimized for the measurement of plant and canopy-level physiology, growth and developmental processes under precisely controlled outdoor, naturally-lit chambers.  Due to this, basic plant processes investigated can be more directly targeted to the environmental variables being studied.  Each SPAR chamber consists of a steel soil bin (1 m deep by 2 m long by 0.5 m wide) and a 1.27 cm thick Plexiglas chamber (2.5 m tall by 2.0 m long by 1.5 m wide) to accommodate root and aerial plant parts. The Plexiglas transmits 97% of the visible solar radiation to pass without spectral variability in absorption (wavelength 400–700 nm).  During an experiment, incoming daily solar radiation is measured with a pyranometer (Model 4-8; The Eppley Laboratory Inc., Newport, RI).  Briefly, air ducts located on the northern side of each SPAR unit are connected to heating and cooling devices. Conditioned air is passed through the chamber and returned to the air-handling unit just above the soil level. Chilled ethylene glycol is supplied to the cooling system via several parallel solenoid valves that opened or closed depending on the cooling requirement. To fine-tune the air temperature, two electrical resistance heaters provide short pulses of heat, as needed. Chamber air temperature, carbon dioxide, and soil watering in each SPAR unit, as well as continuous monitoring of environmental and plant gas exchange variables, is controlled by a dedicated computer system.  The relative humidity of each chamber is monitored with a humidity and temperature sensor (HMV 70Y, Vaisala, Inc., San Jose, CA) installed in the returning path of airline ducts.  Condensate from the cooling coils can be collected in a trough and directed to a pipe leading out of the chamber. The water from this pipe is collected in a tube with a volume of 0.80 L outside the chamber. A transducer, calibrated for liters of water, and located at the bottom of the tube measures the height of water in the column. The height of water is converted to volume of water via a linear calibration with voltage.  Solenoids at the top and bottom of the tube control water flow into and out of the tube. At the end of every 15 min, the upper solenoid valve is closed, water amount measured, and the water dumped via the lower solenoid. One minute later, an empty tube measurement is made and the upper solenoid opened. The volume of water is the difference between these two measurements. This second measurement provides a constant empty tube baseline that minimized effects of temporal variation in transducer response.