Anemometry tools and procedures for greenhouse experiments

Greenhouses provide a useful environment for conducting plant studies, facilitating manipulation and measurement of many variables in the plant microclimate. Photosynthesis, transpiration, thigmomorphogenic responses, and particle transport all depend on the level of air speed at the leaf/atmosphere interface, the microclimate. Yet there seems to exist no standard method of measuring and documenting air velocity in greenhouses.This study was undertaken to determine the airflow parameters for describing the greenhouse microclimate; to investigate anemometer systems best adapted to measurements; to measure airflows in typical greenhouses so that appropriate instruments and procedures might be recommended; and to propose and test a set of measurement procedures for the greenhouse research scientist.Literature review showed a divergence of methodology used in greenhouse versus field crop microclimate studies. Greenhouse research literature predominately used single-leaf models, while atmospheric boundary layer research developed whole-canopy models. An integration of the two approaches is needed so that an entire experimental area in a greenhouse can be characterized with a few key air speed measurements.The greenhouse measurements pointed out the inappropriateness of certain anemometer systems, particularly those which have a markedly directional response. Three research anemometers and three hand-held commercial grade anemometers were evaluated. Most of the kinetic energy in the turbulence spectra was contained in frequencies of less than 5 Hz. Omnidirectional anemometers were shown to be sufficient and convenient for assessing mean velocities over the plant canopies. However, the highly turbulent conditions within the plant canopy may be better studied with tools other than heated element anemometers.Each of the greenhouse rooms measured showed a range of microclimate air velocity means of at least seven to one, except for a commercial fan-tube ventilated greenhouse which had a range of only 2.4 to one. The broad range of means emphasized the need for documentation of air speeds during experiments.Profiles of air speed over the plant canopies showed that the proposed standardized measurement height over the canopy can give meaningful data. A grid system was tested and shown useful in representing rectangular experimental areas of various sizes.U of I OnlyETDs are only available to UIUC Users without author permissio