Development of a Plant Shoot Temperature Model for Greenhouse Climate Management Progress Report — march 1993
Date February 23, 1993
Title of Project Development of a Shoot-tip Temperature Model for Greenhouse Climate Management
Institution where work is being conducted Michigan State University
Amount of Endowment Grant$ 15,000
Covering Period Jan. 1, 1992 to Dec. 31, 1993
Anticipated Date of Project Completion/Final Report Dec. ‘95
Individual(s) Conducting Project:
(List Project Leader First)
Royal D. Heins - Title Professor
Telephone Number 517/353-6628
James E. Faust - Title Graduate Assistant
Development of a Shoot-tip Temperature Model for Greenhouse Climate Management
Dr. Royal D. Heins and James E. Faust
Michigan State University
- A. Project Objectives:
- 1) Identify and measure the critical inputs and outputs for a shoot-tip energy-balance model.
- 2) Develop an accurate model of shoot-tip temperature based on measured environmental inputs which areroutinely measured in commercial greenhouses.
- 3) Compare the reliability of crop timing using air-temperature measurements with modeled shoot-tiptemperature.
- B. Summary:
- A system for measuring the variables influencing energy transfer has been established. The experimentalset-up is presently being used to measure evapotranspiration, convective heat transfer, solar and thermal radiation
of a Vinca plug crop. The data collected from this experiment are being used to develop the shoot-tip temperature
model.
- A datalogger has also been placed in several commercial greenhouses to quantify plant temperaturesoccurring in different greenhouse structures. The collected data are being used to compare to our experimental data
and to validate the shoot-tip temperature model.
- C. Results to Date:
- Initially, an energy-balance model utilizing five environmental variables is being used to predict shoot-tiptemperature. The environmental variables include: air temperature, dewpoint temperature, glazing material
temperature, soil temperature, and shortwave radiation. Shoot-tip temperature is predicted every five minutes.
Ninety-six percent of the predicted shoot-tip temperatures are within +/-1′C (1.8′F) of the actual shoot-tip
temperature, while seventy-two percent are within +/-0.5′C (0.9′F) of the actual temperature.
- Measurements recorded at MSU and commercial greenhouses indicate shoot-tip temperature is usually 2to 4′C (3.6 to 7.2′F) cooler than the air temperature at night. Low air velocity, and cold glazing temperature result
in plant temperature depression at night. Daytime shoot-tip temperature increases relative to air temperature as solar
radiation increases. Shoot-tip temperature is usually below air temperature on overcast days, the same as air
temperature when solar radiation is 15 to 20% of full summer sunlight, and increases above air temperature as the
solar radiation increases above 20% of full summer sunlight. Evapotranspiration increases as solar radiation
increases which results in cooling plant temperature however, shoot-tip temperatures are often 5 to 6′C (9 to
10.8′F) above air temperature when the solar radiation is 45% of full summer sunlight.
- D. Future Plans Covered by the Endowment Grant:
- The five variable shoot-tip temperature model will be reduced to just three variables which are commonlymeasured in commercial greenhouses: wet and dry bulb, and solar radiation. An artificial plant sensor will also
be developed in an attempt to improve and simplify the prediction of shoot-tip temperature.
- The effect of air velocity, thermal radiation, solar radiation, and vapor pressure deficit on plant temperaturewill need to be examined separately in controlled-environment growth chambers in order to understand how the
individual components of the energy balance influence shoot-tip temperature.
- E. Anticipated Benefits for Floral Industry:
- The anticipated benefits to the floral industry will be to improve the grower’s ability to meet increasinglynarrow market-date specifications by 1) improving the prediction accuracy of leaf- and flower-development models,
2) using existing climate-control computers to provide the proper shoot-tip temperatures, and 3) increasing the
grower’s ability to manage the greenhouse environment with climate-control computers.
- A plant temperature model can also be utilized to improve disease control. Fungi, such as Botrytis, requiremoisture on the leaf surface for spore formation. Water condenses on the leaf surface whenever leaf temperature
drops below the dewpoint, a situation not unusual under high humidity conditions. A plant temperature model can
be used predict when dew formation is likely, allowing preventative measures to be undertaken.
