Date 9/1/95

Title of Project Development of a Plant Shoot-Temperature Model for Greenhouse Climate Management

Institution where work is being conducted Michigan State University

Amount of Endowment Grant $23,732
Covering Period 1/95 to 12/95

Anticipated Date of Completion/Final Report 12/96

Individual(s) Conducting Project:

(List Project Leader First)

Royal D. Heins - Title Professor

Telephone Number 517-353-6628

James Faust - Title Graduate Student

Bin Liu - Title Graduate Student

Development of a Plant Shoot-Temperature Model for Greenhouse Climate Management

Royal A Heins, James Faust, Bin Liu

Michigan State University

Progress Report to the American Floral Endowment, 9/1/95

Project Objectives:

1) Develop and test an artificial plant-temperature sensor that mimics the heat transfer properties of a plant

shoot.

2) Control greenhouse temperature in such a fashion to achieve a desired plant temperature using the sensor

and a shoot-tip energy-balance model to account for transpiration.

Summary of Work Conducted:

A model has been developed to predict shoot-tip temperature using four measurements: dry bulb, wet

bulb, solar radiation, and glazing material temperature. Environmental databas been input into the model to

obtain plant temperature predictions wider a range of air temperature, solar radiation, vapor-pressure deficit, and

glazing temperature conditions.

Plant temperature responses have been recorded in several greenhouse enviroiunents, including under

high-pressure sodium lamps, under thermal screens, with horizontal air-flow fans, and with water sprayed onto

the foliage.

Results to Date:

Plant temperature simulations suggest than plant temperatures decrease relative to air temperature as air

temperature increases. At air temperatures less than 65′F, plant temperature is typically warmer than the air

during the day. At air temperatures greater than 75′F, plant temperature is typically cooler than the air

temperature during the day. At night, plant temperature is always below air temperature, unless an infrared heat

source is used.

High-prcssure sodium lamps provide approximately 33% more energy to the plant canopy than an equal

light intensity from sunlight. Consequently, plants under high-pressure sodium lamps are warmer than non-lighted

plants. We observed that vinea shoot-tip temperatures increase 2 to 3′F wben high-pressure sodium lamps deliver

350 to 700 foot candles.

Thermal screens can be used to increase plant temperatures at night. The colder the glazing material

temperature, the greater the increase in plant temperatures. Thermal screens used on cold nights, i.e. outside air

temperature below freezing, can iricrease plant temperatures by as much as 9′F.

Horizontal air-flow fans can be used to reduce the difference between plant and air temperatures. We

observed a 7′F increase in plant temperature when the air velocity above a canopy was increased from 4 to 20

inches per second on a cold night. During sunny days, air velocity can be used to keep plant temperatures from

becoming excessively high.

Misting crop foliage can reduce plant temperatures by 3 to 6′F. Misting for a few hours at sunrise

reduced Easter lily stem elongation by 12%. This can be an effective technique for control of stem elongation.

Jim Faust has written his Ph.D. thesis. The thesis contains four manuscripts quantifying the difference

between plant and air temperature. These manuscripts are being submitted for review and publication.

Future Plans Covered by the Endowment Grant:

Additional work in this area has stopped due to lack of funding.

Anticipated Benefits for Floral Industry:

The anticipated benefits to the floral industry will be to improve the grower’s ability to meet increasingly

narrow market-date specifications by 1) improving the prediction accuracy of leaf- and flower-development

models, 2) using existing cliniate-control computers to provide the proper shoot-tip temperatures, and 3) increasing

the grower’s ability to manage the greenhouse envirviunent with climate-control computers.

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