Development of a Plant Shoot Temperature Model for Greenhouse Climate Management 1995 Proposal
Climate Management
Crop timing is critical to the successful marketing of floriculture
crops. Assuming photoperiodic requirements are met, temperature of the
plant shoot tip is the primary environmental variable influencing crop
timing. The time required for plant development can be more accurately
predicted when shoot-tip temperatures are known since they frequently deviate
from air temperature. However, shoot-tip temperatures are difficult to
measure directly. This project is therefore directed at modeling shoot-tip
temperature. Our first two years of research focused on quantifying plant
temperature responses to the greenhouse environment and developing an energy-balance
model to predict shoot-tip temperature in the greenhouse environment. The
next steps in this project are to develop a sensor that mimics the heat
transfer properties of a plant shoot and to then use our understanding
of plant temperatures to address practical concerns for the control and
manipulation of temperature in the commercial greenhouse industry. The
objective for the coming year is to develop and test an artificial plant-temperature
sensor that mimics the heat transfer properties of a plant shoot.
Introduction
Successful commercial production of greenhouse crops requires that
plants be grown to buyer size and date specifications. Temperature is the
primary environmental factor influencing the rate of plant development
(Kiniry et al., 1991) and ultimately the ability to meet date specifications.
Accurate timing of a crop can be jeopardized when plant shoot temperature
differs from air temperature because plant developmental rate is controlled
by the temperature of the shoot meristematic regions, i.e., the shoot tip,
not air temperature (Ritchie and NeSmith, 1991). A knowledge of plant shoot
temperature improves the ability to time crop development to meet date
specifications (Faust and Heins, in press). Linking a climate-control computer
with a plant-temperature model should result in more accurate control of
plant development and production scheduling since plant temperatures frequently
deviate significantly from air temperatures (Faust, 1992).
If a system of shoot-tip measurement can be developed, we believe the
next important advance in greenhouse climate control will be to base greenhouse
temperature control on plant-temperature models. However, accurate shoot-tip
temperature measurement is not nearly as straightforward and easy as it
might initially seem. Direct measurements are difficult because the shoot-tip
region of the plant is small and moves as the plant grows. Use of infrared
thermometers is limited to conditions where there is a closed canopy, otherwise
it will simultaneously sense plant, soil, and bench temperature. Therefore,
we believe an artificial plant sensor which mimics the heat transfer properties
of a plant shoot in combination with a shoot-tip energy-balance model to
account for transpiration will be necessary to accurately estimate shoot-tip
temperature. Once shoot-tip temperature is accurately estimated, models
relating it to development rate can be used to assist with crop scheduling.
In lieu of resubmitting the literature review presented last year, some
data collected on vinca bedding plants during the second year of this project
will be presented. Our objective was to quantify the response of plant
temperature to the greenhouse environment by examining the influence of
supplemental lighting, thermal screens, horizontal air-flow fans, and syringing
on vinca shoot-tip temperatures.
Supplemental lighting. High-pressure sodium lamps mounted above
a greenhouse crop emit thermal radiation in addition to visible radiation.
As a result, plant temperature increases when HPS lamps are turned on (Fig.
1). Plant temperature increases by approximately 2 to 3F when HPS lamps
deliver 350 to 700 footcandles to the crop canopy (Faust and Heins, 1994b).
Thermal screens. Plants exchange thermal radiation with the surrounding
greenhouse structure. When the greenhouse glazing is cold, the plants experience
a net loss of thermal energy; consequently, plant temperature decreases.
Thermal screens used during the night provide a warm barrier between the
crop canopy and the cold glazing material. As a result, plant temperature
increases when thermal screens are used (Fig. 2). The colder the glazing
material, the greater the benefit of the thermal screen (Faust, Heins,
and Kiefer, 1994).
Horizontal air-flow fans. Air velocity surrounding the plant
canopy increases when horizontal air-flow fans are used in the greenhouse.
Increasing air flow reduces the insulating layer of air surrounding the
plant. As a result, the plant is more closely coupled to the surrounding
air temperature. Thus, air velocity can be used to reduce the difference
between plant and air temperatures. We observed that plant temperature
increased 6F as air velocity increased from 10 to 50 cm*s-1 (Fig. 3) (Faust,
Heins, and Kiefer, 1994). A double-layer thermal screen increased plant
temperature 5.5F on a night when the outside air temperature was -9F and
no horizontal air-flow fans were used, i.e., when air velocity was less
than 10 cm*s-1.
Syringing. Syringing a plant canopy reduces the canopy temperature
as the water evaporates. We syringed Easter lilies during the first three
hours after sunrise to deliver a morning temperature pulse without dropping
the air temperature. The syringed plants were 3 to 6F cooler than the dry
plants (Fig. 4), and stem elongation of the syringed plants was reduced
by 12%. This experiment demonstrates how plant temperature can be manipulated
to control plant height without changing the air temperature (Faust, Verlinden,
and Heins, 1994).
Objectives
The objective during the coming year is as follows:
1) to develop and test an artificial plant-temperature sensor
that mimics the heat transfer properties of a plant shoot.
The objective for the following year is:
2) to 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.
Anticipated Benefits
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 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. Another benefit
is that accurate plant temperature estimates can also be used to improve
disease control. Fungi such as botrytis require moisture on the leaf surface
for spore formation. Water condenses on the leaf surface whenever leaf
temperature drops below the dew point, a common situation under high-humidity
conditions. A plant-temperature model can be used to predict when dew formation
is likely, allowing preventive measures to be taken.
Outline of Materials and Methods
1) Develop and test an artificial plant sensor.
General Procedures: We have designed a prototype for a sensor that
has heat transfer characteristics similar to those of the plant shoot tip.
This sensor will be further developed and tested within a vinca canopy
to determine how well it mimics shoot-tip temperature at night under low
transpiration and net radiation loss conditions. The sensor will be combined
with a transpiration model to predict shoot-tip temperature under high
transpiration and high radiation daytime conditions.
2) Control a greenhouse environment based on a plant temperature
setpoint.
General Procedures: The heating and venting system in a Michigan State
University research greenhouse will be controlled with a datalogger, which
will also measure shoot-tip temperature of a vinca crop. The shoot-tip
temperature will be used to control the greenhouse environment. Thus, plant
temperature will be kept constant, not air temperature. With this system
in place, we will then be able to determine the benefits, in terms of energy
consumption and control of crop development, of controlling the greenhouse
environment based on plant temperatures.
Facilities and equipment available
The floriculture research group at MSU has invested in the instrumentation
necessary to conduct this project. Instrumentation includes flve Campbell
Scientific CR10 dataloggers for sensor measurement, an Eppley pyranometer
for solar radiation, a REBS total hemispherical radiometer for net radiation
measurement, a General Eastern dew point hygrometer for dew point measurement,
a TSI hot-wire anemometer for air speed measurement, and 40-gauge chromel-constantin
thermocouples for shoot-tip temperature measurement. The dataloggers are
linked to a data-acquisition computer running Campbell Scientific software
that has real-time graphics displaying the immediate measurements of the
sensors wired to the datalogger. Computer hardware and software are available
for data analysis and modeling. Adequate greenhouse space is available
for all experimentation.
Literature cited
Faust, J.E. 1992. Modeling leaf and inflorescence development of the
African violet (Saintpaulia ionantha Wendl.). MS Thesis, Michigan State
Univ., East Lansing.
Faust, J.E. and R.D. Heins. 1994a. Modeling leaf development rate of
the African violet. J. Amer. Soc. Hort. Sci. 119(4):727-734.
Faust, J.E. and R. D. Heins. 1994b. Quantifying the influence of high-pressure
sodium lighting on shoot-tip temperature. Acta Hort. (In press).
Faust, J.E., R.D. Heins, and P. Kiefer. 1994. Quantifying the effect
of thermal screens on shoot-tip temperature in glass greenhouses (In review).
Faust, J.E., S. Verlinden, and R.D. Heins. 1994. Pulsing temps at sunrise.
Greenhouse Grower 12(l):82-85.
Kiniry, J.R., W.D Rosenthal, B.S. Jackson, and G. Hoogenboom. 1991.
Predicting leaf development of crop plants, p. 29-42. In: Hodges, T. (ed.).
Predicting crop phenology. CRC Press, Boston.
Ritchie, J.T. and D.S. Nesmith. 1991. Temperature and crop development.
In: J. Hanks and J.T. Ritchie (eds.). Modeling plant and soil systems.
American Society of Agronomy, Madison, WI.
Budget
Graduate Assistantship (Half-time Graduate Assistantship) $16,732
Undergraduate labor (plant care, data collection) $2,000
Greenhouse supplies and maintenance $2,500
Other equipment and supplies (computers, paper, etc.) $2,500
TOTAL $23,732
Project Leader Qualifications
Dr. Heins has extensive experience in plant response to temperature
and use of greenhouse climate control computers. Students under his direction
have investigated and modeled plant response to temperature on many species
including chrysanthemum, poinsettia, Easter lily, Stargazer lily, hibiscus,
and Christmas cacti. Results from these projects led to the DIF concept
of height control and the use of graphical tracking for decision support
in making height-control management decisions, now in use by growers throughout
the world. Dr. Heins has published over 65 refereed scientific manuscripts
and 165 grower articles. He has also given over 130 presentations at grower
meetings.
James Faust is a Ph.D. student who completed his Master of Science
degree in March 1992. His thesis topic was modeling leaf and flower development
of African violet. He spent spring quarter of 1992 working in the lab of
Dr. Bruce Bugbee at Utah State University, where he gained the experience
in environmental measurement and instrumentation necessary to undertake
this project. He studied the effect of shoot-tip temperature on stem elongation
of poinsettia with Dr. Roar Moe at the Agricultural University of Norway
during the spring of 1994. Jim will complete his Ph.D. in the fall of 1994
and take a job at the University of Tennessee. He will continue to provide
input into the project during 1995.
Bin Liu is a beginning Ph.D. student who received her M.S. in
1985 and was promoted at that time to assistant professor at the Institute
of Agrometeorology, Chinese Academy of Agricultural Sciences, Beijing,
China. Her expertise includes statistics, modeling, and agrometeorological
studies involving the survival rate of plants in controlled environments,
improvement of crop productivity, simulation of water requirements for
cucumber production, simulation of evapotranspiration, effects of shelter
belts on micrometeorological factors in orange plantations, and frost damage
in orange production and its relation to local climate.
