Indian Journal of Radio & Space Physics
Vol. 35, June 2006, pp. 193-197
Monitoring and controlling of CO2 concentrations in open top chambers for better
understanding of plants response to elevated CO2 levels
M Vanaja, M Maheswari, P Ratnakumar & Y S Ramakrishna
Central Research Institute for Dryland Agriculture, Santhosh Nagar, Hyderdabad 500 059, India
E-mail: [email protected]
Received 25 July 2005; revised 4 January 2006; accepted 7 February 2006
The exponentially rising concentration of CO2 in the atmosphere is one of the important changes, which effectively
influences the productivity of agricultural crops. Innovative approaches for conducting long-term experiments on plants
have been developed to investigate the growth and yield response of different plants to predicted elevated levels of CO2. The
accuracy of the results depends on the system adopted and its maintenance of the desired CO2 levels with near natural
conditions for other parameters. In one of such efforts, a system for continuous monitoring and maintaining the desired level
of CO2, temperature and relative humidity in open top chambers (OTCs) was developed. Carbon dioxide gas was supplied to
the chambers and maintained at set levels using manifold gas regulators, pressure pipelines, solenoid valves, rotameters,
sampler, pump, CO2 analyzer, PC linked Program Logic Control (PLC) and Supervisory Control And Data Acquisition
(SCADA). These OTCs are cost effective for meeting the requirements of field research on CO2 enrichment.
Keywords: Elevated CO2, Open top chambers, Instrumentation and technology
PACS No.: 89.60-K; 89.60 Ec; 89.60 Fe
IPC Code: G01W1/02
1 Introduction
Population growth, industrial development, burning
of fossil fuels and changing land use practices⎯ all
these man-made changes in nature, contribute to
substantial increase in atmospheric CO2. The
increasing CO2 concentration of earth’s atmosphere
and associated predictions of global warming1 have
stimulated research programmes to determine the
likely effects of future elevated CO2 levels on
agricultural productivity and on the functioning of
natural ecosystems2.
Researchers reported the results on plant responses
to elevated level of CO2 by conducting experiments
with different types of structures, which include
growth
chambers,
controlled
environmental
chambers, greenhouses, phytotrons, open top
chambers (OTCs) and free air carbon dioxide
enrichment (FACE) facility. The effects of
atmospheric CO2 enrichment have been studied for
more than a century in greenhouses, control
environment chambers, OTCs and other elevated
structures to confine the CO2 gas around the
experimental plants3-6. The accuracy on maintenance
of CO2 inside the chamber installed around the crops
did not succeed in many other studies because of
technical constraints. In the enclosed structures, the
environment will not be the same as that in the open
field7. With controlled environmental chambers or
phytotrons, the studies have to be conducted by
growing the plants in pots that cause root growth
restriction. In view of this, attempts are made to make
the structures, which could maintain near-natural
conditions and also maintain elevated levels of CO2
throughout the experimental period in the field
conditions. The OTCs were developed for this purpose
where the basic metal frame fitted in the field would be
covered with highly transparent material PVC
(polyvinyl chloride) sheet to allow maximum natural
light and is open at the top to avoid building up of
temperature and relative humidity. Earlier during 1990s
the Indian Agricultural Research Institute, New Delhi,
initiated the studies on agricultural crops response to
elevated CO2 with open top chambers6,8. However, an
automatic CO2 enrichment technology was developed
by adapting software SCADA that could automatically
maintain the desired and accurate levels of CO2 around
the crop canopy inside the OTCs.
The purpose of the present paper is, therefore, to
introduce the technological development in order to
maintain accurate CO2 concentration inside the OTCs
automatically to study the response of plants to
elevated levels of CO2 or any other gas of interest.
194
INDIAN J RADIO & SPACE PHYS, JUNE 2006
2 System design
2.1 Structure of OTCs
The OTCs are of square type structure
having 3×3×3 m dimension with an automatic closing
door [Fig. 1(a)]. The basic structure of the OTCs was
fabricated with galvanized iron (GI) pipe and installed
in the experimental field. The OTCs were covered
with polyvinyl chloride (PVC) sheet of 120-micron
gauge to have more than 90% transmittance of light.
At 2.4 m height of the each chamber a frustum with
an angle, 0.6 m towards inside, was maintained to
reduce the dilution effect of the air current within the
chamber [Fig. 1(c)]. The upper portion of the chamber
was kept open to maintain the near-natural conditions
of temperature and relative humidity.
2.2 CO2 supply to OTCs and air sampling
The plenum at the base (0.3 m) was provided for
carbon dioxide circulation in the OTCs. The 100%
CO2 gas of commercial grade was used to elevate CO2
levels within the chambers. Four CO2 gas cylinders of
45 kg capacity each were used and the gas was
released to the chambers through a manifold fitted
with copper tubing. Within each chamber the copper
tubing was again fitted with solenoid valve and
rotameters to regulate the gas supply. The normal air
from the air compressor was mixed with CO2, which
is then pumped into CO2 circulating pipe. The CO2 is
released into the OTCs through perforated GI pipe
fitted at the base of each chamber. The uniformity of
the CO2 is maintained by pumping CO2 gas diluted
with air by air compressor. The air is sampled from
the centre point of the chamber through a coiled
copper tube [Fig. 1(b)], which can be adjusted to
different heights as the crop grows.
3 CO2 control and monitoring system
The equipment for monitoring and controlling the
CO2 in OTCs is fully automatic and the desired CO2
level can be maintained throughout the experimental
period in the OTCs with the help of this system. The
schematic diagram of the system is shown in Fig. 2.
The system basically consists of CO2 analyzer,
pump to draw the sample from OTCs, the valves and
meters to control and regulate the CO2 and air flow,
air samplers from each chamber, CO2 gas cylinders
for supply of CO2 gas, air compressor to maintain the
uniformity of CO2 gas at set ppm in the chamber, the
Program Logic Control (PLC) and Supervisory
Control And Data Acquisition (SCADA) platform and
PC.
Fig.1⎯ (a) Open top chambers (b) Controls within the OTC and
(c) Representative diagram of an OTC
3.1 CO2 analyzer
The non-dispersive infrared (NDIR) gas analyzer
(California Analytical), which is microprocessorbased system with single beam optical system (Model
VANAJA et al. : PLANTS RESPONSE TO ELEVATED CO2 LEVELS IN OTCs
195
Fig. 2⎯Schematic diagram of CO2 control and monitoring system
ZRH-1) was used for measuring the concentration of
CO2 of the air sample drawn from OTCs. A pump
(Pump pack II) was fitted with CO2 analyzer to draw
the samples from each OTC. In order to safeguard the
analyzer from excess moisture in the air, a set of four
desiccant glass columns (each column is 18 cm long
with 5 cm inner diameter) of self-indicating coarse
silica gel (Qualigens Product No. 27285) was fitted
before the sampled air enters into the CO2 analyzer as
a precautionary measure. One CO2 analyzer was used
to monitor the CO2 level in all the four OTCs. The
analyzer is regularly purged (twice in a week) with
inert N2 gas for zero setting and is calibrated once in a
month with known concentration of CO2 gas. The air
sample from each OTC is drawn for three minutes and
analyzed by CO2 analyzer. Based on the end reading,
the PLC and SCADA process the analyzer output and
compare with the actual set ppm for that particular
chamber. The signal is given to the chamber solenoid
valves for CO2 supply through PC to close or open
and thereby maintains the desired level of CO2. After
three minutes, the sampling solenoid valve of that
particular OTC automatically closes and the next
chamber solenoid valve opens so that OTC and the
process continue to maintain the set ppm of CO2 in all
the OTCs (Fig. 2).
3.2 PLC and SCADA platform
The PLC and SCADA continuously monitor and
control the desired CO2 level. The software facilitates
to set different concentrations of CO2 in different
OTCs at a time and also modify the time to analyze
the air samples drawn from each OTC. This facility
continuously records and displays the actual CO2
concentration, temperature and relative humidity of
each OTC.
3.3 Temperature and relative humidity
Each chamber was fitted with sensors to measure
temperature and relative humidity and this facilitate
the continuous monitoring of temperature and relative
humidity in all the chambers. Figure 3 shows the
temperature and relative humidity of OTCs with and
without CO2. It also shows the light intensity of OTCs
and open field.
INDIAN J RADIO & SPACE PHYS, JUNE 2006
196
3.4 Control valves and regulators
The CO2 gas supply will be regulated with
manifold regulator and controlled with the help of
pressure gauge. The CO2 gas was supplied through
copper tubing and the solenoid valves were fitted
within the OTC. The opening and closing of these
valves was regulated on the basis of actual
concentration of CO2 within the OTC and the set CO2
Fig. 3⎯Temperature and relative humidity of OTCs with and without CO2 and light intensity of OTCs and open field.
VANAJA et al. : PLANTS RESPONSE TO ELEVATED CO2 LEVELS IN OTCs
197
level for that particular OTC, which is regulated by
PC through PLC and SCADA. To have manual
regulation of CO2 supply, another set of controlsrotameters was also fitted for extra safety. The air
from air compressor mixes with CO2 before it is
released into the OTC. This also facilitates to
distribute the CO2 enriched air uniformly within the
OTCs.
Acknowledgements
The present facility was created with AP-Cess
Program funds and authors are grateful to Indian
Council of Agricultural Research, New Delhi, for
financial support. The assistance from Mr Jainender
and Mr M Srinivasulu, technical staff, is thankfully
acknowledged.
3.5 PC
1 IPCC, Climate Change 1995, Summary for Policy Makers
and Technical Summary of the Working Group I Report,
edited by J T Houghton, L G Meria Fillo, B A Callander, N
Harris, A Kattenberg & K Maskell, Intergovernmental Panel
on Climate Change (Cambridge University Press,
Cambridge, UK), 1996.
2 Dahlman R C, Strain B R & Rogers H H, Research on the
response of vegetation to elevated carbon dioxide, J Environ
Qual (USA), 14 (1985) 1.
3 Drake B G, Rogers H H & Allen L H (Jr), Methods of
exposing plants to elevated carbon dioxide in Direct effects
of increasing carbon dioxide on vegetation, edited by B R
Strain & J D Cure (DOE/ER-0238, United States Dept of
Energy, Washington, DC), 1985.
4 Enoch H Z & Kimball B A, Carbon Dioxide enrichment of
greenhouse crops: volume I, Status and CO2 source and
volume II, Physiology, Yield, and Economics (CRC Press,
Boca Raton, FL, USA), 1986.
5 Schulze E D & Mooney H A, Design and execution of
experiments on CO2 enrichment, ecosystems research report
No. 6 (Commission of the European Communities, Brussels,
Belgium), 1993.
6 Uprety D C, Garg S C, Tiwari M K & Mitra A P, Crop
responses to elevated CO2: Technology and research (India
study), Global Environ Res (Japan), 3 (2000) 155.
7 Kimball B A, Pinter P J, Jr, Wall G W, Garcia R L, LaMorte
R L, Jak P M C, Frumau K F A & Vugts H F, Comparisons
of responses of vegetation to elevated carbon dioxide in free
air and open top chamber facilities in Advances in Carbon
Dioxide Research, edited by L H Allen (Jr), M B Kirkham, D
M Olszyk & C E Whitman (Am. Soc. Agron. Crop Science
Society of America and Soil Science Society of America,
Madison, WI, USA), 1997, pp. 113-130.
8 Uprety D C, Carbon dioxide enrichment technology: Open
top chambers−a new tool for global climate research, J Sci &
Ind Res (India), 57 (1998) 266.
9 Maini H K, Tiwari M K, Bahl M, John T, Singh D, Yadav V
S, Anand R J, Poddar H N, Mitra A P, Garg S C, Uprety D
C, Shrivastava G C, Saxena D C, Dwivedi N, Mohan R,
Miglietta F & Zaldei A, Free air carbon dioxide enrichment
facility development for crop experiments, Indian J Radio &
Space Phys (India), 31 (2002) 404.
10 Kimball B A, Kobayashi K & Bindi M, Adv Agron (USA), 72
(2002) 293.
The Intel Pentium-IV PC with 2.8 GHz, 512 MB
RAM and 40 GB hard disc along with 5 kV UPS with
30 min backup was established for uninterrupted data
recording and storing. The data are continuously
recorded for the temperature, relative humidity and
actual CO2 concentration in ppm. The data of
temperature (°C), relative humidity (%) and actual
CO2 concentration in ppm are displayed on the
monitor continuously and graphical display is also
possible.
4 Conclusions
The OTCs are cost-effective and the design is
simple to construct and maintain when compared with
free air carbon dioxide enrichment (FACE) system.
The volume of CO2 consumed to maintain a FACE
ring of 21 m dia per day is approximately 3000 kg of
CO2, whereas for the Mid-FACE developed at the
Indian Agricultural Research Institute9 it was reported
that around 200-250 kg/day, for 8 m dia ring, is
required to maintain CO2 level at 550 ppm. When
compared with FACE facility to maintain the same
level of CO2 concentration, the requirement of CO2
gas for OTC was found to be very less and ranged
between 15 and 20 kg/day for a 9 m2 area of OTC.
Kimball et al.10 compared the results obtained from
both OTCs and FACE and concluded that the
responses obtained from FACE are almost similar to
the chamber studies except for greater reduction in
stomatal conductance and greater stimulation of root
growth under FACE. Hence, to conduct experiments
to understand the response of crops to elevated CO2,
OTCs will be the cost-effective facility. In OTCs, one
can obtain relative responses, whereas FACE provides
the absolute responses.
References