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.
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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
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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.
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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.
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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.
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