An e-publication by the World Agroforestry Centre
METEOROLOGY AND AGROFORESTRY
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An e-publication by the World Agroforestry Centre |
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METEOROLOGY AND AGROFORESTRY |
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section 4 : measurement and analysis of agroforestry experiments Appropriate instrumentation and the appropriateness of instrumentation for agroforestry and agricultural research in developing countries C.L. Coulson
Department of Crop Science, The University of Nairobi C J. Stigter
Department of Physics and Meteorology, The Agricultural University
Abstract Instruments for the measurement of crop and environmental parameters may be mechanical or electrical, simple or complex. The use of some instruments in developing countries can be problematical for various reasons. General and specific problems of commercial instrumentation as well as the benefits and problems of alternative strategies, as they relate to developing countries, are discussed.
Recent events in certain African countries have highlighted the critical nature of their food production and the catastrophic results which can occur when adverse natural forces impinge on fragile ecosystems. The need for agricultural research in such areas is self evident and represents an important facet of the total endevour aimed at solving or at least ameliorating the problem. Increased food availability will depend on increased crop yields (McCarthy and Mwangi 1982); although pricing systems, extension services, storage technology, etc. will play an important part. Yield sustainability is important. The measurement of environmental variables (temperatures, rain, solar radiation, etc.) in crop space management and an understanding of crop response to these factors is important in assessing a crop's potential productivity for various agroclimatic situations and management practices. Such physiological and agrometeorological research frequently requires electronic or mechanical instrumentation. The electronic instrument may be of the manual kind requiring the presence of the operator or the automatic kind which may be left to collect data, the data being later retrieved at some convenient time. Non-electronic instruments may range from the simple evaporimeter to the more complex actinograph. Here we examine the problems of such instrument-based research in developing countries; propose some solutions, although perhaps partial; and discuss the spin-off benefits and problems arising from the suggested approach.
It can be appreciated that some commercial equipment may not be suitable for use in developing countries (Coulson 1984). Besides some of the reasons that are outlined later, fundamental questions can be raised concerning the validity of measurements made by some instruments. Some of these questions can be asked regardless of the climate in which the instrument is operated, while some may result because of the extreme climate in which they are operated. Both these situations affect researchers in the Third World. In the case where the basic functioning of the equipment is suspect, the developing-country researcher may not have the back-up facilities to investigate the problem. The lack of scientific journals and technical books may be an added disadvantage. In developing countries where food production may be limited by the climate and working conditions, both of these are likely to be extreme. Such factors as the radiation load on equipment and sensors, the effects of dust, high humidity storage conditions, the rough roads that have to be travelled, etc., may render the instrument inappropriate for use in the conditions that prevail. The fact that an instrument may not perform well under them may not be fully apparent to the manufacturer or local researcher at the time when the equipment is ordered. At the more banal end of equipment problems is the fact that some equipment is not easy to physically use outdoors, though this may be as applicable in developed countries as in developing ones. However, what may be minor inconveniences in temperate climates can become major problems in extreme conditions.
In the context of appropriate instrumentation we should initially consider innovation rather than invention. For our purposes, innovation can be regarded as the use of existing technology for appropriate local use. The early stages of appropriate instrument development or the assessment of alternative ones should initially involve the simplest but most useful ones, though complex commercial equipment can be tested, in some cases using relatively simple techniques. If the construction of an electronic instrument is being considered, two main problems should be assessed. The first is that the skill levels available will partially dictate the complexity of the instrument and the probability of its successful completion. Complex equipment can be expected to take longer to make and have a smaller chance of success than simpler equipment. An early and complete failure in an attempt to build or test an instrument does little to encourage further attempts. A second problem is that it is likely the components for a complex instrument may cost a lot more and may not be locally available. The cost of components in a developing country can be very high due to import duty and sales taxes and having to order them from overseas can involve long delays. It is quite possible that to make an instrument can cost more in parts than importing the ready made one, should one be available. In this respect projects with overseas 'back-stopping' have an advantage since urgently needed components or advice can easily be provided.
Electronic The advances in electronics over the recent years have led to increased sophistication and complexity in field instrument design. The miniaturization of circuits resulting from the advances in semiconductor device technology (Page 1985) is starting to revolutionize the instruments used in crop field research in the same way it revolutionized microcomputers. However, the restricted demand for electronic field equipment has not yet led to price reductions and, in some cases, more 'user friendliness', as has been the case with home-based consumer items. The specialized knowledge required to design and produce commercial field equipment successfully separates the majority of users from understanding the principles of instrument sensors and signal conversion systems and thus often from information about its accuracy. The inclusion of internal calculation facilities obviating the tiresome manipulation of raw data or sensor outputs is now commonplace. The fact that some commercial equipment has the facility to interface with a microcomputer can further separate the user from understanding the equipment. Fault finding and maintenance can thus become a critical problem.
Many pieces of non-electronic equipment may be used in agricultural research, particularly in agrometeorology, and some of these may be relatively simple. Simplicity and accuracy, resulting from an understanding of the principles of operation, leads to a more universal use and acceptance. For instance the Gunn-Bellani radiometer which is based on simple principles is routinely used in East Africa because of past work on its calibration. It is possible that other simple instruments could be used for research if the factors influencing their operation were better understood. Some examples are given later.
It would seen axiomatic that countries or global regions that have a high risk potential for food production problems are the ones least able to support the research to ameliorate them. Bilateral and multilateral donors give assistance usually in the form of capital aid. By using such funds, equipment can be purchased, usually in the donor's country. In some cases they may provide local funds from which the recipient country can purchase equipment, again from the donor country, but overcoming the problems of the researcher obtaining foreign exchange. While such funds are of obvious benefit to the recipient country, unexpected problems can and do occur, e.g. mismatch between requirements and the eventually-supplied item, the arrival of non-functional or partly functional equipment and long time delays between purchase initiation and eventual receipt. We have experienced delays amounting to years, for equipment which was essentially 'off the shelf in the donor country. The rapid advances in electronics coupled with delivery delays can mean that newer models of the equipment may have been released in the donor country prior to receipt of the older model by the developing country. This can lead to problems in obtaining spare parts and, coupled with problems of maintenance, this can lead to equipment being shelved. Cost and complexity of some commercial equipment can discriminate against young local researchers in developing countries. Besides having to generate a project in which equipment funding can heavily outweigh other expenses the researcher may be faced with the problems of foreign exchange regulations and future unexpected expenses when spare parts or overseas maintenance are required. The lack of sustainable backup facilities during a project can put the whole scheme at risk. The high cost of commercial equipment will naturally limit its distribution in a developing country which in turn limits both the amount of data taken and possibly where the data are taken. Lack of technical skills is a problem which faces developing countries. Although there maybe the opportunity for both local and overseas training, 'hands on' experience in a local problem situation would seem to have many benefits. The involvement of local staff in, for example, small electronics projects or equipment function investigations raises skill levels and forms a basis for further training. The need for many measurements in agroforestry and agricultural research situations coupled with technical staff with low skill levels may necessitate the use of equipment that is both cheap and easily used. However the validity of using existing equipment may have to be researched. Such an endeavour may bring simpler cheaper equipment into use as well as train staff. Donor projects which provide training and technical 'back-stopping' in such situations can be invaluable in assuring that research and training efforts do not come to a premature end. Endeavours to make appropriate instruments or in some cases assess the appropriateness of others can take place with reference to one or more specific requirements (Appendix). The requirements fall into three categories: (a) an actual need to make a specific measurement not provided by a piece of commercial equipment; (b) to overcome constraints such as the lack of money; (c) to produce a meaningful training exercise. It can readily be appreciated that each of these requirements will have its own set of individual problems. For instance with requirement (a) it could be that novel sensor applications may have to be investigated while in (b) cheap alternatives may be tried out. Being a training exercise, (c) is likely to involve a high time commitment. While requirements (a), (b) and (c) may be identified along with certain problems, interconnected 'spin-off benefits occur. For instance if a novel instrument is produced (e.g., (a) above) or production is attempted to save money (e.g., (b) above), valuable 'hands on' training (c) may result. If the instrument is relatively simple, its potential construction by other users may be possible and the original constructors may then become involved in 'user-friendliness' considerations. In most developing countries training may become an important common factor in all projects, since without elevating the skill levels, the problems of long acquisition time or prospects of more data being obtained may not be solved. Similarly, without the elevation of skills, problems with equipment imported from developed countries will eventually occur. In the case studies that follow, three main areas of endeavour may be identified. One is the production of pieces of equipment, another is the assessment of simpler alternative methods or instruments. The third is the assessment of the functioning of existing commercial equipment. The first two could be considered appropriate instrumentation; the third, the appropriateness of instrumentation. In all these, the authors have noted a strong training component, whether serendipitous or intended.
Solar radiation data have many uses and various types of data exist. Such data may be, for instance, collected from meteorological stations or from within crops or at crop interfaces. Meteorological data in developed countries are increasingly being taken with automated electronic weather stations. Because of the level of technician training, shortage of money, etc., this approach may not be possible in developing countries. In Tanzania non-electrical equipment (the actinograph and Gunn- Bellani) was used to collect data at various sites. The results were compared with more sophisticated equipment at the University of Dar es Salaam in cooperation with the National Directorate of Meteorology (Stigter and Waryoba 1981; Stigter, Jiwaji and Musabilha 1987; Stigter et al. in prep). This allowed the performance of non- electrical equipment to be assessed and simultaneously also allowed simple alternative electrical equipment to be assessed in terms of cost effectiveness. The skill levels of local staff were greatly increased by this project. Thus, in this case, while the central theme was to find appropriate instruments, a spin off was training. Problems of maintenance, repair and power supply have been addressed at the University of Dar es Salaam for the integration of solar energy values (Stigter and Mabuba 1980; Stigter and Kainkwa 1983). Maintenance and repair problems were solved by local technical staff, previously trained through a Dutch University Co-operative Project, as they were able to identify malfunctioning electronic modules which could then be sent to The Netherlands or elsewhere (via the project) for repair or replacement. The problems of unreliable power supply were solved by the use of electro-chemically integrating equipment. Rechargeable batteries which could be recharged using simple solar cells are an alternative and are presently used in the project. Appropriate low-cost solar radiation intruments could be used in the large numbers required particularly in agroforestry or agricultural research. Such instruments have recently been described (Newman 1985). Large numbers of these could be conveniently 'read' using a microcomputer. The basic approach however uses existing technology in an ingenious way. Requests for the loan of solar radiation equipment by graduate students of the University of Nairobi working at various research stations prompted an attempt to produce a cheap electrical instrument for PAR measurement. The problem such students faced was either the lack of any instrument for such measurements or the availability of non-functional commercial equipment which had proved difficult or impossible to get repaired. The construction of the initial instrument involved consideration of available sensors, linearization, cosine response, circuit design and construction, general construction techniques and calibration. During a three- month training scheme conducted by the University of Nairobi and the University of York, an Electronics Link technician (funded by The British Council) was able to 'update' this instrument from analogue to digital. This change has allowed new avenues of data storage to be investigated; for instance a circuit has been designed to allow many light readings to be put into memory and retrieved later. This would allow rapid spot measurements to be made in crops and at crop interfaces. The appropriateness of some commercial solar radiation equipment has come into question during its use in our experiments. In circumstances common in the tropics, particularly in semi-arid and arid regions, it has been found that some of the materials used may deteriorate rapidly under the high solar loads experienced. The manufacturers are aware of the problem, though the field experimenter may not be initially aware of how quickly the deterioration occurs in some tropical conditions. One of us (CLC) found a filter in a solarimeter to break down after only 15 min exposure on the coast just south of Mombasa, Kenya.
Crop and soil temperatures have an impact on crop productivity through various physiological processes. Commercial equipment which measures temperature can have either or both of two main drawbacks. It can be expensive and it may not measure what it purports to (Coulson et al. 1986). Examples can be cited to illustrate both these situations. Measurements on beans indicated that the leaf temperatures obtained depended on the instrument used (Coulson 1985; Coulson et al. 1988). The use of a small thermistor in a simple circuit for measuring leaf temperatures provided encouragement for the production of a simple leaf-temperature measuring device. This was constructed (Coulson and Musyoki 1986) with a view to simplicity and cheapness and to obviate one fault inherent in our commercial instrument. Considerations involved the analysis of problems inherent in contact leaf temperature measurements and calibration methods. Although an appropriate instrument was the initial consideration, cheapness and training were important 'spin-offs'. Problems of non-contact temperature measurements using infra-red thermometers (IRT) have been addressed at the University of Dar es Salaam (Stigter, Jiwaji and Makonda 1982; Stigter, Makonda and Jiwaji 1982, 1983; Stigter Mwampaja and Kainkwa 1984). Besides the drawback of high cost, IRTs may suffer from other faults, calibration not being the least important. Using 'commonly available' equipment and locally developed techniques it was possible to improve the performance of a noncommercial Dutch IRT. Initially the thermocouples necessary for testing the IRT were made in Holland, though during the project it was possible to fabricate them at Dar es Salaam as well as to develop the methodology for the construction of the calibration surface. Problems in making temperature measurements in the tropics may occur because of the high solar radiation levels. Problems may also occur in temperate regions with some types of equipment but they may be potentially more serious in the tropics. Uncontrolled radiation falling on the inlet tubing of an expensive imported piece of equipment was found to be a main cause of erroneous results in an experiment to examine leaf/air temperature differences (Coulson et al. 1988). In field experiments there is a frequent need to take environmental readings over long periods of time, perhaps at frequent intervals. Data loggers are of use in such situations, especially at distant experimental sites. Although commercial data loggers are available, though at high cost, maintenance problems can limit their applicability in developing countries, except where there is adequate back-up. This view depends on the situation of the individual researcher. The breadth of skills at a university can be expected to be greater than in many other situations; and as such may lend itself to the use of more complex instrumentation. For example, because of a previous successful attempt to use a simple technique and a cycling millivolt recorder to record temperatures (Coulson and Taylor 1984) and the wide skill base at the University of Nairobi, the development of a prototype temperature data logger was undertaken. It attempted to solve two problems. In the first case, further investigations on crop flower abscission (Kamweti and Coulson 1984) required the frequent measurement of air temperatures within a crop over a period of weeks; and secondly, a graduate student in the Physics Department of the University of Nairobi required an electronics project for his thesis research. The prototype logger (Namuye 1986) incorporated an existing microprocessor board which simplified the task. In this endeavour it was necessary for people of different disciplines to appreciate problems outside their own. Besides the production of a piece of potentially useful equipment, the enterprise served as an excellent training opportunity in the application of electronics, as well as inducing a great amount of local confidence. As a result of this experience, a field data logger is being developed for use in a Ph.D research on alley cropping in Machakos District.
Information on air movement parameters in and around crops is important. However, the two main problems are that commercial instruments may not measure the wind components that occur in and around crops; and in multi-point simultaneous sampling situations the necessary duplication of commercial equipment may be too expensive. In Dar-es-Salaam and Wad-Medani (Sudan) an investigation of simple appropriate techniques for measuring air movements was undertaken. Work was carried out to elucidate the factors affecting the evaporation of water from shaded Piche evaporimeters, since data from this instrument had been used to replace the aerodynamic term in the Penman evaporation equation (Stigter and Uiso 1981; Stigter, Uiso and Rashidi 1984). The instruments being simple and cheap could possibly be used as multi- point air movement sensors, via mass exchange observations. This work continues. The use of naptha or moth balls as air movement indicators is currently being studied at Wageningen in relation to two ongoing agroforestry projects in the tropics involving air flow in low-density tree plantations. The Piche will also be tried out in these projects.
Information on water availability and use is of obvious importance in many developing countries. Unfortunately their measurement is not easy, particularly if it is necessary to make readings over long periods of time at distant sites. We have been unable to successfully measure soil moisture in Nairobi using commercial psychrometric equipment. The initial interest by the overseas manufacturer in the problem seems to have waned leaving us with expensive but non-functional equipment. The equipment is now over three years old and is well out of its guarantee period. Its complexity, coupled with lack of circuit diagrams means that local repair is probably impossible. Special batteries are not available locally. A similar situation has arisen with a neutron probe. Following return from the manufacturer the probe functioned for about an hour and the new fault was diagnosed as an IC which the manufacturer says is no longer available. Both of these problems illustrate the shortcomings of using complex electronic equipment in developing countries. Both might have been solved had an overseas-linked project been operative to cover the cost of equipment shipment back to the manufacturer and with an overseas contact to explain the fault to the manufacturer and keep track of the instrument during its repair and subsequent shipment back. The use of resistance blocks may offer a cheaper alternative allowing many points to be sampled, an important point considering the possible inhomogeneity of soils and highly variable microclimatic gradients arising in agroforestry situations. The use of an AC bridge eliminates problems of the capacitance effect found with DC techniques, though the electronics of the meter may be sensitive to the high temperatures commonly found in the tropics. However, resistance blocks are not without their problems and some of these are presently being investigated at Wageningen through the TTMI project prior to their use in the field in Kenya, this being an example of the use of a linked project. Lysimeters are large and expensive pieces of equipment. Parts of these could be fabricated in developing countries and it is possible that with the purchase of some parts from overseas a commercial equivalent could be produced. Comparison with simple 'oil drum' lysimeters could then take place locally.
The consideration of instrumentation has been divided into the appropriateness of instrumentation and appropriate instrumentation. The former covers the functioning of commercial equipment under optimum conditions and extreme conditions. Appropriate instrumentation refers to the construction and use of simple equipment whose maintenance and use is within the general skill levels locally available and whose accuracy is acceptable. The cost of locally built appropriate instruments can be assessed. If the development is the first one attempted, the cost will be relatively high and the major part of this will be the development costs. These will include initial equipment such as soldering irons, multimeters, oscilloscopes, trial components; and the time spent by personnel. While hardware can be easily costed, time estimation is more difficult except in an industrial situation where the criterion is profit versus loss. One of the important initial considerations concerning the building of appropriate equipment is the cost advantage of doing so. High customs duties can increase costs so much that it could be cheaper to import a commercial equivalent. If this is the case little encouragement is given to local developments unless duty is waived and even if this is done the time taken to clear such items can be very dispiriting. From the point of view of training, established courses can be costed; but frequently such courses, necessary as they are, lack relevant 'hands on' experience. Such experience is best gained in trying to solve real problems in the country in which they occur. In institutes of learning, training and research or development are the basis of the job and the training of one person helps others. In such a situation costing of time is more difficult. What is more important is the question of which endeavour is most profitably started with reference to perhaps numerous aims (Appendix). Some of the difficulties that occur in the transfer of methodology and technology involve language. The developmental state of a language has important implications in this, since some languages have been able to embrace the abstract concepts associated with modern technology while others have not. Whether we are involved in the testing of commercial equipment or the building of appropriate equipment, this problem will exist. The development of a lingua franca is necessary and will naturally occur with the people involved in the various endeavours. (English has shown itself to be a convenient scientific language). Unless we continue to find ways of dealing with the problems outlined, developing countries will be increasingly and adversely affected.
Coulson, C.L. 1984, Monitoring requirements for agriculture. Presented at UNESCO /KNAP Workshop on Physics and Instrumentation for Environmental Monitoring, Solar Energy and Geophysics. Dec. 1984 Nairobi. Coulson, C.L. and A.R.D. Taylor. 1984. The construction of a thermistor reader to allow the continuous recording of temperature. Kenya J. Sci. Technol. Ser. B.Biol. Sci. 5:67-62. Coulson, C.L. 1985. Leaf temperatures of Phaseolus vulgaris — a warning. Phaseolus Beans Newsletter for Eastern Africa. No. 3. Coulson, C.L. and R.J.K. Musyoki. 1986. The construction of a small instrument to measure leaf temperatures. Kenya J. Sci. Technol. Ser. B, Biol. Sci. In press. Coulson, C.L., C.J. Stigter, E. Akunda and E. Floor-Drees. 1988. Instrument-based distortions of leaf/air temperature differences and interpretations of bean drought-stress resistance. J. Trop. Agric. In press. Kamweti, M.W. and C.L. Coulson. 1984. The effect of water application on flower abscission on three bean cultivars of Phaseolus vulgaris. Nairobi/California, Bean/Cowpea/CRSP Report 62-75. Namuye, S.A. 1986. Low cost, low power data acquisition system. M.Sc. Thesis, Dept. of Physics, University of Nairobi. July 1986. McCarthy, F.D. and M.W. Mwangi. 1982. Kenyan agriculture: toward 2000. Laxenburg, Austria: International Institute for Applied Systems Analysis. Newman, S.M. 1985. Low cost sensor integrators for measuring the transmissivity of complex canopies to photosyntheically-active radiation. Agric. Meteorol. 35: 243-254. Page, E.W. 1985. Semiconductor device technology and digital system design. Comput. Electronics Agric. 1:5-29. Stigter, C J. and K.K. Mabuba. 1980. Application of a cumulatively integrating recorder in solar radiometry. Z. Meteorol. 30: 60-62. Stigter, C J. and J.M. Waryoba. 1981. Campbell-Stokes data for radiation calibration purposes in East Africa. Arch. Meteorol. Geoph. Bioklimatol. Ser. B.29: 99-109. Stigter, C J. and C.B.S. Uiso. 1981. Understanding the Piche evaporimeter as a simple integrating mass transfer meter. Appl. Sci. Res. 37: 213-223. Stigter, C J., N.T. Jiwaji and M.M. Makonda. 1982. A calibration plate to determine the performance of infrared thermometers in field use.Afr. Meteorol. 26:279-283. Stigter, C.J., M.M. Makonda and N.T. Jiwaji. 1982. Improved field use of a simple infrared thermometer. Acta Bot. Neerl. 31: 379-389. Stigter, C J., M.M. Makonda and N.T. Jiwaji. 1983. Sensitivity of simple infrared thermometers. J. Phys. E Sci. Instrum. 16: 613- 614. Stigter, C J. and R.M.R. Kainkwa. 1983. A method of acquiring accurate radiometer data despite frequent interruptions in mains electricity supply. Agric. Meteorol. 16:141-144. Stigter, C J., A.R. Mwampaja and R.M.R. Kainkwa. 1984. Infrared surface and thermistor sub-surface temperatures explaining the thermophysical character of grass mulches. In Proceedings of the Second Symposium of Temperature Measurement in Science and Industry. IMC, Suhl. Stigter, C J., C.B.S. Uiso and A.M.G.M. Rashidi. 1984. Evaporation data from a Piche evaporimeter — A comment using Tanzanian results. J. Hydrol. 73: 193-198. Stigter, C J., R.M.R. Jiwaji and F.M.M. Musabilha. 1987. A near-equatorial comparison of two instruments measuring diffuse solar radiation. Z. Meteorol.36:161-164. Stigter, C J., N.T. Jiwaji, K.I. Mabuba, V.M.M. Musabilha, R.M.R. Kainkwa and F.S. Juma. An intercomparison of four types of Robitzsch actinographs for routine global radiation measurements. In preparation.
Considerations for appropriate instrumentation (AI)
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