Irrigation scheduling is often defined as determining when to irrigate and the amount of water to apply. Despite the seeming importance of this methodology, a relatively small proportion of producers utilize scientific scheduling practices. Competition for agricultural water is rapidly increasing through urban expansion, industrial and recreational uses. Efficient irrigation scheduling based on sound methodology must be emphasized as water supplies become scarce and the price of water increases.
The biggest challenge for irrigation scheduling is to develop methodology specific to various crops and environments. Without economic or social incentives for scientific scheduling, adoption of technical and real time scheduling procedures has been slow or non-existent. Consequently, most irrigators do not use real time procedures despite technological advancements. Techniques must be developed and disseminated effectively so that producers can use them. Otherwise, research and demonstration efforts are wasted (Martin et al. 1990).
The challenge to researchers is to develop economically viable technology that is readily adaptable to rural society. To be effective, agricultural research must be directed to producer needs and results made available to producers readily and conveniently (Seegers and Kaimowitz, 1990). The challenge to extension staff is to deliver this information effectively and ensure proper utilization by the farm clients.
This paper examines the need for the interactive communication between researchers, extensionists and farmers for improving transferability and applicability of irrigation scheduling techniques.
IRRIGATION SCHEDULING METHODS
Irrigation scheduling provides information that can be used to develop irrigation strategies for different crops under varying soil and climate conditions. These strategies may be determined using long-term data representing average conditions or in-season factors based on real time information and short-term predictions (Martin et al., 1990). Successful irrigation scheduling methodology, however, must be simple to implement and easy to understand from the farmer and project management standpoints.
There are various methods for scheduling irrigation. In principle, irrigation can be scheduled by monitoring the soil, plant and/or microclimate interactions (Hillel, 1990). These methods involve:
Soil moisture measurement
All aspects of irrigation management, and especially irrigation scheduling, require an understanding of the soil water balance. Using this balance requires estimating the amount of water in the root zone at any given time.
Soil water affects plant growth directly by influencing plant water potential and indirectly through its influence on soil aeration, soil temperature and nutrient mobility (Phene et al., 1990). Traditionally, irrigation scheduling is based on soil moisture levels. Soil moisture can be measured directly or estimated indirectly using various parameters. Some of the commonly used measures include: gravimetric determination, neutron probe, time domain reflectometry, tensiometer, and gypsum block (Swartwood and Remer, 1992). These measurements are site specific and, therefore, need many observations to properly characterize a field. This can be a laborious and expensive procedure. In addition, some of these methods can require tedious calibration procedures, frequent servicing and constant supervision.
Plants respond interactively to soil and environmental conditions. Hence, they are a logical indicator for irrigation scheduling. Plants can be used to schedule irrigation through visual observation. There are also numerous destructive and non-destructive techniques. These methods are labour intensive. They require many samples. Measurements must be normalized with well watered fields for accurate estimations (Phene et al., 1990). Visual indicators of plant stress are often an after-the-fact method of scheduling. More recently, plant canopy temperature relative to air temperature using infrared thermometers has been used for irrigation scheduling with varying degrees of success (Council for Agricultural Science and Technology, 1988).
Evapotranspiration (ET): Although not actually a method for scheduling irrigation, this approach follows a meterological imposed evapotranspirational demand as it varies over time. The irrigation requirements are determined accordingly (Hillel, 1990). ET is used in combination with other terms of the soil water balance equation to schedule irrigation.
The estimation of potential evapotranspiration, as defined by the Penman and other formulae, can serve as irrigation scheduling criteria. Evaporation pans are widely used all over the world, despite having differences in energy balance, aerodynamics, and vegetative surfaces (Phene et al., 1990). This requires data from well equipped meteorological stations. Lysimeters are used to measure ET. Atmometers are also used to help determine evapotranspiration.
Models: Irrigation scheduling models based on evapotranspiration have been used worldwide (Jensen et al., 1971). In this method, the optimum stage for irrigation is determined by the daily total water use. These models require several input variables and some of them might not be available at the farm level.
Tactical irrigation scheduling models can be used for large areas that include a variety of crops assuming that the weather conditions are similar and the crop coefficients are accurate (Snyder, 1987). They provide farmers with the daily information needed to make timely decisions. Problems with these models include development of appropriate crop coefficients suited for different areas and crop types. Microcomputer capability has vastly improved this technology. However, the concept is difficult to implement in small-scale farming or in arid regions of developing countries.
Burt (1996) suggests that many of the theoretical scheduling models developed could be associated with training but have little or no practical use in implementing a desirable schedule of water delivery if the goal is to maximize yield. In California, less than 5% of the farmers use and own such computer programs for real time information.
PROBLEMS WITH IRRIGATION SCHEDULING
In developing countries, approximately 80% of the total water used is for agricultural purposes. Domestic and industrial needs are relatively low. Demand for water is expected to increase in all sectors, and this will require considerable improvements in efficiency. Major improvement must come from the dominant user, irrigation (Hennessy, 1993). Numerous methods, as previously discussed, are available to facilitate irrigation scheduling. Despite this, the overall use of scheduling methodology is very limited. Some of the constraints encountered include:
Flexibility in irrigation scheduling is essential. Irrigation scheduling becomes redundant if water is not available when required or if supplied on a rigid schedule without due consideration to varying crop water requirements. This is common in older irrigation projects where water is delivered to farmers on a predetermined schedule.
Many developing countries (particularly the Asian and African tropics), are characterized by very small land holdings and, predominantly, a rice-based cropping system. These conditions of rotational supply and the supplemental nature of irrigation render many of the modern irrigation scheduling technologies impractical. Further, the advantages through improved water use efficiency and labour utilization are not the most important considerations to these farmers. Viable methodology must be developed to suit these situations (Bhuiyan and Undan, 1990).
Lack of flexibility can also be caused by system limitations. In the mid western United States, during hot dry conditions, the ET for corn can reach 12 mm/day. A centre pivot irrigation system designed to provide 63 l/s can apply 10 mm in a 24-hour period to a 53 ha area, i.e., a shortfall of 2-4 mm/day. Irrigation scheduling here is designed to operate the system 24 hours per day, seven days per week (Wenstrom, 1980).
Irrigation systems have traditionally been built, operated and maintained by public agencies with minimal charge for services. It is estimated that in the developing countries, the average government revenue from irrigation is only 10-20% of the full cost of delivery (Postel, 1990). The same is true in the developed world where water is allocated to irrigation districts at costs which do not reflect real market values (Ives, 1993). This promotes inefficient water management practices. By contrast, when prices reflect scarcity, then farmers will use water productively and more efficiently.
Cost of scheduling
Irrigation scheduling methods can be costly and time consuming. Unless properly monitored and maintained, they are unreliable.
Many farmers execute proper irrigation scheduling practices without using sophisticated instruments and with limited decision making skills (Jensen, 1981). This will continue until any new technology developed provides directly measurable results or perceived benefits with minimal cost or demand on time. If the benefits are not evident, the acceptance and use of the technology will be limited unless highly subsidized.
Van der Westhuizen et al. (1996) conclude that in South Africa the primary reason farmers do not schedule irrigation is that they do not perceive the net benefit to be positive. Farmers must be assisted in quantifying this net benefit or the process of technology transfer or uptake will be slow.
The degree of acceptance of irrigation scheduling technology through extension depends directly on the educational standards and literacy levels of the farming community. Unfortunately, most of the traditional irrigation systems are located in areas where literacy levels are low. It is essential that good information is developed and disseminated in a simplified manner understandable to the trainers and end users (Hasan et al., 1993). Government agencies, along with universities and the private sector, must deliver the required training. The educational system, however, does not prepare students for roles in the management of water. The number of men and women familiar with on-farm water management practices are limited and there are few colleges, universities and vocational schools offering this training.
In many countries, the institutions and organizations dealing with water management are many and complex (Tollefson, 1993). Often the assessment of water resources along with the planning and construction of irrigation schemes is the responsibility of national water resources institutes staffed primarily by engineers. Irrigation deliveries are set, not based or related to crop needs. On-farm water management is usually handled by the ministry of agriculture. These individuals are often not trained in water issues and are unable to provide adequate assistance to farmers. Lack of coordination and cooperation between these agencies have contributed to poor water use efficiency. Farmers lack the required knowledge to use water efficiently and even when they have it, unreliable supplies make it difficult to apply. Farmers also lack motivation and economic stimulus to manage water better and to organize themselves for purposes of water users associations, which are considered indispensable for good farm level management (Dieleman, 1983).
Technology transfer dictates a change in the way people think and behave. Successful technology transfer should take into consideration the expected behavioural changes of people rather than only the physical impact of the new technology in a new environment (Shearer and Vomocil, 1982). Farmers, by nature, follow a proven example. Technology transfer presented in the form of demonstration plots on a farm scale is a practical and credible method. Emphasis must be placed on this approach.
Mangano (1996) suggests that in the developing countries, irrigation scheduling is important where irrigated agriculture has a long tradition, but in new development projects, attention must be paid to becoming accustomed to the new system. Irrigation scheduling should be delayed until experience is present.
Role of the extension service
Agricultural extension is vital to the development of irrigated agriculture. The extension service is responsible for simplifying research information and delivering it to farmers in an effective and easy to understand manner. The extension service also provides a feedback mechanism to researchers on problems faced by farmers (Bhuiyan, 1978). The research/extension/farmer relationship should be viewed as an interdependent continuum.
Extension should be an integrated part of every irrigation project from the beginning. The high cost of providing water justifies additional investment in extension to make full use of the potential created by irrigation. The efficiency of extension is determined by the quality of personnel, the method, organization and management (Nordhorn, 1983).
Extension workers must be dedicated and in close liaison with the farmers they serve. Gaining the confidence of the farmers is achieved by the well-planned and gradual introduction of proven new technology. Useful means of introducing new technologies have included demonstration plots, field tours, meetings, etc.
Knowledgeable and innovative farmers tend to seek advisory help on their own initiative. Unfortunately, this is not the case for farmers who are less skilled. Ironically, it is this group which badly needs extension help (Sne, 1988).
Introduction of irrigation scheduling methodology can improve water use. Farmers, however, must be convinced that the technology is profitable. Furthermore, they should have sufficient resources and proper knowledge before adopting any new technology. The science of irrigation is complex and comprehensive. The irrigation extension worker must have comprehensive expertise and a good working relationship with subject matter specialists.
Problems with the extension service
There is no disputing that extension efforts, particularly in developing countries have not always achieved the desired results (Hunter, 1970). The former chair of the Board for International Food and Agriculture Development, C. Wharton, emphasized the problem in the following statement: 'If there is an area in which we have been most unsuccessful, it has been in the development of cost effective means for the delivery of scientific and technical knowledge to the millions of farm producers in the third world' (Arnon, 1989).
There are many reasons for this restricted progress. Short comings in the extension service can result from organizational and operational defects; ineffective personnel; economic constraints; poor linkages with other institutions; political, cultural and social constraints (Arnon, 1989).
Extension services in Asia and other developing countries are often badly under-equipped in terms of staff, transport and accommodation. They often lack the technical skills, particularly in water management. Furthermore, in developing countries, where small-scale agriculture is the norm, a wide array of crops are grown in a particular region. This adds another dimension to the level of technical skills and expertise needed by the extensionists. The inadequacy of resources and skills reflect the low priority given by most governments to agricultural extension. It generates poor morale leading to general ineffectiveness. Benor and Harrison (1977) attribute the following reasons for the malaise of the extension service: a) dilution of effort, b) coverage and mobility problems (some extension workers deal with 2 000-4 000 farm families spread over a wide area, c) lack of training, d) lack of ties with research, and e) low status in society (low pay, few incentives, poor facilities).
In developed countries, there tends to be a greater commitment to acceptance of new knowledge and promoting new practices. This allows technology to be advanced more rapidly. In developing countries, however, information is often not freely shared and authority not freely delegated. Despite the differences, farmers and extension workers in developing countries respond positively to recognition, praise and reward like those in developed countries (Shearer, 1987).
Public extension versus private consultants
In most countries of the world, the extension service is the responsibility of the government and is usually part of the Ministry of Agriculture (Arnon, 1989). There is a role, however, for both the public and private sector for research and extension, particularly as related to irrigation. It must be remembered that the needs of developed and developing countries are different. Increased involvement of the private sector has often resulted in rapid acceptance, higher efficiency, and increased profitability. The public sector, however, must also be involved, in order to ensure that the service is extended to more needy farmers and for sociopolitical and equity reasons (Barghouti and Hayward, 1988). A blend of the two will probably produce the best and most sustainable result. The generation of knowledge and dissemination of technology are complex. A structured extension service with effective interaction with farm groups linked to subject matter specialists can be of immense benefit.
In many developed agricultural regions, irrigation scheduling consultants offer pay-for-service activity that includes updates, summaries and projections of the field water status of individual fields. This service is relatively widespread in the intensively irrigated areas of the United States. It can work effectively but has an associated cost. Jensen (1981) states that the survival of private groups depends on the development of usable and cost effective technology that farmers want and need to manage irrigation. Many farmers will not use irrigation scheduling methodology unless it provides directly measurable results and adds little additional cost in terms of time and money.
The challenge for researchers today is to develop economically viable technology that is easily adaptable to rural society. Much of the developed world has traditionally followed the paradigm where research is conducted at universities and the resultant technology is transferred through various extension mechanisms to the producer (Tollefson, 1992). Here, scientists are the source of creative thinking. The new technologies developed are passed to the extension staff who refine and disseminate them to producers in an easily understandable manner. This model assumes minimal interaction among the various groups. This has resulted in a uni-directional information flow, i.e., from researchers to producers. A more interactive approach in communication can be very beneficial.
According to the FAO (1984), public agricultural research institutions often have poor relations with extension agencies. The World Bank (1985) states that bridging the gap between research and extension is the most serious institutional problem in developing a research and extension programme. Extension workers often see researchers as working in an ivory tower generating technologies that are not applicable to the farm (FAO, 1984). Researchers often question the ability of the extension agents to perform their jobs effectively (Quimsumbing, 1984).
Thornley (1990) suggests that farmer involvement in agricultural research has been limited by inadequate funding, institutional policies and hierarchies, specialization, and incompatible personalities. He suggests that priorities for agricultural research using public funding should be identified through a democratic process involving farmers in order to obtain a better balance between basic/applied research and demonstration. Watkins (1990) states that United States land grant institutions follow a 'top-down' model of research and demonstration whereby farmers are the passive recipients of research results based on perceived needs identified by scientists with little input from the end user.
Better communication among the researchers, extension workers, and farmers is an essential component for improving transferability of technology.
Irrigation systems are complex 'socio-technical systems' which involve interaction between a physical environment, technology, agriculture and often contending interests of multiple stakeholders. Sound technical analysis and participation of stakeholders is critical to an optimal outcome (Vermillion and Brewer, 1996). They report that participatory research involving farmers, agency and researchers produced significant improvements in rotational management in west Java and in Bihar, India.
Harun-ur-Rashid (1987) states that in Bangladesh improved water management is a continuous research/development process. This process is based on two principles: a) an interdisciplinary approach to on-farm water management, b) farmer/client involvement. Here physical, biological and social scientists work with farmers in identifying constraints and possible solutions.
Pramanic and Mallick (1996) describe a study in the Damodar Valley Corporation (DVC) project in India, where on-farm participatory research trials were conducted. Positive improvements in water use efficiency were evident when the recommended methods were followed.
Xianjun and Yunbi (1996) describe how in the Jingtaichuan pumping district of China farmer involvement in irrigation management and the introduction of simple techniques has led to the development of a wate- saving irrigation schedule and improvement in on-farm water management.
Generally, the importance of producer and public participation in research, demonstration and extension is better recognized. At present, in Agriculture Canada, greater emphasis is being placed on identification, recognition and satisfaction of client needs. Cooperative ventures with private sector involvement are being encouraged and pursued. The Prairie Farm Rehabilitation Administration (PFRA), as part of Agriculture Canada, has been a leader in encouraging partnerships and private sector involvement in irrigated research and demonstration with an emphasis on rural development and environmental sustainability. Today, in cooperation with private industry, government agencies, producers and universities, PFRA successfully operates research and demonstration centres at Outlook, Saskatchewan, and Carberry, Manitoba.
The Saskatchewan Irrigation Development Centre (SIDC) is a federal/provincial agency. Its purpose is to conduct, fund and facilitate irrigated research and demonstration responsive to farmer and industry needs. Research and demonstration advisory committees, strongly represented by farmers and industry, play a major role in programme development.
The Manitoba Crop Diversification Centre (MCDC) was formed in 1993, as a partnership between PFRA, the government of Manitoba and an association of horticultural producers and processors. Specialty and horticultural crop production, especially potatoes, will be the focus of MCDC. Both centres emphasize addressing problems brought forward by producers and industry.
These changes in the more traditional way of conducting research have created concern among some agricultural scientists. Scientists, in their search for universal truth, tend to overlook concerns at the farm level. Further, some scientists are inclined to design their research projects with the view of producing publications, rather than answering on-farm problems. This is because in the current system their career advancements are based primarily on publications and not on contributions to farming. Producers, on the other hand, want immediate answers to local problems, are not concerned with the career achievement goals of scientists and are not interested in experimental details, such as treatments, replications, etc. Some producers are satisfied with decisions based on one year's data. Many researchers, however, are not prepared to allocate time to projects that are not statistically viable and do not withstand peer review. In many cases, lack of communication of work between farmers and researchers is a major concern.
It has been suggested that a shift must occur away from the top down hierarchial approach, criticized by farmers as elitist, to an egalitarian and participatory approach in which farmers, researchers and extensionists serve as peers (Watkins, 1990). Thornley (1990) suggests that if we want more public and farmer involvement, the following should be examined: a) Basic research is viewed as more important than applied research in the promotional system approach. b) Researchers are specialized often with a reductionist view. Therefore, researchers should take a systems approach. c) Lack of communication between farmers and researchers. Some researchers display a sense of superiority which discourages farmers. Conversely, farmers feel researchers simply do not understand their problems. d) Researchers should work on issues of priority established by a democratic process. Farmers should help set the course and have some decision-making authority and monetary reward. A mechanism is required to satisfy the needs of both groups. Communication is the key to successful participation and interaction of farmers, scientists, and extension personnel. It will only be through improved communication of these groups that any irrigation scheduling methodology that may be developed will be utilized effectively on a field scale.
In many countries, 80% or more of the total water used is for agricultural purposes. Demand for water is expected to increase in all sectors and this will require improvements in efficiency, particularly from agriculture, the dominant user. Irrigation scheduling is a key to efficient use.
Despite the numerous methods available and the seeming importance of irrigation scheduling, a relatively small proportion of farmers use this methodology. Many reasons are given to explain this lack of uptake of scheduling including: a) lack of flexibility, b) non-economic pricing of water, c) cost of irrigation scheduling, d) lack of education and training, e) institutional problems, and f) behavioural adaptation.
A greater obstacle, however, is the lack of interactive communication between researchers, extensionists and farmers. Researchers in the past have developed information which has been transferred through various extension mechanisms to the producer. This approach has resulted in a 'top down' uni-directional information flow with little input from producers. Producer input is critical if the work is to be relevant and utilized. Participatory research integrating the ideas of researchers, extension personnel and producers has shown promise. Perhaps donor support should be more strongly linked to the participatory research concept.
More emphasis is required in applied research and demonstration, particularly at the on-farm level. Farmers by nature follow a proven example that has shown direct benefits to them. Technology transfer presented in the form of a farm-scale demonstration is a practical and credible approach. In addition, major emphasis must be placed on extension ensuring that extensionists are properly trained and that farmers are receiving adequate information.
Communication between the groups involved in the research/extension/producer continuum is key to the development and uptake of relevant and useful irrigation scheduling methodology.
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