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SUMMARY REPORT, CONCLUSIONS AND RECOMMENDATIONS

THE WORKSHOP

M. Smith, Senior Technical Officer (Irrigation Management), Land and Water Development Division, FAO, Rome, Italy

The ICID/FAO Workshop on Irrigation Scheduling was held on 12 and 13 September 1995 on the occasion of the 46th International Executive Council Meeting of the International Commission on Irrigation and Drainage, which was held on 11 to 16 September 1995 at the FAO Headquarters in Rome under the auspices of the Italian National Committee on Irrigation and Drainage. The Workshop was a joint initiative of the ICID Working Group on Sustainable Crop and Water Use and of the Land and Water Development Division of FAO and follows long-standing cooperation between FAO and ICID in this field.

The subject of the Workshop is of direct interest to other ICID Working Groups and in the preparations for the meeting from several ICID Working Groups provided cooperation and inputs.

The Scientific and Organizational Committee assigned to advise on the thematic and organizational aspects of the Workshop consisted of members of various ICID Working Groups, the ICID Italian National Committee and FAO and included the following persons:

· Dr. L. S. Pereira, Chairman ICID Working Group on 'Sustainable Crops and Water Use'

· Dr. J. Berengena, ICID Working Group on 'Sustainable Crops and Water Use'

· Dr. B. Itier, ICID Working Group on 'Sustainable Crops and Water Use'

· Mr. L. Rieul, ICID Working Group on 'On-farm Irrigation Methods'

· Mr. J. Goussard, ICID Working Group on 'Construction, Rehabilitation and Modernization of Irrigation Projects'

· Mr. P. van Hofwegen, ICID Working Group on 'Operation, Maintenance and Management of Irrigation Systems'

· Mr. M. Smith, FAO, Land and Water Development Division, Secretary of the Workshop

· Prof. S. Cavazza, Italian National Committee for ICID

· Prof. D. Dewrachien, Italian National Committee for ICID

· Dr. M. E. Venezian-Scarascia, Italian National Committee for ICID.

Themes of the Workshop

The subject of the meeting covered a range of aspects related to the technical, agricultural, social and institutional aspects of irrigation scheduling. In order adequately and systematically to address and synthesize the information available, six themes were identified to address the various issues in irrigation scheduling. Each theme was assigned a reporter with the specific task of compiling information available on the designated subject and of inviting and analysing the papers submitted for the theme, as specified below:

Theme 1: Applicability and limitations of irrigation scheduling methods and techniques
Reporter: Dr. B. Itier (INRA, Thiverval-Grignon, France)

Theme 2: Inter-relationships between on-farm irrigation systems and irrigation scheduling methods (irrigation performance, profitability and environmental consequences)
Reporter: Dr. L. S. Pereira (ISA - UTL, Lisbon, Portugal)

Theme 3: Constraints and applicability of irrigation scheduling under limited water resources, variable rainfall and saline conditions
Reporter: Dr. R. Ragab (Inst. Hydrology, Wallingford, UK)

Theme 4: Requirements for improved interactive communication between researchers, managers, extensionists and farmers
Reporter: Dr. L. Tollefson (IFRA, Regina, Canada)

Theme 5: Interaction between water delivery and irrigation scheduling
Reporter: Dr. J. Goussard (Consultant, Grenoble, France)

Theme 6: Social, cultural, institutional and policy constraints
Reporter: Dr. P. van Hofwegen (IHE, Delft, The Netherlands)

Dr. J. Berengena of INIA, Cordoba, Spain, was entrusted with the overall review of the papers and allocation to the various themes, as well as the review of the thematic papers.

Papers submitted

The call for papers disseminated through the ICID national committees resulted in a large number of submissions. A total of 80 papers were received from 23 countries and more than 170 different authors.

The papers submitted were evaluated by the team of six reporters for their content and relevance to the various themes of the meeting. The scientific and practical information provided in the papers was of a high standard and made selection of papers for the Workshop and proceedings a difficult task. The first round of reviews resulted in the recommendation of 24 papers to be made available to Workshop participants. The number was increased by an additional eight papers in subsequent reviews during the Workshop. In the proceedings, the total number of papers, including the thematic papers, amounts to 40.

Based on the information provided in the papers and complemented by information compiled from literature, each thematic reporter synthesized a thematic paper which was distributed during the meeting and formed the basis of the presentations and discussions during the Workshop.

Paper review

To improve the readability and information provided in the papers proposed for the proceedings, editorial procedures were established for the peer review of all papers. All authors contributed in the review of at least two papers. Each thematic reporter reviewed the papers included in the theme and consolidated and conveyed the comments to the author concerned. A detailed schedule and timing for the review was worked out, covering a total period of nine months. By July 1996 papers had been received in the FAO secretariat for final editing and formatting.

Agenda and attendance

The Workshop on Irrigation Scheduling formed part of the official programme of the ICID 46th Executive Council Meeting and was held over three sessions, morning and afternoon sessions on 12 September and an afternoon session on 13 September.

The Workshop was opened by the Chief of the FAO Water Resources, Development and Management Service, Mr. H. Wolter. The first day was devoted to presentations of the six thematic reports followed by panel discussions and brief clarifications by the various authors present. The second day of the Workshop included an afternoon session with group discussion of open issues identified by panel members, followed by plenary presentations in which the main points of the conclusions and recommendations were discussed.

More than 120 officials, experts, researchers and practitioners in irrigation attended the various sessions of the Workshop.

Acknowledgments

The number of participants and papers submitted for the Workshop indicated the interest and importance attached to the subject of the meeting. The initiative of the ICID Working Group on Sustainable Crops and Water Use, and in particular its Chairman, Dr. Luis S. Pereira, in organizing this important event proved very rewarding indeed.

The extensive contributions of the many authors who submitted papers provided a wealth of excellent information on the subject and formed the basis for the success of the Workshop. The selection of papers for the proceedings proved difficult as almost all the papers were of high quality.

The support and excellent cooperation of the National Italian Committee on Irrigation and Drainage, in particular its Chairman, Prof. P.L. Romita, and Dr A. Venezia-Scarascia and Dr Siniscalchi, merit special mention.

A quite exceptional contribution was provided by the six thematic reporters and the thematic coordinator, Dr. Berengena, in the review and selection of the papers submitted, in the preparation and synthesis of the thematic papers and, after the Workshop, in coordination with the peer review, in the editing of all papers included in the proceedings.

The support of the FAO secretaries, in particular Mrs. Ornella Loniti, providing secretarial assistance during the preparations and the meeting as well as in coordinating the schedule of submissions and compilation of papers was much appreciated.

The final language editing of the papers by Mr. Julian Plummer should be mentioned and, in particular, so should the substantial efforts of the AGL publications assistant, Ms C. Smith-Redfern, in systematizing and formatting the proceedings into a shape which it is hoped may become a lasting contribution to better irrigation management.

THEMATIC APPROACH

Introduction to irrigation scheduling

Irrigation is essential for food production to overcome deficiencies in rainfall and to stabilize agricultural production especially in arid and semi-arid areas. At present one-sixth of the agricultural land in the world is irrigated and provides more than one-third of global food production. The food requirements of an ever-increasing world population higher necessitate agricultural production, a large share of which comes from irrigated lands. As the availability of water resources for irrigation becomes increasingly difficult, water and the cost of water resource development becomes a severely limiting factor enhancing irrigated agriculture.

Extensive engineering programmes have been undertaken worldwide to make available the large amounts of water required for irrigation, but also for other purposes, such as urban and industrial use. At present approximately 80% of all the available fresh water supply is used for agriculture and food production. The demand for water of good quality has accordingly increased tremendously in the last decade.

The efficiency of water in agricultural production is, however, low. Only 40 to 60% of the water is effectively used by the crop, the remainder of the water is lost in the system, in the farm and on the field, either through evaporation, through runoff to the drainage system, or by percolation into the groundwater. Part of the lost water can perhaps be recovered, but additional costs will be incurred.

Poor management of irrigation water is one of the principal reasons for this low water use efficiency in irrigation. The inadequate and often unreliable water deliveries in the main system cause farmers to face regular shortages in water supply, resulting in reduced yields and incomes as well as in much smaller areas being irrigated than originally planned. At field level, inappropriate field layout and mismanagement leads to further water losses and reduced yields.

A range of environmental problems are linked to ineffective water use, such as waterlogging, leaching of agro-chemicals and consequent groundwater pollution, as well as soil and groundwater salinization resulting from inappropriate water applications.

Irrigation scheduling is the process to decide when to irrigate the crops and how much to apply. It forms the sole means for optimizing agricultural production and for conserving water and is the key to improving performance and sustainability of the irrigation systems. It requires good knowledge of the crops' water requirements and of the soil water characteristics that determine when to irrigate, while the adequacy of the irrigation method determines the accuracy of how much water to apply. In most cases, the skill of the farmer determines the effectiveness of the irrigation scheduling at field level.

However, farmers' dependence on a timely and adequate water supply determines their ability to accurately apply water to the field. Inadequacies in the irrigation system and poor management of the water supply result in inadequate and unreliable water supplies to the field, frustrating any attempts at accurate crop irrigation scheduling.

Appropriate irrigation scheduling should lead to improvements in yields and incomes, result in water saving and, in turn, increase the availability of water resources and should have a positive impact on the quality of soils and groundwater.

Research has made considerable advances over the last few decades and a large number of new techniques and methodologies have been made available for direct use in irrigation scheduling. This concerns in particular:

· Crop water requirement methodologies, such as introduced by FAO, make it possible to routinely estimate actual evapotranspiration from climatic data, using a crop coefficient combined with the reference evapotranspiration, ET0.

· The soil water balance and related concepts and measurement techniques are essential for the application of irrigation scheduling.

· Water stress indicators which help to identify and quantify plant water stress. They include the application of tensiometers sensing the soil water potential in irrigated crops, the canopy temperature, the leaf elongation rate, the leaf water potential, the variations in stem diameter or the sap flow fluxes.

· Water yield functions which reproduce the effects of limited water availability on crop yields, including the variable sensitivity to water stress at different crop growth stages.

· Simulation models with different degrees of sophistication, which can reproduce the complexity of processes and may include decision support tools. They help in the real-time planning and management of both farm and system levels and are useful for scheduling of irrigation.

The problems associated with irrigation management are reasonably well known. Moreover, the use of improved irrigation techniques and research outcomes provide a variety of tools for irrigation scheduling. In spite of this, applications in practice are far below expectations.

Objectives

To find answers to the question as to why farmer adoption of irrigation scheduling techniques is still on a limited scale, notwithstanding the large number of methods available. The objectives of the Workshop were specified as:

· To identify the obstacles that negatively affect the application of available irrigation scheduling methods and techniques, including those related to the transfer of knowledge.

· To identify solutions of a technical, social, cultural or economical nature, which could overcome such obstacles and improve irrigation management in practice.

Themes

To address adequately the various aspects which play a role in the introduction and successful application of irrigation scheduling, six themes were identified to assess specific constraints and offer solutions to improve irrigation management.

Theme 1: Applicability and limitations of irrigation scheduling methods and techniques

Various methods and tools have been developed to determine when crops require water and how much irrigation water needs to be applied. These include the various soil and plant monitoring methods as well as the more common soil water balance and scheduling simulation models.

The use of the various scheduling tools is dependent on the input requirements related to type of data: weather, soil and crop, as well to the frequency of data collection. Estimates of evapotranspiration and crop water requirements play an important role in many of the models and various water stress criteria. Identification of limitations and requirements for use by farmers and managers is important in the selection of the appropriate scheduling methods.

Theme 2: Inter-relationships between on-farm irrigation systems and irrigation scheduling methods

A critical question in irrigation scheduling is how and how much water is to be applied to the crop, and this is determined by the field irrigation method. The suitability and adaptability of the various irrigation scheduling methods and techniques in relation to the irrigation method (surface irrigation, sprinkler and micro-irrigation) are often insufficiently taken into account. The irrigation performance as measured in terms of adequacy and application efficiency, as well as the design criteria of the irrigation method, needs to be considered in the selection and operation of the irrigation scheduling method.

Theme 3: Constraints and applicability of irrigation scheduling under limited water resources, variable rainfall and saline conditions

Irrigation scheduling becomes particularly sensitive under conditions of limited water resources, where water shortages require a refined timing of water applications in order to minimize yield reductions. Similarly, under saline conditions, water scheduling appropriate knowledge of the water-yield functions and salt tolerance levels.

Deficit irrigation requires suitable and reliable water stress indicators, while for the management of saline waters accurate knowledge is needed on yield-salinity relationships.

Variability of rainfall is often difficult to adequately accommodate in the planning of irrigation calendars. The options, special requirements and limitations of irrigation scheduling under variable frequency and amount of rainfall need to be considered.

Theme 4: Extension and irrigation services: requirements for improved interactive communication between researchers, managers, extensionists and farmers

The adoption of irrigation scheduling techniques by farmers has been well below expectations. The involvement of farmers, irrigation managers and extensionists can play an important role in the formulation, implementation, monitoring and testing of research findings in water-saving and irrigation scheduling, i.e. assuring an appropriate feedback between research and practice.

The institutional support to be expected when introducing irrigation scheduling methods needs to be critically considered and adapted to the specific conditions of farmers.

Theme 5: Interaction between water delivery and irrigation scheduling

The introduction of modern irrigation scheduling practices, demands specific conditions from the water delivery systems in terms of flexibility and response to changing demands of the user; the physical conditions as well the management structure required to obtain such flexibility in delivery are seldom found in most surface irrigation systems.

Possibilities and requirements for introducing flow-control systems for flexible water delivery scheduling in main and tertiary systems need to be considered in the modernization of irrigation schemes. Physical and organizational measures to increase flexibility, including cases for automation, on-farm storage, farmer participation, etc. are also required.

Theme 6: Social, cultural, institutional and policy constraints

The adaptation of regulations and rules-in-use in irrigation scheduling and water delivery is determined by the social, cultural and institutional conditions in the irrigation system. The cooperation of farmers and irrigation managers in the introduction of water-saving irrigation scheduling is important and needs to be considered; as do costs and incentives for farmers to apply water saving irrigation scheduling, liberalization of cropping, pricing of water, profitability of irrigation.

Water user organizations can have a positive impact on achieving flexible water delivery and introducing water-saving irrigation scheduling. Similarly, service agreements between user and supplier on reliability of water-delivery are important.

CONCLUSIONS AND RECOMMENDATIONS

The six thematic papers prepared by the reporters, based on the information provided in the papers submitted for the Workshop and complemented by personal experience, presented in a concise way the state of the art of the various technologies and the success and constraints experienced in the introduction of the water saving technologies.

The panel and group discussions further elaborated on the specific issues raised by the reporters on each theme and led to conclusions and recommendations, which are outlined below. For further details reference can be made to the thematic reports and the various papers, which together form a substantive source of information.

The following is a summary of the main findings and recommendations grouped according to the six themes.

Theme 1: Applicability and limitations of irrigation scheduling methods and techniques

A large number of methods and tools have been developed to determine when the crop requires water and when irrigation needs to be applied. They include various soil and plant monitoring techniques as well as a range of scheduling methods based on the soil-water balance and simulation models.

Soil monitoring methods include gravimetric determinations, tensiometers and gypsum blocks as well as neutron probes and more recently introduced devices which use electromagnetic and dielectric constant correlations. In the plant monitoring methods various stress characteristics are determined, such as trunk or branch diameter change, leaf water potential and sap flow. Also, canopy temperature measured through radiometers and infra-red devices, including remote sensing, has shown interesting applications.

Although some of the soil and crop devices have been in use for a long time and have shown their validity, their use has been restricted in most cases to the industrial farms or irrigation advisers and researchers.

Irrigation scheduling based on soil water balance determination has become the most commonly practised scheduling tool as estimates on evapotranspiration and crop water requirements have been considerably refined over the last few decades and much research findings and information is available on this aspect. Numerous models have been developed based on the soil water balance principle, various degrees of sophistication, including mechanistic approaches on crop growth. Several papers provide good examples of the introduction of the models with various support and information services established to help farmers use the models with input data on weather, soils and crops.

Models, per se, have proved difficult to run for farmers. In particular, the real time models have proved, even in well managed farms, to be difficult to adopted despite efforts to facilitate availability and transfer of data. Simple models using average data for the development of simple operational guidelines and irrigation calendars seem more easily adopted, in particular, in systems with limited technologies.

Most farmers have a pretty good idea of when to irrigate and, in many cases, the refinement offered by scientific scheduling does not provide enough benefits to offset the costs and inputs required for the use of the irrigation scheduling methods.

Conclusions

Considerable progress has been made in the development of irrigation scheduling methods and there is a gradual increase in the adoption of irrigation scheduling tools by farmers.

The technology level of the farm will determine the choice of the irrigation scheduling method. Industry farms and farms with high value cash crops are more likely to adopt and invest in sophisticated scheduling methods.

The support and collaboration of the expert irrigation adviser will determine the rate of success in the adoption of the irrigation scheduling technology.

Recommendations

Specific recommendations concerning the use and further development of the various irrigation scheduling techniques were made:

For low technology situations the following scheduling methods were considered more appropriate:

· Predetermined irrigation schedules (calendars) based on average crop/soil/climate situations.

· Simple operational rules with guidelines on fixed intervals and constant water applications should be developed.

For high and intermediate technology situations:

· Use of plant water stress observations.

· Use of weather data for soil water balance models which may include simulations of crop growth, watertable movement, nitrogen leaching and salinity effects.

· Use of weather forecast models.

Under conditions of water shortage:

· Use of soil water content measurements.

· Use of plant water stress observations.

· Use of weather data and irrigation scheduling models.

Under conditions of adequate water supply:

· Use of plant water stress observations.

· Use of weather data and irrigation scheduling models.

· Predetermined irrigation schedules (calendars) for given crop/soil/climate situations.

Future research should investigate:

· Scheduling techniques adapted to irrigation systems with equitable and flexible water delivery.

· Scheduling techniques which account for water restrictions imposed by climate or by the delivery system, before or during the growing season.

· Practical tools and decision support systems (software) which will integrate the farming system and the crop yield value to be taken into account and which can be adapted to various levels of water supply and water shortages.

Theme 2: Interrelationships between on-farm irrigation systems and irrigation scheduling methods

The importance of the on-farm irrigation system in irrigation scheduling is highlighted in this theme as it determines the critical question of how and how much water is applied to the crop and concerns two related disciplines: irrigation engineering and agronomy. The limited number of papers devoted to this theme may possibly be an indication of the underestimation of its relevance to irrigation scheduling and the important role it plays in reducing water losses and improving yield.

The thematic paper elaborates extensively on the concepts of the field irrigation methods and their relevance to irrigation scheduling. The factors determining the performance of surface irrigation, sprinkler and trickle irrigation, are developed in terms of the performance indicators and the environmental and economic aspects.

Conclusions

· Volumetric water control and distribution uniformity, particularly in surface irrigation, are essential factors in achieving accurate water applications.

· Performance of sprinkler and drip irrigation systems prove strongly dependent on the quality of design and materials selected. Inadequate management and variations in pressure are other main causes of low performance of these potentially efficient methods.

· Restrictions in flow deliveries in surface irrigation systems due to rotation, fixed deliveries and unknown discharges, are the main constraints in introducing accurate field applications and irrigation scheduling in those systems.

· Field evaluation of field irrigation performance is an essential tool to improve management and introduction of irrigation scheduling methods.

Recommendations

· Irrigation scheduling simulation models should give due attention to the type of irrigation and differentiate scheduling in relation to the irrigation method used.

· Irrigation scheduling advice should assume simplifications in water depth and provide simple rules adapted to the irrigation method and should be understandable to the farmers.

· Uniformity in field water distribution needs to be considered in irrigation scheduling, and should be adequately evaluated in relation to design, equipment and management.

· Developing programmes for field evaluation of on-farm systems is relevant for improving both irrigation scheduling and water application methods.

· To introduce a more flexible water supply in surface systems, farmers should have control of water flow deliveries.

· The modernization in supply should go together with improved scheduling methods, which take into account the specific requirements and restrictions imposed by field irrigation methods.

· In surface irrigation, the introduction of volumetric control at field level may result in considerable water savings.

· In sprinkler and drip irrigation adequate attention needs to be given to design, choice of equipment and management.

· Environmental and economic benefits should be integrated as part of the objectives of irrigation scheduling. Appropriate methods for respective evaluation of the impact and benefits are required.

Theme 3: Constraints and applicability of irrigation scheduling under limited water resources, variable rainfall and saline conditions

Irrigation scheduling becomes particularly sensitive under conditions of limited water resources, where water shortages require a refined timing of irrigation in order to minimize yield reductions. Similarly, under saline conditions, water scheduling requires optimal knowledge of crop-water-yield functions and salt tolerance levels.

Deficit irrigation is the scheduling method applied under a restricted water supply, where irrigation does not fully cover the water requirements of the crop and where certain stress conditions are allowed. The specific objective is to optimize yields and incomes by allocating water to the most sensitive crop stages and/or valuable crop. It requires reliable estimates on soil water content and crop water stress as well as knowledge of the crop-water production functions. A review is given on water production functions of various techniques available for deficit irrigation and of suitable water stress indicators.

Similarly, the use of saline water for irrigation requires a thorough knowledge of the sensitivity and tolerance of crops. Salinity needs to be controlled by adequate leaching and good drainage. In irrigation scheduling soil moisture status as well as salinity concentration in the soil water need to be accurately monitored in order to prevent excessive salt accumulation and crop damage. The hazards of high water tables are highlighted. Management options for salinity leaching are reviewed and examples are provided of irrigation scheduling models that enable salinity to be monitored.

Variability of rainfall is often too difficult to be adequately accommodated in the planning of irrigation calendars. Management objectives under variable rainfall are to optimize rain and to minimize the harmful effects of excess water. Rain forecasting either on the basis of probability calculations or with the help of rainfall simulations under real-time scheduling, is a technique used in irrigation scheduling. Further options and limitations of irrigation scheduling under variable frequency and amount of rainfall are reviewed.

Conclusions

· For deficit irrigation, close monitoring of soil moisture status and a thorough knowledge of crop-soil water status and crop-water production functions is required to develop reliable irrigation scheduling methods.

· For use of saline waters, close monitoring of the salinity status in the soil and a good understanding of the effect of various salinity levels on crop yields are needed.

· For conditions of varying rainfall, reliable forecasts on rainfall are currently lacking.

· Non-uniform water distribution, spatial variability of soil moisture content and crop water stress determined from point measurements lead to uncertainties in developing accurate irrigation schedules.

Recommendations

· A better insight in yield-water functions is required including factors which effect yield and root behaviour, especially under saline conditions.

· Biological stress indicators, such as sensitive crops, could be developed and introduced at farm level.

· Practical solutions need to be developed to overcome the difficulties raised by uneven water distribution and spatial variability of soil moisture which have a distinct effect under saline and deficit irrigation.

· New ideas and practical solutions need to be developed to enable the safe use of deficit irrigation. These include better timing and reliable supply and the development of a priority list of tolerant crops and irrigation systems suitable for deficit irrigation.

· For more efficient irrigation under variable and untimely rainfall, reliable methods are required to forecast both the frequency and amount of rainfall.

· Guidelines on the use of low quality and saline water for irrigation need to be developed, especially for conditions of shallow water tables.

Theme 4: Extension and irrigation services: requirements for improved interactive communication between researchers, managers, extensionists and farmers

Despite the apparent importance of irrigation scheduling and the large amount of research resources devoted to it, the adoption of scientific irrigation scheduling techniques by farmers has been well below expectations.

The different reasons and causes which affect the adoption of scheduling are reviewed and include: the heavy input requirements of many scheduling techniques, the lack of practical guidelines for practical delivery schedules, the lack of flexibility of water supply caused by system limitations, and the low cost of water in public irrigation systems.

More importantly little attention is paid to the process of introductinag and adaptating the method into the farmer's field. This process requires an appropriate support and communication structure between researchers, system managers, extension workers and farmers.

Highlighted below are several examples of the various aspects and stages for the cooperation of farmers, irrigation managers and extensionists in the formulation, implementation, monitoring and testing of research activities on water-saving irrigation scheduling.

Conclusions

· Many scheduling models require considerable inputs and, unless properly monitored, prove unreliable. Furthermore, many of the sophisticated research models developed for irrigation scheduling have little or no practical use in the implementation of an effective water delivery schedule to the crop.

· Without adequate economic or social incentives, adoption of scientific scheduling methods by farmers will be slow or non-existent.

· Lack of flexibility of the delivery system prevents the introduction of modern scheduling methods.

· Institutional constraints related to the unfamiliarity of civil engineers with crop water needs and of agronomists and extensionists with on-farm water management prevent an effective cooperation in introducing practical irrigation schedules.

· Low water pricing policies in public irrigation schemes provide no economic incentive to invest in water saving scheduling techniques.

Recommendations

· The challenge to researchers is to develop economically viable technologies that are readily adaptable to the rural community and the technological level of the farm and farmer.

· A process of interactive communications and participatory research form desirable and essential conditions for the introduction and adaptation of appropriate irrigation scheduling techniques.

· Close cooperation between researchers, system managers, extension workers and farmers is essential to develop and adopt practical and sustainable scheduling techniques adapted to the specific technical and social context of the irrigation system.

Theme 5: Interaction between water delivery and irrigation scheduling

In order to apply effective irrigation scheduling techniques, the farmers should have full control of the water supply. This is only the case where farmers have their own water resource. In most collective irrigation systems, an effective water supply depends on the physical capability and the management of the system, which implies institutional, social and political constraints.

Only in pressurized systems can an effective on-demand system be realized. In the fixed proportional system, which is used in a majority of irrigation systems in the world, crop-based irrigation scheduling can hardly be applied. An introduction to irrigation scheduling requires therefore a specific adaptation of the physical system combined with an adequate management which can assure reliability and flexibility of supply.

Various solutions and requirements for introducing automatic flow-control systems for flexible water delivery scheduling in main and tertiary systems are presented. Physical and organizational measures to increase flexibility, including cases for automation, on-farm storage, farmer participation, etc., are discussed. Special emphasis is given to institutional requirements, policy decisions and the social adaptation process of modernization of the system.

Several examples of computer aided manual operation and overall management are presented. These can be useful for developing criteria for the operation of the system. The heavy data input requirements of most models proved less useful for day to day operation.

Conclusions

· Most collective irrigation systems cannot adopt crop-based and water saving irrigation scheduling methods in view of the lack of reliability and flexibility in water supply.

· Reliable water supply demands a technically good design, which is adjusted to local conditions, good quality construction and proper operation and maintenance.

· Equity in water supply is seldom achieved due to the inadequacy of adjustable outlets in functioning properly over a wide range of flow, the wide deviation of scheduling practices, loose management.

· Simple operational procedures may provide short-term solutions to improve reliability of supply, but long-term solutions need to be found in modernization and automation of the irrigation system.

· The lack of adequate flow control and measurement devices are main constraints in introducing effective water supply.

· Several good concepts, methods and equipment are available, but not yet widely introduced due to lack of knowledge and understanding of available techniques.

· Integral computer models are useful for project planning, design and evaluation, but have proved too cumbersome for day-to-day operation.

· The cost of irrigation modernization cannot be borne by farmers alone.

Recommendations

· Introduction of irrigation scheduling requires a reliable and flexible water supply and greater autonomy for farmers in determining the water supply to their crops.

· Volumetric water allocation is an essential condition for effective water control and allows the farmer to verify water received, the operator to adjust water flow to agreed water delivery, and the supplier to introduce a fair invoicing system.

· Flexibility of water delivery requires a modernization of the irrigation system and an improved management system with greater autonomy for the users.

· Reliable water supply requires the proper design of a conveyance and distribution system which meets local conditions, good quality construction and proper operation and maintenance.

· To achieve flexibility and reliability, irrigation management requires a decentralization of decision making and responsibilities, good communications and the institutionalization of water allocation criteria.

· Better knowledge of the various techniques available and the introduction of automatic flow control devices will provide attractive options for introducing effective irrigation scheduling techniques.

Theme 6: Social, cultural, institutional and policy constraints

Effective irrigation scheduling and water allocation require rules and regulations which, in addition to the technical capacity of the system and agricultural requirements of the crop, are determined by a set of social, cultural, and institutional conditions. Good coordination and communication between supplier and users are essential to ensure a reliable and timely water delivery.

Several examples of the various conditions to help ensure the cooperation of farmers and irrigation managers in the introduction of water-saving irrigation scheduling are reviewed.

Regulations determining water allocation and costs and incentives for farmers to apply water saving irrigation scheduling are elaborated upon, as are the effects of liberalization of cropping, pricing of water, etc.

The role of water user organizations and the impact of their participation on flexible water delivery and water saving irrigation scheduling is highlighted. The effectiveness of service agreements between user and supplier on reliability of water delivery and water-saving irrigation scheduling play an important role in this.

A framework of institutional responsibilities and a clear policy are needed to set the conditions for water allocation and maintenance of the system.

Conclusions

· Effective irrigation scheduling requires optimum flexibility of delivery and good coordination and communication between supplier and user.

· Fixed water allocation is convenient for engineers but prevents the flexible delivery required for crop-based irrigation scheduling.

· Inadequate hydraulic structures and inefficient and cumbersome gate operation result in inefficient and erratic water supply.

· Attempts to modernize the irrigation system with new devices fail due to the lack of recognition for the required institutional change, related to an inadequate institutional capacity, unwillingness of users to adjust to variable water supply, and lack of social harmony and uniformity.

· Lack of communication and control over water deliveries results in a breakdown in confidence and anarchistic water use.

Recommendations

· The introduction of irrigation scheduling requires proper planning of the framework and rules and regulation for water delivery.

· Approaches for improvement in water deliveries and the introduction of crop- based irrigation scheduling methods include: simplification of irrigation scheduling methods, use of farmer participatory approaches, strengthening the capabilities of the managing institutions, and flexibility at farm level.

· Reliable and flexible delivery of water and provision of relevant information on crops and meteorological conditions are essential services for effective irrigation scheduling.

· Introduction of water-saving irrigation scheduling requires recognition both by supplier and user of the value of water. Publicity and extension campaigns for users and better water use monitoring devices for suppliers are tools for raising awareness about the price of water.

· A clear set of rules and regulations and transparency in water allocation are required with clear organizational arrangements and responsibilities.

· Service agreements between users and suppliers can be a useful arrangement for introducing a more reliable water delivery and providing a basis for payment of water fees.

· Transfer of irrigation management to irrigation groups provides greater autonomy to farmers and greater flexibility in water delivery.


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