Irrigation Advisory Systems

The practical application of irrigation scheduling techniques requires appropriate technology transfer and support to farmers. Irrigation extension or consulting services may provide this support and help in the transfer of technologies from research to practice. Such services should not only provide information but also stress how this information is being used and what the impacts are for improving irrigation systems and management.

Farmer support must be adjusted to the technology level of the user. De Jager and Kennedy [21] define three levels:

1. Top technology. This situation means that there is a weather station in the farmland with a support system for decision making that allows individualized complete scheduling.

2. Intermediate technology. The station is strategically located for a group of farms that receive common information. This general information may be complemented individually with specific data regarding each field, such as soil water properties, crop phenology, and irrigation systems. This information allows for the individual scheduling of irrigation. There is also a collective technical support system available.

3. Low technology. In this situation, fixed irrigation periods and volumes are scheduled for the whole campaign, based on large series of climatic parameters and crop average water requirements. Hill and Allen [8] present an interesting scheduling system for this situation.

Irrigation-scheduling advising systems commonly use an irrigation scheduling system based on the soil-crop water balance. When other methods are used, such as an evaluation of soil or plant water status, they are usually a complement of the water balance and often are used to address the results obtained.

An irrigation-scheduling advising system generally is composed of the following elements:

• A data collection system, including at least an automated weather station and a monitoring system relative to crop phenological evolution. Ideally, it also should include monitoring and evaluation of the irrigation systems used by the farmers.

• A system for information processing able to provide actual reference evapotranspiration data, the ET0 for the climatic conditions prevailing in the area, crop coefficient data relative to crops in the area, as well as information on soils and soil water. With the help of models, indicative information on irrigation depths and frequencies also may be provided.

• An information transmission system. Traditional methods for information spreading were represented by local press, radio, and telephone. At present, using personal computers, one has access to information systems and can access individual information in real time [7, 9, 10].

• A system for information validation and comparison of the results obtained. This is a fundamental piece of the system and may be supported by monitoring selected fields in the study area. Results can be evaluated and compared with those from other fields that have not adopted the systems advice or that are following different irrigation schedules.

The evaluation of irrigation systems should be considered as a main monitoring task of irrigation-scheduling advising services. Knowing the crop water requirements is useless unless the way that water is applied to each field is known. Often, irrigation systems installed a few years ago apply water differently from the original design. This is because supply conditions, such as discharge and pressure, may have changed over time, or the hydraulic structures are not functioning as designed, or the systems have deteriorated. It is necessary not only to evaluate the off-farm systems, but to evaluate the performances of on-farm systems, for uniformity and efficiency, and to provide for improving on-farm irrigation [7, 28] (see Section 5.4).

Consulting services may be provided to individual farmers or to users' associations. Farmers' participatory activities should be encouraged, including the funding.

The transfer of irrigation technologies is a main task of services providing irrigation support to farmers [47]. Burt [48] points out that effective use of irrigation scheduling models requires a process of preparation and training of the users. The lack of such support may be one cause for low adoption of irrigation scheduling advice and for the limited use of irrigation scheduling techniques and models [7].

Several examples of users' participatory activities indicating positive future trends can be provided. An interesting example is presented by Blackmore [49] in the MurrayDarling hydrographic basin in Australia. Tollefson [6] analyzes the role being developed in Canada by the Prairie Farm Rehabilitation Administration in the development of users' participation in water management in collaboration with universities and different institutions. In Castilla-La Mancha (Spain) [23], plans for the exploitation of mined aquifers have been initiated with the scientific and technical support of the university in cooperation with the regional government and with an intense participation of users' organizations.

In developing countries, interesting experiences are also taking place, such as those in West Java and Bihar, India [50], with the Damodar Valley Corporation in India [33], in the Jingtaichuan district in China [51], and in Bangladesh [52].

Other aspects that may be of interest for achieving successful use of irrigation scheduling by farmers are the allocation of water to the farmers in volumetric terms. At the beginning of the campaign, the farmer knows the total volume available and the adequate rate of use; water prices then are established such that the farmer is induced to make the best use of allocated water [6].

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