The basic objective of irrigation is to replace the water deficit produced by an imbalance between crop or orchard evapotranspiration and precipitation or natural water contributions.
To achieve high levels of application efficiency and uniformity, irrigation systems and methods should have an optimal design, an adequate installation, and appropriate management. Irrigation planning is an essential factor to consider because optimal crop or fruit production depends on the frequency and timing of irrigation. It requires knowledge of the hydrophysical characteristics of the soil, the crop's or orchard's root extraction zone, and water demand throughout the irrigation season. Armed with this knowledge, the different dates for irrigation with a particular application system can be estimated. In this manner, the farm manager has a program that permits to carry out cultural and harvesting tasks of crop and orchards without producing plant stress during the productive process. Clearly, yearly and/or seasonal adjustments need to be made in the frequency and timing of irrigation to assure an up-to-date strategy, or real-time strategy, that considers possible precipitation that could occur between irrigations as well as climatic changes. An irrigation system will be efficient and will fulfill the proposed objectives if it is adequately planned and appropriately operated.
Farm-level irrigation operation should consider planning aspects and decision-making activities before and during the crop development season, incorporating long-term and immediate (real-time) planning. In the long term, the optimal crop-and-orchard pattern should be structured with the selection and optimal design of the irrigation system. Under real-time operation, the objective is to maintain an adequate soil water content, which enables storage of probable rain, controls salinity, avoids nutrient lixiviation, reduces energy costs, and minimizes labor costs.
Appropriate planning can reduce irrigation costs and/ or increase production quantity and quality. In general, the objective of most producers is to maximize production, which may or may not be optimal from an economic perspective. Strategic planning and management is needed to ensure an optimal crop production where profits are maximized, considering physical, environmental, financial, equipment, and personnel restrictions.
Several techniques can be used for farm-level irrigation planning. The selection of a specific technique is a function of water availability, access to climatic information, irrigation manager's knowledge, irrigation method, crop value, crop sensitivity to irrigation, costs of technology implementation, and personal preferences of the irrigationists. Among the available irrigation planning techniques are: water balance, soil water content, and plant-water level methodologies.
Water balance is the most used methodology in irrigation planning and is generally based on the area's historical climatologic information, soil type, and crop type, and is adjusted with up-to-date information each season. Soil water content can be a useful programming tool when there is a regular soil water content monitoring program. However, it is mainly used to adjust already existing irrigation planning. Plant-water level or flow measurements are important tools used to determine plant-water requirements and present water conditions. With this information, irrigation programming can be implemented. Furthermore, with this type of technology, frequent-application systems, such as microjet and drip, are likely to be used extensively because skilled personnel are no longer needed to determine an adequate water application since the decision-making process is supported by a computer modeling.
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