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Irrigation Overview
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Plants need water to grow and survive. In humid areas, the water demands of most plants are satisfied by rainfall. In arid and/or semi-arid regions however, plant water requirements are generally larger than what rainfall can provide. Therefore, additional water needs to be provided in the form of irrigation. The practice of irrigation has been around for thousands of years and has evolved into a science that deals with the study of soil-water-plant relationships.
Improper irrigation not only wastes water and resources, but also, if more water than needed is applied, it can leach or transport off nutrients and other amendments. Conversely, if insufficient water is applied, productivity of the soil is impaired affecting plant development or possibly senescence. Therefore, a major part of irrigation management is deciding when to irrigate and how much water to apply. This requires a basic knowledge and understanding of soil-water-plant relationships.
Identification and quantification of the input and output components of water to the plant root zone are very important in irrigation management. Water inputs to the plant root zone include rainfall, irrigation water, and capillary rise from ground water. The outputs include runoff, evapotranspiration, and deep percolation.
Determining the inputs and outputs of water, to and from the plant root zone, is a very complex process. CIMIS was established in 1982 to assist California's irrigators in managing their water resources efficiently by providing estimated and measured values of some of the parameters mentioned above. Specifically, CIMIS provides estimated and measured values of evapotranspiration and rainfall, respectively. Users need to estimate the remaining parameters by utilizing a soil-water budget analysis method includes other factors such as soil type, plant type, slope, rooting depth, plant density, etc.
Tools such as mobile irrigation laboratories (Mobile Labs) and irrigation scheduling software can be used to aid in determining the different soil-water budget method components. Using the soil-water budget method can assist users in their decisions about when to irrigate and how much water to apply. Irrigation consultants can also be hired for advice on irrigation scheduling.
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