Irrigation efficiency involves the ability to minimize water losses. Such factors as loss of water from wind drift and evaporation from the soil surface and plant affect the level of efficiency. Meanwhile, another factor of irrigation efficiency is simply getting water into the soil, and controlling runoff. For mechanized irrigation, the biggest single advancement towards increasing irrigation efficiency has been mounting the sprinkler down out of the wind on drop tubes. Enabling the success of drop tubes are products that spread the water out over a wide area, even when mounted below the truss rods of a center pivot. These rotating, spinning and wobbling devices operating at low pressure have dual benefits, increased soak time and low application rates. A more complete throw pattern can give twice the soak time of fixed sprayheads.
Without sprinkler performance that can apply water at an application rate less than the infiltration rate of the soil, the efficiency gained is soon lost to runoff.
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Research efforts are being expended to determine if a spray can be applied to a plant to decrease transpiration; thus reduce water use. Theoretically, transpiration can be decreased by increasing deffensive resistance to water. The resistance should be interposed between the leaf and dry air rather than between the leaf and its source of water. Most research is being conducted with material that will close the stomata or pores of the leaves of plants.
Carbon dioxide, necessary for photosynthesis, is admitted through these pores that are also the exit means for water. A film that will prevent water from leaving through these pores, while being permeable to carbon dioxide, is the ideal. Therefore, stomatal closure by chemical sprays can decrease transpiration and can also decrease photosynthesis, which may reduce normal plant functions and yields.
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