Field evaluation of very low pressure center-pivot sprinkler devices in the pacific Northwest, U.S.A
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The continued viability of center-pivot sprinkler irrigation in the Pacific Northwest may depend on increasing the efficiency with which water and energy are used. Very low pressure sprinkler devices can contribute greatly to energy savings of center-pivot systems. In the Hiddle Columbia Basin of the Pacific Northwest eight medium and high pressure center-pivot sprinkler systems were completely or partially converted to very low pressure systems (69-138 kPa (10-20 psi)). Field tests were conducted under a variety of field conditions to compare three center-pivot sprinkler devices. The sprinkler devices evaluated were very low pressure fixed-head spray sprinklers (top sprays, drop sprays, and spray booms) and bubblers (furrow drops). These very low pressure sprinkler devices were compared with high to medium pressure impact sprinklers with standard or Flow Control Nozzles. The combined effects of spray losses, uniformity coefficient, soil water and yield were studied. Under similar conditions, spray loss values from high or medium pressure impact sprinklers ranged from two to three times the spray loss values obtained under lower elevation spray sprinklers. Wind speed and spray head elevation influenced spray loss as much as the very low pressure sprinkler devices. Bubblers (furrow drops) effectively eliminated spray loss but their use in low pressure center-pivot conversion in Pacific Northwest is questionable. A full season comparison between these sprinkler devices showed that for low spray head elevations (0.9-1.8 m (3-6 feet)) from the soil surface or crop canopy and low pressures (70-140 kPa 00-20 psi)), and at dealer recommended sprinkler spacings, the spray heads on center-pivot systems appear to be a promising alternative for reducing irrigation energy requirement. This energy reduction is due to a reduction both in sprinkler operating pressure and spray loss.