Water application distribution under center pivot systems

摘要

Application uniformity of center pivots directly influences overall irrigation application efficiency. Improper sprinkler selection or spacing can result in either insufficient or excess water overlap resulting in systematic dry or wet locations inthe field. To maintain acceptable uniformities, sprinklers are typically spaced at distances less than or equal to the wetted radius. The influence of wind on uniformity has typically been ignored. Wind normally lengthens the wetted radius downwind whileshortening it upwind and at right angles to the wind. Overall the wetted diameter is increased parallel and decreased perpendicular to the prevailing wind direction. A computer model using droplet ballistics equations was used to evaluate the influenceof wind on application uniformity based on the Christiansen uniformity coefficient (CU) for various sprinkler spacings. The spray sprinkler had a donut shaped, single-leg distribution with an elliptical application pattern on a moving lateral system. Results indicated a simulated CU greater than 98 percent under no wind was possible for sprinkler spacings less than 2/3 the wetted radius (R_w). Uniformity dropped by 18 and 25 percent for the 2/3 R_w spacing for a 10 m/s wind blowing parallel and perpendicular to the lateral, respectively. When spacings increased to R_w, simulated CU for no wind was lowered to 85 percent, but decreased to less than 72 and 49 percent for 10 m/s wind parallel and perpendicular to the lateral, respectively.