Variable rate water and chemical application for continuous-move sprinkler irrigation systems

Agriculture is beginning to address the production and environmental problems of applying inputs to nonuniform fields by developing equipment which enables input rates to be varied. A prototype control system has been developed to enable continuous move irrigation systems, such as center pivots, to spatially vary water and chemical amounts. The control system was tested from 1992 to 1995 at the University of Idaho on a 100 m long three span linear move irrigation system using catch cans to measure application patterns. Variable flow along the lateral was achieved in a stepwise manner using electric solenoid valves and control modules to operate multiple sprinklers with different nozzle sizes. All signals to the control modules were transmitted along a single cable by a microprocessor according to the position of the irrigation system relative to a target application map. The precision of variable water and chemical applications to different areas within the same field was comparable to that of uniform applications over the entire field.