What measurement is used to compute run time in a constant-rate irrigation system?

• A. Zone output in inches per hour
• B. Rainfall total for the month
• C. Plant height
• D. Root depth

Answer: (A)

Constant-rate irrigation delivers water at a fixed rate, so the run time for a zone is determined by its zone output, expressed as inches of water per hour. To figure how long to run a zone to apply a desired depth, divide the target depth by the zone’s precipitation rate (in inches per hour). For example, to apply 0.5 inches of water with a zone that outputs 0.25 inches per hour, you’d run it for 2 hours. Rainfall totals, plant height, and root depth don’t set the run time for a constant-rate system; they relate to irrigation needs or environmental conditions, not the fixed application rate used to compute runtime.