Which sequence correctly outlines how to calculate run time for a zone to meet plant water needs?

Which sequence correctly outlines how to calculate run time for a zone to meet plant water needs?

• A. Measure soil moisture, estimate plant wilting point, set timer to 30 minutes, rotate zones
• B. Determine ETc, convert to inches, compute required water depth per zone, divide by the zone’s application rate, consider irrigation efficiency, convert to minutes
• C. Determine pump size, measure field capacity, set timer to 60 minutes
• D. Use zone area and nozzle size to estimate time

Answer: (B)

The essential idea is to tailor run time to the plant’s water needs by translating those needs into the actual time your system must run. Start with ETc, which tells you how much water the crop would use over a given period under current conditions. By converting ETc into inches, you express that water requirement as a depth of irrigation, which is how irrigation depth is commonly planned. Next, determine how much water depth is needed for each zone to meet that plant demand, then divide that required depth by the zone’s application rate to get a run-time estimate in hours. Irrigation efficiency is then used to adjust for water lost to inefficiencies like deep percolation, wind drift, and evaporation; effectively you’re increasing the amount of water you need to apply to ensure the correct amount actually reaches the root zone. Finally, convert the resulting time from hours to minutes for your scheduling. Other approaches miss the core idea of tying water delivery directly to plant needs. Simply measuring soil moisture or assuming a fixed timer ignores how much water plants actually require and how much of what you apply reaches the root zone. Options that focus on pump size, field capacity, or using only zone area and nozzle size fail to connect irrigation duration to the crop’s water demand and system efficiency, which is why they aren’t the best method.

The essential idea is to tailor run time to the plant’s water needs by translating those needs into the actual time your system must run. Start with ETc, which tells you how much water the crop would use over a given period under current conditions. By converting ETc into inches, you express that water requirement as a depth of irrigation, which is how irrigation depth is commonly planned. Next, determine how much water depth is needed for each zone to meet that plant demand, then divide that required depth by the zone’s application rate to get a run-time estimate in hours. Irrigation efficiency is then used to adjust for water lost to inefficiencies like deep percolation, wind drift, and evaporation; effectively you’re increasing the amount of water you need to apply to ensure the correct amount actually reaches the root zone. Finally, convert the resulting time from hours to minutes for your scheduling.

Other approaches miss the core idea of tying water delivery directly to plant needs. Simply measuring soil moisture or assuming a fixed timer ignores how much water plants actually require and how much of what you apply reaches the root zone. Options that focus on pump size, field capacity, or using only zone area and nozzle size fail to connect irrigation duration to the crop’s water demand and system efficiency, which is why they aren’t the best method.