Advantages and disadvantages to nozzles above and below the canopy
There has always been some debate about the best height for nozzles, and Derrel Martin has heard it all.
“Some producers have decided to reposition devices at the truss rod height back on top of the pivot pipeline due to the tall corn varieties being grown today,” the University of Nebraska engineer observes. “Others opt to place sprinklers down in the canopy to try to save water. But any comparison between the options should always be between the best-designed sprinklers for above the canopy vs. in-canopy sprinkler packages for a given field in a specific location and water supply.”
Pros and Cons of Positions
Martin shares a few considerations for comparing sprinkler packages, especially if the rotation includes corn or taller crops.
- The canopy may stay dryer during irrigation with in-canopy sprinklers, which would reduce canopy evaporation losses. Yet, sprinklers can drag back in the canopy, resulting in the sprinkler spraying water vertically, not horizontally as intended.
- Low-slung sprinklers can become entangled in the canopy and are frequently stuck in one location until they dislodge following several tower movements, skipping over several feet of the row in the process (up to 6 feet, in some cases) only to be repeated at the next location. Planting in a circle will help keep the devices in the canopy, but many farmers prefer straight rows.
- The benefits of in-canopy sprinklers will be smaller for locations in the eastern High Plains because of higher humidity and smaller annual water requirements. The advantages will also be greater for low-capacity systems because they need to run more hours each year, increasing the opportunity of net canopy evaporation and drift.
- In-canopy packages are most feasible on level fields where runoff due to the increased application rate caused by canopy obstruction of water jets occurs.
- Some dealers and farmers do not like up-top sprinkler placement with high-iron water due to the staining of the pivot and possible issues with alignment linkage.
- In-canopy sprinklers usually come with increased cost due to the need for closer spaced devices, longer drops, and smaller orifices, which may require extra filtration to prevent plugging.
- Well water cooler than the dew point temperature of the air can lead to condensation of water from the air when droplets first travel from the sprinkler device. For the same reason, in-canopy sprinklers hold the advantage if the water source provides warm water from a canal vs. cool well water.
- Electric systems operating on load control are often shut down during the highest wind and most evaporative time of the day. This point is not a disadvantage to in-canopy sprinklers, but it does lower losses for above-canopy devices.
- In-canopy sprinklers and drop components potentially have higher maintenance costs and require more management to get the desired results because they are dragging through the canopy. Also, they’re out of sight, making it difficult to monitor problems during the season.
The challenges of getting uniformity – while preventing runoff or water moving within the field – is greatly increased when sprinklers are placed in the crop canopy, Martin observes. “Spacing needs to be close (5 feet or less is best) but not more than 7.5 feet.”
Still, sprinkler packages placed in the canopy have some potential to increase the efficiency.
“More research is needed to fully quantify the evaporation, transpiration, runoff, and deep percolation for an array of fields with varying slopes and soils,” he says.