Even application

One of the top priorities of an irrigation manager is to ensure that their irrigation system applies a uniform depth of water across the irrigated area. A uniform application ensures that crop water demands are satisfied throughout the field, leaving no areas over- or under-irrigated, and crop yield expectations are met. When the irrigation requirement varies within a field, center pivots equipped with zone-control variable rate irrigation technology have become a useful management tool. Particularly, zone-control VRI systems allow irrigation managers to delineate custom management zones within an irrigated area without the boundaries created by the traditional radial operation pattern of a center pivot system. In operation, each individual sprinkler along the pivot lateral is pulsed on and off via a solenoid-operated valve to apply the prescribed depths to the custom-delineated areas.

While these zone-control systems are good at improving irrigation water use efficiency, they come with quite literally hundreds of additional components in comparison to a traditional center pivot. When it comes time to perform regular system checks and maintenance, additional points of inspection must be added to the checklist to maintain the efficiency gains and ensure the additional investment in the system pays off.

Published during the Irrigation Association’s partnership with the American Society for Agricultural and Biological Engineers for the 6th Decennial National Irrigation Symposium in 2021, a “Sprinkler Irrigation System Field Checklist” serves as an excellent reference for both new and experienced irrigation technicians on maintaining traditional center pivot and linear move irrigation systems. The checklist presents common inspection points for varying inspection frequencies, ranging from daily drive-by visual inspections to five-year performance audits. However, should an irrigation technician, new or experienced, find themselves maintaining a zone-control VRI system, there are some additional maintenance items to be aware of in addition to this checklist.

VRI system checks

Getting out into the field and running water through the system for an evaluation is an integral part of main-taining a system. Just as important with newer connected systems is “virtual” maintenance of the system. It is easy to set and forget many of the configuration options through the online interfaces. Some annual checks and adjustments often need to be made.

If using an online irrigation scheduling tool, perhaps most important of all is to initialize the scheduler by ensuring the proper crop type and hybrid, planting date, tillage practice and target yield. Setting these inputs for every field before the irrigation season will help ensure that the best scheduling decisions can be made. It is also recommended to clear last season’s VRI prescriptions from the system to avoid accidentally selecting an old prescription map and applying water at an undesired rate in the upcoming season. Be sure to keep one or two backups of any custom prescription maps that may be used in the future on both local and cloud-based storage before deleting. Other virtual maintenance items may include renewing premium subscriptions, updating system information should any major changes be made (such as pumping plant or sprinkler package flow rate changes).

At the system’s panel, a few more checks should be made before flowing water. Ensure that the VRI control panel (whether integrated or standalone from the center pivot control panel) has a good cellular connection. Occasionally, wireless routers may become outdated and no longer connect to newer cellular networks and will need replacing. Once a stable cellular connection is established, find the panel’s settings and select the option to update the firmware. Generally, these updates are quick, and contain important bug fixes that will help improve the function of the VRI system. Should your system be equipped with wireless nodes for individual sprinkler control, check that all the nodes are connected. If not, make a note of which are not connected to further inspect for a potentially bad receiver on the lateral. Around the panel, make sure any antennas and electronic flow meter signal wires are present and appear in good condition and are free of any damage from rodents or extreme weather.

Running smoothly

Turning the water on, set the VRI controller to manual mode and enable the “pulse” setting. For visual inspections, a good duty cycle for the sprinklers is 80% of five seconds, or on for four seconds and off for one second. Set the irrigation system to move at a speed that will avoid ponding of water on the surface but allow enough time to walk the length of the system before it moves too far from the testing zone. A good note-taking tool during the pulse test can be a photocopy of the system’s sprinkler package, allowing the maintenance technician to indicate the status of each outlet, whether functioning or not. While walking toward the distal end of the system, be sure to observe at least one pulse cycle for each sprinkler. A single outlet that does not have a pulse, either stuck on or stuck off, generally is indicative of a solenoid valve that needs replacing. On systems with wireless nodes, multiple outlets in a row not pulsing likely indicates that the node’s receiver board has failed and needs to be replaced.

When replacing the wireless nodes, be sure to take note of the position of the dip switches on the old board and set it accordingly on the new one. Also, be sure to note the old and new Media Access Control addresses and update the node through either the panel or online interface to ensure connection to the new board. Additionally, check to ensure sprinkler parts are moving as they should (e.g., rotating) and no leaks are present. Pressure regulators may be more likely to leak and fail on a zone-control VRI system from the continual pulsing of the outlets compared to a steady pressure at the nozzle inlet.

A VRI system adds complexity to a traditional irrigation system maintenance checklist. Most of the necessary additions can easily be incorporated into any operations maintenance checklists to ensure proper operation of their zone-control VRI system.

Eric Wilkening is a graduate research assistant at the University of Nebraska-Lincoln and is available via email.