End Gun Settings — SMART IRRIGATION

By David Hall, UGA Water Agent Southeast District

The end gun on a center pivot is one of the most important pieces of equipment on a system. It is probably the most overlooked object when it comes to maintenance. This piece of equipment, which is a large sprinkler located at the end of the pivot system, is called an end gun for a couple of reasons. One is because it’s at the end of the system and second, it is a big irrigator spraying water a great distance. Because of those two characteristics, it stands to reason that a very large portion of acres are being irrigated from that last piece of equipment. The further you get from the pivot point, the greater the circumference of the pivot circle becomes. On an average, an end gun can extend irrigation spray 80’-100’. Depending on your pivot length and design, it’s like having another half span of irrigation without the cost of pipe and a tower. Therefore, it is critical that the gun is set correctly to apply water evenly as possible.

Fortunately, incorrect end gun application of water can be easily fixed most times. The first step is to visually look for overlap or not enough throw back. If you are uncertain, catch buckets can be set up every 10’-20’ and actually measure how even the application is. Make sure to place buckets past the end gun towards the pivot point at least 40’ to catch any overlap. The next step is to observe the pivot design and see what the angles should be set at. There are usually forward and reverse angles that are not the same. Every pivot is designed differently. The position of the last nozzle or if a spray nozzle is placed in conjunction with the end gun all play a part in correct end gun setting. Spring settings in the flapper can increase or decrease the travel speed. Once set properly, bucket test again. If the end gun is still over or under applying water, talk with your dealer and make sure your nozzle is not worn and that it is indeed the correct end gun for the system.

Some common causes of incorrect end gun settings are directly from hanging limbs pulling the gun past the set stops. Hopefully you will not find a wrecked pivot if this is the case. Worn or sticking rotating parts in the gun can cause the gun to basically spray in one spot or rotate too slow. Finally, a simple but costly installation error could be the issue.

Costly is a great word to describe incorrect end gun settings. As mentioned earlier, the end gun arc on the end of a system covers a large portion of acres. Even set at proper angles, end guns are not nearly as efficient as a rotator or wobbler sprinklers, but for the money they do a good job considering the wind and evaporation. Let’s consider a 30 percent yield loss due to insufficient irrigation coverage on one acre of peanuts. Assuming 5,500 pounds is a reasonable goal, that is a 1,650-pound loss. Considering an average ton of peanuts sells for 400 dollars per ton, that is $330 dollars per acre left on the table from those affected acres. What about a decrease of 60 percent yield due to poor irrigation coverage? Now you are looking at 660 dollars per acre lost on that 60 percent of acres covered under the end gun arc.

So now, what about areas that are getting watered too much due to overlap or incorrectly set angles? Cotton is a great example for this scenario. We begin to see rank growth leading to boll rot and less yield because the plant has put so much energy in growing up and not out with properly timed and applied water. Good defoliation of cotton in these areas will be hard to achieve. A producer can be contributing to yield reductions on the entire end gun arc by over watering in 30 percent of the crop under the arc acres and under watering the remaining 70 percent. Keep in mind, it costs the same amount of dollars to pump water if you apply it evenly or not. The return on your dollars spent irrigating a field uniform on every acre will pay back considerably more.

The bottom line is that correct end gun settings are crucial. Do not leave money on the table, no matter the size of the pivot, due to incorrect end gun settings.