Part 2: Sprinkler criteria – What makes one sprinkler better than the other?

When comparing sprinklers, several key factors determine which performs better in the field. A good sprinkler delivers water efficiently, uniformly, and reliably, while minimising energy use and soil impact. These criteria help ensure long-term performance and optimal crop growth.

As discussed in Part 1, sprinkler selection directly affects irrigation efficiency, crop yield, and water usage, making it essential to understand the performance criteria when comparing sprinkler options.

Longevity and reliability: a sprinkler that passes the test of time 

Sprinklers have many parts that can wear over time, especially when the water has particles of sand or silt in them. This causes wear on the flow paths of the components, especially the regulators and nozzle, compromising delivery and flow. In a good sprinkler, all components are of high quality material and accurate design, giving them a long lifespan while staying effective.

Regulators also have a limited lifespan and become less accurate over time. Faulty regulators can lead to excessive wear on the sprinkler’s plate and/or cap. Generally, you should consider replacing your regulators by testing them for accurate pressure regulation after operating 10 000 hours. This lifespan depends largely on the water quality.

High efficiency: getting the right amount of water to the soil with minimal losses

The efficiency of a pivot sprinkler is the percentage of water delivered to the sprinkler that actually enters the soil and becomes available to crops. Typical center pivot irrigation systems achieve efficiencies of 80–90%, though certain products and methods can further improve this. In effect, a sprinkler with a high efficiency will have minimal water losses due to evaporation, wind drift, run-off, etc. 

Various sprinkler parameters affect sprinkler efficiency. A larger droplet will be less susceptible to wind drift and have less evaporation, while a sharper trajectory angle and a larger wetted radius will have more wind drift and soil evaporation. That is why an option like LEPA is so efficient: the spray pattern almost eliminates wind drift and only wets a narrow path of soil meaning very little evaporation. 

The energy equation: a good sprinkler has a low energy requirement (but not too low!)

With centre pivots, the biggest energy cost doesn’t come from moving the pivot itself, but from the motor driving the pump needed to deliver water at a specific flow rate and pressure.

So, why not always just work at the minimum pressure that a sprinkler is rated for, or even lower? The reason is that for any given nozzle size, higher pressure delivers more water. If you drop the pressure, you’ll need to increase the nozzle size to maintain the required water flow. However, pivot sprinkler nozzles have a limit as to the maximum nozzle size that still works effectively. Also, generally speaking, higher pressure regulators will provide accurate regulation for longer than low pressure regulators.

The bottom line is that lower pressure saves energy, but design limitations, sprinkler requirements, and soil absorption rates must be considered. That’s why working with a skilled irrigation designer is essential!

Application uniformity: getting the right amount of water to your crop, everywhere 

To achieve optimal crop yields, it’s essential to apply the right amount of water evenly across the entire field. This is known as application uniformity.

Good application uniformity depends on two key factors. Firstly, each sprinkler should have an even distribution of water over its wetter area. Secondly, the wetted areas of neighboring sprinklers should overlap to prevent dry or overly wet spots

The ideal sprinkler will thus have a large wetted diameter, proper overlap and droplets large enough to minimise wind drift, while not being so big as to cause soil compaction.

The groundwork: obtaining the least amount of soil compaction

When a water droplet hits the ground, it applies a force to the soil, which can lead to compaction. Two main factors influence how much compaction occurs:

1. Soil type – Some soils, especially those with higher clay content, are more prone to compaction than sandy soils.
2. Droplet kinetic energy – Higher energy droplets exert more force on the soil, increasing the risk of surface sealing and reducing infiltration. 

However, it’s not just about the energy of a single drop. The total energy delivered over an area, known as energy flux density, also matters. A large number of small, fast moving droplets hitting a small area can have higher energy density than fewer large, slower moving ones over a wide area.

So, it’s not just droplet size or speed alone that matters—but also how many droplets hit, how fast, and over what area. The ideal sprinkler produces relatively small droplets distributed over a wide area. This reduces the energy flux density and minimises soil compaction.

The rules of water distribution  

When talking about uniformity, the wetted diameter of a sprinkler becomes important because of two reasons:

1. The larger the wetted diameter, the more overlapping you get between sprinklers and thus, the better uniformity you can get.
2. The larger the wetted diameter, the more time you give the water to infiltrate the soil. Think of receiving 50 mm of rain in two hours, versus the same amount in 1 hour. You will experience less runoff and less water loss. In sprinkler terms, this means a higher efficiency.