Is technological development with centre pivots a luxury or essential?
Can the use of technologically advanced products with pivots or the upgrading of existing pivots bring about a significant savings on running costs and increased yields? – For sure!
If you have an existing centre pivot system, start by evaluating the condition of system. If it is old and inefficient, much can be accomplished by getting the system up to standard. Repair leaks and repair or replace underperforming pumps. Make sure that non return and foot valves are in good working order, keeping the pipe lines filled after shut down. This would eliminate filling empty lines on startup, saving costs.
Spray packages
The biggest technological development in the centre pivot industry over the past 30 years is surely what has been achieved with sprinkler technology.
From our testing and experience over time in the field, we can report with excitement that with the correct sprinkler package we were able to measure the best improvement of water in the soil compared to pivots with cheaper sprinkler packages; an improvement of up to 38%** (**these evaluations were all done with temperatures above 30°C in hot, dry wind conditions in August/September in the North west Province).
To explain this, we will have to look at the variety of pivot sprinklers available in the market, their inherent properties and its effect on sprinkler performance.
To understand the outcome, we must firstly look at the three core characteristics that contribute most to the effectiveness of water-in-the-soil. All three of these characteristics are very important but are the result of a specific sprinkler design and an insurmountable limitation with certain design types.
- Ideal drop size is important. “Too large” droplets compact the soil, leading to runoff and limited infiltration. Despite the fact that the evaporation factor with “too large droplets” is negligible, compacting of soil and resulting runoff leads to more serious problems with less water in the soil. If droplets are too small, evaporation increase exponentially. There is however a very important proven ideal droplet size.
- Uniform water distribution under each sprinkler is important. Why is this of such importance? Even if droplet sized would be perfect but their distribution would be concentrated more to the outside of the spray pattern (due to inherent spray design) the more water on the outside edge would cause faster saturation and runoff, especially on the critical outside edge of the pivot and more so with high application packages and on larger pivots.
- The widest spray diameter is important. If the sprayer diameter (band width) is too small, it also creates higher application rates and resulting runoff. –
Is it possible to get these ideal qualities or as many of them as possible, in a single sprinkler?
There has been tremendous research work in pivot sprinkler development over the years by mainly the three major international pivot sprinkler manufacturers. So, what is available and what has been achieved over the past few years?
- The basic solid spray plate type sprinkler. It represents the oldest type, purpose-built fixed pray plate designs. Although these sprainklers are the cheaper sprinklers in the manufacturers’ ranges, much development has also been done with the jet designs to be more wind resistant through variations of build and playing with exit angles and improved patterns, among other things.
– Advantage is price.
– Disadvantages are limited bandwidth especially at lower pressures and, although much improved, an inherent constraint to achieve the “ideal drop size” throughout. Ideal water distribution is also restrictive due to the inherent design constraints. These sprayers were often put on expensive booms to increase bandwidth and reduce runoff. It is still used today with “LEPA” system (Low Energy Precision Application) by mounting it low (to limit the inherent high evaporation of the type of sprayer), using it at low pressure (to save energy) but then mounting the sprayers very close together (to compensate for the smaller bandwidth and ensure adequate overlap). What it does not address is the resulting very high application rates that will only work on flat surfaces or soils with a high infiltration capacity; It is closer to a controlled flood irrigation system and cannot be used on any soil/crop. Effectiveness of water in the soil is quite high if sealing of the soil surface is not a problem and it is not lost through runoff or in wheel tracks! Wheel track problems often become a headache with these systems.
- Moving sprinklers were the next stage of development and particularly addressed the restrictive bandwidth at lower pressure of the fixed plate sprayers.
– The first developments had a better bandwidth and therefore a slightly lower application rate but could not yet idealize the distribution under the sprinkler nor improved the droplet size much.
– The second breakthrough development by one of the companies was with a moving, free-motion spray plate that for the first time could cut the droplets into very close to the ideal and constant droplet sizes. Secondly, this technological development has managed to distribute the water evenly under the entire sprinkler surface. Thirdly, a wider bandwidth was created by the benefit of the movement energy of the distribution plate projecting the water further. This sprinkler, for the first time, addressed the largest percentage of pivot sprinkler problems and limitations, in one product.
– What this development can offer is therefore better controlled droplets, even distribution under the sprinklers and wider bandwidth all adding to dramatically lower evaporation, better infiltration rates and less runoff, if any, with a wider range of soil types and this at 1 Bar ideal working pressure on the sprinkler. With figures already as high as 95+% of the water pumped through the pivot on a hot dry day measured in the soil and that at 2.7m above ground, this product has made a new breakthrough in pivot spray technology.
– The next technological sprinkler development was done by one of the other companies who further refined this already excellent product principle! This gives us access to a product that has even better droplet size control, a motion mechanism with lower operational resistance (spray pressures are now 0.7 Bar and optionally even 4.2 Bar) and has a lower wear resistance (this ensures that the sprinklers retain its new efficiencies/level of performance over many years; a restriction with the first-generation motion sprayers). We conducted internal trials with these sprinklers (0.7 Bar version) at 2.7m above ground and measured temperatures above 30°C, more than 97% water in the soil and with the 0.42 Bar version with the slightly larger droplet we could not measure any loss.
Advanced soil moisture measurement
The use of multi-level soil moisture probes measuring irrigation depth in the soil can be utilized to manage the minimum and maximum soil moisture levels. Not “too wet” and not “too dry” is equally important; crossing the “too little” line will damage the plant and crossing the “too much” line will temporarily stun growth. When managed correctly there is not only an increased growth/yield but also reduced water consumption!
There are many more that can be done but the above discussed represent the highest cost saving combined with the best yield improvement.
Please contact Theuns Dreyer of SENTER360 for further discussion of this topic on 082 564 5955
