Pumps & Systems, March 2013
Modern agricultural irrigation is a complex interplay of sustainable energy consumption, water use, market conditions, and the application of experience and knowledge to ensure the best design for irrigation applications. Understanding past practices, current water and energy issues, and developments in pump technology contributes to building pumping systems that best service the needs of modern agriculture. The agricultural market is changing rapidly, and farmers cannot rely on the technology and practices of the past.
To keep productivity high and stay competitive in the market, farmers need to focus on profitability, which includes energy optimization and better use of water resources. Pumping systems play a vital role in providing optimized solutions for energy and water use.
A pump system for today’s irrigation is not only about the pumps. Variable speed drives, intelligent control and remote management all necessitate the integration of components in an irrigation system.
What Is Irrigation?
Irrigation is an artificial application of water to plant roots with the purpose of assisting the growth of agricultural crops. Fertilizer and chemicals can be added to an irrigation system. Irrigation can also play a role in frost protection.
Successful agriculture depends on farmers having sufficient access to water. In the middle of the last century, the common perception was that water was an infinite resource. Today, we know that water is a resource that must be managed. This is not only a question of more mouths to feed—people consume more calories and eat more meat. This requires more water to produce food.
Farmers must consider energy consumption. Energy for irrigation pumps is one of the highest single cost drivers for farmers. However, many are unaware of the potential savings from more effective and efficient energy use.
Modern agriculture requires irrigation solutions that optimize uniformity, reduce energy costs, safeguard the water resource and keep productivity at its best. The agricultural market changes require greater focus on applying knowledge, experience and total irrigation solutions integrating all components.
What to Consider When Getting Water to the Crop?
Irrigation starts with sourcing water for the crop from groundwater or surface water from a channel or storage pond. Next is water treatment, if necessary, and perhaps the addition of fertilizer or chemicals. Finally, water is delivered to the crop using different techniques—such as flooding, sprinkler irrigation or drip/micro-spray applications.
Mechanized sprinkler systems, such as pivot irrigation, are effective for covering large areas. These systems are typically attached to a pump that can supply the necessary amount of water, pressure and significantly more, as a precaution. A valve handles the excess flow and pressure.
Drip and micro-spray irrigation are used for low-pressure applications in which reducing as much potential evaporation and run-off as possible is a requirement. Keeping the pressure constant is vital to ensure uniform application throughout each zone in the system. This can be the most energy-efficient method of irrigation, if managed properly. Achieving this requires that the system be able to compensate for variations in flow to ensure constant pressure as zones cut in and out.
Traditional Approaches and Pumping Solutions
Groundwater withdrawal has typically involved submersible or vertical turbine pumps that bring water to the surface. For surface water intake, centrifugal pumps in different configurations, split case pumps and end suction pumps have been traditional solutions.
These pumps are required to meet changing conditions above and below ground, which have an effect on the pressure and flow required from day to day and from season to season. A pumping system must deliver the right amount of pressure and flow at the nozzle. The simple solution is to oversize the pump, so the pump is able to handle a worst case scenario. However, as a result, the pump will almost never operate at its optimal duty point. It will produce too much pressure and consume too much energy, which is not used productively in any way.
Traditionally, water has been distributed from the water source—either groundwater or surface water—at low or constant pressure from pumps operating at single speed. Delivery to the crop has been from nozzles, where the focus has been on surface coverage, without much attention placed on run-off, canopy evaporation and wind drift. Soil moisture monitoring to ensure an even spread over the irrigated area is a relatively new discipline.
In contrast, pressure management has long been an issue. Through the years, pressure reduction valves have been used to reduce pressure in the system. However, valves are costly to install and require frequent service and replacement, and their operation consumes a lot of energy.
If end users think of an agricultural irrigation system as a car and the pump as the motor, would it make sense to drive the car at constant full throttle and control the speed with the brakes? This is a common approach for irrigation pumps.