The same can be said of using valves in sprinkler irrigation. Using a variable speed pump and a pressure sensor on the pivot, which would automatically adjust the pump performance to match the requirements for the pivot, is a much better approach. This would ensure higher irrigation uniformity and keep energy costs down. A pump controller offers the additional advantage of protecting the pump from dry-running or power supply irregularities, which will extend the lifetime of the pump.
The rises and falls in water level, below ground and for surface water, essentially change the specifications for a pumping system because these variations change the head. A single speed pump dimensioned to lift from the lowest water level will burn energy dollars when the level is high. On the other hand, a variable speed pump adjusts its head and flow to compensate for water level changes, reducing energy costs.
Designing an Irrigation System for Today’s Applications
Farmers and pump system providers need to think through the specific irrigation applications in new ways, and in particular they need to think about irrigation system design in the application. The pumps must be much more integrated with the rest of the irrigation system. This means the pump must be designed to match the irrigation equipment or the irrigation equipment must be designed to match the pump.
The range of pump applications in agricultural irrigation is many and varied. The key to success is intelligent pump controls that are designed specifically for each application.
The current approach of simply installing a pump capable of always delivering more than enough water ends up wasting money and energy. Returning to the aforementioned metaphor, which compares the system to a car and the pump to its motor: Purchasing an over-sized motor to place in a car will end up a costly affair and offers no guarantee of a comfortable or fuel-efficient ride.
Think about this in an irrigation system, in which the pump must do more than simply deliver water to the pipes to be effective. For example, adding variable speed drives improves the efficiency of groundwater withdrawal when pumping directly into an irrigation system. Surface water intake and distribution can be improved by using multi-pump pressure boosting systems. Across the board, monitoring and control systems further safeguard the reliable flow of water by protecting the pump from dry-running, motor breakdown or power supply irregularities.
All these elements must be fully integrated into the design to provide the benefits that a modern irrigation pump system can offer the farmer. Maintaining correct pressure and flow in the pipes and at the nozzle means more water per kilowatt hour and savings on energy, which is one of the highest cost items in farming.
Earlier, the importance of maintaining a constant pressure in a pivot irrigation system was explained. This becomes relevant if the pivot is equipped with an end gun and maybe even a corner section. As soon as the end gun or corner section comes on, the pressure in the pivot’s main line will drop. This will impact the irrigation uniformity.
The solution is to replace the pivot’s main pump with a variable speed pump, which will immediately react to a pressure drop when an end gun or corner section cuts in. In such a configuration, it is possible to maintain the same pressure on all the sprinklers and, therefore, deliver high uniformity (see Figure 1).
Figure 1. If a pump is specified to run continuously at the highest level—for example when the corner section comes on—energy is wasted. The different requirements for optimal energy use on a pivot application can be met by using a variable speed pump. This offers substantial energy savings while maintaining pressure requirements.
The Future: Total Solutions, Tailored to the Application
The development in irrigation systems described in this article reveals a need for careful consideration of the entire irrigation system and each component’s integration, tailored to the application.
This requires experience and knowledge. The ability to follow water from the source to the crop—from water intake, water treatment and distribution to the irrigation application—and carefully monitor it along the way is critical for an irrigation pump system.
Modern agriculture requires a broader understanding of component integration, and the system must ensure that the farmer is able to respond to issues of energy consumption and water supply, specifically by isolating areas in which savings can be made, generating increased profit per acre.
This is not an exercise that can be carried out in isolation. All relevant local conditions must be added to the equation—such as soil conditions, the crop, topography and weather patterns. Pump control, including monitoring and intelligent management, is then the way forward.
Energy savings are there to be made and are substantial. The added benefit for the farmer is, in addition to the lower operating costs, that water is delivered with greater precision to the crop. This results in a better harvest, increased profitability and better water management, ensuring sustainable agriculture in the future.