Modern pumping systems for modern agricultural irrigation
Modern agricultural irrigation is a complex interplay of sustainable energy consumption and water use, market conditions, and the application of experience and knowledge to ensure the best design for irrigation applications. Understanding past practices, today’s water and energy issues and developments in pump technology all contribute to build pumping systems that best service the needs of modern agriculture.
Challenges in agriculture require new techniques to boost productivity. The agricultural market is changing rapidly, and today’s farmers cannot rely on the technology and practices of the past.
To keep productivity high and to stay competitive in the market for agricultural products, farmers need increasingly to focus on profitability, which includes energy optimisation and better use of water resources. And here pumping systems play a vital role
What is irrigation?
Put simply, irrigation is an artificial application of water to the plant roots, with the purpose of assisting the growing of agricultural crops. Fertiliser and chemicals can be added to an irrigation system, and irrigation also has a role in frost protection.
Successful agriculture is dependent upon farmers having sufficient access to water. Looking back to the middle of the last century, the common perception was that water was an infinite resource. Today, we are aware that water is a resource that needs to be managed. This is not only a question of more mouths to feed, people today consume more calories and eat more meat, and this requires more water to produce food.
Energy consumption is also an issue for the modern farmer. Energy for irrigation pumps is now one of the highest single cost drivers for farmers, and yet many are unaware of just how great the potential savings can be from more effective energy use.
Modern agriculture requires irrigation solutions that optimise irrigation uniformity, reduce energy costs, safeguard the water resource, and keep productivity at its best. The agricultural market is changing, and these 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. The next step is water treatment, if this is necessary, and perhaps the addition of fertiliser or chemicals. Finally, water is delivered to the crop using various techniques, such as flooding, sprinkler irrigation or drip/micro spray applications.
Mechanised sprinkler systems, such as pivot irrigation, are effective for covering large areas. Such systems are typically attached to a pump that can supply the necessary amount of water and pressure – and a good deal more, just in case. A valve will typically handle the excess amount of flow and pressure.
Drip and micro-spray irrigation are for low pressure applications, where there is a requirement for reducing potential evaporation and runoff as much as possible. Keeping the pressure constant is vital for ensuring uniform application throughout each zone in the system, and this can be the most energy-efficient method of irrigation, if managed properly. Achieving this requires that the system can compensate for the variations in flow to ensure constant pressure, as zones cut in and out.
A Grundfos Hydro MPC booster system fitted with Grundfos CRE − variable speed drive-controlled pumps − is able to adapt to changing conditions and ensure constant pressure.
Traditional approaches and pumping solutions
Groundwater withdrawal has typically involved submersible or vertical turbine pumps that are able to bring water to the surface. For surface water intake, centrifugal pumps in various configurations, split case 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 be able to 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, the result is that 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 from a channel or storage pond – 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 too 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.
However, pressure management has long been an issue, and over the years, pressure reduction valves have been commonly 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 we consider that a modern agricultural irrigation system is a car and the pump is the motor, would it make sense to drive your car at constant full throttle and control the speed with the brakes? This is a very common approach for irrigation pumps.
If a pump is specified to run continuously at the highest level – for example when the corner section comes on – energy is wasted. The varying requirements for optimal energy use on a pivot application can easily be met by using a variable speed pump. This offers substantial savings on energy while maintaining pressure.
Meeting the challenges of modern agriculture
Complete pumping systems instead of large, isolated pumps are the way forward. For example, the costly and time-consuming use of pressure reduction valves to maintain constant pressure can be eliminated by an investment in pump controllers for effective pressure management. This saves costs in the long-term, also with service, and reduces energy consumption.
The same can be said of using valves in sprinkler irrigation. A much better approach would be to use a variable speed pump and a pressure sensor on the pivot, which will then automatically adjust the pump performance to match the requirements for the pivot. This ensures higher irrigation uniformity, and keeps energy costs down. A pump controller offers the additional advantage of protecting the pump from dry-running or power supply irregularities, extending 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. A variable speed pump is on the other hand able to adjust its head and flow to compensate for changes in water level, reducing energy bills.
The range of pump applications in agricultural irrigation is many and varied. The key to success is using intelligent pump controls that are designed for the application in question.
Designing a modern irrigation system
We need to think through the specific applications in irrigation in new ways, and in particular we need to think irrigation system design into the application. The pumps have to be much more integrated with the rest of the irrigation system. This means the pump must be designed to match the rest of the irrigation equipment, or the irrigation equipment must be designed to match the pump.
The current approach of simply installing a pump capable of always delivering more than enough water ends up wasting money and energy. Returning to our pump-as-motor metaphor: Purchasing an over-sized motor as an afterthought to place in your car will end up a costly affair and offers no guarantee of a comfortable or fuel-efficient ride!
Think this into an irrigation system, where the pump must do more than simply deliver water to the pipes in order 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, and 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 pumping system can offer the farmer. Maintaining correct pressure and flow in the pipes and at the nozzle means more water per kWh and savings on energy, which is one of the highest cost items in farming.
Earlier, we discussed the importance of maintaining a constant pressure in a pivot irrigation system. This becomes very 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, and 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 exact same pressure on all the sprinklers, and thereby deliver a high uniformity.
A modern pumping system is not only about pumps. Variable speed drives, intelligent control and even remote management all necessitate the integration of all components in an irrigation system.
The future: total solutions, tailored to the application
The development described above shows the need for the careful consideration of the entire irrigation system and each component’s integration, tailored to the application. This requires experience and knowledge, and the ability to follow water from the source to the crop – from the water intake, through water treatment and distribution to the irrigation application, all carefully monitored and regulated along the way.
Modern agriculture requires a broader understanding of component integration, and the system must ensure the farmer is able to respond to issues of energy consumption and water supply, specifically by isolating areas where savings can be made, generating increased profit per hectare.
This is not an exercise that can be carried out in isolation; all relevant local conditions need to 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.
The 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, resulting in a better harvest, increased profitability, and better water management, ensuring sustainable agriculture in the future.