Subsurface Drip Irrigation Operation and Maintenance to Maximize Potential
Updated: Jul 7
Subsurface drip irrigation systems offer significant advantages for efficient nutrient management, water management, and fertigation. In this blog post, we will delve into the nuts and bolts of drip systems, exploring their operation and maintenance. Understanding your drip system is crucial for optimizing its performance and maximizing its potential.
When considering optimizing your drip system, there are a few key components: water, automation, and fertilizer injection.
Let’s start with water: how many inches of water can you apply? Is your water limiting you, and if so, what can you do about that? Water can be limited by supply (pond, river, well, etc), or even by pump output. For drip, we often look at how many gallons per acre are available. If you are able to pump 100 gallons per minute onto 20 acres, that gives you 5 gallons per minute per acre. How much water do I need? You need enough to match ET (evapotranspiration – how much water is transferred to the atmosphere from the soil and plants via evaporation or transpiration). Generally speaking, ET falls around 2-5 gpm/acres, therefore, that is how much we recommend when installing a drip system.. Translated into inches, that is 0.1-0.26 inches per acre per day. We prefer to aim for 5gpm/acre, so there is room to expand in the future. There are systems that work with less than that, but you have to get creative in watering schedules, etc. One farmer Travis Rokey works with ended up having an opportunity to buy land close by a current drip system and expanded his system to include another 300 acres. With the added acres his gpm/acre is around 1.8. He has had to get creative by doing more with less.
Plant two different crops: This farmer is doing corn, wheat, and cover crops and allowing cattle to graze off the cover crops.
Staged plantings: This year he is trying two corn crops, an early one followed b a cover crop, then planting one later after a wheat crop.
Regenerative Ag practices: this involves cover crops to reduce evaporation of water from the soil and increasing the organic matter in the soil
Utilize soil moisture holding capacity: use your soil as your fuel tank: fill it up with water, so later in the season when you can’t keep up, you have that reservoir.
Soil moisture probes are vital with an operation such as this, so you know where the water needs to go.
Longer run times – Last year this farmer ran 8 hour sets every day, and the corn was so thirsty it was pulling the moisture out as fast as it could be applied. The wetted bubble of water was very small, and the roots were exploring very little of the soil. Running for a full day, then skipping a few days and running another 24 hours proved to be a better option in this situation.
Another part to consider is adding a pond or reservoir to hold or store more water. We do have software that can look at elevations and help give an idea of how much water we could store. This software can also help us know how much water is available so we don’t apply too much too early in the season and run out.
Irrigation design also plays into water availability and how much water can be applied. What is happening in the field and where is my water going? Below is a drip design, followed by a zoomed in image of the text information that can be found in each irrigation zone on the design. You can see the different zone number, the acres in that zone, how much that zone should flow, pressure and uniformity. You can also see the precip rate (how many inches applied per hour). In this example, it is 0.02, so if I run for an hour, I put on two one hundredths of an inch of water. If I run for 10 hours, I am putting on two tenths of water. Obviously, if we are trying to match an ET loss of two tenths per day, I would be running this system for 10 plus hours per day. The design will also tell you what your particular system is sized at, so if you have a drip system and don’t have good access to your design, please let us know. The design is the roadmap to your system and is key to your understanding.
Many of our irrigation systems have been installed with automation. Obviously one of the biggest reasons for this is remote access; being able to control and monitor your drip system from your phone is efficient and effective.
Watch your moisture probes and create your watering schedule based on your plants needs
Schedule around rain events
Set a program and let it do its job. This shows multiple programs scheduled for multiple crops. It can also be set up with different programs for fertilizer applications, or just water.
Fertigation: there are a few ways to inject fertilizer: by quantity, proportional injection or by blending into the fresh water to keep it diluted.
Quantity: the controller is programed to inject a certain amount of fertilizer. For example, tell it to inject 100 gallons: it pumps it out and it is done.
Proportional injection: adding a certain amount of fertilizer for every set amount of water that is pumped out. For example, with sulfuric acid, you could set the program to inject one gallon of acid per every 1000 gallons of water and maintain a set pH.
Blending: mixing fresh water with effluent. Liquid manure is diluted with fresh water to control the EC (salt) and is applied to your soil with no smell.
The controller can also be programed to automatically fill up the zone, inject the fertilizer, then run another hour or so to "rinse" the fertilizer out of the tape. This is important for the health of the drip system. If we have helped you fertigate, it should be set up this way.
Historical data recording: learn from past years, what works and what doesn’t for your specific crops, soil and farming practices. This is also very helpful when it comes to state records that you have to turn in for water management.
Remote diagnostics: our team can watch your controller, help you learn it and guide you in doing the best you can with that controller. It also helps us diagnose any problems your may have. This graph shows the water meter (red) and pressure (gray). Overlaying this data with soil moisture sensors and other data can show us how long a zone ran, where that water went, was it too much or too little?
EC and pH monitoring and alerts: this is especially helpful for effluent control.
Controllers should self-diagnose if set up correctly. When an alert comes through, it should try several things to fix itself. If it can’t, it will start sending you alerts to let you know something is wrong. As we start integrating our probes and weather data into the controller, it should start alerting you with different thresholds such as moisture needed, flow too high, too low, etc.
Drip System Maintenance
Maintenance is key to system longevity. If the system and drip tape stay clean, it will last for many years. Our goal is your success. We do offer several options for helping with your maintenance: spring startup, acid flush, in season agronomy support, winterization. You can do all these on your own, and we want to help you learn your system and how to fix and maintain it. Spring startups and winterization are extremely important. Spring startup is turning everything on. We have a checklist of all the parts we check, fix, and make sure they are operating correctly:
System Startup Checklist
All parts are in place i.e. pressure relief, air vents, fertigation ports, etc…
Any valves that were opened for winterization are shut
Make sure discs on filters are clean (disc filtration)
Check backflush for sand (sand media filtration)
Backflush filter clean (small screen filter on top manifold)
Backflush settings correct and operating as designed
Pressure transducers operating correctly and calibrated
Flow meter reading properly and communicating with controller
No threaded fittings leaking (especially in filter station)
Fertigation pump working correctly
Fertilizer flow meter reading correctly/sending to the controller
Controller starts pumps and all valves as it is supposed to
Gateway is online and communicating
All valves are opening and shutting off properly
VFD is online and maintaining pressure properly
Check valve pressures and record on corresponding spreadsheet
Record number of leaks fixed, what type, and any materials used
Crop/Moisture sensors are in place and communicating
Trash is cleaned up/tape tails are all picked up
All aboveground pipe is painted (color-coded if applicable)
We often get asked, how many leaks will I have? What if I have rodents? It is similar to a shed infested with mice: if you park your combine there for the winter, when you pull it out in the spring you will have problems. If you have a field with rodents, you will have problems unless you address the issue. In your shed, you would put repellents in your combine and in the shed to minimize issues. Likewise in a field, with bait, trapping, and repellent, you will minimize rodent damage to your SDI system. Winterization is done to ensure your pipes don’t freeze and break. A large air compressor is used to blow any water out. This is also a good cleaning, as the air is a lot more aggressive than a water flush.
Two of the most common filters we use are sand media and disc filters. The media filters are for dirtier water; they have more filtering capacity. They are basically sand in a big tank. The water runs through the sand and is filtered. It back flushes to clean itself out; this involves running the water backwards from the bottom, lifting the bed of sand and flushing out the dirt through a separate manifold. There is a valve to keep it from backflushing too much and flushing the sand out. One of our growers was having issues with his sand media filters, and after looking everything over, we realized the backflush valve was cinched down too tight; the sand from his well had built up and filled the filter so it couldn’t backflush properly. Check out this playlist for more information on sand media filters.
The disc filters are small discs packed tightly together; water flows through them, and is cleaned. When the pressure differential reaches a set threshold the backflush valve switches on allowing water to flow backwards through the discs, separating them and washing the dirt particles out. A few advantages of the disc filters are a smaller footprints and not as much water is needed for back flushing. Check out this playlist for more information on disc filters.
For either sand media or disc filters you need 25-30 pounds of pressure after the filters to properly clean them. You can tell what your pressure is by the pressure gauge plumbed to the top of your filters with a little black knob. It’s a three-way selector: one way tells you the pressure on the top manifold, one third of a turn and it tells you the pressure on your bottom manifold. With clean filters under normal operation, there should be about a 2 PSI difference. When there is a 7-10 PSI difference, the controller with tell it to backflush, or clean itself out.
Each emitter in the tape has a filtering mechanism as well, so any larger particles that make it through the filtering system will stay in the drip line. Flushing the system should be done twice a year; we typically do it on start-up and with winterization. That is typically enough for average to good water quality. With poor water quality doing a few flushes during the irrigation season can help out a lot. Flushing is done by opening the valves at the end of the field and allowing the water to rush through the drip tape. For flushing, we recommend increasing your PSI by 10-15 to really clean it out well.
By implementing proper management strategies, drip irrigation systems can significantly enhance crop production while conserving water resources. Understanding your system, utilizing automation, and optimizing fertilizer injection are key factors in maximizing the efficiency of your drip system. With these tools at your disposal, you can achieve optimal results and sustainable agricultural practices with your drip system.