Before you begin irrigating each year, you should prepare your micro-irrigation system for the new season. Many temporary repairs made last year will probably need attention.
Micro-irrigation systems are more than just a method to deliver water to the crop. They are becoming a management tool. A properly designed and maintained system allows the grower to supply precise amounts of water, nutrients, and other materials to the crop.
If the system is used to apply fertilizers or chemicals, varying pressure problems will cause uneven distribution of materials throughout the field. These problems can be due to clogged filters, regulators, or emission devices. Also, problems such as leaking barbs, tubing, emitters, and end plugs can allow water to collect at the base of the plant and invite disorders such as crown rot. Careful management and preseason maintenance can allow the grower to realize the full benefits of a micro-irrigation system.
A pump that has been sitting idle for a few months needs to be checked for rodent activity and nests that could cause a short in the windings. A thorough cleaning is important, especially for pumps operating in dusty conditions. A pump dealer or manufacturer will be able to provide specific instructions for the care of the pump and motor.
The oil levels should be checked and filled at this time, and turbine pumps with automatic oilers should be checked to see that they are functioning properly. After a long layoff, it is also a good idea to start the oiler 24 hours before a deep well pump is started. If you suspect that the efficiency of your pump has declined, a pump test is a quick and reliable way to assess its performance. Some utility companies offer this as a service - or check with your pump dealer.
Several items need to be checked on both screen and media filters prior to start-up. On filters that flush automatically, the controller and valves should be checked for proper operation.
If the controller is equipped with a pressure differential switch, the setting should be checked against the manufacturer's specifications. A differential can be created by removing one of the leads to simulate a high differential. If the differential switch is operating correctly, this will initiate a flush cycle.
Minimum Flush Cycle . Some media filter manufacturers and dealers recommend a minimum flush cycle at two or three hour intervals to prevent fine contaminants from becoming embedded in the media even though the water may be relatively clean. The media filter should be opened to inspect the level of sand in each filter. Ideally, the level should be the same in each filter. Any difference could indicate trouble, such as a faulty valve or problem with the filter cake or underdrain on filters so equipped. Also note the condition of the media itself. If the media is channeled or caked this could represent other problems, such as inadequate flush cycles during irrigation.
When setting the backflush time it is important to allow for travel time - the time required for the valve to move and fully seat. Most manufacturers recommend backflush times between 60 and 90 seconds.
After the filter and controller have been checked and repaired the backflush volume needs to be checked and adjusted. If the backflush volume is too high the result is a loss of media. If it is too low, this can result in improper cleaning.
Screen filters need to be opened and inspected also. The element, whether fabric, plastic, or steel needs to be inspected for damage. The conditions of the seals and O-rings are important in isolating the incoming unfiltered water from the filtered water going to the system.
CHECK EQUIPMENT IN THE FIELD
Once the equipment that filters and delivers the water to the field has been checked and repaired, the drip lines, emitters, and peripheral equipment need to be inspected. A thorough flushing of the system is the first priority, and this should be done in steps.
1. Flush the main line. Depending on the system and pump capabilities, it may be a good idea to close a portion of the system to increase the pressure and velocity. Find out what the safe maximum operating pressure is before flushing.
2. Flush tubing in the field. Hose ends are now opened and again, a portion of the laterals may be closed to ensure good pressure and velocity for a thorough flushing of the drip tubing. After the entire system has been flushed, the system needs to be checked line by line. One of the most efficient methods utilizes an irrigator walking and checking every row, wearing a cloth pouch like you would find in a lumber store. In it are emitters, couplings, punch, plugs, and hose ends to make the necessary repairs.
3. Measure pressure and flow. If the system is equipped with water meters, the flow can be compared with past years. A reduction in flow could indicate problems such as obstructed lines, emitters or micro-sprinklers, or partially closed valves. If it is determined that the emission devices have reduced flow rates, it could indicate a need for chemical treatment.
Another advantage of a meter is that it allows you to monitor actual applications as opposed to time based irrigation.
For example, if your utility company offers off-peak rates you may be able to save on your power bill by irrigating at night. If the power is off for a length of time you may not know that the field did not receive all of the water you had scheduled without such a recording device.
- Walk the field. Check to see if there is a need for a second or third emitter at replant sites. Are there areas in the field where the tree growth is not what it should be? Spot checking pressures in weak or troubled areas may indicate changes are needed or further investigation.
SPEAK WITH YOUR IRRIGATORS
The people who do your irrigations are perhaps the most important link in getting water to your crop. A few short training sessions can help to familiarize the crew with equipment, eliminate misunderstandings, and build a sense of teamwork.
Greg Jorgensen is the Field Research Manager for the Center for Irrigation Technology, California State University, Fresno, CA 93740-0018, telephone (209) 278-2066.