Operation and Maintenance

Operation

SDI systems can be operated in several modes, varying from manual to fully automated. Overall, SDI systems are probably more easily automated than many other types of irrigation. One reason is that most are controlled from a central point using electrical or pneumatic valves and controllers that vary from a simple clock system to microprocessor systems, which are capable of receiving external inputs to initiate and/or terminate irrigation events.

Irrigation scheduling is as important for SDI systems as for any other type of irrigation. Choosing to initiate an irrigation event and how much water to apply during each event depends on crop, soil, and irrigation system type and design. Factors that affect those decisions include soil water storage volume, sensitivity of the crop to water stress, irrigation application rate, weather conditions, and water supply capacity. Camp¹⁵¹ discussed several irrigation scheduling methods that have been used successfully with SDI. However, the important point is that a science-based scheduling method can conserve the water supply and increase profit.

If seed germination and seedling establishment and growth are critical, especially in arid climates when initial soil water content is not adequate, either sprinkler or surface irrigation is often used for germination. However, the need for two systems increases cost and decreases economic return. If subsurface drip is used for germination, an excessive amount of irrigation is often required to wet the seed zone for germination, which could result in excessive leaching and off-site environmental effects as well as increased cost. Surface wetting can also occur when the emitter flow rate exceeds the hydraulic conductivity of the soil surrounding the emitter, but wetted areas are often not uniform.

Because salts tend to accumulate above the lateral, high salt concentrations may occur between the lateral and soil surface in arid areas where rainfall is not available to leach the salts downward. Salts may also be moved under the row when laterals are placed under the furrow.¹⁶! Supplemental sprinkler irrigation may be required in some areas to control salinity if precipitation is inadequate for leaching during several consecutive years.

Maintenance

Often, SDI systems must have a long life (>10 years) to be economical for lower value crops. Thus, appropriate management strategies are required to prevent emitter clogging and protect other system components to ensure proper system operation. Locating and repairing/replacing failed components is much more difficult and more expensive with SDI systems than with surface systems because most system components are buried, difficult to locate, and cannot be directly observed by managers. Consequently, operational parameters such as flow rate and pressure must be measured frequently and used as indicators of system performance. Good system performance requires constant attention to maintain good water quality, proper filtration, and periodic system flushing to remove particulate matter that could plug emitters. Periodic evaluation of SDI system performance in relation to design performance can identify problems before they become serious and significantly affect crop yield and quality.

Conclusion

Although there is a general consensus that use of SDI is increasing on a worldwide basis, this growth is difficult to document. In the 10-year period (2003-2013), SDI in the United States increased by 89% from 164,017 to 310,361 ha according to USDA-NASS irrigation surveys.¹²¹ Use of SDI should continue to increase in the future, depending primarily upon the economic and water conservation benefits in comparison to other irrigation methods. As water supplies become more limited, the high application efficiency and water-conserving features of SDI should increase its application. Also, SDI offers potential advantages such as reduced odors and exposure to pathogens when using recycled domestic and animal wastewater. The SDI technology offers the capability to precisely place water, nutrients, and other chemicals in the plant root zone at the time and frequency needed for optimum crop production. With proper design, installation, and management, SDI systems can provide excellent irrigation efficiency and reliable performance with a system life of 10-20years.

References

• 1. ASABE. Soil and Water Terminology. 49th Ed.; ASAE: St. Joseph, MI, 2001; 970-990.
• 2. Lamm, F. R. 2016. Cotton, tomato, corn, and onion production with subsurface drip irrigation - A review. Trans. ASABE 59 (1), 263-278.
• 3. Lamm, F.R. and C.R. Camp. 2007. Subsurface drip irrigation. In Microirrigation for Crop Production - Design, Operation and Management. F.R. Lamm, J.E. Ayars, and F.S. Nakayama (Eds.), Elsevier Publications: Amsterdam; 473-551.
• 4. ASAE. Design and Installation of Microirrigation Systems. 49th Ed.; ASAE; St. Joseph, MI, 2001; 903-907.
• 5. Camp, C.R. Subsurface drip irrigation: A review. Trans. ASAE 1998, 41 (5), 1353-1367.
• 6. Ayars, J.E.; Phene, C.J.; Schoneman, R.A.; Meso, B.; Dale, F.; Penland, J. Impact of bed location on the operation of subsurface drip irrigation systems. In Microirrigation for a Changing World, Proceedings of the Fifth International Microirrigation Congress, Orlando, FL, April 2-6, 1995; Lamm, F.R., Ed.; ASAE: St. Joseph, MI, 1995; 141-146.