Overview
Drip irrigation systems are a necessary part of any modern greenhouse facility. The simplest drip irrigation system is made up of the following components:
- pressure regulator
- filter
- tubing (irrigation lines)
- emitters (drippers)
Emitters provide a controlled and uniform distribution of water and nutrients between plants located along the irrigation line. However, emitters are prone to clogging from deposits of calcium carbonate, algae or bacteria. So irrigation lines require regular maintenance for better and longer service.
Filter
The drip system filter should be checked every day and cleaned if necessary. Disc and screen filters are available on the market. The preference should be given to disc filters, as they are more resistant to clogging and easier to clean through back flushing. Check lines for leaks.
Emitters
A pH higher than 6.0, and high EC (electrical conductivity), may lead to precipitation of calcium and magnesium salts, which will clog the emitters. Precipitates may build up to the end of the season even when precautions have been taken. Partially clogged emitters may still conduct feeding solution, but they will distribute nutrients unevenly among the plants. Therefore, the lines should be flushed with nitric acid at the end of each season to remove build-up.
Irrigation lines
Caution: When dealing with acids, make sure that appropriate gloves and clothes are used. Always add acid to water, not water to acid.
Although Nitric acid is a most efficient solubilizer, sulphuric and phosphoric acids can be used too. Flushing lines for 1 hour with pH 4.5 solution is usually effective enough. However, you can leave the solution in the lines overnight if you have a particularly tough precipitate build up. Flush the lines with water afterward. Avoid precipitate build-up through preventive measures rather than drastically eliminating it at the end of the season.
Mineral precipitates are relatively easy to remove compared to the organic slime formed by bacteria and algae. The preventive measure would be injections of chlorine or commercial bacterial control agents. Use 2 ppm (parts per million) of chlorine daily to ‘rinse’ at the end of irrigation cycle, and 30 ppm if slime becomes a problem.
If there is already a lot of algae and bacteria growing in the pipeline, emitters can be plugged worse when the slime begins to break off and gets carried downstream. Therefore it is very important to flush the lines extensively before irrigating again. Automatic valves flushing several litres of the feeding solution at the end of each irrigation cycle are not expensive and can be installed at the end of each dripline. This will prevent any build-up of particles or slime at the end of drip lines.
Microorganisms must be eliminated regularly from your irrigation system. At the end of each growing period, inject sulphuric acid (pH 5) through one injector and 50 ppm chlorine through a second injector downstream from the sulphuric acid injection. Leave the solution overnight and flush it out the next morning. See also End of season cleanup.
Acknowledgements
N. Savidov, CDCS and M. Mirza, CDCN. Greenhouse Coverings newsletter (November, 2001).