Boosting irrigation efficiency while conserving water
The overriding aim of using water effectively on nurseries concerns applying it to the target area at the correct rates for suitable periods of time. While adequate irrigation is a key requisite in the production of quality and healthy plants, water conservation is growing in importance as water becomes an increasingly scarce and costly resource.
Here Peter Robinson, Technical Area Sales Manager and irrigation expert, highlights some of the more common issues experienced with different systems and offers advice on how to avoid, or mitigate, these.
Irrigation on UK nurseries usually takes the form of one of the following: -
- Overhead sprinklers - usually solid set, with sprinklers on risers down the centre of the bed, along the edges or in a grid covering the area to be watered
- Drip and capillary systems - employing individual drippers to apply water to pots, troughs and baskets - to apply water to lines of crops in the soil or in troughs. These systems are particularly suited to fertigation.
- Hose pipes – usually via a hose pipe and lance
- Flood Systems - introducing water to the crop, where it stands while the crop absorbs its requirements, then drains the water.
Inherent issues
All four systems offer their own advantages when operated well, although they can be prone to inefficiencies.
Incorrect pressure in overhead sprinkler systems can result in misting and over or under throw of water, while wet and dry spots can be caused by poor sprinkler spacing. These systems are also prone to water wastage when dead areas, such as paths, are watered. Run off can also be an issue.
Drip and capillary systems can suffer from erratic dripper performance - typically the result of poor filtration. Variable emitter outputs can be caused by non-pressure compensated systems, with wet spots repeatedly receive excessive water and water wastage where plants have been removed but dripper(s) have not been closed off.
Flood Systems are very good at only using the water required by the crop and returning the balance to be used again. The main issue with these systems is less about efficiency and more about water quality and the cost of cleaning for reuse.
Correct pressure
Pressure is important - so make sure you know the ideal pressure, or operating parameters, of the sprinklers or drippers in your system. Pressure regulation on headers and valves will ensure excess pressure is corrected.
Check to ensure your pumping system can deliver the correct pressure - allowing for more than one area to be irrigated simultaneously and additional hose pipes to be used. Variable speed pumps are particularly useful in maintaining a set point pressure.
Pressure gauges are essential to monitor pressure; these can be at valve points, ends of irrigation laterals and on sprinkler risers; alternatively, if preferred, there are needle gauges.
Check for accuracy
Sprinkler systems can be tested for accuracy using a catch can test - with the results plotted on a spread sheet to show effectiveness. Dripper systems can be tested by sampling at several points with a measuring cylinder.
A good tip is to watch out for similarities in areas, for example poor dripper accuracy at the end of lines may indicate filtration issues and / or the need for more frequent flushing.
Some irrigation companies may offer these tests or evaluate results.
Regular maintenance
Filtration is the key to any irrigation system. Filter clogging is easily monitored with a pressure gauge either side of the filter; a difference of 0.5 Bars is commonly used as the cleaning ‘trigger point’.
Sprinkler maintenance includes nozzle checks and spring tension - where applicable; sprinkler laterals can be flushed to remove accumulated deposits.
Dripper systems should be regularly flushed according to site specific factors - such as feeds used, dirt loading and dripper type – some are better than others at moving dirt! The ends of dripper lines should have a threaded cap or valve fitted.
Dripper line flushing guide
To assess the need for flushing, check the water quality in the ends of some lines - dirty water means flush is required.
To flush, open half the ends per valve block and commence flushing until clean water appears. By increasing velocity in these drip lines, flushing effectiveness is boosted. Once completed, close those opened, and repeat on the other half.
Alternatively, especially if flush valves are fitted, open 10-20% of a block and commence flushing. When clean water appears shut these valves, one at a time, while opening others - one at a time. This is a two-person rolling operation; try and keep in sync and always ensure clean water is flushing out of the lines.
Cleaning products
To clean and maintain irrigation systems there are several options including Pekacid, Hydrogen Peroxide formulations and Peroxyacetic acid; all must be used according to manufacturers’ instructions.
Be aware that Hydrogen peroxide will remove biofilm from pipe walls – this must be removed prior to using the system again. With larger pipes, manual cleaning using drain rods and pressure jets is possible.
By following the advice above, there are often simple gains to be made, however it can be difficult to have an ideal nursery irrigation system; it is therefore likely to remain irrigation with a degree of irritation!