Nursery irrigation & drainage

Regular reviews of water supply, management and application are key for any nursery, writes Sally Drury.

Nurseries: securing water supplies at a price that makes business sense and irrigating efficiently are two of the major challenges - image: John Adlam
Nurseries: securing water supplies at a price that makes business sense and irrigating efficiently are two of the major challenges - image: John Adlam

Where do you source your water? Where will you be getting it in 10 years’ time? How much will you be paying for it and how will you use it? Securing water supplies at a price that makes business sense and irrigating efficiently are two of the greatest challenges facing nurseries and garden centres.

Whenever there is a drought we are reminded that mains water is primarily for domestic users and it is for drinking. With the UK population continuing to expand, even more pressure is placed on mains water. With bills coming in at up to £1.50 per cubic metre, it can be difficult to justify the use of mains water for keeping plants alive, even if it is
your livelihood.

Obviously some regions of the UK will be in a better position than others. The South East, with its high density of people and tendency towards lower rainfall, constantly comes under pressure to use water wisely. But it is sensible for all growers to review their water supply, management and application on a regular basis. Water is a valuable resource and the industry needs to focus on security and conservation to stay ahead of changes in legislation.

Mains, boreholes, abstraction from rivers and winter abstraction are not the only options. Many commercial horticultural businesses have the opportunity to capture or recycle their  own water, even to the point of becoming self-sufficient. Run-off from overhead irrigation system can be captured, channelled to a holding area and cleaned prior to reuse. Nurseries with glasshouses and polytunnels have the opportunity to harvest water from roofs and drains — in many regions the amounts captured can turn out to be surprisingly generous.

The financial benefits of harvesting and recycling water with leached fertilisers can be doubly rewarding and the environmental benefits extend beyond the prevention of pollution. There is more and more evidence that some systems lead to reduced incidence
of disease.

There is a need for storage — appropriate drains leading to a reservoir or tanks above ground.
For some, space will determine feasibility and size but where there is room it is important to calculate the required capacity.

Access Irrigation has developed a computer modelling programme based on location, catchment area and watering volumes to predict how much storage capacity is needed.

Generally speaking, the larger the catchment area in relation to the areas watered, the smaller the storage tanks or ponds need to be.

Flowering Plants has a spreadsheet that integrates many factors and does the calculus. Where site constraints prevent enough water being caught to ensure self-sufficiency, automatic mains water top-up systems can keep the irrigation system going until the next rainfall.

But for many nurserymen the worry is not the capture or storage of the water but concerns about water quality and the risk of contaminating the crop with pesticides, oils from vehicle activity and diseases. Pythium and Phytophthora are likely in gutters around greenhouses.

Generally there are two stages to cleaning water. Particles are removed at a pre-filter stage. This can involve simple silt traps or fast sand or mesh filters. Centrifugal separators can also be used to remove solids. At Lowaters Nursery, rainwater captured from the roofs of the glasshouses is passed through a large stone-bed bio-filter designed by Flowering Plants before entering the storage pond. From there it flows through a novel floating iris bed and then is pumped to the reservoir, which is aerated. The whole system is designed to digest pathogens and keep them out.

Just as chlorination is used to remove human pathogens from drinking water, so the process can be used to remove plant pathogens. Used on some nurseries, it involves equipment and a chlorine storage facility that must meet certain legal requirements. Results have varied in the past, with some nurseries suffering no chlorine toxicity but others reporting problems.

Ultraviolet light has also been used to disinfect water but there is currently more interest in slow sand filters, biological filters and wetlands such as reed (Phragmites australis) and iris beds.

In 1998 Flowering Plants started work to build on the slow sand filtration projects undertaken by Dr Tim Petitt and his team at HRI Efford in Hampshire. Assays and much practical experience have shown that some of the company’s capillary mats produce the same beneficial microflora as some clean slow sand filters, but in significantly greater numbers. Used outside as part of a water-capture system, the mats have been shown to bring about a 75 per cent reduction in the reliance of water from sources other than rain.

Looking to improve slow sand filters, Flowering Plants has developed the "Manchester Filter System" of reactive filtration for the regeneration of irrigation water. Assays have shown it to be between four and 20 times more effective than slow sand filtration, depending on the time of year.

Systems could involve many stages but should use as few as possible to grow more beneficial bacteria at a faster rate. Using data from fish farming and having tested other media, alternatives can be offered to suit the chemical and microbiology of the water supply.

Other work by Flowering Plants has led to the ability to digest sludge and algae in reservoirs and filter beds, sustain beneficial microflora in large bodies of water and to use air to lift sludge out of the system.

Combined, the measures give a self-cleaning system that has accepted a range of mucky waters and puts out clean water with carefully controlled levels of bicarbonate hardness and populations of microflora that benefit plant health.

Flowering Plants managing director Francis Richardson explains the art is in learning how to "read" the balance of the microflora in the water and adjust the system settings accordingly. "We know that slow sand filters and reed beds, when working properly, provide an environment that encourages beneficial microflora to eat plant pathogens," he says.

"We can measure how effective they are by assaying the population of beneficial microflora in water by using media such as Kings B. We can also do the same for pathogens and calculate the numbers present. In practical terms we know how many ‘good guys’ we need to be able to count to be sure there are sufficient present to eliminate the ‘bad guys’.

"In evolving a Manchester system to suit a particular site, we aim to make the systems self-cleaning. Measurements by microbiologists have shown that these systems generally produce between 3.5 and 20 times as many of the ‘good guys’ as a slow sand filter or a reed bed system when working well. The practical results speak for themselves.

"The systems have controlled not only water- and soil-borne fungal diseases but also some bacterial ones including Erwinia, Pectobacterium, Pseudomonas and Ralstonia. For everyone’s peace of mind, microbiological assays remain essential until growers learn to ‘read their plants’."

Ten tips to save water and cut your bill

1 Pay attention to leaks — they are money down the drain.
2 Consider using water of a lower but acceptable quality, using equipment for sanitising and cleaning the water of pathogens.
3 Allocate bed space carefully and group plants together that have similar water demands.
4 Check run-through rate of growing media, especially when there are changes in origin, supply or supplier.
5 Monitor sprinkler uniformity — the paper cup test.
6 Fast-moving technological changes mean it is important to check out the latest irrigation products and designs.
7 Irrigate on demand, not by the clock — need not be complex or expensive.
8 Link to weather stations to calculate irrigation requirements.
9 Variable-speed pumps can reduce strain on system and save energy.
10 Dual up by using drip irrigation for applying other products such as nematodes for vine weevil control or irrigation gantries that can double up as plant-movement systems.

Helpful contacts

There are many sources of advice and new equipment for irrigating horticultural crops. The following is a selection but more can be found in the HW Buyers Guide.

l Access Irrigation    01788 823811
l AKWA Irrigation Services
    07771 332832
l Aquamatic Irrigation    01282 873333
l Arden Lea Irrigation     01772 812433
l Briggs Irrigation     01536 260338
l City Irrigation     020 8315 8169
l CMW Horticulture     01430 422222
l Davis Instruments     001 510 732 9229
l Delta-T Devices     01638 742922
l Denton Automation     01903 892715
l Dove Associates     01379 741200
l Eden Irrigation     01695 558804
l Electronic & Technical Services
    01516 458491
l Evenproducts     01386 760950
l Field Irrigation     01344 891731
l Flowering Plants     01280 813764
l Flier Systems      00 31 180 615 055
l Hortech Systems     01406 426513
l Horticultural Solutions
     01482 665449
l HortiSystems     01798 815815
l IM Irrigation Services     01327 354282
l Irrigation Technical Services
    01202 874216
l Javelin Irrigation Systems
    01507 607175
l JD Ultasonics     01924 378448
l LBS Horticulture     01282 873333
l Mitchell Technical Services
    01202 892402
l New Leaf Irrigation     01953 681590
l NurseryBitz     01243 554455
l Ripple Aquaplast     01565 777216
l Rotorflush Self-Cleaning Filters
    01297 560229
l Wise Water Solutions     01905 828142

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