Hardy Nursery Stock: Get a grip on water

Better irrigation control can improve crop quality as well as save water, research has found

GP1 logger: allows irrigation only when needed. Image: HDC
GP1 logger: allows irrigation only when needed. Image: HDC

Just before its abrupt termination last month, Defra's HortLINK programme brought forth an irrigation project that demonstrated what industry-led collaborative research can achieve.

The snappily titled HNS 97b Enhancing the Quality of Hardy Nursery Stock and Sustainability of the Industry through Novel Water-saving Techniques, which ended in September, has given the industry a mixture of ready-to-use and plausible technologies.

With the Flood and Water Management Bill looming on the Parliamentary horizon, this is a crucial time for growers to reassess water use (HW, 23 October).

Launched in October 2005, led by Lancaster University's Bill Davies and coordinated by Hillier's John Woodhead, 97b was the second HortLINK-funded project to look at irrigation.

The long list of partners includes the Horticultural Development Company (HDC), HTA, Lancaster University, East Malling Research (EMR), Pera, the University of Dundee, Delta-T Devices, Skye Instruments, Denton Automation, Access Irrigation, InfraRed Integrated Systems, Hillier Nurseries, Coblands Nurseries, Wyevale Container Plants, Palmstead Nurseries, Johnsons of Whixley and John Woods Nurseries.

The justification for the project, says Davies, is obvious. "Predicted changes in the UK climate suggest that water availability, particularly in summer, will become a substantial problem for UK horticulture."

But while water economy is critical, it is only the start of what can be achieved with better scheduling and application, he believes. The techniques pioneered in the project can lead to improvements in crop quality and the possibility of growth regulation - both of which can reduce labour.

The project looked at three areas: uniformity of application through the use of a gantry system; scheduling through the use of Skye Instruments' Evapometer and Evaposensor and Delta-T Devices' SM200 soil moisture probe and GP1 logger and irrigation controller; and regulating growth with the use of buffer solutions to induce drought stress.

While a full cost-benefit analysis is not yet complete, initial results suggest that all three areas have significant potential. And though some technologies involved — such as using infrared cameras in conjunction with gantry sprayers — are still very much in development, others are available to growers now.

The first priority, according to EMR research scientist Olga Grant, is to aim for an even spread of irrigation.

"Improving the uniformity of application is the crucial first step towards water efficiency and maximum plant quality," she says. "It is also important to have a good, even standing base to avoid large variation in uptake through the base of pots. Once the uptake of irrigation water is uniform, you are ready to start scheduling it."

Perhaps the most accessible technologies pioneered in 97b are the Evaposensor, Evapometer and the SM200 soil moisture probe and GP1 data logger, which together measure the crop's demand for water and ensure irrigation matches this.

According to consultant agronomist Chris Burgess: "The Evaposensor measures the general cropping environment, specifically the evaporative demand of the atmosphere. It takes into account radiation, air temperature, humidity, wind speed — a whole range of factors."

By measuring the difference between its two probes — one wet, one dry — it calculates the evaporative demand.

The actual amount the plant uses is also dependent on the crop size and spacing. Grant says the best way to judge this is by weighing representative plants immediately and 24 hours after watering.

By taking an Evaposensor reading at the same time, the amount of water that is used per sensor unit, or degree hour, can be calculated.

Establishing the exact demand of each crop is rather technical, but once achieved the sensor can be linked to an irrigation timer so that irrigation is automatically adjusted according to the readings.

And to avoid the need for regular weighing of crops the team has established a coefficient based on crop height and cover. This will allow growers to quickly adjust their crop coefficients as the plants grow.

Meanwhile, the SM200 soil moisture probe and GP1 logger and irrigation controller enable automatic irrigation control based on the moisture content of the pots.

Trials in the four nurseries involved showed that, once even irrigation is achieved, one probe can be used to represent a relatively large area — 500sq m or more — and even mixed crops, as long as their needs are similar.

The probe offers a closed-loop control system with feedback from the moisture probe accounting for the complex set of factors affecting water delivery and loss to the growing medium.

By setting upper and lower limits for soil moisture, data from the probe can be relayed back to the data logger, which can then trigger irrigation. The GP1 can work with existing timer controls applying water at certain times of day and will simply allow irrigation as needed within these time slots.

The trials found the GP1 scheduling led to less than half the water use of manual methods, while the easier and more efficient irrigation management also saves staff time and can improve crop quality and reduce wastage.

Consultant Richard Harrison-Murray has been charged with developing a cost-benefit analysis for the technologies. In assessing the scheduling techniques, he says there were advantages beyond the simple water and labour savings.

"If you shift from irrigating daily to only when a crop actually needs it, so that the tops of the pots have a chance to dry out, you get the beneficial effect of reduced liverwort and moss growth, which can be very labour-intensive to remove," he says.

Gantry application

One way of achieving the even application of water needed for improved scheduling is to install a gantry.

Hillier Nurseries container production manager Dave Hooker trialled the system for Waterlink, with very positive results.

"The payback time is less than people think," he says. "It is not going to change overnight, but there will be people thinking gantries are now viable options and that's the way I want to go in the future."

Though Harrison-Murray's cost-benefit analysis is not yet complete, his informed estimations suggest that Hooker is right.

"At Hillier, we were able to show it would be cost-effective over an area of approximately 1,500sq m — the full length of their track — and that the payback would be about six to seven years," he says.

"I think it would be hard to justify massive investment in a gantry if you already have a good system, but if you haven't I would think it would be well worth investing in — the benefit will depend on how uneven your current irrigation is. They are more likely to be cost-effective in greenfield situations."

Eliminating the wastage of under-watered edge crops – a hazard of conventional overhead spray irrigation - can already bring substantial savings. And factoring in the cost of maintaining overhead irrigation nozzles means the gantry system begins to look like a more attractive option.

There is also scope for automation of scheduling through software control, as Hillier has already demonstrated by linking its gantry to the data logger and soil moisture probe.

The next step is to link the gantry irrigation to infrared cameras, though the difficulty of differentiating between plants and non-plant matter remains a major barrier.


In another prong of the project, Professor Bill Davies and his colleague Russell Sharp showed how applying buffer solutions and bacteria can be effective in both water management and growth regulation.

The buffer solution induces a plant's drought response, limiting growth without the release of the plant hormone ethylene (which diminishes the plant's quality).

The key advantage is that the buffers and bacteria allow for excellent growth regulation without the need for precise irrigation control. They work by increasing plant pH, which raises the levels of stress hormone abscisic acid, closing plant stomata and so reducing transpiration.

The team estimates that applying buffers at the right time could cut a plant's water requirement by 10 to 20 per cent. And as it reduces growth, the plant needs less pruning, which saves on man-hours.

In theory, the bacteria will be cheap, but as Davies explains there are still problems to work out. "They are not yet commercially available because there are problems with getting a patent, so in an ideal world we need something like the Gates Foundation to step in."

For now, they remain a strategic interest, but should ornamental growers manage to loosen the Technology Strategy Board's purse strings then future development could be highly lucrative.

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