Drip irrigation techniques from the glasshouse used to deliver water and nutrients to field crops

Technology is advancing to apply water to field crops even more efficiently, says Roger Chesher.

EMR potato trials with drip tape. Image: EMR
EMR potato trials with drip tape. Image: EMR

When field drains are running with winter rain, it is easy to forget the vital importance of readily-available water for valuable field crops throughout the growing season.

This is something that protected crop growers never forget because their responsibility is to ensure that the water supply and the nutrients carried in it are entirely controlled and measured.

Varying water and nutrient levels to manipulate quality, evenness and size of samples help these growers to bring crops on spec and on time to market - and in the most cost-effective manner to maximise profit.

The concept of applying water to field crops in the form of irrigation is well known, but driven by future needs to use water more efficiently, scientists across Britain are determining the guidelines for widening the introduction of drip irrigation into the field supported by Defra.

The most valuable crops are coming under the spotlight. Peas and onions are the focus of scientists at Harper Adams University College, while onions are being studied at Broom's Barn and potatoes, herbs and onions at East Malling Research (EMR). Work is ongoing on substrate-grown and pot crops and carrot and parsnips are in the pipeline.

Providing targeted amounts of water to field crops by drip irrigation allows nutrients to be included in the feed. This technique of "fertigation" offers a higher efficiency of nutrient use, fewer losses - both economical and environmental - and a more precise way of manipulating growth, quality and disease resistance by timing the applications of both water and key nutrients to suit growth stage or at times of potential stress. It is therefore not surprising that fertigation forms a major part of the work currently being investigated.

East Malling Research

Headed by Dr Mark Else, the Defra-funded research on potatoes at EMR seeks to find ways to use water more efficiently by using drip irrigation to locate the liquid around the tuber, avoiding the 14-18 per cent loss to evaporation that is usually experienced. This uses less water overall as a consequence. At the same time nutrients are concentrated around the rooting zone, minimising leaching and surface run-off.

"It is a large step to change from conventional field irrigation techniques for potatoes," says Else. "If the requirement is purely to get water onto a ware crop then conventional techniques will suffice. But more growers will undoubtedly switch - and as water-saving implementation kicks in, our task is to lay down scientific guidelines to enable this technology to work efficiently."

Although water for the experiments comes "from the tap", the downstream equipment is provided by commercial organisations already marketing in the UK. Control equipment comes from Priva, the drip irrigation from Wroot Water (some of it from John Deere Water Technology) and soluble nutrients from Prayon UK with nutrient know-how from Mike Daly of Earthcare Technical.

The experiment determines optimal levels of nutrient solution or water required at specific stages in crop growth. For example, field capacity at tuber initiation. Soil analysis determines nutrient requirements and field probes assess water levels. The aim is to achieve a closed-circuit loop via probe, sensors and switches, across the internet, maintaining optimal levels at all times.

Eventually it may be possible to introduce into the loop an EC probe (electrical conductivity) or specific nutrient sensors.

"Upstream" kit

In practice, of course, water will not come from the tap but from boreholes, rivers or other extraction points. Most growers will have the upstream equipment required to adopt new field fertigation technology in the form of pumps, pipes and reels. Technology moves quickly, however, and even in this more established area there are great efficiencies to be made.

A successful pumping system is the bringing together of many elements, not least pumps but valves, controls and manifolds, with the appropriate sizing and selection of all.

"Downstream" kit

While many field-scale soft fruit growers are already drip irrigating, the technical requirements of the techniques for producers of field vegetables may be somewhat of an unknown. Unlike as in boom or rain gun technology, before the water can be drip fed it usually must be filtered.

Next there is the need for soil moisture probes, metering and irrigation control devices and then finally the drip irrigation installation itself. Field fertigation also requires input feed devices, mixers and control, together with specialist soluble nutrients.

At this stage, most people would seek the help of a consultant, either purely for advice or to source at least some of the components. Those involved in the EMR potato project provide a useful snapshot to illustrate some of the range of equipment available to this burgeoning technique.

Earthcare, headquartered in Coventry, can advise on soil water management with particular reference to Decagon soil moisture sensors, loggers and data analysis, optimum deployment and location of sensors with manual readings via PDA or laptop, data-logging, telemetry and automated closed loop control systems. Earthcare supply Decagon from the USA.

The 10HS Large Volume Soil Moisture Sensor, for example, has a large sphere of influence allowing it to measure the volumetric water content of a large soil sample volume (approximately one litre). It does this by measuring the dielectric constant of the media through the use of capacitance/frequency domain technology.

In addition, the 10HS sensors incorporate a high-frequency oscillation, which allows the sensor to accurately measure soil moisture in any with minimal salinity and textural effects. Decagon also manufactures rugged outdoor data logging equipment such as the Em50, suitable for use with the company's sensors.

Wroot Water of Doncaster is also able to supply advice and equipment. Some Wroot Water products are sourced from John Deere's newly-expanded water division. Drip tape often provides the best solution for field vegetables and, in the case of the EMR potato experiments, this is buried just below the surface of the soil.

Filtration is the most important part of a drip irrigation system, claims Wroot Water, with the type of filter dependent on the water supply. Dirty water sources such as rivers and drains will require different filtration to a clean water source such as a borehole. Open watercourses may grow algae in warm weather, which could block emitters. If fertigation is being used, however, this can help keep the pipes clean.

The company is able to offer a comprehensive range of filters - from fully automated back flushing disc and sand media filters to solar-powered screen filters.

Based on a kibbutz in Israel's northern region, Galcon is one of the world's leading manufacturers of computerised irrigation controllers - the final bit of kit required to make the automated system function by controlling irrigation rate and timing. Two model ranges, the Galileo and Galstar, would fit in mediumto large-scale field operations giving a wide combination of settings, inputs, programmes and features. Again, this only serves to illustrate the wisdom of employing a consultant, at least in the first instance.

There are opportunities with Galcon controls to incorporate fertigation, which gives rise to another shopping list of equipment. Galcon can supply nutrient dosers and mixing machines but the one used in our example happens to come from Priva in the Netherlands.

Its latest unit, the NutriJet, is an alternative to mixing tank fertiliser dosing systems. The system injects the nutrient solution directly into the mainstream irrigation water. A major advantage of these systems is that a feeding pump is not necessary.

NutriJet is "modulair" in its set-up and gives a grower the possibility to simultaneously inject up to eight fertiliser solutions, each with its own proportional volume. Like Galcon, Priva can also supply control systems.

Finally, with regard to the nutrients themselves, fertigation requires fully water-soluble, high-quality crystalline fertilisers, which are sold as straights and compounds in various nutrient combinations - mainly nitrogen, phosphate and potash but many also with magnesium, calcium, sulphur and minor or trace elements. The largest global fertiliser manufacturer, Yara, is active in our markets, as is Prayon of Belgium.

Four fertigation regimes are being tested at EMR on potatoes, with nutrients added before tuber initiation and continued for nine weeks. The Prayon materials in use are an acidic 0.60.20 together with potassium nitrate (13.5-0-46) and ammonium nitrate (34.5 per cent nitrogen).

- UK Irrigation Association 01427 717627
- Simon Heelas Powerflow Services 01291672135
- Briggs Irrigation 01536 260338
- RST Irrigation 01353 675265
- Wright Rain 01425 472251
- Fieldwater Ltd 01622 844044
- Hortech Solutions 01531 636511
- New Leaf Irrigation 01953 681590

- Michael Daly Consultant (affiliated to Earthcare and Prayon) 01673
- Earthcare Consultancy and Sales (including Decagon) 024 7651 0051
- Wroot Water Systems 01302 771881
- Prayon UK - 01582 769999
- Galcon (UK distributor) - 0161 793 9703
- Priva UK - 01923 813480
- Yara 07831 120379

- Dosatron 01536 461441
- Field GB 01233 861080
- City Irrigation 020 8462 4630
Fieldwater 01622 844044

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