‘One drop at a time’, part 2: Can drip irrigation work on a commercial potato farm?

British experience shows that drip irrigation can reduce water use and support marketable yield. Turning that potential into a reliable return, however, requires careful engineering, monitoring and integration with the entire farming system.

By Lukie Pieterse, Editor/Publisher of Potato News Today

Editor’s note: Lukie Pieterse is a former South African potato grower who produced drip-irrigated potatoes for several of the country’s major processors at the time, including McCain Foods, Frito-Lay and Heinz. His interest in drip irrigation is therefore grounded in first-hand farming experience.

In the first part of this Potato News Today series, we examined why the potato crop can respond well to drip irrigation. Its shallow root system, sensitivity to moisture fluctuations and concentrated water demand during tuber initiation and bulking make precise delivery into the ridge an attractive proposition.

The agronomy, however, is only half the story.

Commercial success depends on whether the system can be installed, operated and removed without disrupting other field operations—and whether the resulting improvements in water productivity, yield or quality are sufficient to cover the additional costs.

This is particularly relevant in Britain, where potato growers face increasingly variable rainfall, abstraction constraints, rising energy and labour costs, and demanding fresh-market and processing specifications.

Rain guns remain familiar, mobile and comparatively easy to move between rented or dispersed fields. Booms and solid-set systems may improve distribution uniformity. All overhead systems, however, are exposed to some combination of wind drift, evaporation, uneven distribution and canopy wetting.

Drip offers another route, but it is not a simple matter of replacing a rain gun with a length of tape.

British experience: moving from theory into the field

One of the more frequently cited UK commercial examples involved processing-potato grower EG Harrison and Co. in north-east Norfolk.

The farm tested drip tape supplied by British irrigation specialist Wroot Water Ltd in cooperation with its processing customer, Lamb Weston Meijer.

According to a 2016 report published by Crop Production Magazine, the trial reduced water use by 25% while increasing yield by 18%. It was subsequently expanded across 11 hectares.

The figures deserve attention because they emerged from commercial production rather than a small research plot. They must nevertheless be interpreted with caution. The results represented one farm, one crop and one combination of season, soil and management. They should not be treated as a guaranteed outcome elsewhere.

The following season provided an equally valuable lesson. Regular rainfall meant that the expanded system had initially not been required.

This is part of the difficult investment context surrounding irrigation in Britain. In a dry year, drip may protect yield, quality and contractual performance. During a wet season, much of the equipment may serve primarily as insurance.

The value of that insurance will differ between businesses. A grower producing potatoes under a quality-sensitive processing or retail contract may place a higher value on irrigation reliability than one supplying a more flexible market.

The Norfolk farm also used NIAB CUF scheduling guidance, soil-moisture probes and rain gauges. The reported benefit did not arise from drip tape operating in isolation. It was part of a measured and managed irrigation programme.

Placement within the ridge is critical

Drip tape may be placed on the ridge surface and subsequently covered, or installed shallowly within the ridge during planting or as a separate field operation.

Shallow placement protects the tape from sunlight and some physical damage while keeping the emitter relatively close to the active root zone. The selected position must also avoid contact with seed tubers and interference from cultivation or harvest machinery.

Earlier AHDB-supported research into precision irrigation and common-scab suppression illustrates the importance of these details.

In one experiment, tape supplied by Wroot Water was installed after planting at a depth of 25 to 30 millimetres and approximately 20 millimetres to the side of the ridge centre to avoid the seed tuber. In another, tape was laid on top of the ridge at emergence and covered with approximately 25 millimetres of soil.

Irrigation was guided by the Cambridge University Farm Potato Irrigation Scheduling Model, meteorological information and measurements of soil water within the ridge.

The experiments were designed principally to investigate common-scab management, rather than to serve as a commercial comparison between irrigation systems. Their wider message remains relevant: drip performance depends on accurate tape placement, system calibration, measurement and scheduling. The archived AHDB report contains the trial details.

Before committing a complete field, a grower needs to confirm that the selected tape, emitter spacing, flow rate, operating pressure and irrigation duration will produce an adequate wetting pattern under the field’s actual soil conditions.

The hardware requires constant attention

A commercial potato drip system normally includes a pump, filtration equipment, pressure regulation, mainlines, submains, valves, connectors, drip laterals, fertiliser injection equipment and a means of flushing the lines.

Filtration is not optional.

Sand, silt, algae, mineral deposits and biological material can partially or completely obstruct emitters. Even modest differences in emitter flow may translate into variations in emergence, canopy growth, tuber set and size distribution across the field.

Water quality determines the filtration and treatment required. Borehole, reservoir and river water present different risks, while the biological and mineral composition can vary during the season.

System pressure must remain within the tape manufacturer’s operating range. Excessive pressure can damage tape and connections; insufficient pressure leads to uneven delivery, especially over long runs or changes in elevation.

Pressure-compensating emitters may improve uniformity, but generally cost more. Field dimensions and topography also determine practical run lengths and the size of individual irrigation blocks.

The Oregon State University Extension drip-irrigation guide for potatoes stresses that every system should be designed for the individual field. Bed configuration, water source, pump capacity, filtration, maintenance and chemigation requirements must be assessed before installation.

Drip is not a “set it and forget it” technology. Pressure gauges, flow meters and soil-moisture sensors should be regarded as core components. Field inspections remain essential for identifying leaks, damaged tape, obstructed emitters and uneven wetting.

Automation can reduce labour by coordinating pumps, filters and valves, but automation should not be confused with autonomy. The equipment and crop still require human oversight.

Installation and retrieval are part of the calculation

Discussions about drip frequently concentrate on water use and yield. Commercial potato growers must also put the tape into the ridge and recover it without delaying planting, damaging the crop, obstructing harvest or leaving fragments of plastic in the soil.

Potatoes are planted, hilled, desiccated and harvested using machinery that disturbs a substantial volume of soil. Tape installed in the wrong position may be caught during cultivation or lifted into the harvester with soil and tubers.

Annual tape can be removed before harvest, but retrieval requires labour and specialised or adapted equipment. Wet, stretched or soil-contaminated tape may be difficult to handle and recycle.

Permanent subsurface drip avoids annual tape purchase and retrieval, but introduces another compromise. Lines must be deep enough to escape tillage and harvesting machinery while remaining capable of supplying the potato root zone. The installation must also work for other crops in the rotation.

University of Idaho guidance has ranked drip highly for its ability to deliver light, frequent and uniform irrigation. The same guidance recognises that economics, rotation and incompatibility with conventional potato operations frequently make buried drip impractical.

That contradiction lies at the centre of the debate. Drip may be an excellent biological fit for the potato crop while remaining an awkward operational fit for the farming system.

When might the investment be justified?

Drip irrigation is most likely to make commercial sense when several favourable conditions occur together:

Water availability is restricted, unreliable or expensive.
Pumping costs make reductions in applied water financially significant.
The crop has a high value and marketable yield or size distribution carries a clear premium.
Field shape, slope or wind makes overhead application inefficient.
Water quality can be managed with appropriate filtration and treatment.
The soil provides a suitable wetting pattern from the selected emitters.
The farm has the staff and technical support needed for monitoring and fertigation.
Tape placement and retrieval can be integrated with planting, hilling and harvest.
Reusable infrastructure can serve other crops in the rotation.
Greater irrigation reliability improves the farm’s ability to meet contracts.

The case becomes less attractive where rainfall frequently replaces irrigation, existing overhead equipment already provides good uniformity, water and pumping remain comparatively inexpensive, or the rotation includes crops that cannot make practical use of the infrastructure.

A 2024 farmer-led trial reported by Practical Farmers of Iowa provides a warning against assuming that irrigation equipment will automatically generate a return. The season was sufficiently wet that drip had no statistically significant effect on potato yield.

The grower nevertheless considered the trial useful because it helped establish the practical and financial questions that would matter during a drier season.

Water efficiency is not necessarily water conservation

Drip can reduce non-beneficial losses at field level. Less water may be lost through wind drift, surface evaporation, runoff or drainage beneath the root zone. Lower pressure requirements may also reduce pumping energy.

An efficient irrigation system, however, does not automatically reduce total water consumption across a farm or catchment.

If the water “saved” is subsequently used to expand the irrigated area, increase production or grow more water-demanding crops, total consumption may remain unchanged or rise.

This does not diminish the value of drip. It means that irrigation efficiency, crop water productivity and catchment-wide water conservation are different measurements.

For an individual potato business, the practical questions are more immediate: How many tonnes of marketable potatoes are produced per unit of irrigation water? Does tuber quality improve? How much energy, fertiliser and labour are required? Does the additional revenue cover installation, monitoring, maintenance, retrieval and replacement?

Start with a representative field

For growers seriously considering drip, a well-designed commercial-scale trial may provide better evidence than an immediate attempt to convert the entire potato enterprise.

The trial should be large enough to represent normal field operations. Where possible, drip should be compared with the farm’s existing irrigation system under similar soil, crop and management conditions.

Total yield alone will not provide an adequate answer. Records should include:

Water applied and pumping hours.
Energy consumption.
Installation, operating and retrieval labour.
Soil moisture at several positions and depths.
Fertiliser applied through the system.
Marketable yield and tuber-size distribution.
Dry matter or specific gravity.
Processing quality or pack-out.
Common scab and other defects.
Tape damage, blockage and repair costs.
Plastic recovery, disposal or recycling costs.

Ideally, the comparison should continue for several seasons. A wet year may reveal little about yield response but a great deal about installation costs and compatibility with farm operations. A dry year may demonstrate the system’s full agronomic and commercial value.

The purpose should not be to prove that drip irrigation works. Research and commercial experience have already shown that it can. The purpose is to determine whether it works economically and reliably on that particular farm.

A tool for adaptation—not a universal prescription

As drought risk, abstraction constraints, energy costs and competition for water intensify, drip irrigation is likely to receive greater attention in potato-producing regions.

Improved soil-moisture sensing, remote control, automated fertigation and system diagnostics could make it easier to match delivery with crop demand. Lower-cost installation, better retrieval machinery, durable reusable components and credible recycling arrangements could also alter the commercial equation.

Hybrid approaches may emerge. Some growers could retain overhead irrigation for establishment and complete ridge wetting, then use drip for precise in-season water and nutrient delivery. Others may restrict drip to high-value varieties, drought-prone fields or irregular land that conventional equipment irrigates poorly.

The British experience demonstrates both sides of the argument. Drip can operate successfully at commercial scale and produce impressive results. It also demands more than the selection of a tape from a catalogue.

The system must be designed around the field, installed accurately, measured continuously and integrated with the entire production programme.

Drip offers potato growers something genuinely valuable: finer control over one of the crop’s most important and difficult production variables. Precision hardware alone, however, does not create precision agriculture. The benefits emerge only when engineering, soil-water measurement, nutrient timing, economics and human management work together.