‘One drop at a time’, part 1: What drip irrigation can offer the potato crop

Delivering water directly into the potato ridge can improve control, protect tuber development and support carefully timed fertigation. But drip irrigation is not automatically more successful simply because it is more precise.

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.

Water management has always been one of the more unforgiving aspects of potato production. The crop’s relatively shallow and often sparse root system leaves growers little room for error, while the developing tubers require a remarkably stable soil-moisture environment.

Too little water during tuber initiation can reduce tuber numbers. Moisture stress during bulking can restrict yield, disrupt dry-matter accumulation and contribute to misshapen tubers and processing defects.

Too much water creates a different collection of problems. Saturated soil can deprive roots of oxygen, leach mobile nutrients, encourage disease and interfere with skin set and harvest.

Drip irrigation appears, at first sight, almost tailor-made for this biological balancing act. Instead of projecting water through the air and wetting the entire soil surface and canopy, drip systems deliver small, controlled volumes into or immediately beside the potato ridge. Irrigation can be applied frequently, soluble nutrients can be supplied with the water, and losses through wind drift, surface evaporation and runoff can be reduced.

That is the promise. The reality in the field is more complicated.

Drip can be a highly effective potato-production tool, particularly where water is restricted, expensive or unreliable. But it is not a substitute for agronomic judgement. A poorly designed or badly scheduled drip system can stress or overwater potatoes just as surely as a poorly operated rain gun, boom or centre pivot.

Why potatoes respond to stable soil moisture

A 2025 review published in the American Journal of Potato Research identified tuber initiation and tuber bulking as the potato crop stages most sensitive to water stress.

During early growth, much of the active root system is concentrated in the upper 15 to 30 centimetres of soil. This shallow rooting pattern is one reason potatoes generally respond better to relatively light, frequent irrigation than to large, infrequent applications.

Tuber initiation is a short but decisive developmental period. Soil moisture during this stage helps influence how many tubers become established. Once bulking begins, crop water demand rises sharply as the plant builds tuber mass.

A temporary shortage during bulking can interrupt growth and contribute to growth cracks, knobbiness, pointed ends, sugar ends and irregular size distribution. Alternating very dry and very wet conditions can be particularly damaging.

Drip irrigation’s principal agronomic advantage is therefore not simply its potential to use less water. It is the ability to maintain a more stable moisture environment within the ridge.

The distinction is important. Water savings have little value if the wetting pattern fails to reach the active roots and developing tubers. Successful drip irrigation depends on applying the correct volume in the correct place and at the appropriate stage of crop development.

Surface and subsurface drip are different propositions

In a surface system, drip tape or tubing is placed on or close to the soil surface, normally along the potato row. Installation and retrieval can be comparatively straightforward, but the tape remains exposed to sunlight, wildlife, machinery and physical damage.

Subsurface drip places the line beneath the soil. Shallow tape may be installed within the ridge for a single season, keeping the water source close to the root and tuber zone while limiting surface evaporation.

Deeper subsurface drip is generally conceived as a more permanent installation. Although this may avoid annual tape placement and retrieval, it introduces additional complications in potatoes. The lines must remain beyond the reach of cultivation and harvesting equipment while still supplying water effectively to the crop. They must also be compatible with other crops in the rotation.

Neither approach is automatically superior. Suitability depends on soil, bed design, cropping system, machinery and management objectives.

The wetting pattern must fit the soil

Water does not move away from a drip emitter in the same way in every field.

In heavier soils, it tends to move laterally as well as vertically, producing a relatively broad wetted zone. This may permit wider emitter spacing or allow one lateral to serve a larger proportion of the ridge.

In coarse-textured soils, water moves downward more rapidly. The wetting pattern may consequently be narrow, increasing the risk that part of the root zone remains dry even when moisture immediately beside the tape appears adequate.

This is one reason drip-irrigation recommendations cannot simply be transferred from one region—or even one neighbouring field—to another. Tape depth, emitter spacing, flow rate, irrigation duration and the distance between laterals must all be matched to actual soil conditions.

Historic AHDB guidance on irrigation systems for potatoes notes that drip can apply water uniformly over substantial areas, but only if lateral and emitter spacing are appropriate for the soil. The guidance also emphasises the importance of soil-moisture probes.

Probe placement requires care. A sensor positioned too close to an emitter may indicate adequate moisture while another part of the ridge remains dry. Measurements at several positions and depths, supported by physical examination of the soil, provide a more reliable picture.

What the research tells us

A 2023 study published in Scientific Reports examined potatoes receiving drip irrigation at 100%, 66% and 33% of field capacity, combined with six nitrogen treatments. Water supply influenced yield more strongly than nitrogen rate.

Full irrigation produced the highest total yield. The 66% treatment, however, produced the highest water-use efficiency.

That efficiency came at a price. Reducing irrigation to 66% lowered average yield by approximately 10.5% in one season and 14.9% in the other. At 33%, yield declined by roughly 37% to 40%.

The study illustrates an important distinction: the treatment producing the most potatoes per unit of water did not produce the largest crop.

A grower facing a restricted water allocation may decide that a moderate yield reduction is acceptable in return for greater water productivity. That is a legitimate commercial decision, but it should not be interpreted as evidence that potatoes necessarily perform best under substantial deficit irrigation.

A 2024 Chinese experiment published in Frontiers in Sustainable Food Systems compared subsurface drip fertigation with conventional surface drip fertigation in loam soil.

Researchers reported approximately 10% more marketable yield under subsurface drip, accompanied by improved moisture retention at a depth of 20 centimetres. Tuber numbers per plant increased by 18.1%, while average tuber diameter was 6.9 millimetres greater.

The results are encouraging, but they are not a performance guarantee for other regions. The experiment covered one season, location and soil type. The researchers called for longer-term evaluation across different soils and climatic conditions.

The broader lesson from both studies is that water delivery, soil characteristics and nutrient management interact. There is no single irrigation percentage, tape depth or emitter arrangement that can be prescribed for every potato field.

Fertigation may be drip’s most valuable advantage

The ability to apply soluble nutrients through an irrigation system may prove as valuable as any direct reduction in water use.

Potatoes do not take up nutrients at a constant rate throughout the growing season. Nitrogen demand accelerates as canopy development and tuber growth gain momentum. Excessive nitrogen, particularly later in the season, can delay maturity, reduce specific gravity and compromise skin set and storage behaviour.

Drip fertigation allows the seasonal nutrient requirement to be divided into smaller applications. Delivery can be adjusted according to crop development, tissue analysis, soil conditions and expected yield.

This is particularly relevant on sandy soils, where nitrate can move below the active root zone following excessive irrigation or heavy rain. Applying water and nitrogen together in smaller, carefully timed quantities may improve nutrient recovery and reduce leaching risk.

Precision nevertheless cuts both ways. An injection or calculation error can distribute an incorrect nutrient concentration across an entire irrigation block. Incompatible fertilisers may precipitate inside the system, while inadequate flushing can leave deposits that restrict emitters.

Effective fertigation requires reliable injection equipment, backflow prevention, suitable filtration, water-quality testing, pressure management and careful record-keeping. It should strengthen a sound nutrient programme—not replace soil analysis, petiole testing or regular crop observation.

A drier canopy alters the disease environment

Because drip irrigation does not routinely wet the foliage, it can shorten periods of leaf wetness. This may make conditions less favourable for foliar and stem diseases than repeated overhead irrigation.

University of California potato-irrigation guidance estimates that drip systems typically require 10% to 20% less water than sprinklers and may reduce foliar-disease risk. The same guidance warns that drip can complicate field operations, may be difficult to manage on very coarse soils and can contribute to mite problems in dry, dusty canopies.

Drip must not be described as a disease-control system. It changes the crop microclimate and removes one route through which prolonged leaf wetness develops, but it does not prevent inoculum from arriving through wind or rain. A dense canopy can also retain substantial humidity without overhead irrigation.

Common scab presents a different moisture-management challenge. Maintaining sufficient ridge moisture around tuber initiation is an established cultural measure for suppressing the disease in susceptible fields.

Drip can support this strategy, but only if water reaches the complete zone in which young tubers are developing. A narrow wet strip beside the tape will be inadequate if other sections of the ridge become too dry.

Precision is a management discipline

Drip irrigation gives growers finer control over water and nutrients, but it also demands greater attention to detail. Flow, pressure, filtration, soil moisture and crop response must be monitored throughout the season.

Its effectiveness is determined by the complete system: water source, filtration, pump capacity, tape specification, emitter spacing, soil type, placement depth, irrigation scheduling and the people responsible for operating it.

For potatoes, the objective is not simply to apply fewer litres. It is to maintain suitable moisture in the biologically important part of the ridge, particularly during initiation and bulking, without generating waterlogging, nutrient losses or avoidable operational costs.

In Part 2 of this series, Potato News Today will examine how drip irrigation has performed in British commercial potato production, the machinery and management required, and the questions growers should answer before investing.