By Lukie Pieterse, Editor/Publisher Potato News Today
For potato businesses, water is no longer only an agronomic input. It is a cost, a quality variable, a source of production risk and, in more regions each year, a condition of market access.
The useful question is therefore changing from “How much did the field yield?” to “How much saleable value did each unit of water create?”
A well-irrigated potato field can look successful long before the crop has been graded, stored or processed. The canopy may be uniform, the yield monitor encouraging and the harvested tonnage impressive. Yet the commercial result can still disappoint if too much of that tonnage falls outside size, shape, dry-matter, skin-finish or fry-colour requirements.
In a water-constrained or energy-expensive production system, the gap between total yield and marketable yield becomes especially costly.
That is why water productivity deserves a place beside tonnes per hectare, storage loss and packout in the potato industry’s core scorecard. It is not a slogan for using the least possible water. It is a discipline for converting water into the largest dependable volume of specification-compliant potatoes, at an acceptable cost and without damaging the resource on which future crops depend.
The industry’s familiar scoreboard is incomplete
Yield per hectare remains indispensable, but it can hide two very different outcomes.
A 50-tonne crop produced with 5,000 cubic metres of irrigation water appears to deliver 10 kilograms per cubic metre. If only 40 tonnes meet the buyer’s specification, however, marketable irrigation-water productivity is 8 kilograms per cubic metre.
The rejected 10 tonnes still consumed water, pumping energy, fertilizer, crop-protection inputs, harvest capacity and storage space.
The denominator matters just as much as the numerator. Some businesses divide yield by irrigation water applied. Others use total water supplied, including effective rainfall. Basin-level work often focuses on water consumed through evapotranspiration. Economic water productivity expresses saleable value or gross margin per cubic metre.
These measures answer different questions, so a benchmark is meaningful only when the business records exactly what is included.
For most growers, the most actionable starting point is simple: record metered irrigation by field and relate it to marketable yield according to the specification that determines payment. The measure can become more sophisticated later. Consistency is more valuable than theoretical perfection in the first season.
Potatoes make timing more important than totals
Potato is particularly unforgiving of moisture extremes. Water stress around tuber initiation and early development can reduce high-grade yield by increasing rough or misshapen tubers. Sustained stress during bulking reduces canopy function, bulking rate and final size.
Excess water is not a safe alternative. Poor aeration, nutrient movement below the active root zone, disease pressure and wet harvest conditions can all damage yield or storability. University of Idaho guidance describes how potato responses to water stress change across development stages.
The practical target is therefore not a season-long average. It is a stable root-zone environment matched to crop stage, soil texture, rooting depth, cultivar and weather.
A field may receive the “correct” seasonal volume and still perform badly because water arrived too late, in applications too large for the soil, or with poor distribution uniformity.
This is also why generic deficit-irrigation claims should be treated cautiously. A 2024 meta-analysis reported that deficit irrigation reduced potato yield by an average of 16.4% across the studies examined, even though water productivity may improve under certain treatments.
The commercial answer depends on where and when the deficit occurs, which quality attributes are rewarded, and what the saved water is worth elsewhere in the business.
Marketable water productivity connects farm decisions with buyer value
A single “marketable yield” definition will not fit every potato chain.
Fresh-pack operations may prioritize skin finish, shape, freedom from greening and a defined size profile. French-fry plants need length, solids and acceptable defect levels. Crisping plants are sensitive to dry matter, sugars and fry colour. Seed businesses value health, physiological condition and target tuber count.
The benchmark should mirror the actual contract.
A processing grower might calculate accepted tonnes per cubic metre and then add a value-based measure that includes quality bonuses and deductions. A fresh grower may separate Class I packout, secondary packout and waste. A seed producer may track saleable seed-size tonnes or tuber numbers per cubic metre.
The objective is not to create one global standard. It is to make the water score follow the commercial outcome.
This approach can overturn assumptions. A slightly lower-yielding irrigation programme may be more profitable if it improves packout, solids or harvest maturity while reducing pumping and drying costs.
Conversely, aggressive water savings may look efficient in kilograms per cubic metre but destroy margin if the size profile or defect levels move outside specification.
The minimum measurement stack
A credible water-productivity programme does not require a fully autonomous irrigation system. It requires four layers of evidence that can be reconciled after harvest.
First, measure water entering the field. Flow meters, pump-runtime records, pressure checks, nozzle audits and simple catch-can tests establish whether the system applied what the schedule assumed.
Distribution uniformity deserves particular attention. A field average can conceal waterlogged and stressed areas within the same irrigation pass.
Second, measure the soil-water profile. Sensors at more than one depth can show whether irrigation is replenishing the active root zone, barely wetting the surface or moving beyond the useful depth.
Sensor locations should represent the management zones that matter, not merely the easiest point to access. Periodic hand checks remain valuable because sensors can be poorly installed, unrepresentative or misread.
Third, estimate crop demand. Local weather data and evapotranspiration calculations provide a forward-looking schedule, while canopy observations and field sampling test whether the crop is behaving as expected.
The widely used FAO crop-coefficient approach calculates crop evapotranspiration by multiplying reference evapotranspiration by a crop coefficient. Those coefficients and growth-stage dates must nevertheless be adjusted to local conditions.
Fourth, close the loop at harvest and intake. Field-by-field grade, size distribution, specific gravity or dry matter, defects, storage loss and buyer deductions must return to the irrigation record.
Without this final layer, the system optimizes water delivery rather than commercial performance.
Remote sensing can expose the gaps that averages miss
Satellite-derived evapotranspiration and biomass data are making water-productivity analysis possible across larger areas and in regions with limited ground instrumentation.
FAO’s WaPOR platform provides open remotely sensed layers for land and water productivity assessment. In Lebanon’s Bekaa Valley, an FAO–World Bank methodology used remote sensing and economic data to compare irrigation water productivity for wheat and potato farms and identify high- and low-performing areas. FAO reports that the method could be adapted to other water-deficient systems.
The value is diagnostic. Maps can reveal consistently underperforming corners, differences between irrigation blocks or a productivity gap that deserves field investigation. They can also support benchmarking where field data are sparse.
But the technology does not know the grower’s contract, grade profile or local disease pressure. FAO explicitly notes that remote sensing complements rather than replaces field observation.
The economics must include the marginal value of water
Water carries a different price in every production system.
The visible cost may be electricity or diesel for pumping. The larger cost may be a restricted abstraction licence, a falling aquifer, competition within an irrigation district, salinity management or the lost opportunity to irrigate another field.
In predominantly rainfed regions, the issue may be investment in supplemental irrigation—and the probability that it protects quality often enough to repay the capital.
The most useful calculation is therefore marginal: what additional saleable value is created by the next unit of water at this crop stage, and what does that unit cost or displace?
Near tuber initiation, the answer may justify strong protection against stress. Late in the crop, the balance may shift toward maturity, skin set, harvest conditions and storage risk. The decision must be cultivar- and market-specific.
This economic lens also discourages equipment-first thinking. A new sensor, variable-rate system or drip installation is valuable only if it changes a decision, reduces damaging variability or improves the marketable return from water.
Technology should be evaluated against recovered margin, not against the volume of data it creates.
A shared metric can improve contracts and collaboration
Growers cannot optimize marketable water productivity alone.
Seed choice, contract specifications, delivery windows, irrigation advice and factory intake rules all shape the result. When buyers reward only gross tonnage, they may unintentionally encourage water use that adds low-value size or increases quality risk.
When specifications change without agronomic discussion, growers carry the water and production consequences.
A better conversation starts with shared field trials and transparent definitions. Grower, agronomist and buyer can agree on the water measure, target quality attributes, sampling method and economic outcome before the season.
Multi-year results are essential because weather and disease pressure can overwhelm a one-season comparison. The resulting evidence can support cultivar placement, irrigation protocols, bonus structures and investment decisions.
A practical first-season plan
Choose a manageable comparison rather than attempting to digitize the entire enterprise.
Select two or three representative fields with reliable intake or packout data. Calibrate the irrigation equipment before emergence, map meaningful soil zones and install sensors at depths that reflect the active root profile. Record rainfall, irrigation, crop stage and events that could affect interpretation.
During bulking, combine the water balance with regular digs for tuber number, size progression and defects.
At harvest, preserve field identity through grading or factory intake. Calculate total yield per cubic metre, marketable yield per cubic metre and saleable value or gross margin per cubic metre.
Then review the poorest-performing zones first. The largest opportunity often lies in reducing variability, rather than pushing the best area harder.
Repeat the comparison across seasons before establishing targets. A useful benchmark should become more local over time: by soil type, cultivar, market, irrigation method and water source.
Cross-regional comparisons can inspire questions, but local evidence should decide practice.
From “more crop” to “more saleable crop with less risk”
FAO’s 2025 assessment places agriculture at more than 70% of global freshwater withdrawals, while competition for reliable water continues to intensify. The report highlights the combined pressure of water scarcity, land degradation and climate change on agricultural production.
Potato professionals do not need to wait for a universal reporting standard to respond. They can begin by connecting metered water to the grade, quality and value data they already collect.
The resulting benchmark is more demanding than tonnes per hectare, but also more useful. It recognizes that water timing affects shape, size, solids, disease, harvest damage and storage performance.
It makes irrigation a supply-chain question rather than a field-only operation. And it turns sustainability from a distant disclosure exercise into a measure of operational resilience.
The next competitive advantage in potatoes may not come from producing the largest crop. It may come from knowing, with field-level evidence, which water created saleable value, which water merely moved through the system—and how to improve that conversion in the next season.
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