Sustainable water use has become one of the biggest challenges in modern strawberry cultivation — and the tabletop systems used across Northern Europe are one of the toughest places to fix it. In 2023, Proefcentrum Hoogstraten (PCH) ran a full-season trial with Sigrow Soil Mini substrate sensors to find out whether sensor-driven irrigation could reduce drain water on a Mini-Air tabletop system with free drainage.
The results were striking. By using continuous substrate moisture and EC data to steer irrigation in the second half of the season, PCH cut overall water use by 19.5% (from 520 to 419 L/m²) and reduced drain water by 38% (from 189 to 118 L/m²) — all without any loss in yield, fruit size, firmness, Brix, or shelf life. Both trial sections produced nearly 2 kg per plant, or roughly 10 kg/m², with 75% of fruit sorted as large. For growers running tabletop strawberries on free-draining tables, the conclusion is clear: substrate sensors aren't just diagnostic tools — they're a practical lever for cutting water waste while protecting yield.
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The challenge: Free-draining tabletop strawberries are a water blind spot
Over the past twenty years, Belgian and Dutch strawberry growers have made serious progress on sustainable water use. Most production greenhouses now recirculate drain water and capture rainwater on-site — often more than 3,000 m³ per hectare — effectively closing the loop on indoor production cycles.
However, one system has stayed stubbornly open: outdoor or covered tabletop cultivation with free drainage. These are the raised-table strawberry systems growers use from April through September, with grass underneath the tables and no drain recovery. Any water that exits the pots soaks away into the soil below — it's simply lost. The question PCH wanted to answer was straightforward: can we safely reduce drain on these systems without hurting the crop, and can substrate sensors tell us when it's actually safe to hold back water?
Why the traditional approach leaves water on the table
In standard strawberry fertigation, growers dose nutrients at low EC (typically 1.1–1.5 mS/cm) with every drip cycle, then steer the volume of water and the chosen drip EC using two numbers read at the drain: the drain percentage and the drain EC. Typically, target drain percentages range from 15% on dull days up to 40% on bright, sunny days, while target drain EC sits around 1.1–1.3 mS/cm for everbearers and around 1.5 mS/cm for June-bearers. In practice, growers adjust the number and length of drip cycles, often using light-integral triggers like "give 100 ml per dripper for every 120 J/cm² of accumulated light."
It works — but it's indirect. Drain percentage and drain EC tell you what already happened inside the substrate several hours earlier, meaning you're steering by a rear-view mirror. Furthermore, on free-draining tables, any drain percentage above zero is water you'll never see again.
Goals & objectives
PCH designed the 2023 trial to answer a specific set of questions: whether substrate sensors could give growers enough confidence to safely reduce drain water on tabletop systems; what moisture and EC thresholds represent safe limits before the crop suffers; whether sensor-driven irrigation could maintain or improve fruit yield, size, and quality; and whether the approach could work with an everbearing variety like Karima, which is more sensitive to irrigation swings than June-bearers.
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The Sigrow solution
To answer those questions, PCH purchased six Sigrow Soil Mini substrate sensors to monitor the trial. The Soil Mini targets organic substrates and measures substrate moisture content (%), substrate EC (mS/cm), substrate temperature, ambient light, and vapor pressure deficit (VPD). For this trial, moisture and EC were the two parameters that mattered most, while the others were tracked in the background without direct action being taken on them.
The trial ran on a Mini-Air tabletop system, planted with the everbearing variety Karima on 29 March 2023. PCH divided the six sensors evenly across two sections: a control section irrigated using the standard drain-steered strategy, and a test section irrigated from a separate, dedicated fertigation unit steered directly from sensor data. Because the trial used low Meerle trays, each section placed one sensor in a root ball in the corner of the tray, one in a root ball in the middle, and one in the free substrate between root balls — giving PCH a full picture of how moisture and EC moved through different zones.
Phase 1: Learning to read the data (April – mid-July)
For the first roughly 3.5 months of the season, PCH deliberately irrigated the test section the same way as the control. The goal wasn't to save water yet — it was to learn how the sensor values behaved under a known, traditional irrigation strategy. This phase proved essential for two reasons. First, it built a clear baseline of what "normal" substrate moisture and EC looked like across the root balls and the free substrate at different stages of the crop. Second, it caught a real operational problem: on 28 June, drain-EC measurements revealed that the dedicated unit was dripping at a very high EC due to an unexplained spike in the rainwater tank. The team drained and refilled the tank, but the short EC peak left a visible fingerprint in the substrate data for weeks afterward — a contamination event that would likely have gone unnoticed without continuous substrate monitoring.
From that experience, PCH also drew an important early conclusion: substrate EC is less reliable than drain EC as a day-to-day steering signal. Substrate EC rose over time, especially in the root balls, while drain EC remained within the target band — two numbers telling clearly different stories.
Phase 2: Sensor-driven irrigation (mid-July – end of season)
From mid-July onward, the test section switched to sensor-driven irrigation. Based on what the first phase had revealed, PCH established clear substrate moisture thresholds: a minimum of 40% moisture in the root balls where active root uptake happens, and a minimum of 30% in the free substrate between root balls, which could be allowed to dry back further given the lower root mass there. Drain EC was held between 1.1 and 1.3 mS/cm — the standard target range for Karima everbearers — while substrate EC was allowed to climb freely as long as drain EC stayed in range.
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The sensors recorded continuously, though PCH did not automate the dedicated fertigation unit. Instead, staff checked the substrate moisture data several times a week and made manual irrigation decisions: holding back water when moisture was above target, adding a drip cycle when it approached the minimum, or increasing water if drain EC began rising sharply. As a rule, PCH kept drip cycles to the minimum the crop actually needed — not the maximum the system allowed.
Data insights & analysis
The continuous sensor data made several things visible that drain-only monitoring had always hidden, and four findings stood out in particular. First, even with significantly fewer drip cycles than the control, substrate moisture in the root balls stayed comfortably above the 40% target for most of the second half of the season — the crop had reserves in the substrate that drain-steered irrigation had been pushing through unnecessarily. Second, by late July the test section was running at drain percentages well under 5%, far below the traditional 15–40% targets, while drain EC stayed inside the target window. Third, substrate EC climbed steadily through the season, reaching 8–9 mS/cm in September in the corner and middle root balls, while drain EC stayed between 1.3 and 1.8 mS/cm — reinforcing the Phase 1 finding that substrate EC can drift high without drain EC showing it. Fourth, because moisture was visible in real time, irrigation decisions stopped being calendar-driven and became response-driven, meaning fewer cycles on most days, but more on a few hot days — precise either way.
Actions taken
Based on the continuous sensor data, the PCH team shifted the test section from calendar-based drip scheduling to moisture-threshold–based scheduling starting mid-July. They reduced the number of daily drip cycles wherever root-ball moisture stayed above 40%, added cycles proactively when drain EC started climbing, detected and fixed the 28 June rainwater tank contamination before it caused lasting damage, and built a clear set of substrate moisture targets for Karima on tabletop Mini-Air systems that can be reused in future trials and commercial advice.
Results & impact
Over the full season, the numbers tell a clean story. The control section used 520 L/m² of water, while the sensor-driven section used 419 L/m² — a saving of 19.5%. On drain water, the control produced 189 L/m² of drain while the sensor-driven section produced only 118 L/m², a reduction of 38%. Crucially, this reduction came even though PCH only applied sensor-driven irrigation for the second half of the season; had the team run the approach from day one, the savings would almost certainly have been larger.
On yield and fruit quality, the results were equally clear: both sections produced approximately 2 kg per plant or 10 kg/m², with 75% of fruit grading as large in both cases. There were no measurable differences in firmness, visual quality, Brix, or shelf life. In other words, the crop simply didn't notice — it produced the same weight, the same size distribution, and the same quality on 19.5% less water and 38% less drain.
Source: SIGrow
