Electrical conductivity — EC — has become the default parameter for managing nutrient dosing in commercial horticulture. Growers target an EC setpoint, their controller doses fertiliser until EC reaches that number, and they call it done. The problem is that EC does not tell you how much nutrient a plant received. It tells you how many ions are dissolved in the water. These are not the same thing, and treating them as equivalent leads to crops that are simultaneously over- and under-fertilised in ways that the EC reading cannot detect.
What EC Actually Measures
EC is a measure of how well a solution conducts electricity, which increases with ion concentration. Every dissolved salt — whether calcium nitrate, potassium sulphate, magnesium sulphate, or sodium chloride — contributes to EC. The reading does not distinguish between plant-available nitrogen and sodium that will damage roots. It does not differentiate between potassium that drives fruit quality and calcium that prevents blossom-end rot. It registers all dissolved ions equally, without any weighting for agricultural value.
This becomes a problem at the source. The water that enters your irrigation system already has an EC value before any fertiliser is added. Groundwater in Malaysia and Southeast Asia can range from 0.1 mS/cm to over 1.0 mS/cm depending on mineral content, proximity to coastal areas, and seasonal variation. If your target fertigation EC is 2.0 mS/cm and your source water is 0.1 mS/cm, you need to add 1.9 mS/cm worth of fertiliser. If your source water is 0.8 mS/cm on a different day or at a different borehole depth, you only need to add 1.2 mS/cm. An EC-based controller doses to the same endpoint regardless — but the amount of fertiliser nutrients it adds in each case is completely different.
The Fertiliser Composition Problem
Even if source water EC were stable, EC does not map consistently to nutrient content across different fertiliser formulations. A solution at 2.0 mS/cm made with calcium nitrate has a different NPK composition than a solution at 2.0 mS/cm made with a balanced horticultural fertiliser blend. Switching fertiliser brands or formulations — even to products claiming equivalent analysis — changes the ion-to-EC relationship. The EC target that produced healthy tomatoes with one fertiliser will produce deficiency or toxicity symptoms with another, even if the EC reading is identical.
This is why professional growers in the Netherlands and Israel — where precision horticulture is most developed — use EC as a confirmation tool rather than a control parameter. They dose by amount first: calculate the kilograms of nutrient per plant per day required at each growth stage, translate that to millilitres of concentrate per litre of irrigation water, dose that fixed ratio, and then measure EC as a sanity check to confirm the dilution is roughly correct. If EC diverges significantly from expectation, they investigate the source water or fertiliser batch — not adjust the dosing ratio to chase an EC target.
Amount-Oriented Fertigation: mg Per Day Per Plant
The correct approach to fertigation starts from plant physiology, not sensor readings. A commercial tomato plant in vegetative growth requires roughly 150–250 mg of nitrogen per day, 30–50 mg of phosphorus, and 200–350 mg of potassium, depending on the growth stage, light intensity, and temperature. These quantities can be determined from published crop nutrition tables or from leaf tissue analysis. They are then translated into a target daily nutrient delivery per plant based on the number of irrigation events and the water volume per event.
Once the target is expressed as a concentration in the irrigation water — for example, 150 ppm nitrogen — the grower calculates what ratio of fertiliser concentrate to water delivers that concentration. This ratio is fixed. It does not change with flow rate, does not change with time of day, and does not change with source water EC — that variable is handled by the initial water quality assessment and the fertiliser formulation choice, not by dynamic dosing adjustment.
The result is that every litre of irrigation water the plant receives contains the same nutrient concentration, every time. EC is measured at the end of the fertiliser solution to confirm the ratio is correct, and measured at the root zone to assess uptake and salt accumulation. It is a diagnostic tool, not a control input.
Why Batch Automated Systems Default to EC-Oriented Dosing
Automated fertigation controllers — including common batch preparation systems used across Malaysia and the region — typically work by preparing a nutrient solution in a mixing tank, measuring its EC, and dosing fertiliser concentrate until the EC target is reached. This is EC-oriented fertigation: the control loop closes on EC. These systems are simple to operate and require minimal crop nutrition knowledge from the end user, which is why they are commercially popular.
But EC-oriented systems cannot compensate for source water EC variation without a separate conductivity probe on the source water and additional logic to calculate the required additive EC. Most batch systems do not have this. They assume source water EC is constant, which it frequently is not. When source water EC increases — during dry season when the borehole draws more mineralised water, or when rain infiltrates and dilutes — the actual nutrient delivery per litre diverges from the target, even though the batch EC reading looks correct.
How the Dosatron Enables Amount-Oriented Fertigation
The Dosatron is a water-powered proportional dosing device: it draws a mechanically fixed ratio of fertiliser concentrate into the water stream as water flows through it, regardless of flow rate or pressure variation. A Dosatron set to 1:100 delivers exactly 10 ml of concentrate per litre of water — whether that litre passes through in 10 seconds or 30 seconds, at 1 bar or 3 bar, in a 20 mm line or a 32 mm line. The ratio is fixed by the mechanical piston stroke, not by any electronic control loop.
This makes the Dosatron inherently amount-oriented. The grower prepares a fertiliser concentrate — for example, 100x concentrated nutrient solution — sets the Dosatron to 1:100, and every litre of irrigation water receives 10 ml of concentrate. The nutrient delivery per litre is determined entirely by the concentrate formulation and the dilution ratio, both of which are under the grower’s control. Source water EC variation changes the background ion level, but it does not change the amount of fertiliser delivered per litre.
EC measurement is still useful in a Dosatron system — measuring the diluted solution confirms the Dosatron is drawing correctly, and periodic root zone EC monitoring alerts to salt accumulation that requires a flush. But EC is not in the control loop. The Dosatron cannot be fooled into underdosing because the source water happens to be more conductive today. The ratio is fixed.
For growers who want to also operate in EC-oriented mode — for crops where EC tolerance is the primary constraint rather than absolute nutrient amount, such as strawberries or lettuce at harvest — the Dosatron can be used in combination with an EC meter and a manual or automated adjustment to the concentrate strength, while the proportional dosing remains stable. This hybrid approach is flexible in a way that pure EC-controlled batch systems are not.
To discuss Dosatron sizing and concentrate preparation for your crop and irrigation system, contact Autoflo at info@autoflotechnology.com.