Does a 20 percent pressure variation really give 10 percent flow variation?

Only for one kind of emitter. That figure is arithmetic from an emitter exponent of 0.5, the value for a turbulent orifice. A non-compensating emitter with an exponent of 0.8 gives 15.7 percent flow variation for the same pressure swing, and a fully pressure-compensating emitter gives almost none. It is a derived result, not a standards requirement.

How is irrigation uniformity measured?

Through four distinct measures that are often confused. Emission uniformity describes the design, from manufacturer variation and minimum pressure. Distribution uniformity and statistical uniformity describe the installation as built, from measured flows at a minimum of eighteen points per zone. Christiansen's coefficient comes from sprinkler practice and gives only a broad indication for drip.

Are venturi injectors used in Dutch greenhouses?

Dutch sources describe positive-displacement dosing pumps under EC and pH feedback, increasingly with one injector per fertiliser so the recipe can change without remaking a premixed stock. Venturi injection appears in international material aimed at open field, orchards and low-cost tunnels rather than in high-tech glass.

Why should the dosing unit avoid metal fittings?

Because neutralising bicarbonate with acid releases carbon dioxide and leaves the water aggressive to metal. Published Dutch guidance is that the dosing unit and irrigation lines should preferably carry no metal fittings at all, since the corrosion products end up in the emitters.

Irrigation Dosing Units - DutchGreenhouses

Exactness, delivered per dripper

If fertilisation is the recipe, the dosing unit is the kitchen where it is made — the heart of the irrigation room and one of the most important pieces of technology in the whole greenhouse. Its job is to take incoming water and inject the concentrated A and B nutrient stocks and acid into the stream in precisely the right proportions, so that what reaches the crop is mixed to the exact electrical conductivity (EC) and pH the recipe demands. It does this continuously, adjusting on the fly, because the quality of every irrigation depends on getting that mix right.

Crucially, the dosing is not one-size-fits-all across the greenhouse. A large facility is divided into valve sections — different crops, different growth stages, different microclimates — and a good dosing installation delivers the appropriate recipe to each section on each irrigation turn. A young crop just planted and a mature crop in full production sitting under the same roof can each receive their own EC, pH and volume, rather than being forced onto a single compromise setting.

What elevates modern dosing from a mixing machine to a management tool is measurement and logging. Every irrigation turn is recorded — the volume applied, the EC and pH actually achieved, and the drain percentage that comes back — and that data feeds the loop a grower uses to steer the crop. Drain percentage in particular is a vital signal: it tells the grower whether the plants are receiving too much or too little, and lets them tune irrigation frequency and volume to keep the root zone in balance. Without accurate logging, cultivation is guesswork; with it, it becomes a measurable, improvable process.

Reliability matters as much as precision, because the dosing unit sits on the critical path of the entire crop — if it fails or drifts, every plant downstream is affected within hours. DutchGreenhouses® engineers the dosing installation — injectors, measurement, control and redundancy — around the crop, the water source and the recirculation strategy. Get in touch to design the dosing for your greenhouse.

From the knowledge base