Soil & Irrigation · Practical Guide

Fertigation: A Practical Guide to Feeding Crops Through the Irrigation System

Fertigation moves nutrition from a handful of scheduled applications to a continuous, adjustable supply that follows the crop’s demand curve. Done well, it raises nutrient use efficiency, cuts labour and improves uniformity. Done badly, it blocks emitters, burns roots and pushes salts into the wrong part of the profile. The difference is almost entirely procedural.

Why fertigation outperforms broadcast application

A broadcast application puts the season’s nutrients into the soil and hopes the crop finds them. Much of that nitrogen leaches below the root zone after heavy irrigation, phosphorus is fixed by soil chemistry before roots reach it, and the crop’s peak demand rarely coincides with the moment the granules dissolved.

Fertigation replaces that with small, frequent doses delivered exactly where roots are actively taking up water. The result is measurably higher nutrient use efficiency, less loss to the environment, and the ability to change the programme mid-season when a tissue analysis or a weather shift says you should.

What you need before you start

1. A water analysis

This is the non-negotiable first step. The parameters that change your product list are pH, electrical conductivity (EC), bicarbonate, calcium, magnesium, sodium, chloride, sulphate and iron. High bicarbonate water raises pH in the root zone and precipitates calcium carbonate in the lines. High calcium narrows your options for compatible fertilizers. High EC leaves less headroom for adding nutrients before the crop hits salinity stress.

2. Adequate filtration

Screen, disc or media filters sized for your water source, checked and cleaned on a fixed schedule. Fertigation increases the load on filtration, and organic growth inside lines accelerates once nutrients are present.

3. An injection system you can calibrate

Venturi injectors are simple and inexpensive but their rate varies with pressure. Piston or diaphragm dosing pumps hold rate more reliably. Whichever you use, calibrate it, an uncalibrated injector makes every calculation downstream meaningless.

4. Separate stock tanks

At minimum two: one for calcium-containing products, one for sulphates and phosphates. Mixing them produces precipitates that block the system.

The injection cycle

Every fertigation event should follow the same shape. A useful default is to split the irrigation into roughly a quarter clean water, half injection, and a final quarter flushing, then adjust based on your system’s fill and drain times.

1. Irrigate with clean water firstBring soil moisture up and fill the lines. Injecting into dry soil concentrates salts around emitters and risks root damage.
2. Inject the nutrient solutionMaintain a steady rate. Check EC and pH at an emitter at the far end of the block, not at the head, that is where problems appear first.
3. Flush with clean waterLong enough for the last of the solution to clear the furthest lateral. Residual fertilizer left in warm lines feeds algal and bacterial growth and is the main cause of slow emitter clogging.
4. Record what you appliedDate, product, quantity, measured EC and pH. Without records you cannot diagnose a problem three weeks later or repeat a good season.

Managing EC and pH

Two numbers govern day-to-day fertigation. EC measures the total dissolved salt concentration reaching the root zone, too low and the crop is underfed, too high and water uptake is inhibited even in a wet soil. pH in the range of roughly 5.5 to 6.5 keeps most nutrients, particularly phosphorus and the micronutrients, in available form and helps prevent carbonate scaling inside the lines.

On the alkaline, bicarbonate-rich waters common across Egypt and the Gulf, acid injection is often necessary to hold that range. Acid handling requires proper equipment, dilution discipline and trained staff, always add acid to water, never the reverse, and never mix concentrated acid directly with fertilizer stock.

Matching the programme to the growth stage

The core advantage of fertigation is that the ratio can change every week. A broad pattern for most fruiting vegetables:

• Establishment: phosphorus-weighted, moderate nitrogen, low total concentration while the root system is small.
• Vegetative growth: nitrogen-weighted to build canopy, with calcium maintained to support cell wall strength.
• Flowering and fruit set: balanced, with boron and calcium attended to closely, most fruit quality disorders originate here.
• Fruit filling and maturity: potassium-weighted, nitrogen reduced to avoid delayed maturity and soft fruit.

The right grades for each phase are drawn from the water-soluble range described on our crop nutrition page. If you are still deciding between soluble and granular products, the comparison in water-soluble vs granular fertilizers sets out the trade-offs.

Salinity: the risk that builds slowly

Under drip irrigation, salts accumulate at the edge of the wetted bulb, the point where water stops moving outward and evaporates. In arid regions with saline irrigation water, that accumulation compounds season after season and is invisible until roots reach it. Two habits control it: maintain a deliberate leaching fraction so some water moves past the root zone, and use a heavier leaching irrigation between cycles. Monitoring soil EC at two depths gives you warning long before the crop shows symptoms.

Frequently asked questions

Related reading: NPK fertilizers explained · Digital farming · Crop nutrition