Fertilizer Injector & Rate & Flow

A fertigation injector — a dosing pump, proportional injector or venturi — meters concentrated stock solution into the irrigation line so the water reaching the crop carries nutrients at a target concentration. Setting it correctly is what turns a strong stock tank into the precise dilute feed the crop actually receives.

Injection ratio = target concentration ÷ stock concentration. If you want 200 ppm at the emitter from a stock that is 20,000 ppm, the ratio is 200 ÷ 20,000 = 1:100 — one part stock to 100 parts irrigation water. The stock must be far more concentrated than the target so the ratio stays in the injector's working range.

Injector flow = system flow × injection ratio. With a system flow of 1,000 L/h and a 1:100 ratio, the injector must deliver 1,000 × (1/100) = 10 L/h of stock. The tool returns this directly so you can dial in a dosing pump or pick a venturi sized to that flow at your line pressure.

Target and stock concentration just need to be in the same units — ppm, mg/L, g/L or percent — because the ratio is dimensionless. Mixing units (say target in ppm, stock in percent) without converting is the most common mistake; convert both to one scale first and the ratio comes out right.

The injection ratio equals target ÷ stock, and injectors only operate over a limited ratio range (often around 1:50 to 1:500). If the stock is only a little stronger than the target, the ratio is too high for the injector to deliver, and the stock tank empties almost as fast as the irrigation runs. A concentrated stock keeps the ratio practical.

The required ratio and injector flow are the same regardless of device, but how you set them differs: proportional (water-driven) injectors are set as a ratio directly; electric dosing pumps are set by flow rate; venturis are chosen by their suction flow at your line pressure and flow. Use the ratio for proportional units and the injector flow for pumps.

Measure the actual concentration at an emitter with an EC meter or by timing how much stock is drawn down over a known irrigation volume, and compare to your target. EC is the quickest field check for total salts; verify against the calculated ratio and adjust the setting if the measured strength drifts.

The same ratio and flow maths apply to any stock injected proportionally, including acid for pH or chlorine for line cleaning. For acids, work to a target dose rather than a nutrient ppm and always add acid to water, never the reverse — see the dedicated acid injection tool for safe rates.

The ratio and injector flow are exact arithmetic from your inputs. Real delivery depends on the injector's accuracy, line pressure, stock solubility and temperature, so verify in the field and re-check periodically. Treat the result as the correct setpoint and fine-tune to the measured concentration at the emitter.