Chapter 20

Fertigation in Greenhouse Production

Calibrating Fertigation Injectors

Fertigation should never be attempted without accurate calibration. Manufacturers’ suggested settings are helpful guides. However, to ensure that recommended amounts are being applied at the desired concentrations, calibrate the injection pump on-site. The objective of calibrating the injection pump is to adjust the pump injection rate to the desired injection rate. The pump injection rate is determined by measuring the volume of solution pumped through the injection pump (injected volume) during a specific duration of time (usually 60 to 120 seconds).

Input/Output Method

One way to determine if an injector is delivering at the correct injector ratio is to directly measure the fertilizer concentrate input volume and dilute fertilizer output volume. The ratio of the input volume to the output volume should equal the injector ratio set on the injector. Determine the injection ratio using the following formula:

Electrical Conductivity Method

Electrical conductivity (EC) can be used to monitor an injector. For a given water supply and proportioner-mixed irrigation-fertilizer solution, there is an EC reading. The fertilizer is made of salts and therefore will have its own electrical conductivity when properly prepared. Mix carefully measured irrigation water and stock solution in the correct ratio (in a small batch) and check its EC several times. Record the average of these readings. Use the average reading as a guide when you test the irrigation water in the future. Some injectors come with an optional electrical conductivity meter for installation in the line after the injector. This makes it easy to determine whether the injector is functioning properly. Maintenance of the probes on these meters is essential to obtain correct readings. The following steps can be used to determine to determine the EC of the dilute fertilizer solution.

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