Chapter 18

Fertigation Systems for Vineyards

Calibrating Fertigation Injectors

Fertigation should never be attempted without accurate calibration. The manufacturers’ suggested settings are helpful guides. However, to ensure that the recommended amounts are being applied at the desired concentrations, the injection pump must be calibrated 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

The batch method of fertigation is a system in which the required amount of fertilizer is pre-mixed to the desired concentration (EC or ppm) in tank(s) before being distributed to the vineyard through the irrigation system. The irrigation water is diverted through the batch tank (Figure 18.1). The tank size should be large enough to contain the chemicals required for at least one fertigation operation. The size of the batch tank can vary from as small as 5 gallons to as large as 2,000 gallons. If more than one stock tank is in use, each tank should be clearly labeled as to the fertilizer it contains.

In-Line Injection, Continuous 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: Dilution ratio = diluted volume ÷ stock volume

The diluted volume is the known amount of fertilizer solution after it has passed through the injector, and stock volume is the amount of concentrated fertilizer solution that was used during the test. Begin by operating the injector at a rate normally used to fertilize crops. Place the injector siphon tube in a graduated cylinder, such as a measuring cup or graduated cylinder, containing a measured volume of water. Discharge fertilizer solution from a hose into a large container, such as a 5-gallon bucket, until the graduated cylinder is nearly empty.

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 the EC of the dilute fertilizer solution.

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