Many factors involved when considering fertigation system

By Bill Wolfram
T-Systems International
www.vegetablegrowersnews.com
April 2001 27

There are several things to keep in mind when you are considering a fertigation system. Growers have to examine water analysis, irrigation uniformity, source of fertilizer, injection equipment, soil types, filtration, timing, propagation time, plant and soil testing, and safety equipment in order to ensure effective fertigation.

Water analysis
A water analysis is used to determine the suitability of the water for irrigation and the compatibility of it to fertigation. Different contaminants such as calcium and magnesium can bond with phosphorus to form a precipitate and can clog your emitters. Typically, we recommend not using water with phosphorus content. Placing some of your irrigation water in a jar, examine it for cloudiness or settling of particles.

Irrigation uniformity
Irrigation uniformity or distribution uniformity is directly linked to the level dosage of fertilizer. If you have poor uniformity you are putting out more fertilizer and water in one area over another, causing your plants to suffer while you are wasting money. There are many sources of fertilizer.

Injection equipment
There are several types of injection equipment ranging from the volumetric or proportional to the venture types. Brand names include Dos-A-Tron, Chemilizer, Hone On and Mazzei.

Soil types
Soil types play a key role as different types of soil hold the nutrients better than others do. In sandy soils for example, you need to fertigate more frequently. Where as in clay and loam soils, the fertilizer is held in with the soil better and does not leach out as quickly. Over watering will leach out your nutrients. Learn to use either a soil probe or a tensiometer to determine how much water is needed.

Filtration
Certain water sources contain precipitates and particles that can clog your trickle system so all fertilizer should be filtered before it gets to the drip system. It can be injected before your irrigation filters, which is the preferred method, or it can be filtered with a screen filter prior to being injected into the line.

When to fertilize
When to fertigate is a common question and no one has the answer. It depends on your particular program and application. Most frequently growers apply about one-half of their total nitrogen and potassium requirements and their entire phosphorus requirements as prefertilizer. The application depends on the program.

Propagation time
Propagation time is the time it takes water or chemicals to move totally through a line and out the emitters. For example, on a 500 foot run it takes 19.5 minutes form the time the water starts going into the tape till it is out on T-Tape 508-12-450, 12-inch high flow. Rates vary with different tapes.

Plant and soil testing
Plant and soil testing, as well as overall appearances of the crop are tools used to determine plant needs. These include a starting soil test, which you can use to develop fertilization recommendations, and plant tissue and sap tests which tell you what the plant might need as it is growing.

Safety equipment
Depending on your system, certain safety equipment is required by law to prevent contamination of your water source. Check with your local dealer or Extension agent to see what is required.