Richard

This is a topic for both organic and inorganic gardeners. Fertigation is the injection of liquid or water-soluble nutrients directly into irrigation lines. There are many naturally occuring compounds and plenty of synthetics as well which fit this purpose.

I need to upgrade the size of my current fertigation system and after looking at prices in the $2000 range decided to research how to make my own. Along the way I discovered some interesting facts which I'll share here.

There are two categories of fertilizer injectors: Proportional and Non-proportional.
Proportional: The same concentration of fertilizer is added to the water until the fertilizer solution is exhausted.
Non-proportional: Water is "bled" into a container, and then some of the mixture is forced back out into the water stream. This is problematic because the more water that is bled in, the weaker the concentration in the container becomes. In fact, it gets weak very rapidly (hey math geeks: it decreases geometrically).
Here's what happens when you try to feed 100 trees 25 gallons of water each with a proportional vs. a non-proportional 15 gallon injection tank. Notice that if the trees are watered non-proportionally in batches or in rows, then most of the concentration goes to the first 8 trees.



Here's some common non-proportional injectors/feeders on the market, made by Scotts / Miracle Gro and EZ-FLO. Note that EZ-FLO claims to be nearly non-proportional in the lowest ratio setting, but in reality, few people if anyone find that setting and water pressure useful.



... and for comparison, here's some proportional units made by Champin, Ortho, and Strong Enterprises:

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Lilith

I mix my fertilizer up for my greenhouse plants, 2 gallons at a time and pour it on by hand (or spray it on with a pump up sprayer). That way I am sure of its ratio. But I realize for a large scale commercial operation that's just not possible.

For my beds and outdoor plants I usually spread some granular, and every so often use the Miracle Grow feeder.

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2/2009 5 Points of Life Marathon, 26.2, Gainesville FL--4:00
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10/2009 Marine Corps Marathon, DC, 26.2--457
1/2010 Houston Marathon, 26.2--3:55:09
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island cassie

I always thought that the Miraclegrow sprayers would be impossibly strong at the beginning and uselessly weak at the end, and never used the one that someone thoughtfully gave me for Christmas! Good to hear that I am not alone in this. Of course being female I made up my mind in an instant using intuition!! I needed Richard for the data!!

Cassie

Richard

Here is a brand of proportional injectors that have been on the market for awhile: Dosatron

The fertilizer is drawn up from an unpressurized container of unlimited size -- it could be a trash can with a lid! The prices are also very reasonable, a few hundred dollars instead of a few thousand dollars.

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microfarmer

If you do make your own proportional system, please post the assembly process. I would love to see how these work inside...

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Richard

There are several different engineering approaches. All of them involve either a pressurized tank or a moving part (to prevent backflow into the tank). Some of the designs make use of vortex flow to draw from the tank, while others have a fly-wheel or pump. Dosatron happens to use a pump. Here's a great illustration: Dosatron - How It Works

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Richard

Another manufacturer of proportional injectors is Dosmatic. They have small units that every homeowner would appreciate, medium size injectors for home orchards, and all the way up to large industrial size units.

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