Help with fertigation/fertilizer injectors

[spujr]

Hi, I'm modifying my setup to get irrigated with the main water line. I was wondering if anyone had advice about injectors for fertilization.

I did end up finding and buying a used dosatron d25re2 injection system based on what I read on this forum. (Haven't installed it yet)

There's a lot of different fert injection systems on the market and prices range from ~$80-$1000. I know the prices is largely dependent on volume but curious within the same volume sizes is it worth paying more for an injection system?

My water out of the tap is quite low in TDS (~40), and the pH is around 7.5 (sometimes higher). I'm wondering if I need two injection systems to control pH and/or different fertilizers? If anyone has tips about rates and how to set up the concentration tank I would appreciate the advice!

 

[Ray]

With that low of a TDS, the pH is irrelevant and will likely go down with fertilizer addition anyway; don't worry about it.

That model can be set for 0.2%-2% injection. The middle of the range is best in terms of accuracy and mechanical reliability, so I'd recommend setting it at 0.78% (1 ounce/gallon) or 1% (1.28 oz/gal).

When mixing the concentrate, the first require 128x the amount of fertilizer you want to apply per gallon, and the second needs 100x.

For feeding at every watering, I found 25 ppm N to be a good figure - I watered 3-4x per week. Using MSURO as an example, a 25 ppm N solution requires about 0.75 g/gallon, so a gallon of concentrate would require 0.75x128=96 g or 0.75x 100=75 g, respectively, per gallon of concentrate.

If you want to estimate your fertilizer measurement in teaspoons, 25 ppm N requires 0.15 tsp/gal, so those concentrate mix numbers would be 19.2 and 15 teaspoons/gallon, respectively, then just multiply that by the volume of the concentrate tank. A 5-gallon bucket with lid works. Run the feed line through a hole in the lid, but keep it closed to slow evaporation.

19.2 x 5 = 96 teaspoons (2 cups)

 

[kman]

I've used Dosatron D14 series and D45RE15 injectors for decades. They are rugged, accurate and easy to service. About 12 years ago when we were building a new greenhouse I experimented with other manufacturers. All of those ended up at the dump. They are well worth the investment

 

[spujr]

Thank you both for sharing your experience, this is very helpful!