Alright, numbers I like! Any guess as to the volume of the eye dropper? I'll guess a mL here. This'll be a rough calculation, but I'm interested in ranges that people are using.
16-16-16 fertilizer is 16% (
0.16) N by mass. I can't find percentages (they may be on the back of the container though!) but the fertilizer contains urea, nitrate, and ammonium; we'll calculate by bulk N.
We also don't know the weight of a 1/2 tsp of fertilizer, but we can estimate bulk density to get us a rough number. According to google/amazon the size of a 1.5lb container of this fertilizer comes in a 6.5"x3.5"x3.3 (75.075 in^3) container. Let's convert that to something reasonable: 680g comes in a 1230 cm^3 container. Assuming a full container (which is a bit of a fudge factor, but we're going back-of-the-envelope at the moment!) that gives us a bulk density of 0.553 g/cm^3. This is the same as 0.553g/mL. Now we're getting somewhere!
A 1/2tsp = 2.46mL. Volume used times bulk density (mass over volume) gives us the mass used:
1.36g in this case!
A gallon of water is ~
3785mL. So let's put it all together.
(mass used) X (%N total) / (volume water to dilute) = Concentration of N in solution (g/mL)
(1.36g fert ) X (0.16 ) / (3785mL water) = 5.75e^-5 gN/mL
At 1e^6ug / 1g we can convert that to
57.5ugN/mL
At our assumed added volume of 1mL that is, of course,
57.5ugN added per pitcher.
I'd love to hear what some of the rest of you are doing and compile a working list. And as always, feel free to double check my math -- it is getting late.
If anyone is interested I can calculate out some points of reference like agricultural N addition rates, N content of a few types of plants tissues and soils.
Really what I've learned from this experience is that I've been on vacation too long.