What I do, it just get, lawn food, Scotts Super Green or whatever. It has 28% UAN. Urea and Ammonium. Any stronger and it has to be a liquid. It also has some Iron, which is good, too. But, it is strong and meant to cover square meters of lawn.
Since it is very hard to hit a PPM from the bottom, I just make up some by dissolving a pinch of powder, in a 1/2 liter of RO. I stir that around until I can get 300 ppm. It dissolves slowly in cold water....good.
I decant that and toss the rest of powder crystals. Then I cut that to 150 ppm and add a wetting agent and spray it.
So, how dilute will you make it? 200 ppm is probably good for a soil treatment. But, go easy. I find my rooted clones only need it twice, a week apart. And then, if I have a stain that needs a lot to green up. I will spay again, a couple of time, in the first month.
But it really works and I see results in a few days.