Your county Extension office should have a certification class this winter.  There used to be an online version but my experience is its just easier to go to the in person class.

I have an agri inject 110 as well and like it.  It is a bit heavy/awkward to be moving in between pivots but I do it.  I'm getting a mister valve for each pivot this year, it never would fail I would need to take it out while I was irrigating.  

Another think I would like to do is have a tank at each well.  I started out just feeding off a tender trailer but set up a vertical tank at one well this year.  The tender trailers didn't have accurate gallon markings so was really guessing what I was putting on.  After using the vertical tank this year I found I can trust the setting on the 110 pump and it was within a few gallons of the actual usage.