I think it is going to depend a lot on what your soil is. Here my soil is a silt loam with about 20% clay. It is a little on the alkaline side. There seems to be plenty of phosphorus, and potassium so the addition of some nitrogen helps out.
I think the clay is where a lot of the trace minerals come from and if you have a sandy soil, you may not have this benefit. Perhaps a soil test would be in order?
I kinda hate suggesting a soil test, because I have never done one on my soil. This is an agricultural area and the soils have been tested many times. Once the fertilization practices have been established for the area, it seems pointless to do another test. Addition of lots of organic matter and some nitrogen works here.
Perhaps it would be wise to give some credence to what the farmer said?
Gardening at 5000 feet elevation, zone 4/5 Northern Utah, Frost free from May 25 to September 8 +/-