I have had the same independent  man for 25& years.. He soil samples, gives fertilizer blends, irrigation dates, Herbicide/insecticide programs, & harvest planning.  In the fields weekly during growing season.

Charges me $8-12 acre on crops he monitors.  It takes him 1-2 years to get the farmer figured out to ajust the "windage", then he works well with the grower. He understands that sometimes a small crop loss is more profitable than the "cure" & works to make you money.