Fertilizer application is only effective if you ensure uniform coverage. This 5-page document discusses the calibration and use of fertilizer spreaders for successful application. Written by T.W. Shaddox, J.B. Unruh, and L.E. Trenholm and published by the UF/IFAS Environmental Horticulture Department, November 2017.
http://edis.ifas.ufl.edu/lh024