A pretty easy way to figure application rate of product for fertilizer is just put desired rate of the nutrient and divide by the percentage of that nutrient in the fert. If the desired rate is 1 lb. of N per thousand sq. ft. then it would go:
So 2.17 lbs of a 46-0-0 would be added per thousand sq. ft. of spray coverage which obviously depends on how many gallons of water go out /1000.