This equation computes the amount of 15:2:8 fertilizer  -- or an equivalent fertilizer with the same concentration requirements -- that you would need to cover a desired area.

Inputs

• ppm - the desired concentration of fertilizer you want to achieve
• cov - the area you wish to cover at the specified concentration
• wt - the product specification of weight of fertilizer that will cover a standard area
• stdArea - the product specification of are covered by the product weight (wt)

Usage

Most commercial websites offering fertilizers specify the coverage rate using two terms:

• a standard container weight for the fertilizer, which is the input wt
• a standard coverage area, which is the input stdArea

Thus the commercial sites will specify, as an example, that a 15:2:8 fertilizer  covers 7500 `ft^2` with 50 lbs of the fertilizer.

^** Note that most commercial sites do not detail the concentration that is assumed for the coverage rate specified.  In our example of a commercially available 15:2:8 fertilizer which was specified with a 50lb per 7500 `ft^2` coverage rate, the assumed concentration is 20 ppm.¹ This concentration assumption is used in this equation to scale the ppm input.

1. ^ Dr. Clayton Rugh, Manager & Technical Director at Xero Flor America LLC