Next I would like to discuss the mixing of fertilizers. To keep it simple, I'll start with just N-P-K. As I've mentioned before, these numbers are percentages by weight. If you mix two fertilizers, the numbers do not add, but instead average by weight.
Example #1: if you add 1-lb of 10-0-0 with 1-lb of 0-10-0 the result is 2-lbs of 5-5-0.
Example #2: if you add 4-lbs of 10-0-0 with 1-lb of 0-10-0 the result is 5-lbs of 8-2-0.
Here is a small Excel spreadsheet that shows an calculation for example #2:
N-P-K_Mix_1.xls.
In my next post, I'll show how to mix some standard plant nutrients to obtain an N-P-K with ratios 4:4:7.