In order, the three numbers represent the percent nitrogen (N), percent phosphate (P2O5), and percent potash (K2O) contained in the bag. This formula is a national standard for fertilizer labeling. For example, a bag of 15-15-15 contains 15 percent nitrogen, 15 percent phosphate, and 15 percent potash. Every 100 pounds of this fertilizer contains 45 pounds of plant nutrients and 55 pounds of filler.
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