Why the Difference in NPK Numbers on Chemical vs. Organic Fertilizer?
It is easy to become confused when the NPK numbers on a bag of organic fertilizer are smaller than on a bag of chemical fertilizer, when the organic product costs the same or more than the chemical product. To understand the difference, it is important to understand that plants use only as much food as they need for healthy growth. For the nutrients in chemical fertilizer to be available to plants, they must be soluble in water. To be soluble in water, they must be in the form of salt. The problem with salt (chemical) fertilizers is that once dissolved in water, they are subject to evaporation, gasification and runoff, resulting in a significant percentage of their nutrients ending up in underground water tables, streams, lakes and oceans. The NPK numbers on chemical fertilizers are higher to offset the losses to runoff, evaporation and gasification; the NPK on organic fertilizers reflect the actual nutrient content of the ingredients.
