The three numbers separated by hyphens on a fertilizer bag indicate the percentage of nitrogen, phosphate, and potash, respectively, that is available to the plants. The remaining materials in the bag are typically micronutrients and filler material, according to The Fertilizer Institute. Nitrogen Nitrogen comes from the air, which contains about 78 percent nitrogen, but few plants can make direct use of nitrogen in the air. To make it available to plants, it is converted into nitrogen fertilizer. This is done by capturing nitrogen from the air and combining it with hydrogen from natural gas under heat and pressure to […]