Nutrient concentrations for lettuce hydroponic culture. Download Scientific Diagram Understanding NPK: The Three Key Nutrients in Fertilizers When you look at a fertilizer label, you'll often see three numbers. These numbers stand for nitrogen (N), phosphorus (P), and potassium (K). Each Bulletin E 3507 Introduction to Fertilizer Planning for Vegetables Developing and Educating Managers and New Decision makers (DEMaND) Lettuce Fertilizer 8 15 36 Water Soluble Leafy Green Formula 1 Pound by Greenway Biotech, Inc. Lawn Food: 16 4 8 Complete Balanced NPK (32 ounce)