NPK fertilizer is a complex fertilizer comprised primarily of the three primary nutrients required for healthy plant growth. The agriculture industry relies heavily on the use of NPK fertilizer to meet global food supply and ensure healthy crops. Nitrogen Nitrogen is an essential nutrient for numerous plant functions and is one of the elemental components of chlorophyll. Nitrogen fuels vegetative growth, particularly the foliage, stems and branches. Plants can deplete the soil of nitrogen, leaching from the soil faster than any other element. If your plants have yellowing leaves or appear stunted with poor growth, the soil may lack nitrogen. By using a soil test kit, you can determine which element may be missing in your soil. Phosphorus A stimulant for root growth, seed and flower formation, phosphorus is most available to plants when the soil pH is between 5.5 and 7. The pH refers to the acid or alkaline level of the soil and can range from 0 to 15 with 7 regarded as neutral. Different from nitrogen, phosphorus tends to remain in the soil; add it only for new growth. Root vegetables, such as carrots, use large amounts of phosphorus, particularly during early growth. Potassium Potassium promotes root and bud growth and ripening of fruit. It enhances disease resistance as well as tolerance to drought, heat and freezing. This element is essential for all plants to thrive, particularly in changing weather conditions. Potassium also has a tendency to remain in the soil but is heavily used by growing vegetables, so should be supplemented as needed, based on a soil test.