Fertilizers furnish plants with nutrients for growth. Generally, plants take up nutrients dissolved in water. Water solubility, however, cannot be used as the only measure of nutrient availability to plants. Several definitions and terms are important to describe fertilizers. The "grade", for example, describe the N-P205-K20 content in weight percentage. The exact amount of fertilizer required has to be calculated depending on type of fertilizer and area to be fertilized. Mixing of fertilizers makes application easier, however, not all fertilizers can be mixed.