Watching plant growth, testing the soil, and analyzing the plant tissue are ways to assess nutrient needs. The analysis is always printed on the fertilizer label. P2Os, and 12 pounds of K2O. Conversion equations for the amounts of phosphorus and potassium are given for quantities of P2Os and K2O and are shown in Table 2. Fertilizers may be divided into two broad categories, natural and synthetic. Natural fertilizers generally originate from unprocessed organism sources such as plants or animals.
Synthetic fertilizers are man-made or processed.
Most nutrients from living or once-living organisms are not readily available for plant growth because they are bound in organic molecules such as proteins and amino acids and in structures such as cell walls. These nutrients are released only by microorganisms decomposing the organic matter. Slow-release fertilizers may be synthetic or natural. Because nutrients are released over an extended period of time, slow-release fertilizers do not have to be applied as frequently as other fertilizer types. Also, higher amounts of slow-release fertilizer can be added at each application without risking injury to plant roots.