Plant nutrients are available throught root absorption of ions from soil solution. Molecules in solution also can be absorbed by roots in some cases. Thus, a fertilizer must first be dissolved to be used by plants. Fertilizers are categorized as organic or inorganic. Inorganic fertilizers are generally composed of simple, mostly water-soluble nutrient salts in granular, slow release or liquid formulations. A fertilizer qualifies as naturally organic if erived from plant or animal materials or naturally occurring rocks and minerals containing one or more mineral elements that are essential for plant growth.
The relative content of chemical elements nitrogen (N), phosphorus (P), and potassium (K) commonly used in fertilizers is labeled using NPK rating and any additional chemical labeling follows after that. The N value is the percentage of elemental nitrogen by weight in the fertilizer. The values for P and K represent an expression of these elements as oxides in the form of P2O5 and K2O. This usage derives from the traditional practices of reporting elements as oxides.
Materials may be used alone or blended with other fertilizers to form a multiple-nutrient fertilizer. Generally there is no measurable difference in crop response to multiple-nutrient or single-nutrient fertilizers, as long as they supply the same amount of soluble nutrients. The advantage of multiple-nutrient fertilizers over single-nutrient fertilizers is that only on fertilizer would be needed to supply several elements, rather than having to purchase several fertilizers. The following tables are quick reference quides to various fertilizer materials that could be used to address soil nutrient defficiencies. The actual nutrient content may vary from this list depending on the manufacturer and other matierals blended with the product. Most values are for the fertilizer-grade product and not the pure chemical. The chemical formulas are the primary active compound.
Also included is the fertilizer liming and soild acidifying effect. Pure calcium carbonate (CaCO3) is considered as the most commonly used liming material (lime) and is assigned a 100% neutralizing effect index also known as calcium carbonate equivalency (CCE). The effectiveness of a liming matieral is based on the CCE scale where if greater than 100, the material is considered capable of neutralizing more acidity on a weight basis than pure CaCO3.
At the end of the tables there is an explanation with examples on how to calculate the amount of fertilizer to apply to meet agronomic nutrient requirements.
Please open the PDF version of this fact sheet to view tables and formulas.