Chemical fertilizers are made up of the nutrients required for plants to germinate, grow, flower and disperse seed. Plants need a balance of macronutrients and micronutrients, water and light to complete their life cycles. Chemical fertilizers are used to enhance the immediate environment of the plant, usually the soil in which the plant has rooted. The roots then access the nutrients through the enriched soil.
The agricultural practice of fertilizing soil with chemical fertilizers has its roots in the 17th century. German scientist Johann Glauber made up a mixture of saltpeter, lime, phosphoric acid, nitrogen and potash for agricultural use, basing his concoction on earlier discoveries of plants' needs for specific chemical nutrients. In the 18th century, Sir John Lawes patented a formula that essentially became the blueprint for synthetically produced fertilizers.
A packaged chemical fertilizer displays three numbers on the label. These three numbers represent the quantitative ratio of the three macronutrients: N-P-K: nitrogen (N), phosphoros (P) and potassium (K). The fertilizers also include a balance of micronutrients such as calcium, copper, zinc, iron and magnesium. These are referred to as trace elements, and are equally important to plant growth.
Chemical fertilizers are synthetic, unlike organic fertilizers such as compost or green manures. Organic material must be broken down and fully decomposed before nutrients are available for root uptake. Because they are synthesized, the nutrients in chemical fertilizers are readily available to plant roots when the fertilizer is applied to the soil. It is this "quick-acting" feature that makes chemical fertilizers attractive to agribusinesses.
That nutrients are immediately available makes for more rapid growth of crops and plants. Packaged fertilizers also provide choices for the consumer. Different ratios of N-P-K allow consumers to select a formula suited to their gardens' particular needs. For example, gardenias have different nutrient needs than sweet peppers, and consumers are able to choose an appropriate and balanced formula for the type of plants they grow.
Unlike organic fertilizers, packaged chemical fertilizers contain fillers that do not enhance the soil or contribute to long-term health of the soil. Soil amended only with chemical fertilizers designed only for root uptake is more susceptible to nutrient depletion, or sterilization, than those consistently amended with organic materials.