Fertilizer, Soil Amendments

Fertilizers or fertilisers are compounds given to plants with the intention of promoting growth; they are usually applied either via the soil, for uptake by plant roots, or by foliar spraying, for uptake through leaves. Fertilisers can be organic (composed of organic matter, i.e. more...

carbon based), or inorganic (containing simple, inorganic chemicals). They can be naturally-occurring compounds such as peat or mineral deposits, or manufactured through natural processes (such as composting) or chemical processes (such as the Haber process).

Fertilizers typically provide, in varying proportions, the three major plant nutrients (nitrogen, phosphorus, and potassium), the secondary plant nutrients (calcium, sulfur, magnesium), and sometimes trace elements (or micronutrients) with a role in plant nutrition: boron, manganese, iron, zinc, copper and molybdenum.

Inorganic fertilizers

• Examples of naturally-occurring inorganic fertilizers include diatomaceous earth and limestone.
• Examples of manufactured or chemically-synthesized inorganic fertilisers include ammonium nitrate, potassium sulfate, and superphosphate, or triple super phosphate.

Synthesized materials are also called artificial fertilizers, and may be described as straight, where the product predominantly contains the three primary ingredients of nitrogen (N), phosphorous (P) and potassium/potash (K), often described as NPK fertilizers. They are named or labelled according to the content of these three elements, thus a 5-10-5 fertilizer would have 10 percent phosphate in its ingredients. If nitrogen is the main element, they are often described as nitrogen fertilizers.

Alternatively they may be described as compound where there is a mix of nutrients.

Chemist Justus von Leibig (in the 19th century) contributed greatly to understanding the role of inorganic compounds in plant nutrition and devised the concept of Leibig's barrel to illustrate the significance of inadequate concentrations of essential nutrients. At the same time he deemphasized the role of humus. This theory was influential in the great expansion in use of artificial fertilizers in the 20th century.

Nitrogen fertilizer is often synthesized using the Haber-Bosch process, which produces ammonia. This ammonia is applied directly to the soil or used to produce other compounds, notably ammonium nitrate, a dry, concentrated product. It can also be used in the Odda Process to produce compound fertilizers such as 15-15-15. The Haber-Bosch process uses about one percent of the Earth's total energy supply (primarily in the form of natural gas) in order to provide half of the nitrogen needed in agriculture.

Inorganic fertilisers typically do not replace trace mineral elements in the soil which become gradually depleted by crops grown there. This has been linked to studies which have shown a marked fall (up to 75%) in the quantities of such minerals present in fruit and vegetables.

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