Fertilizers are soil amendments applied to promote plant growth.

They are usually applied directly onto the soil, but can also be applied onto leaves (foliar feeding). The main nutrients added in fertilizer are nitrogen, phosphorus, and potassium but other nutrients are added in smaller amounts. Fertilizers can be either organic (e.g. manure) or inorganic (mined or synthesized chemically). Organic fertilizers and some mined inorganic fertilizers have been used for centuries whereas chemically-synthesized inorganic fertilizers were only developed on an industrial scale in the 20th century. Increased understanding and use of fertilizers was an important part of both the pre-industrial British Agricultural Revolution and the industrial green revolution of the 20th century.

Contents 1 Chemical content 1.1 Macronutrients and micronutrients 1.2 Macronutrient fertilizers 1.2.1 Reporting of N-P-K 1.2.2 'Mass fraction' conversion to elemental values 2 History 3 Inorganic fertilizers (synthetic fertilizer) 3.1 Application 3.2 Over-fertilization 3.3 Trace mineral depletion 3.4 Energy consumption 3.5 Long-Term Sustainability 4 Organic fertilizers 4.1 Comparison with inorganic fertilizer 4.2 Sources 4.2.1 Animal 4.2.2 Plant 4.2.3 Mineral 5 Environmental effects of fertilizer use 5.1 Water 5.1.1 Eutrophication 5.1.2 Blue Baby Syndrome 5.2 Soil 5.2.1 Acidification 5.2.2 Toxic persistent organic compounds 5.2.3 Heavy metal accumulation 5.3 Atmosphere 5.4 Increased pest problems 6 See also 7 References 8 External links

[edit] Chemical content

Fertilizers typically provide, in varying proportions, the three major plant nutrients: nitrogen, phosphorus, and potassium, known shorthand as N-P-K). They may also provide secondary plant nutrients such as calcium, sulfur, magnesium. Micronutrients may be provided: boron, chlorine, manganese, iron, zinc, copper, molybdenum and selenium.

[edit] Macronutrients and micronutrients

Fertilizers can be classified by their macronutrients and micronutrients content (concentrations by dry matter). There are six macronutrients: nitrogen, phosphorus, and potassium, often termed "primary macronutrients" because their availability is usually managed with NPK fertilizers, and the "secondary macronutrients" — calcium, magnesium, and sulfur — which are required in roughly similar quantities but whose availability is often managed as part of liming and manuring practices rather than fertilizers^{[citation needed]}.

The macronutrients are consumed in larger quantities and normally present as a whole number or tenths of percentages in plant tissues (on a dry matter weight basis)^{[citation needed]}. There are many micronutrients, required in concentrations ranging from 5 to 100 parts per million (ppm) by mass^{[citation needed]}. Plant micronutrients include iron (Fe), manganese (Mn), boron (B), copper (Cu), molybdenum (Mo), nickel (Ni), chlorine (Cl), and zinc (Zn).

[edit] Macronutrient fertilizers

Synthesized materials are also called artificial, and may be described as straight, where the product predominantly contains the three primary ingredients of nitrogen (N), phosphorus (P), and potassium (K), (known as N-P-K fertilizers or compound fertilizers when elements are mixed intentionally).

[edit] Reporting of N-P-K

Such fertilizers are named according to the content of these three elements. For example, if nitrogen is the main element, the fertilizer is often described as a nitrogen fertilizer.

Regardless of the name, however, they are labeled according to the relative amounts of each of these three elements, by weight (i.e, mass fraction). The percent of nitrogen is reported directly. However, phosphorus is reported as the mass fraction of phosphorus pentoxide (P₂O₅), the anhydride of phosphoric acid, and potassium is reported as the mass fraction of potassium oxide (K₂O), which is the anhydride of potassium hydroxide.^[1]

Fertilizer composition is expressed in this fashion for historical reasons in the way it was analyzed (conversion to ash for P and K mass fractions); this practice dates back to Justus von Liebig.

[edit] 'Mass fraction' conversion to elemental values

Since the N-P-K reporting described does not give the actual fraction of the respective elements, (some packaging also reports elemental mass fractions). The UK fertilizer-labeling regulations ^[2] allow for additionally reporting elemental mass fractions of phosphorous and potassium, rather than phosphoric acid and potassium hydroxide, (but must be listed in parentheses after standardized values). The regulations specify the factors for converting from the P₂O₅ and K₂O values to the respective P and K elemental values as follows:

In phosphorous pentoxide, phosphorous constitutes 43.6% of the total mass^{[citation needed]}. Thus, the official UK mass fraction (percentage) of elemental phosphorus is 43.6%.

Likewise, the mass fraction (percentage) of elemental potassium is 83%. [K] = 0.83 x [K₂O]

Thus an 18−51−20 fertilizer contains, by weight, 18% elemental nitrogen (N) , 22% elemental phosphorus (P), and 16% elemental potassium (K).

(Note: The remaining 11% [100 - (18 + 51 + 20)] is known as ballast or filler^[1] and may or may not be valuable to the plants, depending on what is used as filler.)

[edit] History

While manure, cinder and ironmaking slag have been used to improve crops for centuries, the use of fertilizers is one of the great innovations of the Agricultural Revolution of the 19th Century.

[edit] Inorganic fertilizers (synthetic fertilizer)

Fertilizers are broadly divided into organic fertilizers (composed of enriched organic matter—plant or animal), or inorganic fertilizers (composed of synthetic chemicals and/or minerals). Inorganic fertilizer is often synthesized using the Haber-Bosch process, which produces ammonia. This ammonia is used as a feedstock for other nitrogen fertilizers (e.g. anhydrous ammonium nitrate and urea). These concentrated products may be diluted with water to form a concentrated liquid fertilizer, UAN. Ammonia can also be used in the Odda Process in combination with rock phosphate and potassium fertilizer to produce compound fertilizers.

Major users of nitrogen-based fertilizer^[3]

Country	Total N consumption (Mt pa)	Amount used for feed & pasture
China	18.7	3.0
USA	9.1	4.7
France	2.5	1.3
Germany	2.0	1.2
Brazil	1.7	0.7
Canada	1.6	0.9
Turkey	1.5	0.3
UK	1.3	0.9
Mexico	1.3	0.3
Spain	1.2	0.5
Argentina	0.4	0.1

[edit] Application

Synthetic fertilizers are commonly used to treat fields used for growing maize, followed by barley, sorghum, rapeseed, soy and sunflower^{[citation needed]}. One study has shown that application of nitrogen fertilizer on off-season cover crops can increase the biomass (and subsequent green manure value) of these crops, while having a beneficial effect on soil nitrogen levels for the main crop planted during the summer season.^[4]

[edit] Over-fertilization

Over-fertilization of a vital nutrient can be as detrimental as underfertilization.^[5] "Fertilizer burn" can occur when too much fertilizer is applied, resulting in a drying out of the roots and damage or even death of the plant.^[6]

[edit] Trace mineral depletion

Many inorganic fertilizers do not replace trace mineral elements in the soil which become gradually depleted by crops. This depletion 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.^[7] However, a recent review of 55 scientific studies concluded "there is no evidence of a difference in nutrient quality between organically and conventionally produced foodstuffs" ^[8]

In Western Australia deficiencies of zinc, copper, manganese, iron and molybdenum were identified as limiting the growth of broad-acre crops and pastures in the 1940s and 1950s^{[citation needed]}. Soils in Western Australia are very old, highly weathered and deficient in many of the major nutrients and trace elements^{[citation needed]}. Since this time these trace elements are routinely added to inorganic fertilizers used in agriculture in this state^{[citation needed]}.

[edit] Energy consumption

The production of synthetic ammonia currently consumes about 5% of global natural gas consumption, which is somewhat under 2% of world energy production.^[9]

Natural gas is overwhelmingly used for the production of ammonia, but other energy sources, together with a hydrogen source, can be used for the production of nitrogen compounds suitable for fertilizers. The cost of natural gas makes up about 90% of the cost of producing ammonia.^[10] The increase in price of natural gas over the past decade, along with other factors such as increasing demand, have contributed to an increase in fertilizer price^{[citation needed]}.

[edit] Long-Term Sustainability

Inorganic fertilizers are now produced in ways which cannot be continued indefinitely. Potassium and phosphorus come from mines (or saline lakes such as the Dead Sea) and such resources are limited. While atmospheric nitrogen is effectively unlimited (forming over 70% of atmospheric gases), relatively few plants engage in nitrogen fixation (conversion of atmospheric nitrogen to a plant-accessible form). To make nitrogen accessible to plants, nitrogen fertilizers are synthesized using fossil fuels such as natural gas and coal, which are limited.

[edit] Organic fertilizers

Organic fertilizers include naturally-occurring organic materials, such as manure, worm castings, compost, seaweed, guano and peat moss, or naturally occurring mineral deposits (e.g. saltpeter). In addition to increasing yield and fertilizing plants directly, organic fertilizers can improve the health and long-term productivity of soil. Organic nutrients increase the abundance of soil organisms by providing organic matter and micronutrients for organisms such as fungal mycorrhiza, which aid plants in absorbing nutrients. It is believed by some^[who?] that 'organic' agricultural methods are more environmentally friendly and better maintain soil organic matter (SOM) levels.

[edit] Comparison with inorganic fertilizer

Organic fertilizer nutrient content, solubility, and nutrient release rates are typically all lower than inorganic fertilizers^[11][12]. One study^[which?] found that over a 140-day period, after 7 leachings:

• Organic fertilizers had released between 25% and 60% of their nitrogen content
• Controlled release fertilizers (CRFs) had a relatively constant rate of release
• Soluble fertilizer released most of its nitrogen content at the first leaching

In general, the nutrients in organic fertilizer are both more dilute and also much less readily available to plants. According to UC IPM, all organic fertilizers are classified as 'slow-release' fertilizers, and therefore cannot cause nitrogen burn^[13].

Non-concentrated organic fertilizers with dilute concentrations of nutrients have greater transport and application costs.

Organic fertilizers from treated sewage, composts and other sources can be quite variable from one batch to the next. Without batch testing the amounts of applied nutrient cannot be precisely known. And they are just as good as regular fertilizers.

[edit] Sources

[edit] Animal

Animal-sourced Urea and Urea-Formaldehyde (from urine), are suitable for application organic agriculture, while pure synthetic forms of urea are not^[14][15]. The common thread that can be seen through these examples is that organic agriculture attempts to define itself through minimal processing (e.g. via chemical energy such as petroleum—see Haber process), as well as being naturally-occurring or via natural biological processes such as composting.

Sewage sludge use in organic agricultural operations in the U.S. has been extremely limited and rare due to USDA prohibition of the practice (due to toxic metal accumulation, among other factors)^[16][17][18]. The USDA now requires 3rd-party certification of high-nitrogen liquid organic fertilizers sold in the U.S.^[19]

[edit] Plant

Cover crops are also grown to enrich soil as a green manure through nitrogen fixation from the atmosphere^[20]; as well as phosphorus (through nutrient mobilization)^[21] content of soils. Minerals such as mined rock phosphate, sulfate of potash and limestone are considered organic fertilizers, though by a contain no (carbon) molecules (inorganic chemicals in an organic chemistry sense).

[edit] Mineral

Naturally mined powdered limestone^[22], mined rock phosphate and sodium nitrate, are inorganic (in a chemical sense), and are energetically-intensive to harvest, yet are still approved for usage in organic agriculture in minimal amounts^[22][23][24]. This is a contradictory stance however, because high-concentrate plant nutrients (in the form of salts) obtained from dry lake beds by farmers for centuries in a very minimal fashion^[expand] are excluded from consideration by most^[which?] organic enthusiasts and many governmental definitions of organic agriculture^[which?]. No such dichotomy between organic and chemical exists^[opinion].

[edit] Environmental effects of fertilizer use

[edit] Water

[edit] Eutrophication

The nitrogen-rich compounds found in fertilizer run-off is the primary cause of a serious depletion of oxygen in many parts of the ocean, especially in coastal zones; the resulting lack of dissolved oxygen is greatly reducing the ability of these areas to sustain oceanic fauna.^[25] Visually, water may become cloudy and/or discolored (green, yellow, brown, or red). About half of all the lakes in the United States are now eutrophic, while the number of oceanic dead zones near inhabited coastlines are increasing.^[26] As of 2006, the application of nitrogen fertilizer is being increasingly controlled in Britain and the United States^{[citation needed]}. If eutrophication can be reversed, it may take decades^{[citation needed]} before the accumulated nitrates in groundwater can be broken down by natural processes.

High application rates of inorganic nitrogen fertilizers in order to maximize crop yields, combined with the high solubilities of these fertilizers leads to increased runoff into surface water as well as leaching into groundwater.^[27][28][29] The use of ammonium nitrate in inorganic fertilizers is particularly damaging, as plants absorb ammonium ions preferentially over nitrate ions, while excess nitrate ions which are not absorbed dissolve (by rain or irrigation) into runoff or groundwater.^[30]

[edit] Blue Baby Syndrome

Nitrate levels above 10 mg/L (10 ppm) in groundwater can cause 'blue baby syndrome' (acquired methemoglobinemia), leading to hypoxia (which can lead to coma and death if not treated)^[31].

[edit] Soil

[edit] Acidification

Nitrogen-containing inorganic and organic fertilizers can cause soil acidification^[32]. [4]

[edit] Toxic persistent organic compounds

Dioxins, polychlorinated dibenzo-p-dioxins (PCDDs), and polychlorinated dibenzofurans (PCDFs) have been detected in fertilizers and soil amendments^[33]

[edit] Heavy metal accumulation

The concentration of up to 100 mg/kg of cadmium in phosphate minerals (for example, minerals from Nauru^[34] and the Christmas islands^[35]) increases the contamination of soil with cadmium, for example in New Zealand.^[36] Uranium is another example of a contaminant often found in phosphate fertilizers^{[citation needed]}. Eventually these heavy metals can build up to unacceptable levels and build up in produce.^[36] (See cadmium poisoning)

Steel industry wastes, recycled into fertilizers for their high levels of zinc (essential to plant growth), wastes can include the following toxic metals: lead^[37]arsenic, cadmium^[37], chromium, and nickel. The most common toxic elements in this type of fertilizer are mercury, lead, and arsenic.^[38][39] Concerns have been raised concerning fish meal mercury content by at least one source in Spain^[40]

Also, highly-radioactive Polonium-210 contained in phosphate fertilizers is absorbed by the roots of plants and stored in its tissues^{[citation needed]}. Tobacco derived from plants fertilized by rock phosphates contains Polonium-210 which emits alpha radiation estimated to cause about 11,700 lung cancer deaths each year worldwide.^{[41][42] [43][44][45][46]}

For these reasons, it is recommended that nutrient budgeting, through careful observation and monitoring of crops, take place to mitigate the effects of excess fertilizer application.

[edit] Atmosphere

Through the increasing use of nitrogen fertilizer, which is added at a rate of 120 million tons per year presently^[47] to the already existing amount of reactive nitrogen, nitrous oxide (N₂O) has become the third most important greenhouse gas after carbon dioxide and methane, with a global warming potential 296 times larger than an equal mass of carbon dioxide, while it also contributes to stratospheric ozone depletion.^[48]

Storage and application of some nitrogen fertilizers in some^[which?] weather or soil conditions can cause emissions of the potent greenhouse gas—nitrous oxide. Ammonia gas (NH₃) may be emitted following application of 'inorganic' fertilizers and/or manures and slurries.^{[citation needed]}

The use of fertilizers on a global scale emits significant quantities of greenhouse gas into the atmosphere. Emissions come about through the use of:^[49]

• animal manures and urea, which release methane, nitrous oxide, ammonia, and carbon dioxide in varying quantities depending on their form (solid or liquid) and management (collection, storage, spreading)
• fertilizers that use nitric acid or ammonium bicarbonate, the production and application of which results in emissions of nitrogen oxides, nitrous oxide, ammonia and carbon dioxide into the atmosphere.

By changing processes and procedures, it is possible to mitigate some, but not all, of these effects on anthropogenic climate change^{[citation needed]}.

[edit] Increased pest problems

Excessive nitrogen fertilizer applications can also lead to pest problems by increasing the birth rate, longevity and overall fitness of certain agricultural pests.^{[50] [51] [52] [53] [54] [55]}

[edit] See also

• Agriculture and the environment

[edit] References

[edit] External links

Wikimedia Commons has media related to: Fertilizer

• Nitrogen for Feeding Our Food, Its Earthly Origin, Haber Process
• The Texas Vegetable Growers' Handbook, Chapter 3 Soils and fertilizers in agriculture.
• The Fertilizer Institute (TFI) US Fertilizer Industry Association
• International Fertilizer Industry Association (IFA)
• European Fertiliser Manufacturers Association
• How to read fertilizer tags article

v • d • e Physiological plant disorders : Plant nutrition deficiencies Boron deficiency | Calcium deficiency | Iron deficiency | Magnesium deficiency | Manganese deficiency | Nitrogen deficiency | Phosphorus deficiency | Potassium deficiency | Micronutrient deficiency