Fertilizers are soil amendments applied to promote plant growth, they are usually applied either on soil or onto leaves (foliar feeding). Fertilizers can also be applied to aquatic environments for geoengineering, notably ocean fertilization. The main nutrients added in fertilizer are nitrogen, phosphorus, and potassium but other nutrients are added in smaller amounts. Fertilizers can be either organic, for example manure or inorganic if they are synthesised chemically. Organic fertilizers have been used for centuries whereas inorganic fertilizers were only been developed on an industrial scale in the 20th century. The use of fertilizers was an important part of the green revolution which lead to greatly increased food production in 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 Organic and inorganic fertilizer 3 History 4 Inorganic fertilizers (synthetic fertilizer) 4.1 Application 4.2 Soil health issues 5 Organic fertilizers 5.1 Sources 5.1.1 Animal 5.1.2 Plant 5.1.3 Mineral 5.2 Benefits of organic fertilizer 5.3 Disadvantages of organic fertilizer 6 Environmental effects of fertilizer use 6.1 Nitrate impact 6.2 Atmospheric impacts 6.3 Toxic persistent organic compounds 6.4 Heavy metal accumulation 6.5 Increased pest insect health 6.6 Hazard of over-fertilization 6.7 Trace mineral depletion 6.8 Energy consumption 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 basis just described does not give the actual fraction of the respective elements, some packaging also reports the elemental mass fractions. The UK fertilizer-labelling regulations ^[2] allow for additionally reporting the elemental mass fractions of phosphorous and potassium, rather than phosphoric acid and potassium hydroxide, but these must be listed in parentheses after the standard 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, the element phosphorous constitutes 43.6% of the total mass of the compound. Thus, the official UK mass fraction (percentage) of elemental phosphorus is 43.6%. [P] = 0.436 x [P₂O₅]

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] Organic and inorganic 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). Organic fertilizers are naturally-occurring fertilizers (e.g. peat moss or green manure), or naturally occurring mineral deposits (e.g. saltpeter). Inorganic fertilizers are manufactured through chemical processes (e.g. Haber process) and chemically-altered naturally occurring deposits, (e.g. concentrated triple superphosphate^[3]).

Properly applied, organic fertilizers can improve the health and productivity of soil and plants, as they provide different essential nutrients to encourage plant growth. 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. Chemical fertilizers may have long-term adverse impact on the organisms living in soil^{[citation needed]} and a detrimental long term effect on soil productivity of the soil^{[citation needed]}.

Both organic and inorganic fertilizers were called "manure", however, this term is currently restricted to organic manure^{[citation needed]}. Though nitrogen is plentiful in the Earth's atmosphere, relatively few plants engage in nitrogen fixation (conversion of atmospheric nitrogen to a plant-accessible form). It is believed by some^[who?] that 'organic' agricultural methods are more environmentally friendly and better maintain soil organic matter (SOM) levels.

[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)

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 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^[4]

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.^[5]

[edit] Soil health issues

In many countries^[which?] there is the public perception that inorganic fertilizers "poison the soil" and result in "low quality" produce^{[citation needed]}. When used appropriately, inorganic fertilizers enhance plant growth, the accumulation of organic matter, and the biological activity of the soil, thus preventing overgrazing and soil erosion.

Studies in Australia show 'biodynamic' or 'organic' farms are less productive and less sustainable than conventional farms using inorganic fertilizers.^[6][7] The nutritional value of plants for human and animal consumption is typically improved when inorganic fertilizers are used appropriately.^{[citation needed]}

[edit] Organic fertilizers

As discussed above, organic fertilizers include naturally-occurring substances, such as manure, worm castings, compost, seaweed, and guano. 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)^[8][9][10]. The USDA now requires 3rd-party certification of high-nitrogen liquid organic fertilizers sold in the U.S.^[11]

[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^[12][13]. 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.

[edit] Plant

Cover crops are also grown to enrich soil as a green manure through nitrogen fixation from the atmosphere^[14]; as well as phosphorus (through nutrient mobilization)^[15] 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^[16], 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^[16][17][18]. 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] Benefits of organic fertilizer

Organic fertilizer nutrient content, solubility, and nutrient release rates are typically much lower than mineral (inorganic) fertilizers^[19][20]. 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

[edit] Disadvantages of organic fertilizer

Like inorganic fertilizers, it is possible to over-apply organic fertilizers^{[citation needed]} depending on the type and amount of organic fertilizer used. Because of their dilute concentration of nutrients^{[citation needed]}, transport and application costs are typically much greater for organic than inorganic fertilizers. Organic fertilizers from treated sewage, composts and other sources can be quite variable from one batch to the next, without batch testing, the amounts applied nutrient cannot be precisely known.

[edit] Environmental effects of fertilizer use

The environmental toxicity of fertilizers can come in part from recycled industrial waste that introduce several classes of toxic materials into the environment. Between 1990-1995, 600 companies from 44 different states sent 270 million pounds of toxic waste to farms and fertilizer companies across the country.^[21]

According to the United States Food and Drug Administration^[22]:

"Current information indicates that only a relatively small percentage of fertilizers are manufactured using industrial wastes as ingredients, and that hazardous wastes are used as ingredients in only a small portion of waste-derived fertilizers."

"[the] EPA has continually encouraged the beneficial reuse and recycling of industrial wastes."^[23]

[edit] Nitrate impact

High application rates of nitrogen fertilizers in order to maximize crop yields, combined with the high solubilities of these fertilizers leads to increased leaching of nitrates into groundwater.^[24][25][26]

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 groundwater.^[27]

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)^[28]. Nitrogen-containing inorganic fertilizers in the form of nitrate and ammonium also cause soil acidification^[29].

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.^[30] Anoxic respiration by bacteria in the eutrophicated marine zones also releases nitrous oxide to the atmosphere.

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.^[31] 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.

[edit] Atmospheric impacts

Through the increasing use of nitrogen fertilizer, which is added at a rate of 120 million tons per year presently^[32] 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.^[33]

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:^[34]

• 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] Toxic persistent organic compounds

Dioxins, polychlorinated dibenzo-p-dioxins (PCDDs), and polychlorinated dibenzofurans (PCDFs) have been detected in fertilizers and soil amendments^[35]

[edit] Heavy metal accumulation

The concentration of up to 100 mg/kg of cadmium in phosphate minerals (for example, minerals from Nauru^[36] and the Christmas islands^[37]) increases the contamination of soil with cadmium, for example in New Zealand.^[38] 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.^[38] (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^[39]arsenic, cadmium^[39], chromium, and nickel. The most common toxic elements in this type of fertilizer are mercury, lead, and arsenic.^[21][40] Concerns have been raised concerning fish meal mercury content by at least one source in Spain^[41]

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.^{[42][43] [44][45][46][47]}

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] Increased pest insect health

Excessive nitrogen fertilizer applications can also lead to pest problems by increasing the birth rate, longevity and overall fitness of certain agricultural pests.^{[48] [49] [50] [51] [52] [53]}

[edit] Hazard of over-fertilization

^{[clarification needed]}

Over-fertilization of a vital nutrient can be as detrimental as underfertilization.^[54] "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.^[55]

According to UC IPM, all organic fertilizers, and some specially-formulated inorganic fertilizers are classified as 'slow-release' fertilizers, and therefore cannot cause nitrogen burn^[56] Organic fertilizers are as likely to cause plant burn as inorganic fertilizers.^{[citation needed]}

[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.^[57] 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" ^[58]

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.^[59]

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.^[60] 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]}.

Another problem with inorganic fertilizers is that they 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. Nitrogen sources are effectively unlimited (forming over 70% of atmospheric gases), however, nitrogen fertilizers are presently made using fossil fuels such as natural gas and coal, which are limited.

Innovative thermal depolymerization biofuel schemes are experimenting with the production of byproducts with 9% nitrogen fertilizer from organic waste^[61][62][63]

[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