fertilizer

For more information on fertilizer, visit Britannica.com.

Background

Fertilizer is a substance added to soil to improve plants' growth and yield. First used by ancient farmers, fertilizer technology developed significantly as the chemical needs of growing plants were discovered. Modern synthetic fertilizers are composed mainly of nitrogen, phosphorous, and potassium compounds with secondary nutrients added. The use of synthetic fertilizers has significantly improved the quality and quantity of the food available today, although their long-term use is debated by environmentalists.

Like all living organisms, plants are made up of cells. Within these cells occur numerous metabolic chemical reactions that are responsible for growth and reproduction. Since plants do not eat food like animals, they depend on nutrients in the soil to provide the basic chemicals for these metabolic reactions. The supply of these components in soil is limited, however, and as plants are harvested, it dwindles, causing a reduction in the quality and yield of plants.

Fertilizers replace the chemical components that are taken from the soil by growing plants. However, they are also designed to improve the growing potential of soil, and fertilizers can create a better growing environment than natural soil. They can also be tailored to suit the type of crop that is being grown. Typically, fertilizers are composed of nitrogen, phosphorus, and potassium compounds. They also contain trace elements that improve the growth of plants.

The primary components in fertilizers are nutrients which are vital for plant growth. Plants use nitrogen in the synthesis of proteins, nucleic acids, and hormones. When plants are nitrogen deficient, they are marked by reduced growth and yellowing of leaves. Plants also need phosphorus, a component of nucleic acids, phospholipids, and several proteins. It is also necessary to provide the energy to drive metabolic chemical reactions. Without enough phosphorus, plant growth is reduced. Potassium is another major substance that plants get from the soil. It is used in protein synthesis and other key plant processes. Yellowing, spots of dead tissue, and weak stems and roots are all indicative of plants that lack enough potassium.

Calcium, magnesium, and sulfur are also important materials in plant growth. They are only included in fertilizers in small amounts, however, since most soils naturally contain enough of these components. Other materials are needed in relatively small amounts for plant growth. These micronutrients include iron, chlorine, copper, manganese, zinc, molybdenum, and boron, which primarily function as cofactors in enzymatic reactions. While they may be present in small amounts, these compounds are no less important to growth, and without them plants can die.

Many different substances are used to provide the essential nutrients needed for an effective fertilizer. These compounds can be mined or isolated from naturally occurring sources. Examples include sodium nitrate, seaweed, bones, guano, potash, and phosphate rock. Compounds can also be chemically synthesized from basic raw materials. These would include such things as ammonia, urea, nitric acid, and ammonium phosphate. Since these compounds exist in a number of physical states, fertilizers can be sold as solids, liquids, or slurries.

History

The process of adding substances to soil to improve its growing capacity was developed in the early days of agriculture. Ancient farmers knew that the first yields on a plot of land were much better than those of subsequent years. This caused them to move to new, uncultivated areas, which again showed the same pattern of reduced yields over time. Eventually it was discovered that plant growth on a plot of land could be improved by spreading animal manure throughout the soil.

Over time, fertilizer technology became more refined. New substances that improved the growth of plants were discovered. The Egyptians are known to have added ashes from burned weeds to soil. Ancient Greek and Roman writings indicate that various animal excrements were used, depending on the type of soil or plant grown. It was also known by this time that growing leguminous plants on plots prior to growing wheat was beneficial. Other types of materials added include sea-shells, clay, vegetable waste, waste from different manufacturing processes, and other assorted trash.

Organized research into fertilizer technology began in the early seventeenth century. Early scientists such as Francis Bacon and Johann Glauber describe the beneficial effects of the addition of saltpeter to soil. Glauber developed the first complete mineral fertilizer, which was a mixture of saltpeter, lime, phosphoric acid, nitrogen, and potash. As scientific chemical theories developed, the chemical needs of plants were discovered, which led to improved fertilizer compositions. Organic chemist Justus von Liebig demonstrated that plants need mineral elements such as nitrogen and phosphorous in order to grow. The chemical fertilizer industry could be said to have its beginnings with a patent issued to Sir John Lawes, which outlined a method for producing a form of phosphate that was an effective fertilizer. The synthetic fertilizer industry experienced significant growth after the First World War, when facilities that had produced ammonia and synthetic nitrates for explosives were converted to the production of nitrogen-based fertilizers.

Raw Materials

The fertilizers outlined here are compound fertilizers composed of primary fertilizers and secondary nutrients. These represent only one type of fertilizer, and other single nutrient types are also made. The raw materials, in solid form, can be supplied to fertilizer manufacturers in bulk quantities of thousands of tons, drum quantities, or in metal drums and bag containers.

Primary fertilizers include substances derived from nitrogen, phosphorus, and potassium. Various raw materials are used to produce these compounds. When ammonia is used as the nitrogen source in a fertilizer, one method of synthetic production requires the use of natural gas and air. The phosphorus component is made using sulfur, coal, and phosphate rock. The potassium source comes from potassium chloride, a primary component of potash.

Secondary nutrients are added to some fertilizers to help make them more effective. Calcium is obtained from limestone, which contains calcium carbonate, calcium sulphate, and calcium magnesium carbonate. The magnesium source in fertilizers is derived from dolomite. Sulfur is another material that is mined and added to fertilizers. Other mined materials include iron from ferrous sulfate, copper, and molybdenum from molybdenum oxide.

The Manufacturing
Process

Fully integrated factories have been designed to produce compound fertilizers. Depending on the actual composition of the end product, the production process will differ from manufacturer to manufacturer.

Nitrogen fertilizer component

• Ammonia is one nitrogen fertilizer component that can be synthesized from in-expensive raw materials. Since nitrogen makes up a significant portion of the earth's atmosphere, a process was developed to produce ammonia from air. In this process, natural gas and steam are pumped into a large vessel. Next, air is pumped into the system, and oxygen is removed by the burning of natural gas and steam. This leaves primarily nitrogen, hydrogen, and carbon dioxide. The carbon dioxide is removed and ammonia is produced by introducing an electric current into the system. Catalysts such as magnetite (Fe₃O₄) have been used to improve the speed and efficiency of ammonia synthesis. Any impurities are removed from the ammonia, and it is stored in tanks until it is further processed.
• While ammonia itself is sometimes used as a fertilizer, it is often converted to other substances for ease of handling. Nitric acid is produced by first mixing ammonia and air in a tank. In the presence of a catalyst, a reaction occurs which converts the ammonia to nitric oxide. The nitric oxide is further reacted in the presence of water to produce nitric acid.

• 3 Nitric acid and ammonia are used to make ammonium nitrate. This material is a good fertilizer component because it has a high concentration of nitrogen. The two materials are mixed together in a tank and a neutralization reaction occurs, producing ammonium nitrate. This material can then be stored until it is ready to be granulated and blended with the other fertilizer components.

Phosphorous fertilizer component

• To isolate phosphorus from phosphate rock, it is treated with sulfuric acid, producing phosphoric acid. Some of this material is reacted further with sulfuric acid and nitric acid to produce a triple superphosphate, an excellent source of phosphorous in solid form.
• Some of the phosphoric acid is also reacted with ammonia in a separate tank. This reaction results in ammonium phosphate, another good primary fertilizer.

Potassium fertilizer component

• Potassium chloride is typically supplied to fertilizer manufacturers in bulk. The manufacturer converts it into a more usable form by granulating it. This makes it easier to mix with other fertilizer components in the next step.

Granulating and blending

• To produce fertilizer in the most usable form, each of the different compounds, ammonium nitrate, potassium chloride, ammonium phosphate, and triple superphosphate are granulated and blended together. One method of granulation involves putting the solid materials into a rotating drum which has an inclined axis. As the drum rotates, pieces of the solid fertilizer take on small spherical shapes. They are passed through a screen that separates out adequately sized particles. A coating of inert dust is then applied to the particles, keeping each one discrete and inhibiting moisture retention. Finally, the particles are dried, completing the granulation process.
• The different types of particles are blended together in appropriate proportions to produce a composite fertilizer. The blending is done in a large mixing drum that rotates a specific number of turns to produce the best mixture possible. After mixing, the fertilizer is emptied onto a conveyor belt, which transports it to the bagging machine.

Bagging

• Fertilizers are typically supplied to farmers in large bags. To fill these bags the fertilizer is first delivered into a large hopper. An appropriate amount is released from the hopper into a bag that is held open by a clamping device. The bag is on a vibrating surface, which allows better packing. When filling is complete, the bag is transported upright to a machine that seals it closed. The bag is then conveyored to a palletizer, which stacks multiple bags, readying them for shipment to distributors and eventually to farmers.

Quality Control

To ensure the quality of the fertilizer that is produced, manufacturers monitor the product at each stage of production. The raw materials and the finished products are all subjected to a battery of physical and chemical tests to show that they meet the specifications previously developed. Some of the characteristics that are tested include pH, appearance, density, and melting point. Since fertilizer production is governmentally regulated, composition analysis tests are run on samples to determine total nitrogen content, phosphate content, and other elements affecting the chemical composition. Various other tests are also performed, depending on the specific nature of the fertilizer composition.

Byproducts/Waste

A relatively small amount of the nitrogen contained in fertilizers applied to the soil is actually assimilated into the plants. Much is washed into surrounding bodies of water or filters into the groundwater. This has added significant amounts of nitrates to the water that is consumed by the public. Some medical studies have suggested that certain disorders of the urinary and kidney systems are a result of excessive nitrates in drinking water. It is also thought that this is particularly harmful for babies and could even be potentially carcinogenic.

The nitrates that are contained in fertilizers are not thought to be harmful in themselves. However, certain bacteria in the soil convert nitrates into nitrite ions. Research has shown that when nitrite ions are ingested, they can get into the bloodstream. There, they bond with hemoglobin, a protein that is responsible for storing oxygen. When a nitrite ion binds with hemoglobin, it loses its ability to store oxygen, resulting in serious health problems.

Nitrosamines are another potential byproduct of the nitrates in fertilizer. They are the result of a natural chemical reaction of nitrates. Nitrosamines have been shown to cause tumors in laboratory animals, feeding the fear that the same could happen in humans. There has, however, been no study that shows a link between fertilizer use and human tumors.

The Future

Fertilizer research is currently focusing on reducing the harnful environmental impacts of fertilizer use and finding new, less expensive sources of fertilizers. Such things that are being investigated to make fertilizers more environmentally friendly are improved methods of application, supplying fertilizer in a form which is less susceptible to runoff, and making more concentrated mixtures. New sources of fertilizers are also being investigated. It has been found that sewage sludge contains many of the nutrients that are needed for a good fertilizer. Unfortunately, it also contains certain substances such as lead, cadmium, and mercury in concentrations which would be harmful to plants. Efforts are underway to remove the unwanted elements, making this material a viable fertilizer. Another source that is being developed is manures. The first fertilizers were manures, however, they are not utilized on a large scale because their handling has proven too expensive. When technology improves and costs are reduced, this material will be a viable new fertilizer.

Where to Learn More

Books

Rao, N. S. Biofertilizers in Agriculture & Forestry. IBH, 1993.

Stocchi, E. Industrial Chemistry. Ellis Horwood, 1990.

Lowrison, George. Fertilizer Technology. John Wiley and Sons, 1989.

Periodicals

Kirschner, Elisabeth. "Fertilizer Makers Gear up to Grow." Chemical & Engineering News, March, 31 1997, p. 13-15.

[Article by: Perry Romanowski]

Materials added to the soil, or applied directly to crop foliage, to supply elements needed for plant nutrition. These materials may be in the form of solids, semisolids, slurry suspensions, pure liquids, aqueous solutions, or gases.

The chemical elements nitrogren, phosphorus, and potassium are the macronutrients, or primary fertilizer elements, which are required in greatest quantity. Sulfur, calcium, and magnesium, called secondary elements, are also necessary to the health and growth of vegetation, but they are required in lesser amounts compared to the macronutrients. The other elements of agronomic importance, called micronutrients and provided for plant ingestion in small (or trace) amounts, include boron, cobalt, copper, iron, manganese, molybdenum, and zinc. All these fertilizer elements, along with other chemical elements, occur naturally in agricultural soils in varying concentrations and mineral compositions which may or may not be in forms readily accessible to root systems of plants. The addition of fertilizer to soils used for the production of commercial crops is necessary to correct natural deficiencies and to replace the components absorbed by the crops in their growth.

Crop requirements of fertilizer components could be satisfied by the spreading of individual materials for each element deficient in the soil. However, economy favors the single application of a balanced mixture that satisfies all nutritional needs of a crop. Many commercial fertilizers therefore contain more than one of the primary fertilizer elements.

The compositions of fertilizer mixtures, in terms of the primary fertilizer elements, are identified by an N-P-K code: N denotes elemental nitrogen; P denotes the anhydride of phosphoric acid (P₂O₅); K denotes the oxide of potassium (K₂O). All are expressed numerically in percentage composition, or units of 20 lb each per short ton (10 kg per metric ton) of finished fertilizer as packaged. Formula 8-32-16 thus contains a mixture aggregating 8 wt % N in some form of nitrogen compounds, 32 wt % P₂O₅ in some form of phosphates, and 16 wt % K₂O in some form of potassium compounds, to give a product with a total of 56 fertilizer units. The commercial N-P-K formulas are generally in whole numbers. None of the N-P-K formulas totals 100% plant nutrients because the formulas indicate only the nutrient portions of the primary-element compounds and do not account for any other materials present.

Aqueous solutions of urea, ammonia, and ammonium nitrate (UAN solutions) are used directly by the farmers as well as in the preparation of granular N-P-K products by mixing with other materials. UAN solutions are also spread directly by field application or used to prepare complete N-P-K fertilizer solutions or suspensions. Suspension fertilizers consist of aqueous slurries of fine crystals in saturated solutions that are stabilized by small amounts of gelling materials, such as attapulgite clay. Suspensions can be maintained in uniform composition during spreading on the fields, and give better dispersion than granular material. See also Fertilizing.

Organic fertilizers are organic materials of vegetable and animal origin which contain certain macro, secondary, or micro nutrients that can be utilized by plants after application to agricultural soils. The primary nutrient sources of vegetable origin are crop residues, green manures, oilseed cakes, seaweeds, and miscellaneous food processing and distillery wastes. Also included in this category is biologically fixed nitrogen from legumes in association with root-nodulating bacteria of the genus Rhizobium. Animal sources include animal manures and urine, sewage sludge, septage, latrine wastes, and to a lesser extent materials such as blood meal, bone meal, and fish scraps. Often organic fertilizers are of mixed animal and vegetable origin, such as most farmyard manures, rural and urban composts, and sewage effluents and sludges. See also Nitrogen fixation; Soil microbiology.

That which fertilizes, i.e., acts as a nutrient, whether organic or inorganic; may be natural or artificial.

Fertilizers, natural or artificial substances composed of the chemical elements that enhance plant growth and productivity by adding nutrients to soil, have been used since the earliest days of agriculture. The three major fertilizer elements are nitrogen, phosphorus, and potassium. Natural fertilizers include manures, compost, plant ashes, lime, gypsum, and grasses. Chemical fertilizers may be derived from natural sources or may be synthetic compounds.

Commercial chemical fertilizers have only been in general use since the nineteenth century. Early American colonists used natural fertilizers, but overuse and lack of crop rotation quickly depleted both the nutrient poor coastal soil and the more fertile soil of the prairies. Eighteenth-and nineteenth-century European chemists experimented with the effects of chemical fertilization. In 1840, Justus von Liebig published Organic Chemistry in Its Application to Agriculture and Physiology. His research demonstrated that adding nitrogen, phosphorus, and potassium to the soil stimulated plant growth. By 1849, mixed chemical fertilizers were sold commercially in the United States, though their use did not become widespread until after 1900.

Fertilizers represent one of the largest market commodities for the chemical industry. On modern farms, machines are used to apply synthetic fertilizers in solid, gaseous, or liquid form. There is also a growing movement, dating to the 1940s, toward organic agriculture, which rejects the use of chemically formulated fertilizers, growth stimulants, antibiotics, and pesticides in favor of traditional natural fertilizers, of plant or animal origin, and crop rotation.

Bibliography

Havlin, John, Samuel L. Tisdale, and James D. Beaton, eds. Soil Fertility and Fertilizers: An Introduction to Nutrient Management. 6th ed., Upper Saddle River, N.J.: Prentice Hall, 1999.

—Deirdre Sheets

Material added to soil to improve its fertility by adding to its chemical composition. Usually infers a chemical agent such as superphosphate but blood and bone and kelp humus are included also. Some of them, e.g. calcium cyanamide, ammonium sulfate, urea, can cause poisoning.

A substance that contains one or more of the necessary plant nutrients.

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). 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 (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.

Fertilizer spreader, New South Wales

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 References 7 External links

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.

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).

Tennessee Valley Authority: "Results of Fertilizer" demonstration 1942

Further information: Plant nutrition

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).

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.

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.)

History

Main article: History of fertilizer

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.

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

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]

Over-fertilization

Main article: Fertilizer burn

Fertilizer burn

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]

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]}.

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]}.

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.

Organic fertilizers

Main article: Organic fertilizer

A compost bin

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.

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.

Sources

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]

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).

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].

Environmental effects of fertilizer use

See also: Human impacts on the nitrogen cycle

Water

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] 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.^[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]

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].

Soil

Acidification

Nitrogen-containing inorganic fertilizers in the form of nitrate and ammonium cause soil acidification^[32].

Toxic persistent organic compounds

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

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.

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]}.

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]}

References

1. ^ ^{a b} http://www.ncagr.gov/cyber/kidswrld/plant/label.htm
2. ^ UK Fertilizers Regulations 1990, Schedule 2 Part 1, Para. 7.
3. ^ United Nations Food and Agriculture Organization, Livestock's Long Shadow: Environmental Issues and Options, Table 3.3 retrieved 29 Jun 2009
4. ^ Nitrogen Applied Newswise, Retrieved on October 1, 2008.
5. ^ Nitrogen Fertilization: General Information
6. ^ Avoiding Fertilizer Burn
7. ^ Lawrence, Felicity (2004). "214". in Kate Barker. Not on the Label. Penguin. pp. 213. ISBN 0-14-101566-7. 
8. ^ Dangour et al. 2009. Nutritional quality of organic foods: a systematic approach. Am. J. Clin. Nutr.
9. ^ IFA - Statistics - Fertilizer Indicators - Details - Raw material reserves (2002-10; accessed 2007-04-21)
10. ^ Sawyer JE (2001). "Natural gas prices affect nitrogen fertilizer costs". IC-486 1: 8. 
11. ^ http://www.actahort.org/members/showpdf?booknrarnr=644_20
12. ^ http://ag.arizona.edu/pubs/garden/mg/soils/organic.html
13. ^ http://www.ipm.ucdavis.edu/TOOLS/TURF/SITEPREP/amenfert.html
14. ^ http://www.ecochem.com/t_natfert.html
15. ^ http://www.cababstractsplus.org/abstracts/Abstract.aspx?AcNo=20023145231
16. ^ http://www.epa.gov/oecaagct/torg.html
17. ^ http://www.ewg.org/reports/sludgememo
18. ^ http://www.calorganicfarms.com/news/full.php?id=22
19. ^ Schrack, Don (2009-02-23). "USDA Toughens Oversight of Organic Fertilizer: Organic fertilizers must undergo testing". The Packer. http://www.organicconsumers.org/articles/article_17001.cfm. Retrieved 19 November 2009. 
20. ^ http://www.pubmedcentral.nih.gov/pagerender.fcgi?artid=373994&pageindex=6#page
21. ^ http://books.google.com/books?id=XO3pio5Opy8C&pg=PA564&lpg=PA564&dq=phosphorus+addition+fava+bean&source=bl&ots=Rjkls81sXS&sig=KpWCnyWUNvcB9eKX4tNLsrB98o4&hl=en&ei=_LzZSfyvKJKatAPx4oiwCg&sa=X&oi=book_result&ct=result&resnum=1
22. ^ ^{a b} http://209.85.173.132/search?q=cache:_KrbNzgsjrQJ:extension.agron.iastate.edu/sustag/pubs/Soil_Quality_Brochure.doc+limestone+organic+agriculture&cd=3&hl=en&ct=clnk&gl=us&client=opera
23. ^ http://www.extension.org/article/18321/print/
24. ^ http://www.nal.usda.gov/afsic/pubs/ofp/ofp.shtml#resources
25. ^ "Rapid Growth Found in Oxygen-Starved Ocean ‘Dead Zones’", NY Times, Aug. 14, 2008
26. ^ http://dsc.discovery.com/news/2006/10/20/deadzone_pla.html
27. ^ http://www.extension.umn.edu/distribution/horticulture/DG2923.html
28. ^ http://www.sciencedirect.com/science?_ob=ArticleURL&_udi=B6V94-3VW172B-1&_user=10&_rdoc=1&_fmt=&_orig=search&_sort=d&view=c&_acct=C000050221&_version=1&_urlVersion=0&_userid=10&md5=a887208bd6509db7ab1557a4fc43c5fa
29. ^ http://www.nofa.org/tnf/nitrogen.php
30. ^ Roots, Nitrogen Transformations, and Ecosystem Services Annual Review of Plant Biology Vol. 59: 341-363
31. ^ http://www.ehponline.org/docs/2000/108p675-678knobeloch/abstract.html
32. ^ http://www.sciencemag.org/cgi/content/full/324/5928/721-b#R1
33. ^ pg 33: http://www.epa.gov/osw/hazard/recycling/fertiliz/risk/
34. ^ Syers JK, Mackay AD, Brown MW, Currie CD (1986). "Chemical and physical characteristics of phosphate rock materials of varying reactivity". J Sci Food Agric 37: 1057–1064. doi:10.1002/jsfa.2740371102. .
35. ^ Trueman NA (1965). "The phosphate, volcanic and carbonate rocks of Christmas Island (Indian Ocean)". J Geol Soc Aust 12: 261–286. 
36. ^ ^{a b} Taylor MD (1997). "Accumulation of Cadmium derived from fertilizers in New Zealand soils". Science of Total Environment 208: 123–126. doi:10.1016/S0048-9697(97)00273-8. 
37. ^ ^{a b} http://community.seattletimes.nwsource.com/archive/?date=19970703&slug=2547772
38. ^ http://www.pirg.org/toxics/reports/wastelands/
39. ^ http://www.mindfully.org/Farm/Toxic-Waste-Fertilizers.htm
40. ^ "The catfish 'Toxic' suitable for fishmeal production". NowPublic. November 16, 2009. http://www.nowpublic.com/environment/catfish-toxic-suitable-fishmeal-production. Retrieved 23 November 2009. 
41. ^ Hussein EM (1994). "Radioactivity of phosphate ore, superphosphate, and phosphogypsum in Abu-zaabal phosphate". Health Physics 67: 280–282. doi:10.1097/00004032-199409000-00010. 
42. ^ Barisic D, Lulic S, Miletic P (1992). "Radium and uranium in phosphate fertilizers and their impact on the radioactivity of waters". Water Research 26: 607–611. doi:10.1016/0043-1354(92)90234-U. .
43. ^ Scholten LC, Timmermans CWM (1992). "Natural radioactivity in phosphate fertilizers". Nutrient cycling in agroecosystems 43: 103–107. doi:10.1007/BF00747688. 
44. ^ American Public Health Association, Framing Health Matters, Waking a Sleeping Giant: The Tobacco Industry’s Response to the Polonium-210 Issue: Monique E. Muggli, MPH, Jon O. Ebbert, MD, Channing Robertson, PhD and Richard D. Hurt, MD [1]
45. ^ Journal of the Royal Society of Medicine, The big idea: polonium, radon and cigarettes, Tidd J R Soc Med.2008; 101: 156-157 [2]
46. ^ The Age Melbourne Australia, Big Tobacco covered up radiation danger, William Birnbauer [3]
47. ^ "Galloway, James et al., The Nitrogen Cascade", BioScience 53:341-356
48. ^ "Human alteration of the nitrogen cycle, threats, benefits and opportunities" UNESCO - SCOPE Policy briefs, April 2007
49. ^ Food and Agricultural Organization of the U.N. retrieved 9 Aug 2007
50. ^ Jahn GC (2004). "Effect of soil nutrients on the growth, survival and fecundity of insect pests of rice: an overview and a theory of pest outbreaks with consideration of research approaches. Multitrophic interactions in Soil and Integrated Control". International Organization for Biological Control (IOBC) wprs Bulletin 27 (1): 115–122. .
51. ^ Jahn GC, Sanchez ER, Cox PG (2001). "The quest for connections: developing a research agenda for integrated pest and nutrient management". International Rice Research Institute - Discussion Paper 42: 18. 
52. ^ Jahn GC, Cox PG, Rubia-Sanchez E, Cohen M (2001). "The quest for connections: developing a research agenda for integrated pest and nutrient management. pp. 413-430,". S. Peng and B. Hardy [eds.] "Rice Research for Food Security and Poverty Alleviation". Proceeding the International Rice Research Conference, 31 March – 3 April 2000, Los Baños, Philippines. Los Baños (Philippines): International Rice Research Institute.: 692. 
53. ^ Jahn GC, Almazan LP, Pacia J (2005). "Effect of nitrogen fertilizer on the intrinsic rate of increase of the rusty plum aphid, Hysteroneura setariae (Thomas) (Homoptera: Aphididae) on rice (Oryza sativa L.)". Environmental Entomology 34 (4): 938–943. .
54. ^ Preap V, Zalucki MP, Nesbitt HJ, Jahn GC (2001). "Effect of fertilizer, pesticide treatment, and plant variety on realized fecundity and survival rates of Nilaparvata lugens (Stål); Generating Outbreaks in Cambodia". Journal of Asia Pacific Entomology 4 (1): 75–84. .
55. ^ Preap V, Zalucki MP, Jahn GC (2002). "Effect of nitrogen fertilizer and host plant variety on fecundity and early instar survival of Nilaparvata lugens (Stål): immediate response". Proceedings of the 4th International Workshop on Inter-Country Forecasting System and Management for Planthopper in East Asia. 13-15 November 2002. Guilin China. Published by Rural Development Administration (RDA) and the Food and Agriculture Organization (FAO): 163–180,226. 

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

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Dansk (Danish)
n. - kunstgødning, bestøver

Nederlands (Dutch)
kunstmest, mest

Français (French)
n. - engrais

Deutsch (German)
n. - Dünger

Ελληνική (Greek)
n. - λίπασμα

Italiano (Italian)
fertilizzante, concime

Português (Portuguese)
n. - fertilizante (m)

Русский (Russian)
удобрение

Español (Spanish)
n. - fertilizante, abono, abono artificial, abono químico

Svenska (Swedish)
n. - gödningsmedel, pollenöverförare, befruktare (bildl.)

中文（简体）(Chinese (Simplified))
肥料, 受精媒介物

中文（繁體）(Chinese (Traditional))
n. - 肥料, 受精媒介物

한국어 (Korean)
n. - 비료, 수정 매개자

日本語 (Japanese)
n. - 肥料

العربيه (Arabic)
‏(الاسم) سماد‏

עברית (Hebrew)
n. - ‮דשן, זבל כימי‬

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