Misplaced Pages

This is an old revision of this page, as edited by Smokefoot (talk | contribs) at 05:41, 26 July 2014 (→Organic fertilizer: remove 98% of section to revised article on organic fertilizer.). The present address (URL) is a permanent link to this revision, which may differ significantly from the current revision.

This article or section is in a state of significant expansion or restructuring. You are welcome to assist in its construction by editing it as well. This template was placed by Smokefoot (talk · contribs). If this article or section has not been edited in several days, please remove this template. If you are the editor who added this template and you are actively editing, please be sure to replace this template with {{in use}} during the active editing session. Click on the link for template parameters to use. This article was last edited by Smokefoot (talk | contribs) 10 years ago. (Update timer)

Fertilizer (or fertiliser) is any organic or inorganic material of natural or synthetic origin (other than liming materials) that is applied to soils or to plant tissues (usually leaves) to supply one or more plant nutrients essential to the growth of plants. Conservative estimates report 30 to 50% of crop yields are attributed to natural or synthetic commercial fertilizer. Global market value is likely to rise to more than US$185 billion until 2019. The European fertilizer market will grow to earn revenues of approx. €15.3 billion in 2018.

Fertilizers typically provide, in varying proportions:

• three main macronutrients: nitrogen (N), phosphorus (P), potassium (K);
• three secondary macronutrients: calcium (Ca), magnesium (Mg), and sulfur (S);
• eight micronutrients: boron (B), chlorine (Cl), copper (Cu), iron (Fe), manganese (Mn), molybdenum (Mo), zinc (Zn) and nickel (Ni) (1987).

The macronutrients are consumed in larger quantities and are present in plant tissue in quantities from 0.15% to 6.0% on a dry matter (DM) (0% moisture) basis. Micronutrients are consumed in smaller quantities and are present in plant tissue on the order of parts per million (ppm), ranging from 0.15 to 400 ppm DM, or less than 0.04% DM.

Only three other structural elements are required by all plants: carbon, hydrogen, and oxygen. These nutrients are supplied by water (through rainfall or irrigation) and carbon dioxide in the atmosphere.

Labeling and rating of chemical fertilizer

In Africa, the Americas, Asia, Europe, a popular labeling scheme consisting of three numbers separated by dashes (e.g. 10-10-10 or 16-4-8) is employed to describe the chemical content of fertilizers. The first number represents the percentage of nitrogen in the product; the second number, P₂O₅ consists of 56.4% oxygen and 43.6% elemental phosphorus; the third, K₂O consists of 17% oxygen and 83% elemental potassium. The generalized form is N-P-K. A 50-pound bag of fertilizer labeled 16-4-8 contains 8 pounds of nitrogen (16% of the 50 pounds), 2 pounds of P₂O₅ (4% of 50 pounds), and 4 pounds of K₂O (8% of 50 pounds). Australian convention adds a fourth number for Sulphur.

Physical forms of fertilizers

Although available in various forms, fertilizer is typical solid as granulated or powdered forms. The next most common form is liquid fertilizer; some advantages of liquid fertilizer are its more rapid effect and easier coverage. Slow-release fertilizers (various forms including fertilizer spikes, tabs, etc.) which reduce the problem of "burning" the plants due to excess nitrogen. Polymer coating of fertilizer ingredients gives tablets and spikes a 'true time-release' or 'staged nutrient release' (SNR) of fertilizer nutrients. Organic fertilizer usually contain less nutrients, but offer other advantages as well as appealling to environmentally friendly users.

Inorganic fertilizer

Fertilizers are broadly divided into organic fertilizers (composed of organic plant or animal matter), or inorganic fertilizers. Plants can only absorb their required nutrients if they are present in easily dissolved chemical compounds. Both organic and inorganic fertilizers provide the same needed chemical compounds. Organic fertilizers provided other macro and micro plant nutrients and are released as the organic matter decays—this may take months or years. Organic fertilizers nearly always have much lower concentrations of plant nutrients and have the usual problems of economical collection, treatment, transportation and distribution.

Inorganic fertilizers nearly always are readily dissolved and unless added have few other macro and micro plant nutrients nor added any 'bulk' to the soil. Nearly all nitrogen that plants use is in the form of NH₃ or NO₃ compounds. The usable phosphorus compounds are usually in the form of phosphoric acid (H₃PO₄) and the potassium (K) is typically in the form of potassium chloride (KCl). In organic fertilizers nitrogen, phosphorus and potassium compounds are released from the complex organic compounds as the animal or plant matter decays. In commercial fertilizers the same required compounds are available in easily dissolved compounds that require no decay—they can be used almost immediately after water is applied. Inorganic fertilizers are usually much more concentrated with up to 64% (18-46-0) of their weight being a given plant nutrient, compared to organic fertilizers that only provide 0.4% or less of their weight as a given plant nutrient.

Nitrogen fertilizers are often made using the Haber-Bosch process (invented 1909) which uses natural gas (CH₄) for the hydrogen and nitrogen gas (N₂) from the air at an elevated temperature and pressure in the presence of a catalyst to form ammonia (NH₃) as the end product. This ammonia is used as a feedstock for other nitrogen fertilizers, such as anhydrous ammonium nitrate (NH₄NO₃) and urea (CO(NH₂)₂). These concentrated products may be diluted with water to form a concentrated liquid fertilizer (e.g. UAN). Deposits of sodium nitrate (NaNO₃) (Chilean saltpeter) are also found the Atacama desert in Chile and was one of the original (1830) nitrogen rich inorganic fertilizers used. It is still mined for fertilizer.

In the nitrophosphate process or Odda process (invented in 1927), phosphate rock with up to a 20% phosphorus (P) content is dissolved with nitric acid (HNO₃) to produce a mixture of phosphoric acid (H₃PO₄) and calcium nitrate (Ca(NO₃)₂). This can be combined with a potassium fertilizer to produce a compound fertilizer with the three macronutrients N, P and K in easily dissolved form.

Phosphate rock can also be processed into water-soluble phosphate (P₂O₅) with the addition of sulfuric acid (H₂SO₄) to make the phosphoric acid in phosphate fertilizers. Phosphate can also be reduced in an electric furnace to make high purity phosphorus; however, this is more expensive than the acid process.

Potash can be used to make potassium (K) fertilizers. All commercial potash deposits come originally from marine deposits and are often buried deep in the earth. Potash ores are typically rich in potassium chloride (KCl) and sodium chloride (NaCl) and are obtained by conventional shaft mining with the extracted ore ground into a powder. For deep potash deposits hot water is injected into the potash which is dissolved and then pumped to the surface where it is concentrated by solar induced evaporation. Amine reagents are then added to either the mined or evaporated solutions. The amine coats the KCl but not NaCl. Air bubbles cling to the amine + KCl and float it to the surface while the NaCl and clay sink to the bottom. The surface is skimmed for the amine + KCl which is then dried and packaged for use as a K rich fertilizer—KCl dissolves readily in water and is available quickly for plant nutrition.

Compound fertilizers often combine N, P and K fertilizers into easily dissolved pellets. The N:P:K ratios quoted on fertilizers give the weight percent of the fertilizer in nitrogen (N), phosphate (P₂O₅) and potash (K₂O equivalent)

The use of commercial inorganic fertilizers has increased steadily in the last 50 years, rising almost 20-fold to the current rate of 100 million tonnes of nitrogen per year. Without commercial fertilizers it is estimated that about one-third of the food produced now could not be produced. The use of phosphate fertilizers has also increased from 9 million tonnes per year in 1960 to 40 million tonnes per year in 2000. A maize crop yielding 6–9 tonnes of grain per hectare requires 31–50 kg of phosphate fertilizer to be applied, soybean requires 20–25 kg per hectare. Yara International is the world's largest producer of nitrogen based fertilizers.

Controlled-release types

Urea and formaldehyde, reacted together to produce sparingly soluble polymers of various molecular weights, is one of the oldest controlled-nitrogen-release technologies, having been first produced in 1936 and commercialized in 1955. The early product had 60 percent of the total nitrogen cold-water-insoluble, and the unreacted (quick release) less than 15%. Methylene ureas were commercialized in the 1960s and 1970s, having 25 and 60% of the nitrogen cold-water-insoluble, and unreacted urea nitrogen in the range of 15 to 30%. Isobutylidene diurea, unlike the methylurea polymers, is a single crystalline solid of relatively uniform properties, with about 90% of the nitrogen water-insoluble.

In the 1960s, the National Fertilizer Development Centre began developing Sulfur-coated urea; sulfur was used as the principle coating material because of its low cost and its value as a secondary nutrient. Usually there is another wax or polymer which seals the sulfur; the slow release properties depend on the degradation of the secondary sealant by soil microbes as well as mechanical imperfections (cracks, etc.) in the sulfur. They typically provide 6 to 16 weeks of delayed release in turf applications. When a hard polymer is used as the secondary coating, the properties are a cross between diffusion-controlled particles and traditional sulfur-coated.

Other coated products use thermoplastics (and sometimes ethylene-vinyl acetate and surfactants, etc.) to produce diffusion-controlled release of urea or soluble inorganic fertilizers. "Reactive Layer Coating" can produce thinner, hence cheaper, membrane coatings by applying reactive monomers simultaneously to the soluble particles. "Multicote" is a process applying layers of low-cost fatty acid salts with a paraffin topcoat.

Besides being more efficient in the utilization of the applied nutrients, slow-release technologies also reduce the impact on the environment and the contamination of the subsurface water.

Application

Synthetic fertilizers are commonly used for growing all crops, with application rates depending on the soil fertility, usually as measured by a soil test and according to the particular crop. Legumes, for example, fix nitrogen from the atmosphere and generally do not require nitrogen fertilizer.

Studies have 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.

Nutrients in soil can be thrown out of balance with high concentrations of fertilizers. The interconnectedness and complexity of this soil ‘food web’ means any appraisal of soil function must necessarily take into account interactions with the living communities that exist within the soil. Stability of the system is reduced by the use of nitrogen-containing fertilizers, which cause soil acidification.

Applying excessive amounts of fertilizer has negative environmental effects, and is expensive. By assessing the physical symptoms of the crop, the appropriate level of fertilization can be determined. Nitrogen deficiency, for example has a distinctive presentation in some species. However, quantitative tests are more reliable for detecting nutrient deficiency before it has significantly affected the crop. Both soil tests and Plant Tissue Tests are used in agriculture to fine-tune nutrient management to the crops needs.

Problems with fertilizers

Water pollution

The nutrients, especially nitrates, in fertilizers can cause problems for natural habitats and for human health if they are washed off soil into watercourses or leached through soil into groundwater. In Europe these problems are being addressed by the European Union's Nitrates Directive. Within Britain farmers are encouraged to manage their land more sustainably in 'catchment-sensitive farming'. In the US, high concentrations of nitrate and phosphorus in runoff and drainage water are classified as non-point source pollutants due to their diffuse origin; this pollution is regulated at state level.

Contamination with impurities

Phosphate rocks all contain hazardous elements such as fluorine, heavy metals and radioactive elements. Consequently, common agricultural grade phosphate fertilizers (which are derived from these phosphate rocks) usually contain impurities such as fluorides, cadmium and uranium, although concentrations of the latter two heavy metals are dependent on the source of the phosphate and the fertilizer production process. These potentially harmful impurities can be removed; however, this significantly increases cost. Highly pure fertilizers are widely available and perhaps best known as the highly water soluble fertilizers containing blue dyes used around households. These highly water soluble fertilizers are used in the plant nursery business and are available in larger packages at significantly less cost than retail quantities. There are also some inexpensive retail granular garden fertilizers made with high purity ingredients.

Oregon and Washington, both in the United States, have fertilizer registration programs with on-line databases listing chemical analyses of fertilizers.

The fluoride content of many widely used phosphate fertilizers has increased soil fluoride concentrations, prompting considerable research into the possibility that soil productivity and food quality may be compromised. It has been found that food contamination from fertilizer is of little concern as plants accumulate little fluoride from the soil; of greater concern is the possibility of fluoride toxicity to livestock that ingest contaminated soils. Also of possible concern are the effects of fluoride on soil microorganisms.

Soil acidification

Also regular use of acidulated fertilizers generally contribute to the accumulation of soil acidity in soils which progressively increases aluminium availability and hence toxicity. The use of such acidulated fertilizers in the tropical and semi-tropical regions of Indonesia and Malaysia has contributed to soil degradation on a large scale from aluminium toxicity, which can only be countered by applications of limestone or preferably magnesian dolomite, which neutralises acid soil pH and also provides essential magnesium.

Overfertilization

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

Fertilizers vary in their tendency to burn roughly in accordance with their salt index.

High energy consumption

In the USA in 2004, 317 billion cubic feet of natural gas were consumed in the industrial production of ammonia, less than 1.5% of total U.S. annual consumption of natural gas. A 2002 report suggested that the production of ammonia consumes about 5% of global natural gas consumption, which is somewhat under 2% of world energy production.

Ammonia is overwhelmingly produced from natural gas, but other energy sources, together with a hydrogen source such as water (via water splitting or electrolysis), 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. The increase in price of natural gases over the past decade, along with other factors such as increasing demand, have contributed to an increase in fertilizer price.

Contribution to climate change

The greenhouse gases carbon dioxide, methane and nitrous oxide are produced during the manufacture of nitrogen fertilizer. The effects can be combined into an equivalent amount of carbon dioxide. The amount varies according to the efficiency of the process. The figure for the United Kingdom is over 2 kilogrammes of carbon dioxide equivalent for each kilogramme of ammonium nitrate. Nitrogen fertilizer can be converted by soil bacteria to nitrous oxide, a greenhouse gas.

Impacts on mycorrhizas

High levels of fertilizer may cause the breakdown of the symbiotic relationships between plant roots and mycorrhizal fungi.

Lack of long-term sustainability

Inorganic fertilizers are now produced in ways which theoretically cannot be continued indefinitely by definition as the resources used in their production are non-renewable. Potassium and phosphorus come from mines (or saline lakes such as the Dead Sea) and such resources are limited. However, more effective fertilizer utilization practices may decrease present usage from mines. Improved knowledge of crop production practices can potentially decrease fertilizer usage of P and K without reducing the critical need to improve and increase crop yields. Atmospheric (unfixed) nitrogen is effectively unlimited (forming over 70% of the atmospheric gases), but this is not in a form useful to plants. To make nitrogen accessible to plants requires nitrogen fixation (conversion of atmospheric nitrogen to a plant-accessible form).

Artificial nitrogen fertilizers are typically synthesized using fossil fuels such as natural gas and coal, which are limited resources. In lieu of converting natural gas to syngas for use in the Haber process, it is also possible to convert renewable biomass to syngas (or wood gas) to supply the necessary energy for the process, though the amount of land and resources (ironically often including fertilizer) necessary for such a project may be prohibitive.

Organic fertilizer

The main "organic fertilizers" are in ranked order: peat, animal wastes (often from slaugherhouses), plant wastes from agriculture, and sewage sludge.

Peat is the main source of organic fertilizer. This immature form of coal confers no nutritional value to the plants, but improves the soil by aeration and absorbing water. Animal sources include the products of the slaughter of animals. Bloodmeal, bone meal, hides, hoofs, and horns are typical components.

Environmental effects

Surface water and Groundwater

Eutrophication

The nitrogen-rich compounds found in fertilizer runoff are the primary cause of serious oxygen depletion in many parts of oceans, especially in coastal zones, lakes and rivers. The resulting lack of dissolved oxygen is greatly reducing the ability of these areas to sustain oceanic fauna. Visually, water may become cloudy and 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. As of 2006, the application of nitrogen fertilizer is being increasingly controlled in northwestern Europe and the United States. If eutrophication can be reversed, it may take decades before the accumulated nitrates in groundwater can be broken down by natural processes.

Nitrate pollution

High application rates of nitrogen-containing fertilizers in order to maximize crop yields, combined with the high solubility of nitrate in soil water leads to increased runoff into surface water as well as leaching into groundwater. The use of excessive rates of nitrogen-containing fertilizers (whether they are commercial inorganic fertilizers or manures) is particularly damaging, as much of the nitrogen that is not taken up by plants is transformed into nitrate which is easily leached.

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).

Atmosphere

Methane emissions from crop fields (notably rice paddy fields) are increased by the application of ammonium-based fertilizers; these emissions contribute greatly to global climate change as methane is a potent greenhouse gas.

Through the increasing use of nitrogen fertilizer, which is was used at a rate of about 110 million tons (of N) per year in 2012 to the already existing amount of reactive nitrogen, nitrous oxide (N₂O) has become the third most important greenhouse gas after carbon dioxide and methane. It has a global warming potential 296 times larger than an equal mass of carbon dioxide and it also contributes to stratospheric ozone depletion.

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

• animal manures and urea, which release methane, nitrous oxide, 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 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.

Food production and food quality

Soil acidification

Nitrogen-containing inorganic and organic fertilizers can cause soil acidification when added. This may lead to decreases in nutrient availability which may be offset by liming.

Persistent organic pollutants

Toxic persistent organic pollutants ("POPs"), such as Dioxins, polychlorinated dibenzo-p-dioxins (PCDDs), and polychlorinated dibenzofurans (PCDFs) have been detected in agricultural fertilizers and soil amendments as documented in a 1999 EPA report. However, that report stated that "generally, the potential risk from certain liming agents and micronutrient fertilizers can be attributed to a single product sample with a single high constituent concentration that far exceeds contaminant levels found in other similar fertilizer products. With these few exceptions, the contaminant levels found in the fertilizer products analyzed for this report are not expected to cause risks of concern, either through contamination of food products or through incidental ingestion of either the fertilizer product or of soil amended with fertilizer."

Heavy metal accumulation

The concentration of cadmium in phosphorus-containing fertilizers varies considerably; for example, mono-ammonium phosphate fertilizer may have a cadmium content of as low as 0.14 mg/kg or as high as 50.9 mg/kg. This is because the phosphate rock used in their manufacture can contain as much as 188 mg/kg cadmium (examples are deposits on Nauru and the Christmas islands). Continuous use of high-cadmium fertilizer can contaminate soil (as shown in New Zealand) and plants. A proposal to limit the cadmium content of phosphate fertilizers is being considered by the European Commission.

Steel industry wastes, recycled into fertilizers for their high levels of zinc (essential to plant growth), wastes can include the following toxic metals: lead arsenic, cadmium, chromium, and nickel. The most common toxic elements in this type of fertilizer are mercury, lead, and arsenic.

Radioactive element accumulation

The radioactive content of the fertilizers varies considerably and depends both on their concentrations in the parent mineral and on the fertilizer production process. Uranium-238 concentrations range can range from 7 to 100 pCi/g in phosphate rock and from 1 to 67 pCi/g in phosphate fertilizers. Where high annual rates of phosphorus fertilizer are used, this can result in uranium-238 concentrations in soils and drainange waters that are several times greater than are normally present. However, the impact of these increases on the risk to human health from radinuclide contamination of foods is very small (less than 0.05 mSv/y).

Trace mineral depletion

Scientific investigations have indicated a trend of decreasing concentrations of minerals (such as iron, zinc, copper and magnesium) in many foods over the last 50-60 years. Intensive farming practices, including the use of inorganic fertilizers are frequently suggested as reasons for these declines and organic farming is often suggested as a solution. Although improved crop yields resulting from inorganic NPK fertilizers are known to dilute the concentrations of other nutrients in plants, much of the measured decline can be attributed to the use of progressively higher-yielding crop varieties which produce foods with lower mineral concentrations than their less productive ancestors. It is, therefore, unlikely that organic farming or reduced use of inorganic fertilizers will solve the problem; foods with high nutrient density are more likely to be achieved using older, lower-yielding varieties or the development of new high-yield, nutrient-dense varieties.

Inorganic fertilizers are, in fact, more likely to solve trace mineral deficiency problems than cause them: 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. Soils in Western Australia are very old, highly weathered and deficient in many of the major nutrients and trace elements. Since this time these trace elements are routinely added to inorganic fertilizers used in agriculture in this state. Many other soils around the world are deficient in zinc, leading to deficiency in both plants and humans, and inorganic zinc fertilizers are widely used to solve this problem.

Increased pest fitness

Excessive nitrogen fertilizer applications can also lead to pest problems by increasing the birth rate, longevity and overall fitness of certain agricultural pests, such as aphids (plant lice).

History

Management of soil fertility has been the pre-occupation of farmers for thousands of years. The start of the modern science of plant nutrition dates to the 19th century and the work of German chemist Justus von Liebig, among others.

John Bennet Lawes, an English entrepreneur, began to experiment on the effects of various manures on plants growing in pots in 1837, and a year or two later the experiments were extended to crops in the field. One immediate consequence was that in 1842 he patented a manure formed by treating phosphates with sulphuric acid, and thus was the first to create the artificial manure industry. In the succeeding year he enlisted the services of Joseph Henry Gilbert, with whom he carried on for more than half a century on experiments in raising crops at the Institute of Arable Crops Research.

The Birkeland–Eyde process was one of the competing industrial processes in the beginning of nitrogen based fertilizer production. It was developed by Norwegian industrialist and scientist Kristian Birkeland along with his business partner Sam Eyde in 1903, based on a method used by Henry Cavendish in 1784. This process was used to fix atmospheric nitrogen (N₂) into nitric acid (HNO₃), one of several chemical processes generally referred to as nitrogen fixation. The resultant nitric acid was then used as a source of nitrate (NO₃) in the reaction

HNO₃ → H + NO₃

which may take place in the presence of water or another proton acceptor. Nitrate is an ion which plants can absorb.

A factory based on the process was built in Rjukan and Notodden in Norway, combined with the building of large hydroelectric power facilities.

The Birkeland-Eyde process is relatively inefficient in terms of energy consumption. Therefore, in the 1910s and 1920s, it was gradually replaced in Norway by a combination of the Haber process and the Ostwald process. The Haber process produces ammonia (NH₃) from methane (CH₄) gas and molecular nitrogen (N₂). The ammonia from the Haber process is then converted into nitric acid (HNO₃) in the Ostwald process, or added to phosphoric acid to produce monoammonium phosphate (NH₄H₂PO₄) or diammonium phosphate.

Mined inorganic fertilizers have been used for many centuries, whereas chemically synthesized inorganic fertilizers were only widely developed during the industrial revolution. Increased understanding and use of fertilizers were important parts of the pre-industrial British Agricultural Revolution and the industrial Green Revolution of the 20th century.

Inorganic fertilizer use has also significantly supported global population growth — it has been estimated that almost half the people on the Earth are currently fed as a result of synthetic nitrogen fertilizer use.

See also

• Fertigation
• History of organic farming
• Milorganite
• Phosphogypsum
• Soil defertilisation
• History of fertilizer

References

1. Stewart, W.M.; Dibb, D.W.; Johnston, A.E.; Smyth, T.J. (2005). "The Contribution of Commercial Fertilizer Nutrients to Food Production". Agronomy Journal. 97: 1–6. doi:10.2134/agronj2005.0001.
2. Ceresana, Market Study Fertilizers - World, May 2013, http://www.ceresana.com/en/market-studies/agriculture/fertilizers-world/
3. "Market Study Fertilizers - Europe". Ceresana.com.
4. "AESL Plant Analysis Handbook – Nutrient Content of Plant". Aesl.ces.uga.edu. Retrieved 25 August 2010.
5. H.A. Mills, J.B. Jones Jr. (1996). Plant Analysis Handbook II: A practical Sampling, Preparation, Analysis, and Interpretation Guide. ISBN 1-878148-05-2.
6. "Summary of State Fertilizer Laws" (PDF). EPA. Retrieved 14 March 2013.
7. "Label Requirements of specialty and other bagged fertilizers". Michigan Department of Agriculture and Rural Development. Retrieved 14 March 2013.
8. "National Code of Practice for Fertilizer Description & Labelling" (PDF). Australian Government Department of Agriculture, Fisheries and Forestry. Retrieved 14 March 2013.
9. NPK ratios of common organic materials Accessed 9 April 2012
10. "Supplemental technical report for sodium nitrate (crops)". www.ams.usda.gov. Retrieved 6 July 2014.
11. "Caliche Ore". www.sqm.com. Retrieved 6 July 2014.
12. EFMA (2000). "Best available techniques for pollution prevention and control in the European fertilizer industry. Booklet No. 7 of 8: Production of NPK fertilizers by the nitrophosphate route" (PDF). www.fertilizerseurope.com. European Fertilizer Manufacturers’ Association. Retrieved 28 June 2014.
13. Potash KCl fertilizer production Accessed 9 April 2012
14. Glass, Anthony (September 2003). "Nitrogen Use Efficiency of Crop Plants: Physiological Constraints upon Nitrogen Absorption". Critical Reviews in Plant Sciences. 22 (5): 453. doi:10.1080/713989757.
15. Commercial fertilizers increase crop yields Accessed 9 April 2012
16. Vance, Carroll P; Uhde-Stone & Allan (2003). "Phosphorus acquisition and use: critical adaptations by plants for securing a non renewable resource". New Phythologist. 157 (3). Blackwell Publishing: 423–447. doi:10.1046/j.1469-8137.2003.00695.x. JSTOR 1514050.
17. "Mergers in the fertiliser industry". The Economist. 18 February 2010. Retrieved 21 February 2010.
18. ^ J. B. Sartain, University of Florida (2011). "Food for turf: Slow-release nitrogen". Grounds Maintenance.
19. Livestock's Long Shadow: Environmental Issues and Options, Table 3.3. Retrieved 29 June 2009 United Nations Food and Agriculture Organization
20. "Nitrogen Applied". Newswise.com. 19 July 2008. Retrieved 22 July 2012.
21. Debra. "Nitrates and watercourses".
22. European Union. "Nitrates Directive".
23. Defra. "Catchment-Sensitive Farming".
24. "Polluted Runoff: Nonpoint Source Pollution". EPA. Retrieved 23 July 2014.
25. Zapata, F; Roy, RN (2004). Use of phosphate rocks for sustainable agriculture (PDF). Rome: FAO. p. 82. Retrieved 16 July 2014.
26. ^ Mortvedt, JJ; Beaton, JD. "Heavy Metal And Radionuclide Contaminants In Phosphate Fertilizers". Retrieved 16 July 2014.
27. McLaughlin, M. J.; Tiller, K. G.; Naidu, R.; Stevens, D. P. (1996). "Review: the behaviour and environmental impact of contaminants in fertilizers". Soil Research. 34: 1–54.
28. ^ Chaney, R.L. (2012). "Food safety issues for mineral and organic fertilizers". Advances in Agronomy. 117: 51–99.
29. "Washington State Dept. of Agriculture Fertilizer Product Database". Agr.wa.gov. 23 May 2012. Retrieved 17 June 2012.
30. http://www.regulatory-info-sc.com/ Washington and Oregon links
31. ^ Loganathan, P.; Hedley, M.J.; Grace, N.D. (2008). "Pasture soils contaminated with fertilizer-derived cadmium and fluorine: livestock effects". Reviews of Environmental Contamination and Toxicology. 192: 29–66. doi:10.1007/978-0-387-71724-1_2. {{cite journal}}: |access-date= requires |url= (help)
32. ^ Cronin, S. J.; Manoharan, V.; Hedley, M. J.; Loganathan, P. (2000). "Fluoride: A review of its fate, bioavailability, and risks of fluorosis in grazed‐pasture systems in New Zealand". New Zealand Journal of Agricultural Research. 43: 295–3214. doi:10.1080/00288233.2000.9513430. {{cite journal}}: |access-date= requires |url= (help)
33. Wilke, B.M. (1987). "Fluoride-induced changes in chemical properties and microbial activity of mull, moder and mor soils". Biology and Fertility of Soils. 5: 49–55. doi:10.1007/BF00264346. {{cite journal}}: |access-date= requires |url= (help)
34. "Nitrogen Fertilization: General Information". Hubcap.clemson.edu. Retrieved 17 June 2012.
35. "Avoiding Fertilizer Burn". Improve-your-garden-soil.com. Retrieved 17 June 2012.
36. "Understanding Salt index of fertilizers" (PDF). Retrieved 22 July 2012.
37. Aleksander Abram and D. Lynn Forster (2005). "A Primer on Ammonia, Nitrogen Fertilizers, and Natural Gas Markets". Department of Agricultural, Environmental, and Development Economics, Ohio State University: 38. {{cite journal}}: Cite journal requires |journal= (help)
38. IFA – Statistics – Fertilizer Indicators – Details – Raw material reserves, (2002–10)
39. Häussinger, Peter; Reiner Lohmüller, Allan M. Watson (2000). Ullmann's Encyclopedia of Industrial Chemistry, Volume 18. Weinheim, Germany: Wiley-VCH Verlag GmbH & Co. KGaA. pp. 249–307. ISBN 9783527306732.
40. Appl, Max (2000). Ullmann's Encyclopedia of Industrial Chemistry, Volume 3. Weinheim, Germany: Wiley-VCH Verlag GmbH & Co. KGaA. pp. 139–225. ISBN 9783527306732. Retrieved 3 January 2013.
41. Sawyer JE (2001). "Natural gas prices affect nitrogen fertilizer costs". IC-486. 1: 8.
42. "Table 8—Fertilizer price indexes, 1960–2007".
43. Sam Wood and Annette Cowie (2004). "A Review of Greenhouse Gas Emission Factors for Fertiliser Production". IEA Bioenergy IEA Bioenergy. {{cite journal}}: Cite journal requires |journal= (help)
44. Carroll and Salt, Steven B. and Steven D. (2004). Ecology for Gardeners. Cambridge: Timber Press. ISBN 9780881926118.
45. Heinrich Dittmar, Manfred Drach, Ralf Vosskamp, Martin E. Trenkel, Reinhold Gutser, Günter Steffens "Fertilizers, 2. Types" in Ullmann's Encyclopedia of Industrial Chemistry, 2009, Wiley-VCH, Weinheim. doi:10.1002/14356007.n10_n01
46. "Rapid Growth Found in Oxygen-Starved Ocean ‘Dead Zones’", NY Times, 14 August 2008
47. John Heilprin, Associated Press. "Discovery Channel :: News – Animals :: U.N.: Ocean 'Dead Zones' Growing". Dsc.discovery.com. Retrieved 25 August 2010.
48. Van Grinsven, H. J. M.; Ten Berge, H. F. M.; Dalgaard, T.; Fraters, B.; Durand, P.; Hart, A.; ... & Willems, W. J. (2012). "Management, regulation and environmental impacts of nitrogen fertilization in northwestern Europe under the Nitrates Directive; a benchmark study" (PDF). Biogeosciences. 9: 5143–5160. doi:10.5194/bg-9-5143-2012. Retrieved 3 July 2014.{{cite journal}}: CS1 maint: multiple names: authors list (link) CS1 maint: unflagged free DOI (link)
49. "A Farmer's Guide To Agriculture and Water Quality Issues: 3. Environmental Requirements & Incentive Programs For Nutrient Management". www.cals.ncsu.edu. Retrieved 3 July 2014.
50. State-EPA Nutrient Innovations Task Group (2009). "An Urgent Call to Action – Report of the State-EPA Nutrient Innovations Task Group" (PDF). water.epa.gov. Retrieved 3 July 2014.
51. C. J. Rosen and B. P. Horgan (9 January 2009). "Preventing Pollution Problems from Lawn and Garden Fertilizers". Extension.umn.edu. Retrieved 25 August 2010.
52. "Journal of Contaminant Hydrology - Fertilizer-N use efficiency and nitrate pollution of groundwater in developing countries". ScienceDirect.com. Retrieved 17 June 2012.
53. "NOFA Interstate Council: The Natural Farmer. Ecologically Sound Nitrogen Management. Mark Schonbeck". Nofa.org. 25 February 2004. Retrieved 25 August 2010.
54. Roots, Nitrogen Transformations, and Ecosystem Services Annual Review of Plant Biology Vol. 59: 341–363
55. Lynda Knobeloch, Barbara Salna, Adam Hogan, Jeffrey Postle, and Henry Anderson. "Blue Babies and Nitrate-Contaminated Well Water". Ehponline.org. Retrieved 25 August 2010.{{cite web}}: CS1 maint: multiple names: authors list (link)
56. Self, J.R. (2014). "Nitrates in Drinking Water". www.ext.colostate.edu. Colorado State University Extension. Retrieved 23 July 2014.
57. Bodelier, Paul, L.E.; Peter Roslev3, Thilo Henckel1 & Peter Frenzel1 (November 1999). "Stimulation by ammonium-based fertilizers of methane oxidation in soil around rice roots". Nature. 403 (6768): 421–424. Bibcode:2000Natur.403..421B. doi:10.1038/35000193. PMID 10667792. Retrieved 2 February 2009.{{cite journal}}: CS1 maint: multiple names: authors list (link) CS1 maint: numeric names: authors list (link)
58. Banger, K.; Tian, H.; Lu, C. (2012). "Do nitrogen fertilizers stimulate or inhibit methane emissions from rice fields?". Global Change Biology. 18 (10): 3259–3267. doi:10.1111/j.1365-2486.2012.02762.x. Retrieved 3 July 2014.
59. FAO (2012). Current world fertilizer trends and outlook to 2016 (PDF). Rome: Food and Agriculture Organization of the United Nations. p. 13. Retrieved 3 July 2014.
60. http://www.nature.com/nature/journal/v451/n7176/fig_tab/nature06592_F1.html An Earth-system perspective of the global nitrogen cycle Nicolas Gruber & James N. Galloway Nature 451, 293–296(17 January 2008) doi:10.1038/nature06592
61. "Human alteration of the nitrogen cycle, threats, benefits and opportunities" UNESCO – SCOPE Policy briefs, April 2007
62. Roy, R. N.; Misra, R. V.; Montanez, A. (2002). "Decreasing reliance on mineral nitrogen-yet more food" (PDF). AMBIO: A Journal of the Human Environment. 31 (2): 177–183. doi:10.1579/0044-7447-31.2.177. Retrieved 3 July 2014.
63. http://www.sciencemag.org/cgi/content/full/324/5928/721-b#R1
64. http://soil.scijournals.org/cgi/content/full/72/1/238
65. US EPA (1999). "Estimating Risk from Contaminants Contained in Agricultural Fertilizers" (PDF). http://www.epa.gov/osw/hazard/recycling/fertiliz/risk/. U.S. Environmental Protection Agency. pp. 33–34. Retrieved 22 July 2014. {{cite web}}: External link in |website= (help)
66. US EPA (1999). "Estimating Risk from Contaminants Contained in Agricultural Fertilizers" (PDF). http://www.epa.gov/osw/hazard/recycling/fertiliz/risk/. U.S. Environmental Protection Agency. p. 15. Retrieved 22 July 2014. {{cite web}}: External link in |website= (help)
67. Lugon-Moulin, N.; Ryan, L.; Donini, P.; Rossi, L. (2006). "Cadmium content of phosphate fertilizers used for tobacco production" (PDF). Agron. Sustain. Dev. 26: 151–155. Retrieved 27 June 2014.
68. Zapata, F.; Roy, R.N. (2004). "Use of Phosphate Rocks for Sustainable Agriculture: Secondary nutrients, micronutrients, liming effect and hazardous elements associated with phosphate rock use". www.fao.org. FAO. Retrieved 27 June 2014.
69. 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 (11): 1057–1064. doi:10.1002/jsfa.2740371102.{{cite journal}}: CS1 maint: multiple names: authors list (link)
70. Trueman NA (1965). "The phosphate, volcanic and carbonate rocks of Christmas Island (Indian Ocean)". J Geol Soc Aust. 12: 261–286.
71. 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.
72. Oosterhuis, F.H.; Brouwer, F.M.; Wijnants, H.J. (2000). "A possible EU wide charge on cadmium in phosphate fertilisers: Economic and environmental implications" (PDF). dare.ubvu.vu.nl. Retrieved 27 June 2014.
73. Fertilizers Europe (2014). "Putting all the cards on the table" (PDF). http://www.fertilizerseurope.com/. Retrieved 27 June 2014. {{cite web}}: External link in |website= (help)
74. Wates, J. (2014). "Revision of the EU fertilizer regulation and cadmium content of fertilisers". www.iatp.org. Retrieved 27 June 2014.
75. ^ Wilson, Duff (3 July 1997). "Business | Fear In The Fields – How Hazardous Wastes Become Fertilizer – Spreading Heavy Metals On Farmland Is Perfectly Legal, But Little Research Has Been Done To Find Out Whether It's Safe | Seattle Times Newspaper". Community.seattletimes.nwsource.com. Retrieved 25 August 2010.
76. "Waste Lands: The Threat Of Toxic Fertilizer". Pirg.org. 3 July 1997. Retrieved 25 August 2010.
77. mindfully.org. "Waste Lands: The Threat of Toxic Fertilizer Released by PIRG Toxic Wastes Found in Fertilizers Cat Lazaroff / ENS 7may01". Mindfully.org. Retrieved 25 August 2010.
78. "Radiation Protection:Fertilizer and Fertilizer Production Wastes". US EPA. 2012. Retrieved 17 July 2014.
79. Khater, A. E. M. (2008). "Uranium and heavy metals in phosphate fertilizers" (PDF). www.radioecology.info. Retrieved 17 July 2014.
80. ^ NCRP (1987). Radiation Exposure of the U.S. Population from Consumer Products and Miscellaneous Sources. National Council on Radiation Protection and Measurements. pp. 29–32. Retrieved 17 July 2014.
81. Hussein EM (1994). "Radioactivity of phosphate ore, superphosphate, and phosphogypsum in Abu-zaabal phosphate". Health Physics. 67 (3): 280–282. doi:10.1097/00004032-199409000-00010. PMID 8056596.
82. Barisic D, Lulic S, Miletic P (1992). "Radium and uranium in phosphate fertilizers and their impact on the radioactivity of waters". Water Research. 26 (5): 607–611. doi:10.1016/0043-1354(92)90234-U.{{cite journal}}: CS1 maint: multiple names: authors list (link)
83. Hanlon, E. A. (2012). "Naturally Occurring Radionuclides in Agricultural Products". edis.ifas.ufl.edu. University of Florida. Retrieved 17 July 2014.
84. Sharpley, A. N.; Menzel, R. G. (1987). "The impact of soil and fertilizer phosphorus on the environment". Advances in Agronomy. 41: 297–324.
85. ^ Davis, D.R.; Epp, M.D.; Riordan, H.D. (2004). "Changes in USDA Food Composition Data for 43 Garden Crops, 1950 to 1999". Journal of the American College of Nutrition. 23: 669–682.
86. ^ Thomas, D. (2007). "The mineral depletion of foods available to us as a nation (1940–2002) – A Review of the 6th Edition of McCance and Widdowson". Nutrition and Health. 19: 21–55.
87. Jarrell, W.M.; Beverly, R.B. (1981). "The Dilution Effect in Plant Nutrition Studies". Advances in Agronomy. 34: 197–224.
88. Fan, M. S.; Zhao, F. J.; Fairweather-Tait, S. J.; Poulton, P. R.; Dunham, S. J.; McGrath, S. P. (2008). "Evidence of decreasing mineral density in wheat grain over the last 160 years". Journal of Trace Elements in Medicine and Biology. 22: 315–324.
89. Zhao, F. J.; Su, Y. H.; Dunham, S. J.; Rakszegi, M.; Bedo, Z.; McGrath, S. P.; Shewry, P. R. (2009). "Variation in mineral micronutrient concentrations in grain of wheat lines of diverse origin". Journal of Cereal Science. 49: 290–295.
90. Saltzman, A.; Birol, E.; Bouis, H. E.; Boy, E.; De Moura, F.F.; Islam, Y.; Pfeiffer, W. H. (2013). "Biofortification: progress toward a more nourishing future". Global Food Security. 2: 9–17.
91. ^ Moore, Geoff (2001). Soilguide - A handbook for understanding and managing agricultural soils (PDF). Perth, Western Australia: Agriculture Western Australia. pp. 161–207. ISBN 0 7307 0057 7.
92. "Zinc in Soils and Crop Nutrition". Scribd.com. 25 August 2010. Retrieved 17 June 2012.
93. 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.
94. Jahn GC, Sanchez ER, Cox PG (2001). "The quest for connections: developing a research agenda for integrated pest and nutrient management" (PDF). International Rice Research Institute – Discussion Paper. 42: 18.{{cite journal}}: CS1 maint: multiple names: authors list (link)
95. 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 "Rice Research for Food Security and Poverty Alleviation". Proceeding the International Rice Research Conference, March 31,  – April 3, 2000, Los Baños, Philippines. Los Baños (Philippines): International Rice Research Institute.: 692.{{cite journal}}: CS1 maint: multiple names: authors list (link)
96. 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. doi:10.1603/0046-225X-34.4.938.{{cite journal}}: CS1 maint: multiple names: authors list (link)
97. 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. doi:10.1016/S1226-8615(08)60107-7.{{cite journal}}: CS1 maint: multiple names: authors list (link)
98. 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. November 13–15, 2002. Guilin China. Published by Rural Development Administration (RDA) and the Food and Agriculture Organization (FAO): 163–180, 226.{{cite journal}}: CS1 maint: multiple names: authors list (link)
99.  This article incorporates text from a publication now in the public domain: Chisholm, Hugh, ed. (1911). Encyclopædia Britannica (11th ed.). Cambridge University Press. {{cite encyclopedia}}: Missing or empty |title= (help)
100. Aaron John Ihde (1984). The development of modern chemistry. Courier Dover Publications. p. 678. ISBN 0-486-64235-6.
101. G. J. Leigh (2004). The world's greatest fix: a history of nitrogen and agriculture. Oxford University Press US. pp. 134–139. ISBN 0-19-516582-9.
102. Trevor Illtyd Williams; Thomas Kingston Derry (1982). A short history of twentieth-century technology c. 1900-c. 1950. Oxford University Press. pp. 134–135. ISBN 0-19-858159-9.
103. IPNI. "Monoammonium Phosphate (MAP)" (PDF). www.ipni.net. International Plant Nutrition Institute. Retrieved 21 July 2014.
104. IPNI. "Diammonium Phosphate" (PDF). www.ipni.net. International Plant Nutrition Institute. Retrieved 21 July 2014.
105. Erisman, Jan Willem; MA Sutton, J Galloway, Z Klimont, W Winiwarter (October 2008). "How a century of ammonia synthesis changed the world". Nature Geoscience. 1 (10): 636. Bibcode:2008NatGe...1..636E. doi:10.1038/ngeo325. Retrieved 22 October 2010.{{cite journal}}: CS1 maint: multiple names: authors list (link)

External links

• Nitrogen for Feeding Our Food, Its Earthly Origin, Haber Process
• The Fertilizer Institute (TFI) US Fertilizer Industry Association
• International Fertilizer Industry Association (IFA)
• European Fertiliser Manufacturers Association
• How to read fertilizer tags article
• Agriculture Guide, Complete Guide to Fertilizers and Fertilization
• 4R's Nutrient Stewardship program from The Fertilizer Institute

• Fertilizers