fertilizer web

History

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

Key people

In the 1730s Viscount Charles Townshend first studied the improving effects of the four-crop rotation system that he had observed in use in Flanders. For this he gained the nickname of Turnip Townshend.

Chemist Justus von Liebig contributed greatly to the advancement in the understanding of plant nutrition. His influential works first denounced the vitalist theory of humus, arguing first the importance of ammonia, and later the importance of inorganic minerals. Primarily his work succeeded in setting out questions for agricultural science to address over the next 50 years. In England he attempted to implement his theories commercially through a fertilizer created by treating phosphate of lime in bone meal with sulphuric acid. Although it was much less expensive than the guano that was used at the time, it failed because it was not able to be properly absorbed by crops.

At that time in England Sir John Bennet Lawes was experimenting with crops and manures at his farm at Harpenden and was able to produce a practical superphosphate in 1842 from the phosphates in rock and coprolites. Encouraged, he employed Sir Joseph Henry Gilbert, who had studied under Liebig at the University of Giessen, as director of research. To this day, the Rothamsted research station that they founded still investigates the impact of inorganic and organic fertilizers on crop yields.

In France, Jean Baptiste Boussingault pointed out that the amount of nitrogen in various kinds of fertilizers is important.

Metallurgists Percy Gilchrist and Sidney Gilchrist Thomas invented the Thomas-Gilchrist converter, which enabled the use of high phosphorus acidic Continental ores on steelmaking. The dolomite lime lining of the converter turned in time into calcium phosphate, which could be used as fertilizer known as Thomas-phosphate.

In the early decades of the 20th Century the Nobel prize-winning chemists Carl Bosch of IG Farben and Fritz Haber developed the process that enabled nitrogen to be cheaply synthesised into ammonia, for subsequent oxidisation into nitrates and nitrites.

In 1927 Erling Johnson developed an industrial method for producing nitrophosphate, also known as the Odda process after his Odda Smelteverk of Norway. The process involved acidifying phosphate rock (from Nauru and Banaba Islands in the southern Pacific Ocean) with nitric acid to produce phosphoric acid and calcium nitrate which, once neutralized, could be used as a nitrogen fertilizer.

Industry

The Englishmen James Fison, Edward Packard, Thomas Hadfield and the Prentice brothers each founded companies in the early 19th century to create fertilizers from bonemeal. The developing sciences of chemistry and Paleontology, combined with the discovery of coprolites in commercial quantities in East Anglia, led Fisons and Packard to develop sulfuric acid and fertilizer plants at Bramford, and Snape, Suffolk in the 1850s to create superphosphates, which were shipped around the world from the port at Ipswich. By 1870 there were about 80 factories making superphosphate. After World War I these businesses came under financial pressure through new competition from guano, primarily found on the Pacific islands, as their extraction and distribution had become economically attractive.

The interwar period saw innovative competition from Imperial Chemical Industries who developed synthetic ammonium sulfate in 1923, Nitro-chalk in 1927, and a more concentrated and economical fertilizer called CCF based on ammonium phosphate in 1931. Competition was limited as ICI ensured it controlled most of the world's ammonium sulfate supplies. Other European and North American fertilizer companies developed their market share, forcing the English pioneer companies to merge, becoming Fisons, Packard, and Prentice Ltd. in 1929. Together they were producing 80,000 tonnes of superphosphate per annum by 1934 from their new factory and deep-water docks in Ipswich. By World War II they had acquired about 40 companies, including Hadfields in 1935, and two years later the large Anglo-Continental Guano Works, founded in 1917.

The post-war environment was characterized by much higher production levels as a result of the "Green Revolution" and new types of seed with increased nitrogen-absorbing potential, notably the high-response varieties of maize, wheat, and rice. This has accompanied the development of strong national competition, accusations of cartels and supply monopolies, and ultimately another wave of mergers and acquisitions. The original names no longer exist other than as holding companies or brand names: Fisons and ICI agrochemicals are part of today's Yara International and AstraZeneca companies.

Inorganic fertilizers (mineral fertilizer)

Naturally occurring inorganic fertilizers include Chilean sodium nitrate, mined rock phosphate, and limestone (a calcium source).

Macronutrients and micronutrients

Fertilizers can be divided into macronutrients or micronutrients based on their concentrations in plant 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. 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). There are many micronutrients, required in concentrations ranging from 5 to 100 parts per million (ppm) by mass. Plant micronutrients include iron (Fe), manganese (Mn), boron (B), copper (Cu), molybdenum (Mo), nickel (Ni), chlorine (Cl), and zinc (Zn).

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), which are known as N-P-K fertilizers or compound fertilizers when elements are mixed intentionally. They are named or labeled according to the content of these three elements, which are macronutrients. The mass fraction (percent) nitrogen is reported directly. However, phosphorus is reported as phosphorus pentoxide (P₂O₅), the anhydride of phosphoric acid, and potassium is reported as potassium oxide (K₂O), which is the anhydride of potassium hydroxide. Fertilizer composition is expressed in this fashion for historical reasons in the way it was analyzed (conversion to ash for P and K); this practice dates back to Justus von Liebig (see more below). Consequently, an 18-51-20 fertilizer would have 18% nitrogen as N, 51% phosphorus as P₂O₅, and 20% potassium as K₂O, The other 11% is known as ballast and may or may not be valuable to the plants, depending on what is used as ballast. Although analyses are no longer carried out by ashing first, the naming convention remains. If nitrogen is the main element, they are often described as nitrogen fertilizers.In general, the mass fraction (percentage) of elemental phosphorus, [P] = 0.436 x [P₂O₅] and the mass fraction (percentage) of elemental potassium, [K] = 0.83 x [K₂O] (These conversion factors are mandatory under the UK fertilizer-labelling regulations if elemental values are declared in addition to the N-P-K declaration.)
An 18−51−20 fertilizer therefore contains, by weight, 18% elemental nitrogen (N), 22% elemental phosphorus (P) and 16% elemental potassium (K).

Agricultural versus horticultural

In general, agricultural fertilizers contain only one or two macronutrients. Agricultural fertilizers are intended to be applied infrequently and normally prior to or along side seeding. Examples of agricultural fertilizers are granular triple superphosphate, potassium chloride, urea, and anhydrous ammonia. The commodity nature of fertilizer, combined with the high cost of shipping, leads to use of locally available materials or those from the closest/cheapest source, which may vary with factors affecting transportation by rail, ship, or truck. In other words, a particular nitrogen source may be very popular in one part of the country while another is very popular in another geographic region only due to factors unrelated to agronomic concerns.

Horticultural or specialty fertilizers, on the other hand, are formulated from many of the same compounds and some others to produce well-balanced fertilizers that also contain micronutrients. Some materials, such as ammonium nitrate, are used minimally in large scale production farming. The 18-51-20 example above is a horticultural fertilizer formulated with high phosphorus to promote bloom development in ornamental flowers. Horticultural fertilizers may be water-soluble (instant release) or relatively insoluble (controlled release). Controlled release fertilizers are also referred to as sustained release or timed release. Many controlled release fertilizers are intended to be applied approximately every 3-6 months, depending on watering, growth rates, and other conditions, whereas water-soluble fertilizers must be applied at least every 1-2 weeks and can be applied as often as every watering if sufficiently dilute. Unlike agricultural fertilizers, horticultural fertilizers are marketed directly to consumers and become part of retail product distribution lines.

Nitrogen fertilizer

Major users of nitrogen-based fertilizer
Country	Total N consumption (Mt pa)	of which used for feed & pasture
USA	9.2	4.7
China	18.7	3.0
France	2.5	1.3
Germany	2.0	1.2
Canada	1.6	0.9
UK	1.3	0.9
Brazil	1.7	0.7
Spain	1.2	0.5
Mexico	1.3	0.3
Turkey	1.5	0.3
Argentina	0.4	0.1

Nitrogen fertilizer is often synthesized using the Haber-Bosch process, which produces ammonia. This ammonia is applied directly to the soil or used to produce other compounds, notably ammonium nitrate and urea, both dry, concentrated products that may be used as fertilizer materials or mixed with water to form a concentrated liquid nitrogen fertilizer, UAN. Ammonia can also be used in the Odda Process in combination with rock phosphate and potassium fertilizer to produce compound fertilizers such as 10-10-10 or 15-15-15.

The production of ammonia currently consumes about 5% of global natural gas consumption, which is somewhat under 2% of world energy production. 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.The price increases in natural gas in the past decade, among other factors such as increasing demand, have contributed to an increase in fertilizer price.

Nitrogen-based fertilizers are most commonly used to treat fields used for growing maize, followed by barley, sorghum, rapeseed, soyabean and sunflower.

Health and sustainability issues

Inorganic fertilizers sometimes do not replace trace mineral elements in the soil which become gradually depleted by crops grown there. This has been linked to studies which have shown a marked fall (up to 75%) in the quantities of such minerals present in fruit and vegetables.One exception to this is in Western Australia where deficiencies of zinc, copper, manganese, iron and molybdenum were identified as limiting the growth of 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.

In many countries there is the public perception that inorganic fertilizers "poison the soil" and result in "low quality" produce. However, there is very little (if any) scientific evidence to support these views. When used appropriately, inorganic fertilizers enhance plant growth, the accumulation of organic matter and the biological activity of the soil, overgrazing and soil erosion. The nutritional value of plants for human and animal consumption is typically improved when inorganic fertilizers are used appropriately.

There are concerns though about arsenic, cadmium and uraz nium accumulating in fields treated with phosphate fertilizers. The phosphate minerals contain trace amounts of these elements and if no cleaning step is applied after mining the continuous use of phosphate fertilizers leads towards an accumulation of these elements in the soil. Eventually these can build up to unacceptable levels and get into the produce. (See cadmium poisoning.)

Another problem with inorganic fertilizers is that they are presently produced in ways which cannot be continued indefinitely. Potassium and phosphorus come from mines (or from saline lakes such as the Dead Sea in the case of potassium fertilizers) and resources are limited. Nitrogen is unlimited, but nitrogen fertilizers are presently made using fossil fuels such as natural gas. Theoretically fertilizers could be made from sea water or atmospheric nitrogen using renewable energy, but doing so would require huge investment and is not competitive with today's unsustainable methods. Innovative thermal depolymerization biofuel schemes are trialling the production of byproducts with 9% nitrogen fertilizer sourced from organic waste

Organic fertilizers

A compost bin

Naturally occurring organic fertilizers include manure, slurry, worm castings, peat, seaweed, sewage , and guano. Green manure crops are also grown to add nutrients to the soil. Naturally occurring minerals such as mine rock phosphate, sulfate of potash and limestone are also considered Organic Fertilizers.

Manufactured organic fertilizers include compost, bloodmeal, bone meal and seaweedfish meal, and feather meal. extracts. Other examples are natural enzyme digested proteins,

The decomposing crop residue from prior years is another source of fertility. Though not strictly considered "fertilizer", the distinction seems more a matter of words than reality.

Some ambiguity in the usage of the term 'organic' exists because some of synthetic fertilizers, such as urea and urea formaldehyde, are fully organic in the sense of organic chemistry. In fact, it would be difficult to chemically distinguish between urea of biological origin and that produced synthetically. On the other hand, some fertilizer materials commonly approved for organic agriculture, such as powdered limestone, mined rock phosphate and Chilean saltpeter, are inorganic in the use of the term by chemistry.

Although the density of nutrients in organic material is comparatively modest, they have some advantages. Some or all organic fertilizer can be produced on-site, lowering transport costs. The majority of nitrogen supplying organic fertilizers contain insoluble nitrogen and act as a slow-release fertilizer.

Modern theories of organic agriculture admit the obvious success of Leibig's theory, but stress that there are serious limitations to the current methods of implementing it via chemical fertilization. They re-emphasize the role of humus and other organic components of soil, which are believed to play several important roles:

• Mobilizing existing soil nutrients, so that good growth is achieved with lower nutrient densities while wasting less
• Releasing nutrients at a slower, more consistent rate, helping to avoid a boom-and-bust pattern
• Helping to retain soil moisture, reducing the stress due to temporary moisture stress
• Improving the soil structure

Organics also have the advantage of avoiding certain problems associated with the regular heavy use of artificial fertilizers:

• the possibility of "burning" plants with the concentrated chemicals (i.e. an over supply of some nutrients)
• the progressive decrease of real or perceived "soil health", apparent in loss of structure, reduced ability to absorb precipitation, lightening of soil color, etc.
• the necessity of reapplying artificial fertilizers regularly (and perhaps in increasing quantities) to maintain fertility
• extensive runoff of soluble nitrogen and phosphorus, leading to eutrophication
• the cost (substantial and rising in recent years) and resulting lack of independence

Organic fertilizers can have disadvantages:

• As, typically, a dilute source of nutrients when compared to inorganic fertilizers, applying significant amounts of nutrients in a distant location from the source would incur increased costs for transportation
• The composition of organic fertilizers tends to be more complex and variable than a standardized inorganic product.
• Improperly-processed organic fertilizers may contain pathogens from plant or animal matter that are harmful to humans or plants. However, proper composting should remove them.

In non-organic farming a compromise between the use of artificial and organic fertilizers is common, often using inorganic fertilizers supplemented with the application of organics that are readily available such as the return of crop residues or the application of manure.

Risks of fertilizer use

The problem of over-fertilization is primarily associated with the use of artificial fertilizers, because of the massive quantities applied and the destructive nature of chemical fertilizers on soil nutrient holding structures. The high solubilities of chemical fertilizers also exacerbate their tendency to degrade ecosystems, particularly through eutrophication.

Storage and application of some nitrogen fertilizers in some weather or soil conditions can cause emissions of the greenhouse gas nitrous oxide (N₂O). Ammonia gas (NH₃) may be emitted following application of inorganic fertilizers, or manure or slurry. Besides supplying nitrogen, ammonia can also increase soil acidity (lower pH, or "souring"). Excessive nitrogen fertilizer applications can also lead to pest problems by increasing the birth rate, longevity and overall fitness of certain pests.

The concentration of up to 100 mg/kg of Cadmium in phosphate minerals (for example, minerals from Nauru and the Christmas islands) increases the contamination of soil with Cadmium, for example in New Zealand. Uranium is another example of a contaminant often found in phosphate fertilizers.

For these reasons, it is recommended that knowledge of the nutrient content of the soil and nutrient requirements of the crop are carefully balanced with application of nutrients in inorganic fertilizer especially. This process is called nutrient budgeting. By careful monitoring of soil conditions, farmers can avoid wasting expensive fertilizers, and also avoid the potential costs of cleaning up any pollution created as a byproduct of their farming.

It is also possible to over-apply organic fertilizers; however, their nutrient content, their solubility, and their release rates are typically much lower than chemical fertilizers. By their nature, most organic fertilizers also provide increased physical and biological storage mechanisms to soils, which tend to mitigate their risks.

Global issues

The growth of the world's population to its current figure has only been possible through intensification of agriculture associated with the use of fertilizers. There is an impact on the sustainable consumption of other global resources as a consequence.

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, 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.

Plant nutrition
Plant nutrition is the study of the chemical elements that are necessary for plant growth. There are several principles that apply to plant nutrition.

Some elements are essential, meaning that the absence of a given mineral element will cause the plant to fail to complete its life cycle; that the element cannot be replaced by the presence of another element; and that the element is directly involved in plant metabolism (Arnon and Stout, 1939). However, this principle does not leave any room for the so-called beneficial elements, whose presence, while not required, has clear positive effects on plant growth.

Plants require specific elements for growth and, in some cases, for reproduction.

Major nutrients include:

• C = Carbon 450,000 ppm
• H = Hydrogen 60,000 ppm
• O = Oxygen 450,000 ppm
• P = Phosphorus 2,000 ppm
• K = Potassium 10,000 ppm
• N = Nitrogen 15,000 ppm
• S = Sulfur 1,000 ppm
• Ca = Calcium 5,000 ppm
• Mg = Magnesium 2000 ppm

Minor Nutrients:

• Fe = Iron 100 ppm
• Mo = Molybdenum 0.1 ppm
• B = Boron 20 ppm
• Cu = Copper 6 ppm
• Mn = Manganese 50 ppm
• Zn = Zinc 20 ppm
• Cl = Chlorine 100 ppm

These nutrients are further divided into the mobile and immobile nutrients. A plant will always supply more nutrients to its younger leaves than its older ones, so when nutrients are mobile, the lack of nutrients is first visible on older leaves. When a nutrient is less mobile, the younger leaves suffer because the nutrient does not move up to them but stays lower in the older leaves. Nitrogen, phosphorus, and potassium are mobile nutrients, while the others have varying degrees of mobility. Concentration of ppm (parts per million) represents the dry weight of a representative plant.

Plant uses for essential nutrients

Each of these nutrients is used in a different place for a different essential function.

• Carbon

Carbon is what most of the plant is made of. It forms the backbone of many plant biomolecules, including starches and cellulose. Carbon is fixed through photosynthesiscarbon dioxide in the air and is a part of the carbohydrates that store energy in the plant. from the

• Hydrogen

Hydrogen also is necessary for building sugars and building the plant. It is obtained from air and liquid water.

• Oxygen

Oxygen is necessary for cellular respiration. Cellular respiration is the process of generating energy-rich adenosine triphosphate (ATP) via the consumption of sugars made in photosynthesis. It is obtained from the air.

• Phosphorus

Phosphorus is important in plant bioenergetics. As a component of ATP, phosphorus is needed for the conversion of light energy to chemical energy (ATP) during photosynthesis. Phosphorus can also be used to modify the activity of various enzymes by phosphorylation, and can be used for cell signalling. Since ATP can be used for the biosynthesis of many plant biomolecules, phosphorus is important for plant growth and flower/seed formation.

• Potassium

Potassium regulates the opening and closing of the stoma by a potassium ion pump. Since stomata are important in water regulation, potassium reduces water loss from the leaves and increases drought tolerance. Potassium deficiency may cause necrosis or interveinal chlorosis.

• Nitrogen

Nitrogen is an essential component of all proteins, and as a part of DNA, it is essential for growth and reproduction as well. Nitrogen deficiency most often results in stunting.

• Sulfur

Sulfur produces energy in plants, which is important to growth.

• Calcium

Calcium regulates transport of other nutrients into the plant. Calcium deficiency results in stunting.

• Magnesium

Magnesium is an important part of chlorophyll, a critical plant pigment important in photosynthesis. It is important in the production of ATP through its role as an enzyme cofactor. There are many other biological roles for magnesium-- see Magnesium in biological systems for more information. Magnesium deficiency can result in interveinal chlorosis.

• Iron

Iron is necessary for photosynthesis and is present as an enzyme cofactor in plants. Iron deficiency can result in interveinal chlorosis and necrosis.

• Molybdenum

Molybdenum is a cofactor to enzymes important in building amino acids.

• Boron

Boron is important in sugar transport, cell division, and synthesizing certain enzymes. Boron deficiency causes necrosis in young leaves and stunting.

• Copper

Copper is important for photosynthesis. Symptoms for copper deficiency include chlorosis.

• Manganese

Manganese is necessary for building the chloroplasts. Manganese deficiency may result in coloration abnormalities, such as discolored spots on the foliage.

• Zinc

Zinc is required in a large number of enzymes and plays an essential role in DNA transcription. A typical symptom of zinc deficiency is the stunted growth of leaves, commonly known as "little leaf" and is caused by the oxidative degradation of the growth hormone auxin

• Nickel

Nickel is required in a nitrogen metabolism, however the requirement is vague in all but a very few select plants.

Additional elements include silicon, also used only in a few select plants. Cobalt has proven to be beneficial to at least some plants, but is essential in others, such as legumes where it is required for nitrogen fixation. Vanadium may be required by some plants, but at very low concentrations. It may also be substituting for molybdenum. Selenium and sodium may also be beneficial. Sodium can replace potassium's regulation of stomatal opening and closing.

Plant nutrition is a difficult subject to understand completely, partially because of the variation between different plants and even between different species or individuals of a given clone. Elements present at low levels may demonstrate deficiency, and toxicity is possible at levels that are too high. Further, deficiency of one element may present as symptoms of toxicity from another element, and vice-versa. Carbon and oxygen are absorbed from the air, while other nutrients are absorbed from the soil. Green plants obtain their carbohydrate supply from the carbon dioxide in the air by the process of photosynthesis.