fertilizer

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(fûr'tl-ī'zər) pronunciation
n.
Any of a large number of natural and synthetic materials, including manure and nitrogen, phosphorus, and potassium compounds, spread on or worked into soil to increase its capacity to support plant growth.



Natural or artificial substance containing the chemical elements that improve growth and productiveness of plants. Fertilizers enhance the natural fertility of the soil or replace the chemical elements taken from the soil by previous crops. The use of manure and composts as fertilizers is probably almost as old as agriculture. Modern chemical fertilizers include one or more of the three elements most important in plant nutrition: nitrogen, phosphorus, and potassium. Of secondary importance are the elements sulfur, magnesium, and calcium.

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How is fertilizer made?

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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

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fertilizer, organic or inorganic material containing one or more of the nutrients-mainly nitrogen, phosphorus, and potassium, and other essential elements required for plant growth. Added to the soil or other medium, fertilizers provide plant nutrients that are naturally lacking or that have been removed by harvesting or grazing, or by physical processes such as leaching or erosion. Organic fertilizers include animal and green manure, fish and bone meal, and compost (see also humus). Microorganisms in the soil decompose organic material, making its elements available for use by plants. Inorganic or artificial fertilizers (also called chemical or mineral fertilizers) are formulated in appropriate concentrations and combinations for various crops and growing conditions. The most popular inorganic fertilizers include: anhydrous ammonia, a gas that is 82% nitrogen; urea, a solid compound containing 46% nitrogen; superphosphate; and diammonium phosphate, containing 18% nitrogen and 46% phosphate. Fertilizers may be spread over the soil surface or plowed under, drilled into deep or shallow layers of the soil, applied in bands under the rows where the seeds are to be sown, drilled into the bands at the time of planting, applied in small doses (micro-dosing) to the seeds at the time of planting, or side-dressed between planted rows. Nitrogen fertilizer washing from farms into surface waters promotes overgrowth of aquatic vegetation, which degrades water quality and can cause eutrophication. Use of inorganic nitrogen suppresses nitrogen-fixing soil bacteria, making agriculture increasingly dependant on artificial fertilizer. See nitrogen cycle.

Bibliography

See publications of the U.S. Dept. of Agriculture.



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

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fertilizer

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pronunciation

IN BRIEF: A substance to make soil produce healthier plant life.

pronunciation The best fertilizer is the gardener's shadow. — Unknown.

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or fertiliser
  1. any substance or mixture of substances that is added to soil or water to assist the growth of plants.
  2. any object or organism, e.g. an insect, that fertilizes an animal or plant.

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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.

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Tennessee Valley Authority: "Results of Fertilizer" demonstration 1942
A large, modern fertilizer spreader

Fertilizer (or fertiliser) is any organic or inorganic material of natural or synthetic origin (other than liming materials) that is added to a soil to supply one or more plant nutrients essential to the growth of plants.[1] A recent assessment found that about 40 to 60% of crop yields are attributable to commercial fertilizer use.[2] They are essential for high-yield harvest: European fertilizer market is expected to grow to €15.3 billion by 2018.[3]

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.[4]

Fertilizers typically provide, in varying proportions:

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 (0% moisture) basis (DM). 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.[5][6]

Only three other macronutrients are required by all plants: carbon, hydrogen, and oxygen. These nutrients are supplied by water and carbon dioxide.

The nitrogen-rich fertilizer ammonium nitrate is also used as an oxidizing agent in improvised explosive devices, sometimes called fertilizer bombs, leading to sale regulations.[7]

Contents

Labeling

The labeling of fertilizers varies. In most countries the macronutrients are labeled with an NPK analysis (in Australia, "N-P-K-S" adding sulfur).[8]

The three numbers on the fertilizer label represent an analysis of the composition by weight. These three numbers correspond to nitrogen, phosphorus, and potassium (N-P-K) and always appear in that specific order. When a 4th number is included, it indicates the sulfur content (N-P-K-S).

While the number for "N" represents the percentage weight of nitrogen, in some European countries, the other two components are not for the analysis of the element, but rather, the analysis of the "available" or "soluble" form of the element. In traditional chemical analysis, the tests used treated the sample so as to measure the equivalent P2O5 and K2O. For instance, some potassium-bearing rocks do not count as having available potassium.

Similarly the number for "P" in some countries is actually the weight of an equivalent quantity of P2O5 whereas in others (including Australia) it refers to elemental phosphorus. In order to calculate the weight of P in the formulation, the weight of P2O5 can be multiplied by 0.44 to compensate for the weight of the oxygen in the molecule. For example, a bag of 10-10-10 has 10 pounds of nitrogen, 10 pounds of P2O5, but only 4.4 pounds of P.

Likewise, the number for "K" in Europe can refer to the weight of an equivalent quantity of K2O, whereas in Australia it refers to elemental potassium. In order to calculate the weight of K in the formulation, the weight of K2O can be multiplied by 0.83 to compensate for the weight of the oxygen in the molecule. For example, a bag of 10-10-10 has 10 pounds of K2O, but only 8.3 pounds of K.

As an example, the fertilizer potash (in modern times, muriate of potash or potassium chloride) is composed of 52% potassium and 48% chlorine by weight; chemical analysis of 100g of potassium chloride (KCl), would show 63g of equivalent potassium oxide (K2O) when done in the manner of fertilizer analysis. The percentage yield of K2O from the original 100g of fertilizer is the number shown on the label. A potash fertilizer would thus be labeled 0-0-63, and not' (except in Australia and some other countries) ' 0-0-52.

History

Founded in 1812, Mirat, producer of manures and fertilizers, is claimed to be the oldest industrial business in Salamanca (Spain).

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 Justus von Liebig, among others.

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.[9] 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.[10]

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.[11]

Forms

Fertilizers come in various forms. The most typical form is solid fertilizer in granulated or powdered. The next most common form is liquid fertilizer; some advantages of liquid fertilizer are its immediate effect and wide coverage.

There are also 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.

More recently, organic fertilizer is on the rise as people are resorting to environmental friendly (or 'green') products. Although organic fertilizer usually contain less nutrients, some people still prefer organic due to natural ingredients[citation needed].

Inorganic commercial fertilizer

Fertilizers are broadly divided into organic fertilizers (composed of organic plant or animal matter), or inorganic or commercial 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. Nearly all nitrogen that plants use are 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 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 typically often have only 0.4% or less of a their weight a given plant nutrient.[12]

Nitrogen fertilizers are often made using the Haber-Bosch process (invented about 1915) 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) (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 all three N:P:K: plant nutrients 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.[13]

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.[14] Without commercial fertilizers it is estimated that about one-third of the food produced now could not be produced.[15] 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.[16] Yara International is the world's largest producer of nitrogen based fertilizers.[17]

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.[18] 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 Center 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.[18] 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.[18]

Top users of nitrogen-based fertilizer[19]
Country Total N use

(Mt pa)

Amt. used for feed/pasture

(Mt pa)

China 18.7 3.0
U.S. 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 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.[20]

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 wastes the growers' time and money. To avoid over-application, the nutrient status of crops should be assessed. Nutrient deficiency can be detected by visually assessing the physical symptoms of the crop. 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 inorganic fertilizer

Common agricultural grade phosphate fertilizers 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 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 Washing in U. S. have fertilizer registration programs with on-line databases listing chemical analyses of fertilizers.[21][22]

The most widely used inorganic fertilizer is super-phosphate and its double and triple strengthed derivatives double super and triple super. Super phosphate was first developed by Lawes at the Rothamstead Agricultural Research Institute in England in the early 19th Century (reference required). Lawes added sulfuric acid to conventional rock phosphate containing the mineral apatite, a calcium fluoro-phosphate. The resulting water soluble phosphorus was able to significantly improve yields on a variety of crops at the Rothamstead Centre and the Superphosphate industry was born. Unfortunately over decades of subsequent useage - it became clear that the solubilisation of fluorine also occurred in the process and this had the same effect as the other halogen sterilants(chlorine, bromine, iodine) over time - soil sterilization. Effectively farmers unknowingly became 100% dependent on 'bought in' water soluble, inorganic fertilizers since the sterilization of soil microflora including its micorhizza, reduced the availability of other natural and trace minerals within the soil. This to some extent explains the resurgence of interest in organic and particularly 'biodynamic' farming systems since these systems replace the essential soil organisms so essential to converting soil minerals into plant available (but rarely water soluble) nutrients. They do this by a variety of processes including chelation whereby essential minerals become plant available - as measured by weak citric acid extraction techniques. Hence the citric acid solubility of phosphate rocks has emerged as a measure of plant availability and enabled so-called 'reactive' phosphate rocks to be used as fertilizer minerals. These should not be confused with high fluorine apatite rocks in which the fluoride content performs a similar function to its role in hardening teeth enamel, ie immobilizing phosphorus. This explains the oceanic origins of many of these high fluorine rocks (Christmas Island, Ocean Island) since the fluorine absorbed from the sea has prevented what were originally massive deposits of bird guano - from being leached from the coral based limestone rocks on which they were originally deposited.

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 degredation 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.

Trace mineral depletion

Many inorganic fertilizers, particularly those based on superphosphate, may 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.[23] Explanations for this include the early encouragement of so-called "luxury consumption" of trace elements as a result of their acidulation and subsequent dissolution in soil water, by free sulphuric acid sourced from superphosphate. This mechanism has also been identified as a possible causal agent for take-up of the heavy metal cadmium from superphosphate based fertilizers. 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]. Such nutrients are described as 'rate limiting' nutrients. 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].

Many soils around the world are deficient in zinc, leading to deficiency in plants and humans.[24]

Overfertilization

Fertilizer burn

Over-fertilization of a vital nutrient can be as detrimental as underfertilization.[25] "Fertilizer burn" can occur when too much fertilizer is applied, resulting in a drying out of the leaves and damage or even death of the plant.[26]

Fertilizers vary in their tendency to burn roughly in accordance with their salt index.[27]

High energy consumption

In the USA in 2004, 317 billion cubic feet of natural gas was consumed in the industrial production of ammonia, less than 1.5% of total U.S. annual consumption of natural gas.[28] 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.[29]

Ammonia is overwhelmingly produced from natural gas, 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.[30] 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.[31]

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

Compost bin for small-scale production of organic fertilizer
A large commercial compost operation

Organic fertilizers include naturally occurring organic materials, (e.g. chicken litter, manure, worm castings, compost, seaweed, guano, bone meal) or naturally occurring mineral deposits (e.g. saltpeter). Poultry litter and cattle manure often create environmental and disposal problems, making their use as fertilizer beneficial. Bones can be processed into phosphate rich bone meal; however, most are simply buried in landfills.

Even if all bones, human, animal and plant wastes were recovered to the extent practical and used for fertilizer, mineral fertilizers and synthetic nitrogen would still be required to make for losses to leaching, to the atmosphere, runoff and the losses impractical to recover.

Benefits of organic fertilizer

Organic fertilizers have been known to improve biodiversity (soil life) and long-term productivity of soil,[32][33] and may prove a large depository for excess carbon dioxide.[34][35][36]

Organic nutrients increase the abundance of soil organisms by providing organic matter and micronutrients for organisms such as fungal mycorrhiza,[37] (which aid plants in absorbing nutrients), and can drastically reduce external inputs of pesticides, energy and fertilizer, at the cost of decreased yield.[38]

Disadvantages of organic fertilizers

  • Organic fertilizers may contain pathogens and other disease causing organisms if not properly composted
  • Nutrient contents are very variable and their release to available forms that the plant can use may not occur at the right plant growth stage
  • Organic fertilizers are comparatively voluminous and can be too bulky to deploy the right amount of nutrients that will be beneficial to plants
  • More expensive to produce

Comparison with inorganic fertilizer

Organic fertilizer nutrient content, solubility, and nutrient release rates are typically all lower than inorganic fertilizers.[39][40] 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 the University of California's integrated pest management program, all organic fertilizers are classified as 'slow-release' fertilizers, and therefore cannot cause nitrogen burn.[41]

Organic fertilizers from composts and other sources can be quite variable from one batch to the next.[42] Without batch testing, amounts of applied nutrient cannot be precisely known. Nevertheless they are at least as effective as chemical fertilizers over longer periods of use.[43]

Example of organic fertilizer

Chicken litter, which consists of chicken manure mixed with sawdust, is an organic fertilizer that has been shown to better condition soil for harvest than synthesized fertilizer. Researchers at the Agricultural Research Service (ARS) studied the effects of using chicken litter, an organic fertilizer, versus synthetic fertilizers on cotton fields, and found that fields fertilized with chicken litter had a 12% increase in cotton yields over fields fertilized with synthetic fertilizer. In addition to higher yields, researchers valued commercially sold chicken litter at a $17/ton premium (to a total valuation of $78/ton) over the traditional valuations of $61/ton due to value added as a soil conditioner.[44]

Other ARS studies have found that algae used to capture nitrogen and phosphorus runoff from agricultural fields can not only prevent water contamination of these nutrients, but also can be used as an organic fertilizer. ARS scientists originally developed the "algal turf scrubber" to reduce nutrient runoff and increase quality of water flowing into streams, rivers, and lakes. They found that this nutrient-rich algae, once dried, can be applied to cucumber and corn seedlings and result in growth comparable to that seen using synthetic fertilizers.[45]

Organic fertilizer sources

Animal

Decomposing animal manure, an organic fertilizer source

Animal-sourced and human urea are suitable for application organic agriculture, while pure synthetic forms of urea are not.[46] The common thread that can be seen through these examples is that organic agriculture attempts to define itself through minimal processing (in contrast to the man-made Haber process), as well as being naturally occurring or via natural biological processes such as composting.[citation needed]

Besides immediate application of urea to the soil, urine can also be improved by converting it to struvite already done with human urine by a Dutch firm.[47] The conversion is performed by adding magnesium to the urine. An added economical advantage of using urine as fertilizer is that it contains a large amount of phosphorus.

Sewage sludge (aka biosolids) use is only available to less than 1% of US ag[clarification needed] land. USDA prohibits use of sewage sludge in organic agricultural operations in the U.S. has been extremely limited and rare due to of the practice (due to toxic metal accumulation, among other factors).[48][49] The USDA now requires 3rd-party certification of high-nitrogen liquid organic fertilizers sold in the U.S.[50]

Plant

Leguminous cover crops are also grown to enrich soil as a green manure through nitrogen fixation from the atmosphere;[51] as well as phosphorus (through nutrient mobilization)[52] content of soils.

Mineral

Mined powdered limestone,[53] rock phosphate and sodium nitrate, are inorganic (not of biologic origins) compounds which are energetically intensive to harvest and are approved for usage in organic agriculture in minimal amounts.[53][54][55]

Negative environmental effects

Runoff of soil and fertilizer during a rain storm
An algal bloom causing eutrophication

Water quality

Eutrophication

The nitrogen-rich compounds found in fertilizer runoff are the primary cause of serious oxygen depletion 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.[56] 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.[57] 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.

Blue baby syndrome

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.[58][59][60] 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.[61]

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).[62]

Soil

Soil acidification

Nitrogen-containing inorganic and organic fertilizers can cause soil acidification when added.[63] [7]. 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[64]

Heavy metal accumulation

The concentration of up to 100 mg/kg of cadmium in phosphate minerals (for example, minerals from Nauru[65] and the Christmas islands[66]) increases the contamination of soil with cadmium, for example in New Zealand.[67]

Steel industry wastes, recycled into fertilizers for their high levels of zinc (essential to plant growth), wastes can include the following toxic metals: lead[68] arsenic, cadmium,[68] chromium, and nickel. The most common toxic elements in this type of fertilizer are mercury, lead, and arsenic.[69][70] Concerns have been raised concerning fish meal mercury content by at least one source in Spain[71]

Radioactive element accumulation

Uranium is another example of a contaminant often found in phosphate fertilizers (at levels from 7 to 100 pCi/g).[72] Eventually these heavy metals can build up to unacceptable levels and build up in vegetable produce.[67] Average annual intake of uranium by adults is estimated to be about 0.5 mg (500 μg) from ingestion of food and water and 0.6 μg from breathing air.[73]

Also, highly radioactive Polonium-210 contained in phosphate fertilizers is absorbed by the roots of plants and stored in its tissues; 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.[74][75][76][77][78][79]

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

Global methane concentrations (surface and atmospheric) for 2005; note distinct plumes

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.[80]

Through the increasing use of nitrogen fertilizer, which is added at a rate of 1 billion tons per year presently[81] 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.[82]

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:[83]

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

Other problems

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).[84][85][86][87][88][89]

See also

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External links



Translations:

Fertilizer

Top

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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