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Afarmerspreadingmanureto improvesoil fertility

Afertilizer(American English) orfertiliser(British English) is any material of natural or synthetic origin that is applied to soil or to plant tissues to supplyplant nutrients.Fertilizers may be distinct fromliming materialsor other non-nutrientsoil amendments.Many sources of fertilizer exist, both natural and industrially produced.[1]For most modern agricultural practices, fertilization focuses on three main macro nutrients:nitrogen(N),phosphorus(P), andpotassium(K) with occasional addition of supplements likerock flourfor micronutrients. Farmers apply these fertilizers in a variety of ways: through dry or pelletized or liquid application processes, using large agricultural equipment or hand-tool methods.

Historically fertilization came from natural or organic sources:compost,animal manure,human manure,harvested minerals,crop rotationsand byproducts of human-nature industries (i.e.fish processing waste,orbloodmealfromanimal slaughter). However, starting in the 19th century, after innovations inplant nutrition,anagricultural industrydeveloped around synthetically created fertilizers. This transition was important in transforming theglobal food system,allowing for larger-scaleindustrial agriculturewith large crop yields.

Nitrogen-fi xingchemical processes, such as theHaber processinvented at the beginning of the 20th century, and amplified by production capacity created during World War II, led to a boom in using nitrogen fertilizers.[2]In the latter half of the 20th century, increased use of nitrogen fertilizers (800% increase between 1961 and 2019) has been a crucial component of the increased productivity ofconventional food systems(more than 30% per capita) as part of the so-called "Green Revolution".[3]

The use of artificial and industrially-applied fertilizers has caused environmental consequences such aswater pollutionandeutrophicationdue to nutritional runoff;carbonand other emissions from fertilizer production and mining; andcontamination and pollution of soil.Varioussustainable-agriculturepractices can be implemented to reduce the adverse environmental effects of fertilizer andpesticideuse as well as otherenvironmental damagecaused byindustrial agriculture.

History

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Main article:History of fertilizer
Total fertilizer production by type.[4]
World population supported with and without synthetic nitrogen fertilizers.[5]
Founded in 1812,Mirat,producer ofmanuresand fertilizers, is claimed to be the oldest industrial business inSalamanca(Spain).
Cropland nitrogen budget by component and region, a large proportion comes from fertilizers.

Management ofsoil fertilityhas preoccupied farmers since the beginning of agriculture. Middle Eastern, Chinese, Mesoamerican, and Cultures of the Central Andes were all early adopters of agriculture. This is thought to have led to their cultures growing faster in population which allowed an exportation of culture to neighboring hunter gatherer groups. Fertilizer use along with agriculture allowed some of these early societies a critical advantage over their neighbors, leading them to become dominant cultures in their respective regions (P Bellwood - 2023[6])[7].Egyptians, Romans, Babylonians, and early Germans are all recorded as using minerals or manure to enhance the productivity of their farms.[1]The scientific research of plant nutrition started well before the work of German chemistJustus von Liebigalthough his name is most mentioned as the "father of the fertilizer industry".[8]Nicolas Théodore de Saussureand scientific colleagues at the time were quick to disprove the simplifications of von Liebig. Prominent scientists on whom von Liebig drew wereCarl Ludwig SprengerandHermann Hellriegel.In this field, a 'knowledge erosion'[9]took place, partly driven by an intermingling of economics and research.[10]John Bennet Lawes,an Englishentrepreneur,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 sulfuric acid, and thus was the first to create the artificial manure industry. In the succeeding year he enlisted the services ofJoseph Henry Gilbert;together they performed crop experiments at theInstitute of Arable Crops Research.[11]

TheBirkeland–Eyde processwas one of the competing industrial processes in the beginning of nitrogen-based fertilizer production.[12]This process was used to fix atmosphericnitrogen(N2) intonitric acid(HNO3), one of several chemical processes generally referred to asnitrogen fixation.The resultant nitric acid was then used as a source ofnitrate(NO3−). A factory based on the process was built inRjukanandNotoddenin Norway, combined with the building of largehydroelectric powerfacilities.[13]

The 1910s and 1920s witnessed the rise of theHaber processand theOstwald process.The Haber process produces ammonia (NH3) frommethane(CH4) (natural gas) gas and molecular nitrogen (N2) from the air. The ammonia from the Haber process is then partially converted intonitric acid(HNO3) in theOstwald process.[14]It is estimated that a third of annual global food production uses ammonia from the Haber–Bosch process, and that this supports nearly half the world's population.[15][16]After World War II, nitrogen production plants that had ramped up for wartime bomb manufacturing were pivoted towards agriculture uses.[17]The use of synthetic nitrogen fertilizers has increased steadily over the last 50 years, rising almost 20-fold to the current rate of 100 milliontonnesof nitrogen per year.[18]

The development of synthetic nitrogen fertilizer has 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.[19]The use of phosphate fertilizers has also increased from 9 million tonnes per year in 1960 to 40 million tonnes per year in 2000.

Agricultural use of inorganic fertilizers in 2021 was 195 million tonnes of nutrients, of which 56% was nitrogen.[20]Asia represented 53% of world total agricultural use of inorganic fertilizers in 2021, followed by the Americas (29%), Europe (12%), Africa (4%) and Oceania (2%). This ranking of the regions is the same for all nutrients. The main users of inorganic fertilizers are, in descending order, China, India, Brazil and the United States of America (see Table 15), with China the largest user of each nutrient.[20]

A maize crop yielding 6–9 tonnes of grain perhectare(2.5 acres) requires 31–50 kilograms (68–110 lb) ofphosphatefertilizer to be applied; soybean crops require about half, 20–25 kg per hectare.[21]Yara Internationalis the world's largest producer of nitrogen-based fertilizers.[22]

Mechanism

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Six tomato plants grown with and without nitrate fertilizer on nutrient-poor sand/clay soil. One of the plants in the nutrient-poor soil has died.
Inorganic fertilizer use by region[23]

Fertilizers enhance the growth of plants. This goal is met in two ways, the traditional one being additives that provide nutrients. The second mode by which some fertilizers act is to enhance the effectiveness of the soil by modifying its water retention and aeration. This article, like many on fertilizers, emphasizes the nutritional aspect. Fertilizers typically provide, in varyingproportions:[24]

The nutrients required for healthy plant life are classified according to the elements, but the elements are not used as fertilizers. Insteadcompoundscontaining these elements are the basis of fertilizers. The macro-nutrients are consumed in larger quantities and are present in plant tissue in quantities from 0.15% to 6.0% on adry matter(DM) (0% moisture) basis. Plants are made up of four main elements: hydrogen, oxygen, carbon, and nitrogen. Carbon, hydrogen and oxygen are widely available respectively incarbon dioxideand in water. Although nitrogen makes up most of theatmosphere,it is in a form that is unavailable to plants. Nitrogen is the most important fertilizer since nitrogen is present inproteins(amide bondbetweenamino-acids),DNA(puricandpyrimidicbases) and other components (e.g.,tetrapyrrolichemeinchlorophyll). To be nutritious to plants, nitrogen must be made available in a "fixed" form. Only some bacteria and their host plants (notablylegumes) can fix atmospheric nitrogen (N2) by converting it toammonia(NH3).Phosphate(PO3−4) is required for the production ofDNA(genetic code) andATP,the main energy carrier incells,as well as certainlipids(phospholipids,the main components of thelipidic double layerof thecell membranes).

Microbiological considerations

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Two sets ofenzymatic reactionsare highly relevant to the efficiency of nitrogen-based fertilizers.

Urease

The first is thehydrolysis(reaction with water) ofurea(CO(NH2)2). Manysoilbacteriapossess the enzymeurease,whichcatalyzesthe conversion of urea toammoniumion (NH+4) andbicarbonateion(HCO−3).

Ammonia oxidation

Ammonia-oxidizing bacteria(AOB), such as species ofNitrosomonas,oxidizeammonia (NH3) tonitrite(NO−2), a process termednitrification.[26]Nitrite-oxidizing bacteria,especiallyNitrobacter,oxidizenitrite(NO−2) tonitrate(NO−3), which is extremelysolubleand mobile and is a major cause ofeutrophicationandalgal bloom.

Classification

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Fertilizers are classified in several ways. They are classified according to whether they provide a single nutrient (e.g., K, P, or N), in which case they are classified as "straight fertilizers". "Multinutrient fertilizers" (or "complex fertilizers" ) provide two or more nutrients, for example N and P. Fertilizers are also sometimes classified as inorganic (the topic of most of this article) versus organic. Inorganic fertilizers exclude carbon-containing materials exceptureas.Organic fertilizers are usually (recycled) plant- or animal-derived matter. Inorganic are sometimes called synthetic fertilizers since various chemical treatments are required for their manufacture.[27]

Single nutrient ( "straight" ) fertilizers

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The main nitrogen-based straight fertilizer isammonia(NH3)ammonium(NH4+) or its solutions, including:

  • Ammonium nitrate(NH4NO3) with 34-35% nitrogen is also widely used.
  • Urea(CO(NH2)2), with 45-46% nitrogen, another popular source of nitrogen, having the advantage that it is solid and non-explosive, unlike ammonia and ammonium nitrate.
  • Calcium ammonium nitrateIs a blend of 20-30%limestoneCaCO3ordolomite(Ca,Mg)CO3and 70-80%ammonium nitratewith 24-28 % nitrogen.
  • Calcium nitratewith 15,5% nitrogen and 19% calcium, reportedly holding a small share of the nitrogen fertilizer market (4% in 2007).[28]

The main straight phosphate fertilizers are thesuperphosphates:

  • "Single superphosphate" (SSP) consisting of 14–18% P2O5,again in the form of Ca(H2PO4)2,but alsophosphogypsum(CaSO4· 2 H2O).
  • Triple superphosphate(TSP) typically consists of 44–48% of P2O5and no gypsum.

A mixture of single superphosphate and triple superphosphate is called double superphosphate. More than 90% of a typical superphosphate fertilizer is water-soluble.

The main potassium-based straight fertilizer ismuriate of potash(MOP, 95–99% KCl). It is typically available as 0-0-60 or 0-0-62 fertilizer.

Multinutrient fertilizers

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These fertilizers are common. They consist of two or more nutrient components.

Binary (NP, NK, PK) fertilizers

Major two-component fertilizers provide both nitrogen and phosphorus to the plants. These are called NP fertilizers. The main NP fertilizers are 

About 85% of MAP and DAP fertilizers are soluble in water.
NPK fertilizers
Main article:Labeling of fertilizer

NPK fertilizers are three-component fertilizers providing nitrogen, phosphorus, and potassium. There exist two types of NPK fertilizers: compound and blends. Compound NPK fertilizers contain chemically bound ingredients, while blended NPK fertilizers are physical mixtures of single nutrient components.

NPK ratingis a rating system describing the amount of nitrogen, phosphorus, and potassium in a fertilizer. NPK ratings consist of three numbers separated by dashes (e.g., 10-10-10 or 16-4-8) describing the chemical content of fertilizers.[29][30]The first number represents the percentage of nitrogen in the product; the second number, P2O5;the third, K2O. Fertilizers do not actually contain P2O5or K2O, but the system is a conventional shorthand for the amount of the phosphorus (P) or potassium (K) in a fertilizer. A 50-pound (23 kg) bag of fertilizer labeled 16-4-8 contains 8 lb (3.6 kg) of nitrogen (16% of the 50 pounds), an amount of phosphorus equivalent to that in 2 pounds of P2O5(4% of 50 pounds), and 4 pounds of K2O (8% of 50 pounds). Most fertilizers are labeled according to this N-P-K convention, although Australian convention, following an N-P-K-S system, adds a fourth number for sulfur, and uses elemental values for all values including P and K.[31]

Micronutrients

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Micronutrientsare consumed in smaller quantities and are present in plant tissue on the order ofparts-per-million(ppm), ranging from 0.15 to 400 ppm or less than 0.04% dry matter.[32][33]These elements are often required for enzymes essential to the plant's metabolism. Because these elements enable catalysts (enzymes), their impact far exceeds their weight%age. Typical micronutrients areboron,zinc,molybdenum,iron,andmanganese.[24]These elements are provided as water-soluble salts. Iron presents special problems because it converts to insoluble (bio-unavailable) compounds at moderate soil pH and phosphate concentrations. For this reason, iron is often administered as achelate complex,e.g., theEDTAorEDDHAderivatives. The micronutrient needs depend on the plant and the environment. For example,sugar beetsappear to requireboron,andlegumesrequirecobalt,[1]while environmental conditions such as heat or drought make boron less available for plants.[34]

Production

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The production of synthetic, or inorganic, fertilizers requires prepared chemicals, whereas organic fertilizers are derived from the organic processes of plants and animals inbiological processesusing biochemicals.

Nitrogen fertilizers

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Total nitrogenous fertilizer consumption per region, measured in tonnes of total nutrient per year.

Nitrogen fertilizers are made fromammonia(NH3)producedby theHaber–Bosch process.[28]In this energy-intensive process,natural gas(CH4)usuallysupplies the hydrogen,and the nitrogen (N2) isderived from the air.This ammonia is used as afeedstockfor all other nitrogen fertilizers, such asanhydrous ammonium nitrate(NH4NO3) andurea(CO(NH2)2).

Deposits ofsodium nitrate(NaNO3) (Chilean saltpeter) are also found in theAtacama desertinChileand was one of the original (1830) nitrogen-rich fertilizers used.[35]It is still mined for fertilizer.[36]Nitrates are also produced from ammonia by theOstwald process.

Phosphate fertilizers

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An apatite mine for phosphates inSiilinjärvi,Finland

Phosphate fertilizers are obtained by extraction fromphosphate rock,which contains two principal phosphorus-containing minerals,fluorapatiteCa5(PO4)3F (CFA) andhydroxyapatiteCa5(PO4)3OH. Billions of kg of phosphate rock are mined annually, but the size and quality of the remaining ore is decreasing. These minerals are converted into water-soluble phosphate salts by treatment withacids.[37]The large production ofsulfuric acidis primarily motivated by this application.[38]In thenitrophosphate processor Odda process (invented in 1927), phosphate rock with up to a 20% phosphorus (P) content is dissolved withnitric acid(HNO3) to produce a mixture of phosphoric acid (H3PO4) andcalcium nitrate(Ca(NO3)2). This mixture can be combined with a potassium fertilizer to produce acompound fertilizerwith the three macronutrients N, P and K in easily dissolved form.[39]

Potassium fertilizers

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Potashis a mixture of potassium minerals used to make potassium (chemical symbol: K) fertilizers. Potash is soluble in water, so the main effort in producing this nutrient from the ore involves some purification steps; e.g., to removesodium chloride(NaCl) (commonsalt). Sometimes potash is referred to as K2O, as a matter of convenience to those describing the potassium content. In fact, potash fertilizers are usuallypotassium chloride,potassium sulfate,potassium carbonate,orpotassium nitrate.[40]

NPK fertilizers

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Main article:NPK fertilizer

There are three major routes for manufacturing NPK fertilizers (named for their main ingredients: nitrogen (N), phosphorus (P), and potassium (K)):

  1. bulk blending. The individual fertilizers are combined in the desired nutrient ratio.
Bulk blending. Ingredient kg/ton
Blend ingredient NPK 17-17-17 NPK 19-19-19 NPK 9-23-30 NPK 8-32-16
ammonium nitrate 310
urea 256
diammonium phosphate (DAP) 376 421 500 462
triple superphosphate 261
potassium chloride 288 323 500 277
filler 26
  1. The wet process is based on chemical reactions between liquid raw materialsphosphoric acid,sulfuric acid,ammonia) and solid raw materials (such aspotassium chloride.

Step 2. Removal of Calcium Nitrate. It is important to remove thecalcium nitratebecause calcium nitrate is extremelyhygroscopic.

  • Method 1.(Odda process) Calcium nitrate crystals are removed by centrifugation.
  • Method 2. Sulfonitric Process Ca(NO3)2+ H2SO4+ 2NH3→ CaSO4+ 2NH4NO3
  • Method 3.Phosphonitric Process Ca(NO3)2+ H3PO4+ 2NH3→ CaHPO4+ 2NH4NO3
  • Method 4.Carbonitric Process Ca(NO3)2+ CO2+ H2O + 2NH3→ CaCO3+ 2NH4NO3

Organic fertilizers

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Main article:Organic fertilizer
Compost bin for small-scale production of organic fertilizer
A large commercial compost operation

"Organic fertilizers"can describe those fertilizers with a biologic origin—derived from living or formerly living materials. Organic fertilizers can also describe commercially available and frequently packaged products that strive to follow the expectations and restrictions adopted by"organic agriculture"and"environmentally friendly"gardening – related systems of food and plant production that significantly limit or strictly avoid the use of synthetic fertilizers and pesticides. The" organic fertilizer "productstypically contain both some organic materials as well as acceptable additives such as nutritive rock powders, ground sea shells (crab, oyster, etc.), other prepared products such as seed meal or kelp, and cultivated microorganisms and derivatives.

Fertilizers of an organic origin (the first definition) includeanimal wastes,plant wastes from agriculture,seaweed,compost,and treatedsewage sludge(biosolids). Beyond manures, animal sources can include products from the slaughter of animals –bloodmeal,bone meal,feather meal,hides, hoofs, and horns all are typical components.[24]Organically derived materials available to industry such as sewage sludge may not be acceptable components of organic farming and gardening, because of factors ranging from residual contaminants to public perception. On the other hand, marketed "organic fertilizers" may include, and promote, processed organicsbecausethe materials have consumer appeal. No matter the definition nor composition, most of these products contain less-concentrated nutrients, and the nutrients are not as easily quantified. They can offer soil-building advantages as well as be appealing to those who are trying to farm / garden more "naturally".[41]

In terms of volume,peatis the most widely used packaged organic soil amendment. It is an immature form of coal and improves the soil by aeration and absorbing water but confers no nutritional value to the plants. It is therefore not a fertilizer as defined in the beginning of the article, but rather an amendment.Coir,(derived from coconut husks), bark, and sawdust when added to soil all act similarly (but not identically) to peat and are also considered organic soil amendments – or texturizers – because of their limited nutritive inputs. Some organic additives can have a reverse effect on nutrients – fresh sawdust can consume soil nutrients as it breaks down, and may lower soil pH – but these same organic texturizers (as well as compost, etc.) may increase the availability of nutrients through improved cation exchange, or through increased growth of microorganisms that in turn increase availability of certain plant nutrients. Organic fertilizers such as composts and manures may be distributed locally without going into industry production, making actual consumption more difficult to quantify.

Statistics

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Fertilizer use (2018). From FAO's World Food and Agriculture – Statistical Yearbook 2020[42]

Top users of nitrogen-based fertilizer[43]
Country Total
N use
(Mt pa) 		N use for
feed and
pasture
(Mt pa)
China 18.7 3.0
India 11.9 n/a[44]
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

China has become the largest producer and consumer of nitrogen fertilizers[45]while Africa has little reliance on nitrogen fertilizers.[46]Agricultural and chemical minerals are very important in industrial use of fertilizers, which is valued at approximately $200 billion.[47]Nitrogen has a significant impact in the global mineral use, followed by potash and phosphate. The production of nitrogen has drastically increased since the 1960s. Phosphate and potash have increased in price since the 1960s, which is larger than the consumer price index.[47]Potash is produced in Canada, Russia and Belarus, together making up over half of the world production.[47]Potash production in Canada rose in 2017 and 2018 by 18.6%.[48]Conservative estimates report 30 to 50% of crop yields are attributed to natural or synthetic commercial fertilizers.[40][49]Fertilizer consumption has surpassed the amount of farmland in the United States.[47]

Data on the fertilizer consumption per hectarearable landin 2012 are published byThe World Bank.[50]The diagram below shows fertilizer consumption by the European Union (EU) countries as kilograms per hectare (pounds per acre). The total consumption of fertilizer in the EU is 15.9 million tons for 105 million hectare arable land area[51](or 107 million hectare arable land according to another estimate[52]). This figure equates to 151 kg of fertilizers consumed per ha arable land on average by the EU countries.

The diagram displays the statistics of fertilizer consumption in western and central European counties from data published by The World Bank for 2012.

Application

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Fertilizersprayer
Applyingsuperphosphatefertilizer by hand, New Zealand, 1938

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

Liquid vs solid

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Fertilizers are applied to crops both as solids and as liquid. About 90% of fertilizers are applied as solids. The most widely used solid inorganic fertilizers areurea,diammonium phosphate and potassium chloride.[53]Solid fertilizer is typically granulated or powdered. Often solids are available asprills,a solid globule. Liquid fertilizers comprise anhydrous ammonia, aqueous solutions of ammonia, aqueous solutions of ammonium nitrate or urea. These concentrated products may be diluted with water to form a concentrated liquid fertilizer (e.g.,UAN). Advantages of liquid fertilizer are its more rapid effect and easier coverage.[24]The addition of fertilizer to irrigation water is called "fertigation".[40]

Urea

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Main article:urea

Urea is highly soluble in water and is therefore also very suitable for use in fertilizer solutions (in combination with ammonium nitrate: UAN), e.g., in 'foliar feed' fertilizers. For fertilizer use, granules are preferred over prills because of their narrower particle size distribution, which is an advantage for mechanical application.

Urea is usually spread at rates of between 40 and 300 kg/ha (35 to 270 lbs/acre) but rates vary. Smaller applications incur lower losses due to leaching. During summer, urea is often spread just before or during rain to minimize losses fromvolatilization(a process wherein nitrogen is lost to the atmosphere as ammonia gas).

Because of the high nitrogen concentration in urea, it is very important to achieve an even spread. Drilling must not occur on contact with or close to seed, due to the risk of germination damage. Urea dissolves in water for application as a spray or through irrigation systems.

In grain and cotton crops, urea is often applied at the time of the last cultivation before planting. In high rainfall areas and on sandy soils (where nitrogen can be lost through leaching) and where good in-season rainfall is expected, urea can be side- or top-dressed during the growing season. Top-dressing is also popular on pasture and forage crops. In cultivating sugarcane, urea is side-dressed after planting, and applied to eachratooncrop.

Because it absorbs moisture from the atmosphere, urea is often stored in closed containers.

Overdose or placing urea near seed is harmful.[54]

Slow- and controlled-release fertilizers

[edit]
This section is an excerpt fromControlled-release fertiliser.[edit]
Methylene diurea (MDU) is component of the most popularcontrolled-release fertilizers.[55]
Acontrolled-release fertiliser(CRF) is agranulatedfertiliserthat releasesnutrientsgradually into thesoil(i.e., with acontrolled releaseperiod).[56]Controlled-release fertilizer is also known as controlled-availability fertilizer, delayed-release fertilizer, metered-release fertilizer, or slow-acting fertilizer. Usually CRF refers to nitrogen-based fertilizers. Slow- and controlled-release involve only 0.15% (562,000 tons) of the fertilizer market (1995).

Foliar application

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Foliar fertilizersare applied directly to leaves. This method is almost invariably used to apply water-soluble straight nitrogen fertilizers and used especially for high-value crops such as fruits. Urea is the most common foliar fertilizer.[24]

Fertilizer burn

Chemicals that affect nitrogen uptake

[edit]
N-Butylthiophosphoryltriamide, an enhanced efficiency fertilizer.

Various chemicals are used to enhance the efficiency of nitrogen-based fertilizers. In this way farmers can limit thepolluting effects of nitrogen run-off.Nitrificationinhibitors (also known as nitrogen stabilizers) suppress the conversion of ammonia intonitrate,an anion that is more prone to leaching. 1-Carbamoyl-3-methylpyrazole (CMP),dicyandiamide,nitrapyrin(2-chloro-6-trichloromethylpyridine) and 3,4-dimethylpyrazole phosphate (DMPP) are popular.[57]Urease inhibitorsare used to slow the hydrolytic conversion of urea into ammonia, which is prone to evaporation as well as nitrification. The conversion of urea to ammonia catalyzed by enzymes calledureases.A popular inhibitor of ureases isN-(n-butyl)thiophosphoric triamide (NBPT).

Overfertilization

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Careful use of fertilization technologies is important because excess nutrients can be detrimental.[58]Fertilizer burncan occur when too much fertilizer is applied, resulting in damage or even death of the plant. Fertilizers vary in their tendency to burn roughly in accordance with theirsalt index.[59][60]

Environmental effects

[edit]
Runoffofsoiland fertilizer during a rain storm
See also:Environmental impact of agriculture,Human impact on the nitrogen cycle,Nitrogen fertilizer § Problems with inorganic fertilizer,andNitrogen Cycle

Synthetic fertilizer used in agriculture haswide-reaching environmental consequences.

According to theIntergovernmental Panel on Climate Change (IPCC)Special Report on Climate Change and Land,production of these fertilizers and associatedland usepractices are drivers ofglobal warming.[3]The use of fertilizer has also led to a number of direct environmental consequences:agricultural runoffwhich leads to downstream effects likeocean dead zonesand waterway contamination,soil microbiomedegradation,[61]and accumulation of toxins in ecosystems. Indirect environmental impacts include: theenvironmental impacts of frackingfornatural gasused in theHaber process,the agricultural boom is partially responsible for the rapidgrowth in human populationand large-scale industrial agricultural practices are associated withhabitat destruction,pressure on biodiversityand agriculturalsoil loss.

In order to mitigate environmental andfood securityconcerns, the international community has included food systems inSustainable Development Goal 2which focuses on creating aclimate-friendlyandsustainable food production system.[62]Most policy and regulatory approaches to address these issues focus on pivoting agricultural practices towardssustainableorregenerative agriculturalpractices: these use less synthetic fertilizers, bettersoil management(for exampleno-till agriculture) and more organic fertilizers.

Large pile ofphosphogypsumwaste nearFort Meade, Florida.

For each ton of phosphoric acid produced by the processing of phosphate rock, five tons of waste are generated. This waste takes the form of impure, useless, radioactive solid calledphosphogypsum.Estimates range from 100,000,000 and 280,000,000 tons of phosphogypsum waste produced annually worldwide.[63]

Water

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Main article:Eutrophication
Red circles show the location and size of manydead zones.

Phosphorus and nitrogen fertilizers can affect soil, surface water, and groundwater due to the dispersion of minerals[47]into waterways due to high rainfall,[64][65]snowmelt and can leaching into groundwater over time.[66]Agricultural run-off is a major contributor to the eutrophication of fresh water bodies. For example, in the US, about half of all the lakes areeutrophic.The main contributor to eutrophication is phosphate, which is normally a limiting nutrient; high concentrations promote the growth of cyanobacteria and algae, the demise of which consumes oxygen.[67]Cyanobacteria blooms ('algal blooms') can also produce harmfultoxinsthat can accumulate in the food chain, and can be harmful to humans.[68][69]Fertilizer run-off can be reduced by using weather-optimized fertilization strategies.[64]

The nitrogen-rich compounds found in fertilizer runoff are the primary cause of serious oxygen depletion in many parts ofoceans,especially in coastal zones,lakesandrivers.The resulting lack of dissolved oxygen greatly reduces the ability of these areas to sustain oceanicfauna.[70]The number of oceanicdead zonesnear inhabited coastlines is increasing.[71]

As of 2006, the application of nitrogen fertilizer is being increasingly controlled in northwestern Europe[72]and the United States.[73][74]In cases where eutrophication can be reversed, it may nevertheless take decades[75]and significant soil management[76]before the accumulated nitrates ingroundwatercan be broken down by natural processes.

Nitrate pollution

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Only a fraction of the nitrogen-based fertilizers is converted to plant matter. The remainder accumulates in the soil or is lost as run-off.[77]High application rates of nitrogen-containing fertilizers combined with the highwater solubilityof nitrate leads to increasedrunoffintosurface wateras well asleachinginto groundwater, thereby causinggroundwater pollution.[78][79][80]The excessive use of nitrogen-containing fertilizers (be they synthetic or natural) is particularly damaging, as much of the nitrogen that is not taken up by plants is transformed into nitrate which is easily leached.[81]

Nitrate levels above 10 mg/L (10 ppm) in groundwater can cause 'blue baby syndrome' (acquiredmethemoglobinemia).[82]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.[83]Run-off can lead to fertilizing blooms of algae that use up all the oxygen and leave huge "dead zones" behind where other fish and aquatic life can not live.[84]

Soil

[edit]

Acidification

[edit]

Soil acidification refers to the process by which the pH level of soil becomes more acidic over time. Soil pH is a measure of the soil's acidity or alkalinity and is determined on a scale from 0 to 14, with 7 being neutral. A pH value below 7 indicates acidic soil, while a pH value above 7 indicates alkaline or basic soil.

Soil acidification is a significant concern in agriculture and horticulture. It refers to the process of the soil becoming more acidic over time.

See also:Soil pHandSoil acidification

Nitrogen-containing fertilizers can causesoil acidificationwhen added.[85][86]This may lead to decrease in nutrient availability which may be offset byliming.These fertilizers release ammonium or nitrate ions, which can acidify the soil as they undergo chemical reactions.

When these nitrogen-containing fertilizers are added to the soil, they increase the concentration of hydrogen ions (H+) in the soil solution, which lowers the pH of the soil.

Accumulation of toxic elements

[edit]
Cadmium
[edit]

The concentration ofcadmiumin phosphorus-containing fertilizers varies considerably and can be problematic.[87]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.[88]The phosphate rock used in their manufacture can contain as much as 188 mg/kg cadmium[89](examples are deposits onNauru[90]and theChristmas islands[91]). Continuous use of high-cadmium fertilizer can contaminate soil (as shown in New Zealand)[92]andplants.[93]Limits to the cadmium content of phosphate fertilizers has been considered by theEuropean Commission.[94][95][96]Producers of phosphorus-containing fertilizers now select phosphate rock based on the cadmium content.[67]

Fluoride
[edit]

Phosphate rocks contain high levels of fluoride. Consequently, the widespread use of phosphate fertilizers has increased soil fluoride concentrations.[93]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.[97][98]Also of possible concern are the effects of fluoride on soil microorganisms.[97][98][99]

Radioactive elements
[edit]

The radioactive content of the fertilizers varies considerably and depends both on their concentrations in the parent mineral and on the fertilizer production process.[93][100]Uranium-238 concentrations can range from 7 to 100 pCi/g (picocuries per gram) in phosphate rock[101]and from 1 to 67 pCi/g in phosphate fertilizers.[102][103][104]Where high annual rates of phosphorus fertilizer are used, this can result in uranium-238 concentrations in soils and drainage waters that are several times greater than are normally present.[103][105]However, the impact of these increases on therisk to human healthfrom radinuclide contamination of foods is very small (less than 0.05 mSv/y).[103][106][107]

Other metals
[edit]

Steel industry wastes, recycled into fertilizers for their high levels ofzinc(essential to plant growth), wastes can include the followingtoxic metals:lead[108]arsenic,cadmium,[108]chromium, and nickel. The most common toxic elements in this type of fertilizer aremercury,lead, and arsenic.[109][110][111]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, such asMiracle-Gro.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. Some inexpensive retail granular garden fertilizers are made with high purity ingredients.

Trace mineral depletion

[edit]

Attention has been addressed to the decreasing concentrations of elements such as iron, zinc, copper and magnesium in many foods over the last 50–60 years.[112][113]Intensive farmingpractices, including the use of synthetic fertilizers are frequently suggested as reasons for these declines and organic farming is often suggested as a solution.[113]Although improved crop yields resulting from NPK fertilizers are known to dilute the concentrations of other nutrients in plants,[112][114]much of the measured decline can be attributed to the use of progressively higher-yielding crop varieties that produce foods with lower mineral concentrations than their less-productive ancestors.[112][115][116]It is, therefore, unlikely that organic farming or reduced use of fertilizers will solve the problem; foods with high nutrient density are posited to be achieved using older, lower-yielding varieties or the development of new high-yield, nutrient-dense varieties.[112][117]

Fertilizers are, in fact, more likely to solve trace mineral deficiency problems than cause them: In Western Australia deficiencies ofzinc,copper,manganese,iron andmolybdenumwere identified as limiting the growth of broad-acre crops and pastures in the 1940s and 1950s.[118]Soils in Western Australia are very old, highly weathered and deficient in many of the major nutrients and trace elements.[118]Since this time these trace elements are routinely added to fertilizers used in agriculture in this state.[118]Many other soils around the world are deficient in zinc, leading to deficiency in both plants and humans, and zinc fertilizers are widely used to solve this problem.[119]

Changes in soil biology

[edit]
Further information:soil biology

High levels of fertilizer may cause the breakdown of thesymbioticrelationships between plant roots andmycorrhizalfungi.[120]

Hydrogen consumption and sustainability

[edit]

Most fertilizer is made from dirty hydrogen.[121]Ammonia is produced fromnatural gasand air.[122]The cost of natural gas makes up about 90% of the cost of producing ammonia.[123]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.[124]

Contribution to climate change

[edit]
See also:Greenhouse gas emissions from agriculture

The amount ofgreenhouse gasescarbon dioxide,methaneandnitrous oxideproduced during themanufactureand use of nitrogen fertilizer is estimated as around 5% ofanthropogenic greenhouse gas emissions.One third is produced during the production and two thirds during the use of fertilizers.[125]Nitrogen fertilizer can be converted bysoil bacteriatonitrous oxide,agreenhouse gas.[126]Nitrous oxide emissions by humans, most of which are from fertilizer, between 2007 and 2016 have been estimated at 7 million tonnes per year,[127]which is incompatible with limiting global warming to below 2 °C.[128]

Atmosphere

[edit]
Globalmethaneconcentrations (surface and atmospheric) for 2005; note distinct plumes

Through the increasing use of nitrogen fertilizer, which was used at a rate of about 110 million tons (of N) per year in 2012,[129][130]adding to the already existing amount of reactive nitrogen,nitrous oxide(N2O) has become the third most importantgreenhouse gasafter carbon dioxide and methane. It has aglobal warming potential296 times larger than an equal mass of carbon dioxide and it also contributes to stratospheric ozone depletion.[131] By changing processes and procedures, it is possible to mitigate some, but not all, of these effects on anthropogenicclimate change.[132]

Methane emissionsfrom crop fields (notably ricepaddy fields) are increased by the application of ammonium-based fertilizers. These emissions contribute to global climate change as methane is a potent greenhouse gas.[133][134]

Policy

[edit]

Regulation

[edit]

In Europe, problems with high nitrate concentrations in runoff are being addressed by the European Union's Nitrates Directive.[135]WithinBritain,farmers are encouraged to manage their land more sustainably in 'catchment-sensitive farming'.[136]In theUS,high concentrations of nitrate and phosphorus in runoff and drainage water are classified as nonpoint source pollutants due to their diffuse origin; this pollution is regulated at the state level.[137]OregonandWashington,both in the United States, have fertilizer registration programs with on-line databases listing chemical analyses of fertilizers.[138][139]

InChina,regulations have been implemented to control the use of N fertilizers in farming. In 2008, Chinese governments began to partially withdraw fertilizer subsidies, including subsidies to fertilizer transportation and to electricity and natural gas use in the industry. In consequence, the price of fertilizer has gone up and large-scale farms have begun to use less fertilizer. If large-scale farms keep reducing their use of fertilizer subsidies, they have no choice but to optimize the fertilizer they have which would therefore gain an increase in both grain yield and profit.[140]

In March 2022, the United States Department of Agriculture announced a new $250M grant to promote American fertilizer production. Part of the Commodity Credit Corporation, the grant program will support fertilizer production that is independent of dominant fertilizer suppliers, made in America, and utilizing innovative production techniques to jumpstart future competition.[141]

Two types of agricultural management practices include organic agriculture and conventional agriculture. The former encourages soil fertility using local resources to maximize efficiency. Organic agriculture avoids synthetic agrochemicals. Conventional agriculture uses all the components that organic agriculture does not use.[142]

See also

[edit]

References

[edit]
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