Fertilizer/ja: Difference between revisions

==Mechanism==

[[File:Reuse of urine demonstration - fertilised and not fertilised tomato plant experiment (3617543234).jpg|thumb|upright=1.4|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.]]

[[File:Inorganic Fertilizer Use By Region.svg|thumb|upright=1.5|Inorganic fertilizer use by region]]

Fertilizers typically provide, in varying [[Proportionality (mathematics)|proportions]]:

*[[Labeling of fertilizer|Three main macronutrients (NPK)]]:

** [[Nitrogen]] (N): leaf growth and stems

** [[Phosphorus]] (P): development of roots, flowers, seeds and fruit;

** [[Potassium]] (K): strong stem growth, movement of water in plants, promotion of flowering and fruiting;

* three secondary macronutrients: [[calcium]] (Ca), [[magnesium]] (Mg), and [[sulfur]] (S);

* Micronutrients: [[copper]] (Cu), [[Iron fertilisation|iron]] (Fe), [[manganese]] (Mn), [[molybdenum]] (Mo), [[zinc]] (Zn), and [[boron]] (B). Of occasional significance are [[silicon]] (Si), [[cobalt]] (Co), and [[vanadium]] (V).

The nutrients required for healthy plant life are classified according to the elements, but the elements are not used as fertilizers. Instead, [[chemical compound|compounds]] containing 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 a [[dry 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 in [[carbon dioxide]] and in water. Although nitrogen makes up most of the [[atmosphere]], it is in a form that is unavailable to plants. Nitrogen is the most important fertilizer since nitrogen is present in [[protein]]s ([[amide bond]]s between [[amino-acid|amino acid]]s), [[DNA]] ([[purine|puric]] and [[pyrimidine|pyrimidic]] bases), and other components (e.g., [[porphyrin|tetrapyrrolic]] [[heme]] in [[chlorophyll]]). To be nutritious to plants, nitrogen must be made available in a "fixed" form. Only some bacteria and their host plants (notably [[legume]]s) can fix atmospheric nitrogen ({{chem2|N2}}) by converting it to [[ammonia]] ({{chem2|NH3}}). [[Phosphate]] ({{chem2|PO4(3-)}}) is required for the production of [[Deoxyribonucleic acid|DNA]] ([[genetic code]]) and [[Adenosine triphosphate|ATP]], the main energy carrier in [[Cell (biology)|cells]], as well as certain [[lipid]]s ([[phospholipid]]s, the main components of the [[liposome|lipidic double layer]] of the [[cell membrane]]s).

===Microbiological considerations===

Two sets of [[enzymatic reaction]]s are highly relevant to the efficiency of nitrogen-based fertilizers.

;Urease

The first is the [[hydrolysis]] (reaction with water) of [[urea]] ({{chem2|CO(NH2)2}}). Many [[soil]] [[bacteria]] possess the enzyme [[urease]], which [[catalysis|catalyzes]] the conversion of urea to [[ammonium]] ion ({{chem2|NH4+}}) and [[bicarbonate]] [[ion]] ({{chem2|HCO3-}}).

;Ammonia oxidation

[[Ammonia-oxidizing bacteria]] (AOB), such as species of ''[[Nitrosomonas]]'', [[Redox|oxidize]] ammonia ({{chem2|NH3}}) to [[nitrite]] ({{chem2|NO2-}}), a process termed [[nitrification]]. [[Nitrite-oxidizing bacteria]], especially ''[[Nitrobacter]]'', oxidize [[nitrite]] ({{chem2|NO2-}}) to [[nitrate]] ({{chem2|NO3-}}), which is extremely [[solubility|soluble]] and mobile and is a major cause of [[eutrophication]] and [[algal bloom]].

==Classification==

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 except [[ureas]]. 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.

===Single nutrient ("straight") fertilizers===

The main nitrogen-based straight fertilizer is [[ammonia]] (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 nitrate]] Is a blend of 20-30% [[limestone]] CaCO₃ or [[Dolomite (mineral)|dolomite]] (Ca,Mg)CO₃ and 70-80% [[ammonium nitrate]] with 24-28  % nitrogen.

*[[Calcium nitrate]] with 15,5% nitrogen and 19% calcium, reportedly holding a small share of the nitrogen fertilizer market (4% in 2007).

The main straight phosphate fertilizers are the [[superphosphate]]s:

* "Single superphosphate" (SSP) consisting of 14–18% P₂O₅, again in the form of Ca(H₂PO₄)₂, but also [[phosphogypsum]] ({{chem2|Ca[[SO4]] * 2 H2O}}).

* [[Triple superphosphate]] (TSP) typically consists of 44–48% of P₂O₅ and 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 is [[muriate of potash]] (MOP, 95–99% KCl). It is typically available as 0-0-60 or 0-0-62 fertilizer.

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===Multinutrient fertilizers===

;Binary (NP, NK, PK) fertilizers

*[[monoammonium phosphate]] (MAP) NH₄H₂PO₄. With 11% nitrogen and 48% P₂O₅.

*[[diammonium phosphate]] (DAP). (NH₄)₂HPO₄. With 18% nitrogen and 46% P₂O₅

About 85% of MAP and DAP fertilizers are soluble in water.

;NPK fertilizers

{{Main|Labeling of fertilizer}}

| width = 200

| footer =  

| image1 = Compound fertiliser.jpg

| alt1 = Compound fertiliser

| caption1 = Compound fertilizer

| image2 = Bulk-blend fertiliser.jpg

| alt2 = Bulk-blend fertiliser

| caption2 = Bulk-blend fertilizer

}}

[[NPK rating]] is 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. The first number represents the percentage of nitrogen in the product; the second number, P₂O₅; the third, K₂O. Fertilizers do not actually contain P₂O₅ or K₂O, but the system is a conventional shorthand for the amount of the phosphorus (P) or potassium (K) in a fertilizer. A {{convert|50|lb|adj=on}} bag of fertilizer labeled 16-4-8 contains {{cvt|8|lb}} 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.

===Micronutrients===

[[Micronutrients]] are consumed in smaller quantities and are present in plant tissue on the order of [[Parts-per notation|parts-per-million]] (ppm), ranging from 0.15 to 400 ppm or less than 0.04% dry matter. 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 are [[boron]], [[zinc]], [[molybdenum]], [[iron]], and [[manganese]]. 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 a [[Chelation|chelate complex]], e.g., the [[Ethylenediaminetetraacetic acid|EDTA]] or [[EDDHA]] derivatives. The micronutrient needs depend on the plant and the environment. For example, [[sugar beet]]s appear to require [[boron]], and [[legume]]s require [[cobalt]],

==Production==

The production of synthetic, or inorganic, fertilizers require prepared chemicals, whereas organic fertilizers are derived from the organic processes of plants and animals in [[biological process]]es using biochemicals.

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===Nitrogen fertilizers===

[[File:Nitrogen fertilizer consumption, OWID.svg|thumb|left|Total nitrogenous fertilizer consumption per region, measured in tonnes of total nutrient per year.]]

Nitrogen fertilizers are made from [[ammonia]] (NH₃) [[ammonia production|produced]] by the [[Haber process|Haber–Bosch process]]. In this energy-intensive process, [[natural gas]] (CH₄) [[Hydrogen production|usually]] [[Steam reforming|supplies the hydrogen]], and the nitrogen (N₂) is [[Nitrogen#Production|derived from the air]]. This ammonia is used as a [[feedstock]] for all other nitrogen fertilizers, such as [[ammonium nitrate|anhydrous ammonium nitrate]] (NH₄NO₃) and [[urea]] (CO(NH₂)₂).

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Deposits of [[sodium nitrate]] (NaNO₃) ([[Chilean saltpeter]]) are also found in the [[Atacama Desert]] in [[Chile]] and was one of the original (1830) nitrogen-rich fertilizers used. It is still mined for fertilizer. Nitrates are also produced from ammonia by the [[Ostwald Process|Ostwald process]].

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===Phosphate fertilizers===

[[File:Siilinjärvi Särkijärvi pit.jpg|thumb|left|An apatite mine for phosphates in [[Siilinjärvi carbonatite|Siilinjärvi]], Finland]]

Phosphate fertilizers are obtained by extraction from [[phosphate rock]], which contains two principal phosphorus-containing minerals, [[fluorapatite]] Ca₅(PO₄)₃F (CFA) and [[hydroxyapatite]] Ca₅(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 with [[acid]]s. The large production of [[sulfuric acid]] is primarily motivated by this application. 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 mixture can be combined with a potassium fertilizer to produce a ''compound fertilizer'' with the three macronutrients N, P and K in easily dissolved form.

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===Potassium fertilizers===

[[Potash]] is 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 remove [[sodium chloride]] (NaCl) (common [[salt]]). Sometimes potash is referred to as K₂O, as a matter of convenience to those describing the potassium content. In fact, potash fertilizers are usually [[potassium chloride]], [[potassium sulfate]], [[potassium carbonate]], or [[potassium nitrate]].

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===NPK fertilizers===

{{main|NPK fertilizer}}

# 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|| ||   ||

# The wet process is based on chemical reactions between liquid raw materials [[phosphoric acid]], [[sulfuric acid]], [[ammonia]]) and solid raw materials (such as [[potassium chloride]]).

*The Nitrophosphate Process. Step 1. Nitrophosphates are made by acidiculating [[phosphate rock]] with [[nitric acid]].

*Nitric acid + Phosphate rock → [[Phosphoric acid]] + [[Calcium sulfate|Calcium sulphate]] + [[hexafluorosilicic acid]].

*Ca₅F(PO₄)₃ + 10 HNO₃ →6 H₃PO₄ + 5 Ca(NO₃)₂ + HF    

*6 HF + SiO₂ →H₂SiF₆ + 2 H₂O

Step 2. Removal of Calcium Nitrate. It is important to remove the [[calcium nitrate]] because calcium nitrate is extremely [[Hygroscopy|hygroscopic]].

*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

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===Organic fertilizers===

{{Main|Organic fertilizer}}

[[File:HomeComposting Roubaix Fr59.JPG|thumb|Compost bin for small-scale production of organic fertilizer]]

[[File:Krechty kompostarna.jpg|thumb|A large commercial compost operation]]

"[[Organic fertilizer]]s" 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" ''products'' typically contain both some organic materials as well as acceptable additives such as nutritive rock powders, ground seashells (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) include [[manure|animal wastes]], plant wastes from agriculture, [[Seaweed fertilizer|seaweed]], [[compost]], and treated [[sewage sludge]] ([[biosolid]]s). 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. 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 organics ''because'' the 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".

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In terms of volume, [[peat]] is 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.

==Fertilizer consumption==

[[File:FERTILIZER USE (2018).svg|right|thumb|upright=1.5|Fertilizer use (2018). From FAO's World Food and Agriculture – Statistical Yearbook 2020]]

[[File:Fertilizer consumption in Europe.png|right|thumb|upright=1.5|The diagram displays the statistics of [https://docs.google.com/spreadsheets/d/1HzGlIAHphywl3AO2-S_aXDAS0VLL4IU6V19fVptSnjs/pubchart?oid=1097435817&format=interactive fertilizer consumption] in western and central European counties from data published by The World Bank for 2012.]]

|+ Top users of nitrogen-based fertilizer

! Country

! Total<br />N use<br />(Mt pa)

! N use for<br />feed and<br />pasture<br />(Mt pa)

| China

| India

| U.S.

| France

| Germany

| [[Brazil]]

| Canada

| [[Turkey]]

| UK

| [[Mexico]]

| Spain

| [[Argentina]]

China has become the largest producer and consumer of nitrogen fertilizers while Africa has little reliance on nitrogen fertilizers. Agricultural and chemical minerals are very important in industrial use of fertilizers, which is valued at approximately $200 billion. 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. Potash is produced in Canada, Russia and Belarus, together making up over half of the world production. Potash production in Canada rose in 2017 and 2018 by 18.6%. Conservative estimates report 30 to 50% of crop yields are attributed to natural or synthetic commercial fertilizers. Fertilizer consumption has surpassed the amount of farmland in the United States.

Data on the fertilizer consumption per hectare [[arable land]] in 2012 are published by [[The World Bank]]. 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 (or 107 million hectare arable land according to another estimate). This figure equates to 151&nbsp;kg of fertilizers consumed per ha arable land on average by the EU countries.

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==Application==

[[File:Farm fertilizer.jpg|thumb|Fertilizer [[sprayer]]]]

[[File:Drone crop fertilizer.jpg|thumb|[[Agricultural drone|Drone crop fertilizer]]]]

[[File:7252 Hand top-dressing of super phosphate on Banks Peninsula.jpg|thumb|Applying [[superphosphate]] fertilizer 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 a [[soil test]] and according to the particular crop. Legumes, for example, fix nitrogen from the atmosphere and generally do not require nitrogen fertilizer.

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===Liquid vs solid===

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 are [[urea]], diammonium phosphate and potassium chloride. Solid fertilizer is typically granulated or powdered. Often solids are available as [[prill]]s, 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. The addition of fertilizer to irrigation water is called "[[fertigation]]".

====Urea====

{{Main|urea}}

Urea is usually spread at rates of between 40 and 300&nbsp;kg/ha (35 to 270&nbsp;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 from [[ammonia volatilization from urea|volatilization]] (a process wherein nitrogen is lost to the atmosphere as ammonia gas).

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 each [[ratooning|ratoon]] crop.

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===Slow- and controlled-release fertilizers===

{{excerpt|Controlled-release fertilizer}}

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===Foliar application===

[[Foliar feeding|Foliar fertilizers]] are 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.

[[File:Fertilizer-Burn.jpg|upright|thumb|Fertilizer burn]]

===Chemicals that affect nitrogen uptake===

[[File:N-butylthiophosphoryltriamide.svg|thumb|left|N-Butylthiophosphoryltriamide, an enhanced efficiency fertilizer.]]

Various chemicals are used to enhance the efficiency of nitrogen-based fertilizers. In this way farmers can limit the [[nitrogen pollution|polluting effects of nitrogen run-off]]. [[Nitrification]] inhibitors (also known as nitrogen stabilizers) suppress the conversion of ammonia into [[nitrate]], 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. [[Urease inhibitor]]s are 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 called [[urease]]s. A popular inhibitor of ureases is ''N''-(''n''-butyl)thiophosphoric triamide ([[NBPT]]).

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===Overfertilization===

Careful use of fertilization technologies is important because excess nutrients can be detrimental. [[Fertilizer burn]] can 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 their [[salt index]].

==Environmental effects==

[[File:Runoff of soil & fertilizer.jpg|thumb|[[Surface runoff|Runoff]] of [[soil]] and fertilizer during a rain storm]]{{See also|Environmental impact of agriculture|Human impact on the nitrogen cycle|Nitrogen fertilizer#Problems with inorganic fertilizer|Nitrogen Cycle}}Synthetic fertilizer used in agriculture has [[Environmental impact of agriculture|wide-reaching environmental consequences]].

According to the [[Intergovernmental Panel on Climate Change|Intergovernmental Panel on Climate Change (IPCC)]] [[Special Report on Climate Change and Land]], production of these fertilizers and associated [[land use]] practices are drivers of [[global warming]]. The use of fertilizer has also led to a number of direct environmental consequences: [[agricultural runoff]] which leads to downstream effects like [[Dead zone (ecology)|ocean dead zones]] and waterway contamination, [[soil microbiome]] degradation, and accumulation of toxins in ecosystems. Indirect environmental impacts include: the [[Hydraulic fracturing|environmental impacts of fracking]] for [[natural gas]] used in the [[Haber process]], the agricultural boom is partially responsible for the rapid [[Human population growth|growth in human population]] and large-scale industrial agricultural practices are associated with [[habitat destruction]], [[Biodiversity loss|pressure on biodiversity]] and agricultural [[soil loss]].

In order to mitigate environmental and [[food security]] concerns, the international community has included food systems in [[Sustainable Development Goal 2]] which focuses on creating a [[Effects of climate change on agriculture|climate-friendly]] and [[sustainable food system|sustainable food production system]]. Most policy and regulatory approaches to address these issues focus on pivoting agricultural practices towards [[Sustainable agriculture|sustainable]] or [[Regenerative agriculture|regenerative agricultural]] practices: these use less synthetic fertilizers, better [[soil management]] (for example [[No-till farming|no-till agriculture]]) and more organic fertilizers.

[[File:GypStack.JPG|thumb|Large pile of [[phosphogypsum]] waste near [[Fort 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 called [[phosphogypsum]]. Estimates range from 100,000,000 and 280,000,000 tons of phosphogypsum waste produced annually worldwide.

===Water===

{{Main|Eutrophication}}

[[File:Aquatic Dead Zones.jpg|thumb|Red circles show the location and size of many [[Dead zone (ecology)|dead zones]].]]

Phosphorus and nitrogen fertilizers can affect soil, surface water, and groundwater due to the dispersion of minerals into waterways due to high rainfall, snowmelt and can leaching into groundwater over time. Agricultural run-off is a major contributor to the eutrophication of freshwater bodies. For example, in the US, about half of all the lakes are [[eutrophic]]. 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. Cyanobacteria blooms ('[[algal blooms]]') can also produce harmful [[Eutrophication#Toxicity|toxins]] that can accumulate in the food chain, and can be harmful to humans. Fertilizer run-off can be reduced by using weather-optimized fertilization strategies.

The nitrogen-rich compounds found in fertilizer runoff are the primary cause of serious oxygen depletion in many parts of [[ocean]]s, especially in coastal zones, [[lake]]s and [[river]]s. The resulting lack of dissolved oxygen greatly reduces the ability of these areas to sustain oceanic [[fauna]]. The number of oceanic [[Dead zone (ecology)|dead zones]] near inhabited coastlines is increasing.

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

====Nitrate pollution====

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. High application rates of nitrogen-containing fertilizers combined with the high [[water solubility]] of nitrate leads to increased [[Surface runoff#Agricultural issues|runoff]] into [[surface water]] as well as [[Leaching (agriculture)|leaching]] into groundwater, thereby causing [[groundwater pollution]]. 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.

Nitrate levels above 10&nbsp;mg/L (10 ppm) in groundwater can cause '[[blue baby syndrome]]' (acquired [[methemoglobinemia]]). 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.

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===Soil===

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==== Acidification ====

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 [[Seven (1995 film)|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 pH|Soil acidification}}

Nitrogen-containing fertilizers can cause [[soil acidification]] when added. This may lead to decrease in nutrient availability which may be offset by [[liming (soil)|liming]]. These fertilizers release ammonium or nitrate ions, which can acidify the soil as they undergo chemical reactions.

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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.

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====Accumulation of toxic elements====

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=====Cadmium=====

The concentration of [[cadmium]] in phosphorus-containing fertilizers varies considerably and can be problematic. For example, mono-ammonium phosphate fertilizer may have a cadmium content of as low as 0.14&nbsp;mg/kg or as high as 50.9&nbsp;mg/kg. The phosphate rock used in their manufacture can contain as much as 188&nbsp;mg/kg cadmium (examples are deposits on [[Nauru]] and the [[Christmas Island]]s). Continuous use of high-cadmium fertilizer can contaminate soil (as shown in New Zealand) and [[Phytotoxicity|plants]]. Limits to the cadmium content of phosphate fertilizers has been considered by the [[European Commission]]. Producers of phosphorus-containing fertilizers now select phosphate rock based on the cadmium content.

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=====Fluoride=====

Phosphate rocks contain high levels of fluoride. Consequently, the widespread use of phosphate fertilizers has increased soil fluoride concentrations. It has been found that food contamination from fertilizer is of little concern as plants accumulate little fluoride from the soil; of greater concern is the possibility of fluoride toxicity to livestock that ingest contaminated soils. Also of possible concern are the effects of fluoride on soil microorganisms.

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=====Radioactive elements=====

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

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=====Other metals=====

Steel industry wastes, recycled into fertilizers for their high levels of [[zinc]] (essential to plant growth), wastes can include the following [[Toxic heavy metal|toxic metals]]: [[lead]] [[arsenic]], [[cadmium]], chromium, and nickel. The most common toxic elements in this type of fertilizer are [[Mercury (element)|mercury]], lead, and arsenic. 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 as [[Miracle-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.

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====Trace mineral depletion====

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. [[Intensive farming]] practices, including the use of synthetic fertilizers are frequently suggested as reasons for these declines and organic farming is often suggested as a solution. Although improved crop yields resulting from NPK fertilizers are known to dilute the concentrations of other nutrients in plants, much of the measured decline can be attributed to the use of progressively higher-yielding crop varieties that produce foods with lower mineral concentrations than their less-productive ancestors. 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.

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

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====Changes in soil biology====

{{Further|soil biology}}

High levels of fertilizer may cause the breakdown of the [[Symbiosis|symbiotic]] relationships between plant roots and [[mycorrhiza]]l fungi.

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===Organic agriculture===

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===Hydrogen consumption and sustainability===

Most fertilizer is made from dirty hydrogen. Ammonia is produced from [[natural gas]] and air. The cost of natural gas makes up about 90% of the cost of producing ammonia. The increase in price of natural gases over the past decade, along with other factors such as increasing demand, have contributed to an increase in fertilizer price<!-- over which period? -->.

====Contribution to climate change====

{{See also|Greenhouse gas emissions from agriculture}}

The amount of [[greenhouse gas]]es [[carbon dioxide]], [[methane]] and [[nitrous oxide]] produced during the [[Haber process|manufacture]] and use of nitrogen fertilizer is estimated as around 5% of [[anthropogenic greenhouse gas emissions]]. One third is produced during the production and two thirds during the use of fertilizers. Nitrous oxide emissions by humans, most of which are from fertilizer, between 2007 and 2016 have been estimated at 7 million tonnes per year, which is incompatible with limiting global warming to below 2&nbsp;°C.

===Atmosphere===

[[File:AtmosphericMethane.png|thumb|Global [[methane]] concentrations (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, adding 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.

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

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

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==Policy==

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===Regulation===

In Europe, problems with high nitrate concentrations in runoff are being addressed by the European Union's Nitrates Directive. Within [[Great Britain|Britain]], farmers are encouraged to manage their land more sustainably in 'catchment-sensitive farming'. In the [[United States|US]], 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. [[Oregon]] and [[Washington (state)|Washington]], both in the United States, have fertilizer registration programs with on-line databases listing chemical analyses of fertilizers. [[Carbon emission trading]] and [[eco-tariff]]s affect the production and price of fertilizer.

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===Subsidies===

In [[China]], regulations have been implemented to control the use of N fertilizers in farming. In 2008, Chinese governments began to partially withdraw fertilizer [[subsidy|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.

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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.