Fertilizer: Difference between revisions

{{Short description|Substance added to soil to enhance plant growth}}

[[File:Manure spreading Hlokozi 2007 11 29.jpg|thumb|upright=1.35|A [[farmer]] spreading [[manure]] to improve [[soil fertility]]]]

Historically, fertilization came from natural or organic sources: [[compost]], [[Manure|animal manure]], [[Human waste|human manure]], harvested minerals, [[crop rotation]]s, and byproducts of human-nature industries (e.g. [[Fish meal|fish processing waste]], or [[Blood meal|bloodmeal]] from [[animal slaughter]]). However, starting in the 19th century, after innovations in [[plant nutrition]], an [[Industrial agriculture|agricultural industry]] developed around synthetically created [[Agrochemical|agrochemical fertilizers]]. This transition was important in transforming the [[Food system|global food system]], allowing for larger-scale [[Intensive farming|industrial agriculture]] with large crop yields.

[[File:Fertilization (JOKAMT2Pe14-1).tif|thumb|A farmer throws solid fertilizer into his field in [[Janakkala|Janakkala, Finland]] in 1960]]

[[Nitrogen fixation|Nitrogen-fixing]] chemical processes, such as the [[Haber process]] invented 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. 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 of [[conventional food systems]] (more than 30% per capita) as part of the so-called "[[Green Revolution]]".

The use of artificial and industrially applied fertilizers has caused environmental consequences such as [[water pollution]] and [[eutrophication]] due to nutritional runoff; [[Carbon emissions|carbon]] and other emissions from fertilizer production and mining; and [[Soil contamination|contamination and pollution of soil]]. Various [[sustainable agriculture]] practices can be implemented to reduce the adverse environmental effects of fertilizer and [[pesticide]] use and [[Environmental impact of agriculture|environmental damage]] caused by [[industrial agriculture]].

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==History==

{{Main|History of fertilizer}}

Management of [[soil fertility]] has 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''''''. Egyptians, Romans, Babylonians, and early Germans are all recorded as using minerals or manure to enhance the productivity of their farms. The scientific research of plant nutrition started well before the work of German chemist [[Justus von Liebig]] although his name is most mentioned as the "father of the fertilizer industry". [[Nicolas Théodore de Saussure]] and scientific colleagues at the time were quick to disprove the simplifications of von Liebig. Prominent scientists whom von Liebig drew were [[Carl Ludwig Sprenger]] and [[Hermann Hellriegel]]. In this field, a 'knowledge erosion' took place, partly driven by an intermingling of economics and research. [[John Bennet Lawes]], an English [[entrepreneur]], began experimenting 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 of [[Joseph Henry Gilbert]]; together they performed crop experiments at the [[Rothamsted Research|Institute of Arable Crops Research]].

The 1910s and 1920s witnessed the rise of the [[Haber process]] and the [[Ostwald process]]. The Haber process produces ammonia (NH₃) from [[methane]] (CH₄) ([[natural gas]]) gas and molecular nitrogen (N₂) from the air. The ammonia from the Haber process is then partially converted into [[nitric acid]] (HNO₃) in the [[Ostwald process]]. 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. After World War II, nitrogen production plants that had ramped up for wartime bomb manufacturing were pivoted towards agricultural uses. The use of synthetic nitrogen fertilizers has increased steadily over the last 50 years, rising almost 20-fold to the current rate of 100 million [[tonnes]] of nitrogen per year.

The development of synthetic nitrogen fertilizers has significantly supported global population growth. It has been estimated that almost half the people on the Earth are currently fed due to synthetic nitrogen fertilizer use. 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. Asia represented 53% of the world's 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.

A maize crop yielding 6–9 tonnes of grain per [[hectare]] ({{cvt|1|ha|acre |1|disp=out}}) requires {{convert|31|–|50|kg}} of [[phosphate]] fertilizer to be applied; soybean crops require about half, 20–25 kg per hectare.

==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.]]

* 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.  

[[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:

*[[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.

===Multinutrient fertilizers===

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  

*[[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}}

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 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.

===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).

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]].

===Phosphate fertilizers===

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

===Potassium fertilizers===

===NPK fertilizers===

{{main|NPK fertilizer}}

*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 4.Carbonitric Process Ca(NO₃)₂ + CO₂ + H₂O + 2NH₃ → CaCO₃ + 2NH₄NO₃

===Organic fertilizers===

{{Main|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".

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]]

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 kg of fertilizers consumed per ha arable land on average by the EU countries.

==Application==

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

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.

===Liquid vs solid===

====Urea====

{{Main|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 from [[ammonia volatilization from urea|volatilization]] (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 each [[ratooning|ratoon]] crop.

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

Overdose or placing urea near seed is harmful.

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

{{excerpt|Controlled-release fertilizer}}

===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]]).

===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]].

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}}

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 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.

==== 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.

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.

=====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 mg/kg or as high as 50.9 mg/kg. The phosphate rock used in their manufacture can contain as much as 188 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.

=====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.

=====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).

=====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.

====Trace mineral depletion====

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.

====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.

===Organic agriculture===

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.

===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]]

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.

===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.

===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.

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.

==See also==

* [[Agroecology]]

* [[Seaweed fertilizer]]

==External links==

{{Commons category|Fertilizers}}

* [https://extension.oregonstate.edu/crop-production/organic/nitrogen-phosphorus-potassium-values-organic-fertilizers Nitrogen-Phosphorus-Potassium Values of Organic Fertilizers]. {{Webarchive|url=https://web.archive.org/web/20210226191906/https://extension.oregonstate.edu/crop-production/organic/nitrogen-phosphorus-potassium-values-organic-fertilizers |date=26 February 2021 }}.

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[[Category:Fertilizers| ]]

[[Category:Horticulture]]

[[Category:Climate change and agriculture]]

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