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

Mined inorganic fertilizers have been used for many centuries, whereas chemically synthesized inorganic fertilizers were only widely developed during the industrial revolution. Increased understanding and use of fertilizers were important parts of the pre-industrial British Agricultural Revolution and the industrial Green Revolution of the 20th century.

Inorganic fertilizer use has also significantly supported global population growth — it has been estimated that almost half the people on the Earth are currently fed as a result of synthetic nitrogen fertilizer use.

Fertilizers typically provide, in varying proportions:

• six macronutrients:

1. nitrogen (N),
2. phosphorus (P),
3. potassium (K),
4. calcium (Ca),
5. magnesium (Mg), and
6. sulfur (S);

• seven micronutrients:

1. boron (B),
2. chlorine (Cl),
3. copper (Cu),
4. iron (Fe),
5. manganese (Mn),
6. molybdenum (Mo), and
7. zinc (Zn).

The macronutrients are consumed in larger quantities and are present in plant tissue in quantities from 0.15% to 6.0% on a dry matter (0% moisture) basis (DM). Micronutrients are consumed in smaller quantities and are present in plant tissue on the order of parts per million (ppm), ranging from 0.15 to 400 ppm DM, or less than 0.04% DM.

Only three other macronutrients are required by all plants:

1. carbon,
2. hydrogen, and
3. oxygen.

These nutrients are supplied by water and carbon dioxide.

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

Negative environmental effectsEdit

Water qualityEdit

EutrophicationEdit

The nitrogen-rich compounds found in fertilizer runoff is the primary cause of a serious depletion of oxygen in many parts of the ocean, especially in coastal zones; the resulting lack of dissolved oxygen is greatly reducing the ability of these areas to sustain oceanic fauna.^[1] Visually, water may become cloudy and discolored (green, yellow, brown, or red).

About half of all the lakes in the United States are now eutrophic, while the number of oceanic dead zones near inhabited coastlines are increasing.^[2] As of 2006, the application of nitrogen fertilizer is being increasingly controlled in Britain and the United States^{[citation needed]}. If eutrophication can be reversed, it may take decades^{[citation needed]} before the accumulated nitrates in groundwater can be broken down by natural processes.

Blue Baby SyndromeEdit

High application rates of inorganic nitrogen fertilizers in order to maximize crop yields, combined with the high solubilities of these fertilizers leads to increased runoff into surface water as well as leaching into groundwater.^[3][4][5] The use of ammonium nitrate in inorganic fertilizers is particularly damaging, as plants absorb ammonium ions preferentially over nitrate ions, while excess nitrate ions which are not absorbed dissolve (by rain or irrigation) into runoff or groundwater.^[6]

Nitrate levels above 10 mg/L (10 ppm) in groundwater can cause 'blue baby syndrome' (acquired methemoglobinemia), leading to hypoxia (which can lead to coma and death if not treated).^[7]

SoilEdit

Soil acidificationEdit

Nitrogen-containing inorganic and organic fertilizers can cause soil acidification when added.^[8] [4]. This may lead to decreases in nutrient availability which may be offset by liming.

Persistent organic pollutantsEdit

Main article: Persistent organic pollutants

Toxic persistent organic pollutants ("POPs"), such as Dioxins, polychlorinated dibenzo-p-dioxins (PCDDs), and polychlorinated dibenzofurans (PCDFs) have been detected in agricultural fertilizers and soil amendments^[9]

Heavy metal accumulationEdit

The concentration of up to 100 mg/kg of cadmium in phosphate minerals (for example, minerals from Nauru^[10] and the Christmas islands^[11]) increases the contamination of soil with cadmium, for example in New Zealand.^[12]

Steel industry wastes, recycled into fertilizers for their high levels of zinc (essential to plant growth), wastes can include the following toxic metals: lead^[13] arsenic, cadmium,^[13] chromium, and nickel. The most common toxic elements in this type of fertilizer are mercury, lead, and arsenic.^[14][15] Concerns have been raised concerning fish meal mercury content by at least one source in Spain^[16]

Radioactive element accumulationEdit

Uranium is another example of a contaminant often found in phosphate fertilizers (at levels from 7 to 100 pCi/g).^[17] Eventually these heavy metals can build up to unacceptable levels and build up in vegetable produce.^[12] Average annual intake of uranium by adults is estimated to be about 0.5 mg (500 μg) from ingestion of food and water and 0.6 μg from breathing air.^[18]

Also, highly radioactive Polonium-210 contained in phosphate fertilizers is absorbed by the roots of plants and stored in its tissues; tobacco derived from plants fertilized by rock phosphates contains Polonium-210 which emits alpha radiation estimated to cause about 11,700 lung cancer deaths each year worldwide.^[19][20]

^{[21][22][23][24]}

For these reasons, it is recommended that nutrient budgeting, through careful observation and monitoring of crops, take place to mitigate the effects of excess fertilizer application.

AtmosphereEdit

Methane emissions from crop fields (notably rice paddy fields) are increased by the application of ammonium-based fertilizers; these emissions contribute greatly to global climate change as methane is a potent greenhouse gas.^[25]

Through the increasing use of nitrogen fertilizer, which is added at a rate of 1 billion tons per year presently^[26] 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.^[27]

Storage and application of some nitrogen fertilizers in some^[which?] weather or soil conditions can cause emissions of the potent greenhouse gas—nitrous oxide. Ammonia gas (NH₃) may be emitted following application of 'inorganic' fertilizers and/or manures and slurries.^{[citation needed]}

The use of fertilizers on a global scale emits significant quantities of greenhouse gas into the atmosphere. Emissions come about through the use of:^[28]

• animal manures and urea, which release methane, nitrous oxide, ammonia, and carbon dioxide in varying quantities depending on their form (solid or liquid) and management (collection, storage, spreading)
• fertilizers that use nitric acid or ammonium bicarbonate, the production and application of which results in emissions of nitrogen oxides, nitrous oxide, ammonia and carbon dioxide into the atmosphere.

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

Other problemsEdit

Increased pest fitnessEdit

Excessive nitrogen fertilizer applications can also lead to pest problems by increasing the birth rate, longevity and overall fitness of certain agricultural pests, such as aphids (plant lice).^{[29][30][31][32][33][34]}

ReferencesEdit