Fertilizers are substances that supply plant nutrients or amend soil fertility. They are the most effective means of increasing crop production and of improving the quality of food and fodder. Fertilizers are used in order to supplement the natural nutrient supply in the soil, especially to correct the (yield-limiting) minimum factor.
Fertilizers are soil amendments applied to promote plant growth; the main nutrients present in fertilizer are nitrogen, phosphorus, and potassium (the ‘macronutrients’) and other nutrients (‘micronutrients’) are added in smaller amounts. Fertilizers are usually directly applied to soil, and also sprayed on leaves (‘foliar feeding’).
Organic fertilizers or and some 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 artificial nitrogen fertilizer use.
Fig 1
Fertilizers typically provide, in varying proportions:
The three primary macronutrients: nitrogen (N), phosphorus (P), and potassium (K).
The three secondary macronutrients: calcium (Ca), sulfur (S), magnesium (Mg).
and the micronutrients or trace minerals: boron (B), chlorine (Cl), manganese (Mn), iron (Fe), zinc (Zn), copper (Cu), molybdenum (Mo) and selenium (Se).
The macronutrients are consumed in larger quantities and are present in plant tissue in quantities from 0.2% to 4.0% (on a dry matter weight basis).
There are some examples of it:-
Fig 2 Fig 3

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Different Types of Fertilizers
Fertilizers are chemical compounds applied to promote plentiful plant and fruit growth. Fertilizers are applied through soil for uptake by plant roots, or by applying liquid fertilizer directly to plant leaves. They typical fertilizer provides proportions of the three major plant nutrients; nitrogen, phosphorus, and potassium. The secondary plant nutrients such as calcium, sulfur, and magnesium are also contained in fertilizers. Fertilizers can be placed into categories of organic fertilizers and inorganic fertilizers.
Organic Fertilizers
Naturally occurring fertilizers include:
Manure
Worm castings
Peat moss
Seaweed
Sewage
Guano
Organic fertilizers are used to enrich soil through nitrogen fixation from the atmosphere by bacterial nodules on plant roots, as well as phosphorus content of soils. Processed organic materials from natural sources include compost, blood meal powdered blood, and bone (crushed ground bones) meal from organic meat production facilities, and seaweed extracts.
There is more diversity with organic fertilizers, so choosing the right one is not always easy. In general organic fertilizers cannot cause plant burns, get into ground water, affect surrounding growth, and do not need as strict of watering schedules.
Organic fertilizer sources:-
Animals
Animals:-
Sourced urea , are suitable for application organic agriculture, while pure synthetic forms of urea are not. The common thread that can be seen through these examples is that organic agriculture attempts to define itself through minimal processing (in contrast to the man-made Haber process), as well as being naturally occurring or via natural biological processes such as composting.
Sewage sludge use in organic agricultural operations in the U.S. has been extremely limited and rare due to USDA prohibition of the practice (due to toxic metal accumulation, among other factors). The USDA now requires 3rd-party certification of high-nitrogen liquid organic fertilizers sold in the U.S.
Plant:-
Cover crops are also grown to enrich soil as a green manure through nitrogen fixation from the atmosphere; as well as phosphorus (through nutrient mobilization) content of soils.
Mineral:-
Naturally mined powdered limestone, mined rock phosphate and sodium nitrate, are inorganic (in a chemical sense), are energetically intensive to harvest, and yet are approved for usage in organic agriculture in minimal amounts.
Benefits of Organic Material
By nature organic fertilizers provide increased physical and biological storage mechanisms to soils, reducing risks of over fertilization. Organic fertilizers nutrient content, solubility, and nutrient release rates are typically much lower than inorganic fertilizers. Over fertilization of a vital nutrient can be as detrimental as under fertilization to a plant. Fertilizer burn can occur when too much fertilizer is applied resulting in the drying out of roots along with damage and even death to plants. All organic fertilizers are classified as slow release fertilizers. Studies have found that organic fertilizers:
Release 25% to 60% of nitrogen as inorganic.
Controlled release fertilizers had a relatively constant rate of release.
Soluble fertilizer released most of its nitrogen content at the first leaching.
Inorganic Fertilizers: – Naturally occurring inorganic fertilizers include sodium nitrate, mined rock phosphate and lime stone which is used to raise pH and calcium sources.
Macronutrients and Micronutrients
Fertilizers can be divided into macronutrients and micronutrients based on their concentration levels in dry plant matter. There are six macronutrients; nitrogen, phosphorus, potassium (3 main primary elements), calcium, magnesium, and sulfur.
Macronutrient Fertilizers:-
Synthesized materials are also called artificial, and may also be called straight were a product contains the three primary elements of nitrogen, phosphorus, and potassium. Fertilizers are named according to the content of the three elements in the fertilizer. If the main ingredient in the fertilizer is nitrogen, then the fertilizer will be described as a nitrogen fertilizer. But regardless of the name of the fertilizer they are labeled according to the amounts of each of these primary elements, by their weight.
The amount of nitrogen will encourage growth of stems and leaves by promoting protein and chlorophyll. More Flowers, bigger fruits, and healthier roots will result from added phosphorus, and it will also help plants resist certain diseases. Potassium thickens stems and leaves by fostering protein development, meaning the vegetables would prefer a different potassium ratio than flowers or fruit plants would.
Benefits of inorganic fertilizers
Synthetic fertilizers are commonly used to treat fields used for growing maize, followed by barley, sorghum, rapeseed, soy and sunflower. One study has shown that application of nitrogen fertilizer on off-season cover crops can increase the biomass (and subsequent green manure value) of these crops, while having a beneficial effect on soil nitrogen levels for the main crop planted during the summer season.
Nutrients in soil develop in symbiosis, which can be thrown out of balance with high concentrations of fertilizers. The interconnectedness and complexity of this soil ‘food web’ means any appraisal of soil function must necessarily take into account interactions with the living communities that exist within the soil. Stability of the system is reduced by the use of nitrogen-containing inorganic and organic fertilizers, which cause soil acidification.
Problem with inorganic fertilizers
Trace mineral depletion:-
Many inorganic fertilizers may not replace trace mineral elements in the soil which become gradually depleted by crops. This depletion has been linked to studies which have shown a marked fall (up to 75%) in the quantities of such minerals present in fruit and vegetables.
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 inorganic fertilizers used in agriculture in this state.
Over fertilization:-
Over-fertilization of a vital nutrient can be as detrimental as under fertilization. “Fertilizer burn” can occur when too much fertilizer is applied, resulting in a drying out of the roots and damage or even death of the plant.
Burning of plants
High energy consumption:-
The production of synthetic ammonia currently consumes about 5% of global natural gas consumption, which is somewhat fewer than 2% of world energy productions.
Natural gas is overwhelmingly used for the production of ammonia, but other energy sources, together with a hydrogen source, can be used for the production of nitrogen compounds suitable for fertilizers. The cost of natural gas makes up about 90% of the cost of producing ammonia. The increase in price of natural gases over the past decade, along with other factors such as increasing demand, has contributed to an increase in fertilizer price.
Long-Term Sustainability:-
Inorganic fertilizers are now produced in ways which theoretically cannot be continued indefinitely. Potassium and phosphorus come from mines (or saline lakes such as the Dead Sea) and such resources are limited. More effective fertilizer utilization practices may, however, decrease present usage from mines. Improved knowledge of crop production practices can potentially decrease fertilizer usage of P and K without reducing the critical need to improve and increase crop yields. Atmospheric (unfixed) nitrogen is effectively unlimited (forming over 70% of the atmospheric gases), but this is not in a form useful to plants. To make nitrogen accessible to plants requires nitrogen fixation (conversion of atmospheric nitrogen to a plant-accessible form).
Artificial nitrogen fertilizers are typically synthesized using fossil fuels such as natural gas and coal, which are limited resources. In lieu of converting natural gas to syngas for use in the Haber process, it is also possible to convert renewable biomass to syngas (or wood gas) to supply the necessary energy for the process, though the amount of land and resources (ironically often including fertilizer) necessary for such a project may be prohibitive (see Energy conservation in the United States).
Applications of fertilizer
There are so many fields where fertilizer is used in high proportion. Agriculture is the one of field among them. There is some region where fertilizer is used:-
Broadcast:-
Broadcasting consists of uniformly distributing dry or liquid materials over the soil surface, usually before sowing. The fertilizer maybe incorporated into the soil mechanically, or left on the surface to be washed in by rainfall or irrigation. Incorporation into the AP horizon can be by harrow (2-3 cm depth), a cultivator (4-6 cm depth) or by plough (incorporation to plough depth). Broadcasting is the simplest and cheapest method and is best suited for high-speed operations and heavy application rates, especially before planting.
Side or top dressing:-
Fertilizer is side or top-dressed when it is applied after the crop has emerged, and/or when the dose is split for two or more applications. Split applications can be beneficial in some cases, especially for annual crops with a long growing period. Split application of KCl is also recommended for crops growing on low CEC soils, where K can be lost by leaching K following high rainfall or excess irrigation. Soybean responded significantly up to 50 kg K ha-1 when applied half at planting and half at flower initiation, or applying one third at planting, one third at flower initiation and one third at pod development. Splitting the K application is also used in orchards and for other perennial crops, especially for alfalfa and grasses. In trials in a Commercial field of Lucerne, the largest yields, up to 3.15 t ha-1 in 26 days, were on plots treated with 948 kg K ha-1 as KCl in 3 applications. In areas of Cl deficient soils, top-dressed applications of KCl for autumn sown small grains may be more effective than preplant applications because of the potential for Cl leaching from the root zone due to rainfall.
Foliar application:
Foliar application involves the use of KCl in solution. It results in fast K absorption and utilization and has the advantage of quickly correcting deficiencies diagnosed by observation or foliar analysis. Other advantages are low application rates, and uniform distribution of fertilizer.
However, foliar fertilization is supplementary to and cannot replace the basal fertilization.
Foliar application should be done during periods of low temperature and relatively high humidity, such in the early morning or late evening. Otherwise the salts may cause leaf burning and necrosis especially when applied in concentrations above those recommended. Because of its osmotic action, KCl applied on leaves is not well tolerated by plants and so is not usually used for foliar application. Nevertheless, it can be beneficial in some cases.
Rice:-
A foliar application of 10 kg KCl m-3 to rice at panicle initiation, boot leaf and 50% flowering stages, both in the monsoon and winter seasons, significantly increased seed yield and improved quality (seed germination and 100-seed weight). Splitting a total of 95 kg ha-1 of KCl to rice, a third at sowing in soil, a third as a foliar spray at flag leaf stage and a third as foliar spray at grain development, gave larger yields than a soil application all at sowing .A foliar spray applying 3.9 kg K ha-1 (as 10 kg KCl m-3) three times at one week intervals from full head of rice cv.
Environmental effects of fertilizer use
Water Eutrophication:-
The nitrogen-rich compounds found in fertilizer run-off 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.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. As of 2006, the application of nitrogen fertilizer is being increasingly controlled in Britain and the United States. If Eutrophication can be reversed, it may take decades before the accumulated nitrates in groundwater can be broken down by natural processes.
High application rates of inorganic nitrogen fertilizers in order to maximize crop yields, combined with the high solubility’s of these fertilizers leads to increased runoff into surface water as well as leaching into groundwater. 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.
Fig 10
Soil acidification: Nitrogen-containing inorganic and organic fertilizers can cause soil acidification when added. This may lead to decreases in nutrient availability which may be offset by liming.
Heavy metal accumulation:-
The concentration of up to 100 mg/kg of cadmium in phosphate minerals (for example, minerals from Nauru and the Christmas islands)increases the contamination of soil with cadmium, for example in New Zealand.
Uranium is another example of a contaminant often found in phosphate fertilizers (at levels from 7 to 100 pCi/g). Eventually these heavy metals can build up to unacceptable levels and build up in vegetable produce. (See cadmium poisoning) 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.
Steel industry wastes, recycled into fertilizers for their high levels of zinc (essential to plant growth), wastes can include the following toxic metals: lead arsenic, cadmium, chromium, and nickel. The most common toxic elements in this type of fertilizer are mercury, lead, and arsenic. Concerns have been raised concerning fish meal mercury content by at least one source in Spain.
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.
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.
Atmospheric effects:-
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.
Through the increasing use of nitrogen fertilizer, which is added at a rate of 1 billion tons per year presently 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.
Storage and application of some nitrogen fertilizers in some 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.
The use of fertilizers on a global scale emits significant quantities of greenhouse gas into the atmosphere.
Emissions come about through the use of:
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.