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A fertilizer American English or fertiliser British English ; see spelling differences is any material of natural or synthetic origin other than liming materials that is applied to soils or to plant tissues to supply one or more plant nutrients essential to the growth of plants.
Many sources of fertilizer exist, both natural and industrially produced. Fertilizers enhance the growth of plants. This goal is met in two ways, the traditional one being additives that provide nutrients. The second mode by which some fertilizers act is to enhance the effectiveness of the soil by modifying its water retention and aeration.
This article, like many on fertilizers, emphasises the nutritional aspect. Fertilizers typically provide, in varying proportions: The nutrients required for healthy plant life are classified according to the elements, but the elements are not used as fertilizers. Instead 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. Plants are made up of four main elements: Carbon, hydrogen and oxygen are widely available as water and carbon dioxide. 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 proteins , DNA and other components e.
To be nutritious to plants, nitrogen must be made available in a "fixed" form. Only some bacteria and their host plants notably legumes can fix atmospheric nitrogen N 2 by converting it to ammonia.
Phosphate is required for the production of DNA and ATP , the main energy carrier in cells, as well as certain lipids. Micronutrients are consumed in smaller quantities and are present in plant tissue on the order of parts-per-million ppm , ranging from 0. Because these elements enable catalysts enzymes their impact far exceeds their weight percentage. Fertilizers are classified in several ways. They are classified according to whether they provide a single nutrient e. 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. The main nitrogen-based straight fertilizer is ammonia or its solutions.
Ammonium nitrate NH 4 NO 3 is also widely used. Urea is another popular source of nitrogen, having the advantage that it is solid and non-explosive, unlike ammonia and ammonium nitrate, respectively. The main straight phosphate fertilizers are the superphosphates. A mixture of single superphosphate and triple superphosphate is called double superphosphate. Major two-component fertilizers provide both nitrogen and phosphorus to the plants. These are called NP fertilizers.
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. Fertilizers do not actually contain P 2 O 5 or K 2 O, but the system is a conventional shorthand for the amount of the phosphorus P or potassium K in a fertilizer. 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.
The main micronutrients are molybdenum, zinc, and copper. 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 chelate complex , e. The micronutrient needs depend on the plant. For example, sugar beets appear to require boron , and legumes require cobalt. Nitrogen fertilizers are made from ammonia NH 3 , which is sometimes injected into the ground directly.
The ammonia is produced by the Haber-Bosch process. Deposits of sodium nitrate NaNO 3 Chilean saltpeter are also found in the Atacama desert in Chile and was one of the original nitrogen-rich fertilizers used. In rare cases, fields are treated with the crushed mineral, but most often more soluble salts are produced by chemical treatment of phosphate minerals.
The most popular phosphate-containing minerals are referred to collectively as phosphate rock. These minerals are converted to water-soluble phosphate salts by treatment with sulfuric H 2 SO 4 or phosphoric acids H 3 PO 4.
The large production of sulfuric acid as an industrial chemical is primarily due to its use as cheap acid in processing phosphate rock into phosphate fertilizer. The global primary uses for both sulfur and phosphorus compounds relate to this basic process. 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.
Potash is a mixture of potassium minerals used to make potassium chemical symbol: Potash is soluble in water, so the main effort in producing this nutrient from the ore involves some purification steps; e. Sometimes potash is referred to as K 2 O, 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.
Compound fertilizers, which contain N, P, and K, can often be produced by mixing straight fertilizers. In some cases, chemical reactions occur between the two or more components.
For example, monoammonium and diammonium phosphates, which provide plants with both N and P, are produced by neutralizing phosphoric acid from phosphate rock and ammonia:. Fertilizers of an organic origin the first definition include such animal wastes , plant wastes from agriculture, compost , and treated sewage sludge biosolids. Beyond manures, animal sources can include products from the slaughter of animals — bloodmeal , bone meal , feather meal , hides, hoofs, and horns all are typical components.
No matter the definition nor composition, most of these products contain less concentrated nutrients, and the nutrients are not as easily quantified. In terms of volume, peat is the most widely used packaged organic soil amendment. Since this immature form of coal, which improves the soil by aeration and absorbing water, confers no nutritional value to the plants, it is thus 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.
Organic fertilizers such as composts and manures may be distributed locally without going into industry production, making actual consumption more difficult to quantify. 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. Fertilizers are applied to crops both as solids and as liquid.
The most widely used solid inorganic fertilizers are urea, diammonium phosphate and potassium chloride. Often solids are available as prills , 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. Advantages of liquid fertilizer are its more rapid effect and easier coverage. Slow- and controlled-release involve only 0. Their utility stems from the fact that fertilizers are subject to antagonistic processes. In addition to their providing the nutrition to plants, excess fertilizers can be poisonous to the same plant.
Competitive with the uptake by plants is the degradation or loss of the fertilizer. Microbes degrade many fertilizers, e. Furthermore, fertilizers are lost by evaporation or leaching. Most slow-release fertilizers are derivatives of urea, a straight fertilizer providing nitrogen. Isobutylidenediurea "IBDU" and urea-formaldehyde slowly convert in the soil to free urea, which is rapidly uptaken by plants.
Besides being more efficient in the utilization of the applied nutrients, slow-release technologies also reduce the impact on the environment and the contamination of the subsurface water. Polymer coating of fertilizer ingredients gives tablets and spikes a 'true time-release' or 'staged nutrient release' SNR of fertilizer nutrients.
Controlled release fertilizers are traditional fertilizers encapsulated in a shell that degrades at a specified rate. Sulfur is a typical encapsulation material. Other coated products use thermoplastics and sometimes ethylene-vinyl acetate and surfactants, etc. Foliar fertilizers are applied directly to leaves. The method is almost invariably used to apply water-soluble straight nitrogen fertilizers and used especially for high value crops such as fruits. Various chemicals are used to enhance the efficiency of nitrogen-based fertilizers.
In this way farmers can limit the 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.
The conversion of urea to ammonia catalyzed by enzymes called ureases. Careful fertilization technologies are important because excess nutrients can be detrimental. Fertilizers vary in their tendency to burn roughly in accordance with their salt index. Recently nitrogen fertilizers have plateaued in most developed countries. China although has become the largest producer and consumer of nitrogen fertilizers. The production of nitrogen has drastically increased since the s. Phosphate and potash have increased in price since the s, which is larger than the consumer price index.