Fertilizers are soil amendments applied to promote plant growth.
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Fertilizers are usually applied directly onto the soil, but can also be applied onto leaves (foliar feeding). The main nutrients added in fertilizer are nitrogen, phosphorus, and potassium but other nutrients are added in smaller amounts. Fertilizers can be either organic (e.g. manure) or inorganic (mined or synthesized chemically). Organic fertilizers and some mined inorganic fertilizers have been used for centuries whereas chemically-synthesized inorganic fertilizers were only developed on an industrial scale in the 20th century. Increased understanding and use of fertilizers was an important part of both the pre-industrial British Agricultural Revolution and the industrial green revolution of the 20th century.
Fertilizers typically provide, in varying proportions, the three major plant nutrients: nitrogen, phosphorus, and potassium, known shorthand as N-P-K). They may also provide secondary plant nutrients such as calcium, sulfur, magnesium. Micronutrients may be provided: boron, chlorine, manganese, iron, zinc, copper, molybdenum and selenium.
Fertilizers can be classified by their macronutrients and micronutrients content (concentrations by dry matter). There are six macronutrients: nitrogen, phosphorus, and potassium, often termed "primary macronutrients" because their availability is usually managed with NPK fertilizers, and the "secondary macronutrients" — calcium, magnesium, and sulfur — which are required in roughly similar quantities but whose availability is often managed as part of liming and manuring practices rather than fertilizers.
The macronutrients are consumed in larger quantities and normally present as a whole number or tenths of percentages in plant tissues (on a dry matter weight basis). There are many micronutrients, required in concentrations ranging from 5 to 100 parts per million (ppm) by mass. Plant micronutrients include iron (Fe), manganese (Mn), boron (B), copper (Cu), molybdenum (Mo), nickel (Ni), chlorine (Cl), and zinc (Zn).
Plant nutrition is the study of the chemical elements that are necessary for plant growth. There are several principles that apply to plant nutrition. Some elements are directly involved in plant metabolism. However, this principle does not account for the so-called beneficial elements, whose presence, while not required, has clear positive effects on plant growth. A nutrient that is able to limit plant growth according to Liebig's law of the minimum, is considered an essential plant nutrient if the plant can not complete its full life cycle without it. There are 16 essential plant nutrients.
Macronutrient fertilizers (N-P-K): Collectively, the main nutrients vital to plants by weight are called macronutrients, including: nitrogen (N), phosphorus (P), and potassium (K) (i.e. N-P-K).
Synthetic macronutrient fertilizer can be referred to as artificial or straight, where the product predominantly contains the three main nutrients. Compound fertilizers are N-P-K fertilizers with other elements purposely intermixed.
Fertilizers are broadly divided into organic fertilizers (composed of enriched organic matter—plant or animal), or inorganic fertilizers (composed of synthetic chemicals and/or minerals). Inorganic fertilizer is often synthesized using the Haber-Bosch process, which produces ammonia. This ammonia is used as a feedstock for other nitrogen fertilizers (e.g. anhydrous ammonium nitrate and urea).
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.
Fertilizer burn is a defined as leaf scorch resulting from over-fertilization, usually referring to excess nitrogen salts. Fertilizer burn is the result of dessication of plant tissues due to chemiosmosis, creating a state of hypertonicity.
are now produced in ways which cannot be continued indefinitely. Potassium and phosphorus come from mines (or saline lakes such as the Dead Sea) and such resources are limited. While atmospheric nitrogen is effectively unlimited (forming over 70% of atmospheric gases), relatively few plants engage in nitrogen fixation (conversion of atmospheric nitrogen to a plant-accessible form). To make nitrogen accessible to plants, nitrogen fertilizers are synthesized using fossil fuels such as natural gas and coal, which are limited.
Organic fertilizers are naturally-occurring fertilizers (e.g. peat moss or green manure), or naturally occurring mineral deposits (e.g. saltpeter). Naturally occurring organic fertilizers include manure, slurry, worm castings, peat, seaweed,humic,brassin and guano. 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). Processed organic fertilizers include compost, bloodmeal, bone meal,humic acid,amino acid,brassin and seaweed extracts. Other examples are natural enzyme digested proteins, fish meal, and feather meal. Decomposing crop residue from prior years is another source of fertility.
Agriculture and the environment are intimately linked and much debate has taken place in recent years about the sustainability of some farming practices. Farming efficiencies, technological innovations and organic farming are all used to reduce the environmental impact of farming.
The chemical compound ammonium nitrate, the nitrate of ammonia with the chemical formula NH4NO3, is a white crystalline solid at room temperature and standard pressure. It is commonly used in agriculture as a high-nitrogen fertilizer, and it has also been used as an oxidizing agent in explosives, including improvised explosive devices. It is the main component of ANFO, a very popular explosive.
Seaweed fertiliser, also spelt seaweed fertilizer, several of the 12,000+ varieties in the ocean have been shown to be valuable additions to the organic garden and can be abundantly available free for those living near the coast. However, caution should be observed when collecting seaweed, particularly from areas that are liable to pollution, such as downriver (including estuaries) of industrial activities as seaweed is susceptible to contamination. There are also legal implications relating to gathering seaweed, and concerns about sustainability.
Potash is the common name given to potassium carbonate and various mined and manufactured salts that contain the element potassium in water-soluble form. In some rare cases, potash can be formed with traces of organic materials such as plant remains. Potassium is the seventh most abundant element in the Earth's crust, and is the third major plant and crop nutrient after nitrogen and phosphate.
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