   #copyright

Fertilizer

2007 Schools Wikipedia Selection. Related subjects: Food and agriculture

   spreading manure, an organic fertilizer
   Enlarge
   spreading manure, an organic fertilizer

   Fertilizers (British English, also fertilisers) are compounds given to
   plants to promote growth; they are usually applied either via the soil,
   for uptake by plant roots, or by foliar feeding, for uptake through
   leaves. Fertilizers can be organic (composed of organic matter, i.e.
   carbon based), or inorganic (containing simple, inorganic chemicals).
   They can be naturally-occurring compounds such as peat or mineral
   deposits, or manufactured through natural processes (such as
   composting) or chemical processes (such as the Haber process).

   Fertilizers typically provide, in varying proportions, the three major
   plant nutrients (nitrogen, phosphorus, and potassium), the secondary
   plant nutrients (calcium, sulfur, magnesium), and sometimes trace
   elements (or micronutrients) with a role in plant nutrition: boron,
   chlorine, manganese, iron, zinc, copper and molybdenum.

Inorganic fertilizers (Mineral Fertilizer)

     * Examples of naturally-occurring inorganic fertilizers include
       Chilean sodium nitrate, mined "rock phosphate" and limestone (a
       calcium source, but mostly used to reduce soil acidity).
     * Examples of manufactured or chemically-synthesized inorganic
       fertilizers include ammonium nitrate, potassium sulfate, and
       superphosphate, or triple superphosphate.

Macronutrients and micronutrients

   FERTILIZERS can be divided into macronutrients or micronutrients based
   on their concentations in plant dry matter. There are six
   macronutrients: nitrogen, potassium, and phosphorus, often termed
   'primary macronutrients' because their availability is often managed
   with NPK fertilizers, and the 'secondary macronutrient', and calcium,
   magnesium, and sulfur, which are required in 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 whole number or tenths of
   percentages in plant tissues. There are many micronutrients, and their
   importance and occurrence differ somewhat from plant to plant. In
   general, most present from 5 to 100 parts per million (ppm) by mass.
   Examples of micronutrients are as follows: iron (Fe), manganese (Mn),
   boron (B), copper (Cu), molybdenum (Mo), and zinc (Zn).

Macronutrient fertilizers

   Synthesized materials are also called artificial , and may be described
   as straight, where the product predominantly contains the three primary
   ingredients of nitrogen (N), phosphorus (P) and potassium (K), which
   are known as N-P-K fertilizers or compound fertilizers when elements
   are mixed intentionally. They are named or labeled according to the
   content of these three elements, which are macronutrients. The mass
   fraction (percent) nitrogen is reported directly. However, phosphorus
   is reported as diphosphorus pentoxide (P[2]O[5]), the anhydride of
   phosphoric acid, and potassium is reported as potash or potassium oxide
   (K[2]O), which is the anhydride of potassium hydroxide. Fertilizer
   composition is expressed in this fashion for historical reasons in the
   way it was analyzed (conversion to ash for P and K); this practice
   dates back to Justus von Liebig (see more below). Consequently, an
   18-51-20 fertilizer would have 18% nitrogen as N, 51% phosphorus as
   P[2]O[5], and 20% potassium as K[2]O, The other 11%is known as ballast
   and has no value to the plants.Although analyses are no longer carried
   out by ashing first, the naming convention remains. If nitrogen is the
   main element, they are often described as nitrogen fertilizers.

   In general, the mass fraction (percentage) of elemental phosphorus, [P]
   = 0.436 x [P[2]O[5]]

   and the mass fraction (percentage) of elemental potassium, [K] = 0.83 x
   [K[2]O]

   (These conversion factors are mandatory under the UK
   fertiliser-labelling regulations if elemental values are declared in
   addition to the N-P-K declaration.)

   An 18−51−20 fertiliser therefore contains, by weight, 18% elemental
   nitrogen (N), 22% elemental phosphorus (P) and 16% elemental potassium
   (K).

Agricultural versus Horticultural Fertilizers

   In general, agricultural fertilizers contain only one or two
   macronutrients. Agricultural fertilizers are intended to be applied
   infrequently and normally prior to or along side seeding. Examples of
   agricultural fertilizers are granular triple superphosphate, potassium
   chloride, urea, and anhydrous ammonia. The commodity nature of
   fertilizer, combined with the high cost of shipping, leads to use of
   locally available materials or those from the closest/cheapest source,
   which may vary with factors affecting transportation by rail, ship, or
   truck. In other words, a particular nitrogen source may be very popular
   in one part of the country while another is very popular in another
   geographic region only due to factors unrelated to agronomic concerns.

   Horticultural or specialty fertilizers, on the other hand, are
   formulated from many of the same compounds and some others to produce
   well-balanced fertilizers that also contain micronutrients. Some
   materials, such as ammonium nitrate, are used minimally in large scale
   production farming. The 18-51-20 example above is a horticultural
   fertilizer formulated with high phosphorus to promote bloom development
   in ornamental flowers. Horticultural fertilizers may be water-soluble
   (instant release) or relatively insoluble (controlled release).
   Controlled release fertilizers are also referred to as sustained
   release or timed release. Many controlled release fertilizers are
   intended to be applied approximately every 3-6 months, depending on
   watering, growth rates, and other conditions, whereas water-soluble
   fertilizers must be applied at least every 1-2 weeks and can be applied
   as often as every watering if sufficiently dilute. Unlike agricultural
   fertilizers, horticultural fertilizers are marketed directly to
   consumers and become part of retail product distribution lines.

Justus von Liebig

   Chemist Justus von Liebig (in the 19th century) contributed greatly to
   understanding the role of inorganic compounds in plant nutrition and
   devised the concept of Liebig's barrel to illustrate the significance
   of inadequate concentrations of essential nutrients. At the same time
   he deemphasized the role of humus. This theory was influential in the
   great expansion in use of artificial fertilizers in the 20th century.

   Nitrogen fertilizer is often synthesized using the Haber-Bosch process,
   which produces ammonia. This ammonia is applied directly to the soil or
   used to produce other compounds, notably ammonium nitrate, a dry,
   concentrated product. It can also be used in the Odda Process to
   produce compound fertilizers such as 15-15-15.

   Inorganic fertilizers sometimes do not replace trace mineral elements
   in the soil which become gradually depleted by crops grown there. This
   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. One
   exception to this is in Western Australia where deficiencies of zinc,
   copper, manganese, iron and molybdenum were identified as limiting the
   growth of crops and pastures in the 1940's and 1950's. 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.

   In many countries there is the public perception that inorganic
   fertilizers "poison the soil" and result in "low quality" produce.
   However, there is very little (if any) scientific evidence to support
   these views. When used appropriately, inorganic fertilizers enhance
   plant growth, the accumulation of organic matter and the biological
   activity of the soil, while reducing the risk of water run-off,
   overgrazing and soil erosion. The nutritional value of plants for human
   and animal consumption is typically improved when inorganic fertilizers
   are used appropriately.

Organic fertilizers

     * Examples of naturally occurring organic fertilizers include manure,
       slurry, worm castings, peat, seaweed and guano. Green manure crops
       are also grown to add nutrients to the soil. Naturally occurring
       minerals such as mine rock phosphate, sulfate of potash and
       limestone are also considered Organic Fertilizers.
     * Examples of manufactured organic fertilizers include compost,
       bloodmeal, bone meal and seaweed extracts. Other examples are
       natural enzyme digested proteins, fish meal, and feather meal.

   The decomposing crop residue from prior years is another source of
   fertility. Though not strictly considered "fertilizer", the distinction
   seems more a matter of words than reality.

   Some ambiguity in the usage of the term 'organic' exists because some
   of synthetic fertilizers, such as urea and urea formaldehyde, are fully
   organic in the sense of organic chemistry. In fact, it would be
   difficult to chemically distinguish between urea of biological origin
   and that produced synthetically. On the other hand, some fertilizer
   materials commonly approved for organic agriculture, such as powdered
   limestone, mined "rock phosphate" and Chilean saltpeter, are inorganic
   in the use of the term by chemistry.

   Although the density of nutrients in organic material is comparatively
   modest, they have some advantages. For one thing organic growers
   typically produce some or all of their fertilizer on-site, thus
   lowering operating costs considerably. Then there is the matter of how
   effective they are at promoting plant growth, chemical soil test
   results aside. The answers are encouraging. Since the majority of
   nitrogen supplying organic fertilizers contain insoluble nitrogen and
   are slow release fertilizers their effectiveness can be greater than
   conventional nitrogen fertilzers.

   Implicit in modern theories of organic agriculture is the idea that the
   pendulum has swung the other way to some extent in thinking about plant
   nutrition. While admitting the obvious success of Leibig's theory, they
   stress that there are serious limitations to the current methods of
   implementing it via chemical fertilization. They re-emphasize the role
   of humus and other organic components of soil, which are believed to
   play several important roles:
     * Mobilizing existing soil nutrients, so that good growth is achieved
       with lower nutrient densities while wasting less
     * Releasing nutrients at a slower, more consistent rate, helping to
       avoid a boom-and-bust pattern
     * Helping to retain soil moisture, reducing the stress due to
       temporary moisture stress
     * Improving the soil structure

   Organics also have the advantage of avoiding certain long-term problems
   associated with the regular heavy use of artificial fertilizers:
     * the possibility of "burning" plants with the concentrated chemicals
       (i.e. an over supply of some nutrients)
     * the progressive decrease of real or perceived "soil health",
       apparent in loss of structure, reduced ability to absorb
       precipitation, lightening of soil colour, etc.
     * the necessity of reapplying artificial fertilizers regularly (and
       perhaps in increasing quantities) to maintain fertility
     * the cost (substantial and rising in recent years) and resulting
       lack of independence

   Organic fertilizers also have their disadvantages:
     * As acknowledged above, they are typically a dilute source of
       nutrients compared to inorganic fertilizers, and where significant
       amounts of nutrients are required for profitable yields, very large
       amounts of organic fertilizers must be applied. This results in
       prohibitive transportation and application costs, especially where
       the agriculture is practiced a long distance from the source of the
       organic fertilizer.
     * The composition of organic fertilizers tends to be highly variable,
       so that accurate application of nutrients to match plant production
       is difficult. Hence, large-scale agriculture tends to rely on
       inorganic fertilizers while organic fertilizers are cost-effective
       on small-scale horticultural or domestic gardens.

   In practice a compromise between the use of artificial and organic
   fertilizers is common, typically by using inorganic fertilizers
   supplemented with the application of organics that are readily
   available such as the return of crop residues or the application of
   manure.

   It is important to differentiate between what we mean by organic
   fertilizers and fertilizers approved for use in organic farming and
   organic gardening by organizations and authorities who provide organic
   certification services. Some approved fertilizers may be inorganic,
   naturally occurring chemical compounds, e.g. minerals...

Environmental effects of fertilizer use

   Over-application of chemical fertilizers, or application of chemical
   fertilizers at a time when the ground is waterlogged or the crop is not
   able to use the chemicals, can lead to surface runoff (particularly
   phosphorus) or leaching into groundwater (particularly nitrates). One
   of the adverse effects of excess fertilizer in lacustrine systems are
   algal blooms, which can lead to excessive mortality rates for fish and
   other aquatic organisms. When prolonged algae blooms occur over many
   years, the effect is a process called eutrophication. Worldwide the
   issues of nutrient fate are analyzed using hydrology transport models.

   Excessive nitrogen fertilizer applications can lead to pest problems by
   increasing the birth rate, longevity and overall fitness of certain
   pests (Jahn 2004; Jahn et al. 2001a,b, 2005; Preap et al. 2002, 2001).

   It is also possible to over-apply organic fertilizers. However: their
   nutrient content, their solubility, and their release rates are
   typically much lower than chemical fertilizers, partially because by
   their nature, most organic fertilizers also provide increased physical
   and biological storage mechanisms to soils.

   The problem of over-fertilization is primarily associated with the use
   of artificial fertilizers, because of the massive quantities applied
   and the destructive nature of chemical fertilizers on soil nutrient
   holding structures. The high solubilities of chemical fertilizers also
   exacerbate their tendency to degrade ecosystems.

   Storage and application of some fertilizers in some weather or soil
   conditions can cause emissions of the greenhouse gas nitrous oxide
   (N[2]O). Ammonia gas (NH[3]) may be emitted following application of
   inorganic fertilizers, or manure or slurry. Besides supplying nitrogen,
   ammonia can also increase soil acidity (lower pH, or "souring").

   For these reasons, it is recommended that knowledge of the nutrient
   content of the soil and nutrient requirements of the crop are carefully
   balanced with application of nutrients in inorganic fertiliser
   especially. This process is called nutrient budgeting. By careful
   monitoring of soil conditions, farmers can avoid wasting expensive
   fertilizers, and also avoid the potential costs of cleaning up any
   pollution created as a byproduct of their farming.

   The concentration of up to 100 mg/kg of Cadmium in phosphate minerals
   (for example Nauru and the Christmas islands ) increases the
   contamination of soil with Cadmium, for example in New Zealand. Uranium
   is another example for impurities of fertilizers
   Retrieved from " http://en.wikipedia.org/wiki/Fertilizer"
   This reference article is mainly selected from the English Wikipedia
   with only minor checks and changes (see www.wikipedia.org for details
   of authors and sources) and is available under the GNU Free
   Documentation License. See also our Disclaimer.
