Fertilizer
10-13-2010
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').
Fertilizers are roughly broken up between organic and inorganic fertilizer, with the main difference between the two being sourcing, and not necessarily differences in nutrient content.
Organic fertilizers 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.
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). Micronutrients are consumed in smaller quantities and are present in plant tissue in quantities measured in parts per million (ppm), ranging from 5 to 200 ppm, or less than 0.02% dry weight
Macronutrient fertilizers
Macronutrient fertilizers are labeled with an NPK analysis and also "N-P-K-S" in Australia.[2]
An example of labeling for the fertilizer potash is composed of 1:1 potassium to carbonate by volume, or 47:53 by weight (owing to differences in molecular weight between the potassium and carbonate). Traditional analysis of 100g of KCl would yield 60g of K2O. The percentage yield of K2O from the original 100g of fertilizer is the number shown on the label. A potash fertilizer would thus be labeled 0-0-60, not 0-0-52.
[edit] History
Main articles: History of organic farming and History of fertilizer
The modern understanding of plant nutrition dates to the 19th century and the work of Justus von Liebig, among others. Management of soil fertility, however, has been the pre-occupation of farmers for thousands of years.
[edit] Type of Fertilizer
Fertilizers come in various shapes and forms. The most typical form is granular fertilizer (powder form), usually come in a bag / box. The next most common form is liquid fertilizer; some advantages of liquid lawn fertilizer are its immediate effect and wide coverage. Moreover, there is also a form of slow-release fertilizer which solves the problem of "burning" the plants due to excessive nutrients. This kind of fertilizer come in various form like fertilizer spikes, tabs, etc. Finally, organic fertilizer is on the rise as people are resorting to a green / environmental friendly products. Although organic fertilizer usually contain less nutrients, some people still prefer organic due to natural ingredients.
[edit] Inorganic fertilizer (synthetic fertilizer)
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 as the end product. This ammonia is used as a feedstock for other nitrogen fertilizers, such as anhydrous ammonium nitrate and urea. These concentrated products may be diluted with water to form a concentrated liquid fertilizer (e.g. UAN). Ammonia can be combined with rock phosphate and potassium fertilizer in the Odda Process to produce compound fertilizer.
The use of synthetic nitrogen fertilizers has increased steadily in the last 50 years, rising almost 20-fold to the current rate of 100 million tonnes of nitrogen per year.[3] The use of phosphate fertilizers has also increased from 9 million tonnes per year in 1960 to 40 million tonnes per year in 2000. A maize crop yielding 6-9 tonnes of grain per hectare requires 30–50 kg of phosphate fertilizer to be applied, soybean requires 20–25 kg per hectare.[4] Yara International is the world's largest producer of nitrogen based fertilizers.
Application
Synthetic fertilizers are commonly used to treat fields used for growing maize, followed by barley, sorghum, rapeseed, soy and sunflower[citation needed]. 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.[7]
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.
[edit] Problems with inorganic fertilizer
[edit] 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.[8]
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[citation needed]. Soils in Western Australia are very old, highly weathered and deficient in many of the major nutrients and trace elements[citation needed]. Since this time these trace elements are routinely added to inorganic fertilizers used in agriculture in this state[citation needed].
[edit] Overfertilization
See also: Fertilizer burn
Fertilizer burnOver-fertilization of a vital nutrient can be as detrimental as underfertilization.[9] "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.[10]
[edit] High energy consumption
The production of synthetic ammonia currently consumes about 5% of global natural gas consumption, which is somewhat under 2% of world energy production.[11]
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.[12] The increase in price of natural gases over the past decade, along with other factors such as increasing demand, have contributed to an increase in fertilizer price[13].
[edit] Long-Term Sustainability
Inorganic fertilizers are now produced in ways which theoretically cannot be continued indefinitely[citation needed]. 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).