One exception to this is in Western Australia where deficiencies of
zinc, copper, manganese, iron and molybdenum were identifed 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.
|Examples of naturally occurring organic fertilizers include manure and slurry, urine, 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, dried blood, bone meal and seaweed
extracts. Other examples are natural enzyme digested proteins, fish
meal, and feather meal. A listing of products may be found at Organic Materials Review Institute and California Organic Fertilizers Inc..
|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
|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 color, 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
fertilisers 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. Finally, some organic fertilizers
such as manures can contain bacteria or heavy metals harmful to human
|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
|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). Excessive surface runoff of easily soluble
nutrients often pollutes lakes and streams is a process called eutrophication. This can lead to algal blooms which are destructive and even deadly to wildlife.
|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 contribute to their tendency to rapidly pollute
|Storage and application of some fertilizers in some weather or soil conditions can cause emissions of the greenhouse gasnitrous oxide (N2O). Ammonia gas (NH3)
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 Nauru2 - and the Christmas islands3 - ) increases the contamination of soil with Cadmium, for example in New Zealand. 4 - Uranium is an other example for impurities of fertilizers
Soil conditioners, also called soil amendments, are materials added to soil to improve plant growth and health. The type of conditioner added depends on the current soil composition, climate and the type of plant. Some soils lack nutrients necessary for proper plant growth and others hold too much or too little water. A conditioner or a combination of conditioners corrects the soil's deficiencies. Lime is used to make soil less acidic. Fertilizers, such as peat, manure or compost, add depleted plant nutrients. Materials such as clay, vermiculite, hydrogel and shredded bark will make soil hold more water. Gypsum releases nutrients and improves soil structure. Sometimes a soil inoculant is added for legumes.
|Lawrence, Felicity (2004). 214, Kate Barker Not on the Label , 213, Penguin. ISBN 0-141-01566-7. -
|Syers JK, Mackay AD, Brown MW, Currie CD (1986). Chemical and physical
characteristics of phosphate rock materials of varying reactivity. J Sci Food Agric - 37 - : 1057-1064. -
|Trueman NA (1965). The phosphate, volcanic and carbonate rocks of Christmas Island (Indian Ocean). J Geol Soc Aust - 12 - : 261-286. -
|Taylor MD (1997). Accumulation of Cadmium derived from fertilisers in New Zealand soils. Science of Total Environment - 208 - : 123-126. -
|Articles on Various Kinds of Fertilizer Lawn Care