|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 ecosystems.
|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