copyied from wiki also check out night soil... its all grose.
Urine contains large quantities of nitrogen (mostly as
urea), as well as significant quantities of dissolved phosphates and potassium, the main macronutrients required by plants. Diluted at least 8:1 with water it can be applied directly to soil as a fertilizer. Undiluted, it can chemically burn the roots of some plants, but it can be safely used as a source of complementary nitrogen in carbon rich
compost.
[14] Urine typically contains 70% of the
nitrogen and more than half the
phosphorus and
potassium found in urban waste water flows, while making up less than 1% of the overall volume. Thus source separation and on-site treatment has been studied in
Sweden as a way to partially close the cycle of agricultural nutrient flows, to reduce the cost and energy intensivity of sewage treatment, and the ecological consequences such as
eutrophication, resulting from an influx of nutrient rich effluent into aquatic or marine ecosystems. The fertilization effect of urine has been found to be comparable to that of commercial fertilizers with an equivalent
NPK rating.
[15]
However, depending on the diet of the producer, urine may also have undesirably high concentrations of various inorganic
salts such as
sodium chloride, which are also excreted by the
renal system. Concentrations of heavy metals such as
lead,
mercury, and
cadmium, commonly found in solid human waste, are much lower in urine (though not low enough to qualify for use in
organic agriculture under current EU rules).
[16] Proponents of urine as an agricultural fertilizer usually claim the risks to be negligible or acceptable, and point out that sewage causes more environmental problems when it is treated and disposed of compared with when it is used as a resource.
It is unclear whether source separation and on site treatment of urine can be made cost effective, and to what degree the required behavioral changes would be regarded as socially acceptable, as the largely successful trials performed in Sweden may not readily generalize to other industrialized societies.
[15] In developing countries, the application of pure urine to crops is rare, but the use of whole raw sewage (termed
night soil) has been common throughout history.