Urine--a valuable fertilizer with low risk after storage in the tropics.

Urine contains a considerable amount of nutrients and potentially could be used as supplement commercial mineral fertilizer; however, it carries risk of contamination. The effect of urine storage as a simple treatment method was examined under tropical conditions. Initial concentrations of total coliforms (2.3 x 10(5) CFU/100 mL), E. coli (<1.0 x 10(4) CFU/100 mL), and Salmonella sp. were less than detection limit after four weeks. Open storage led to nitrogen losses of 90%, whereas closed storage containers retained 93% of total nitrogen. Under storage, the N:P ratio of 8:1 in fresh urine changed to 14:1 in the supernatant and to 1:12 in the precipitate, and 100% of magnesium and 96% of calcium was precipitated. A model showed that, depending on plant requirements, using the mixture of supernatant and precipitate as fertilizer for crops such as cassava was reasonable. To fertilize crops such as rice, however, additional P and K was needed. The nutrient-based flux of heavy metals to soils was negligible.