Urine Fertilisation (Large-scale)

Urine is a liquid product of the human body that is secreted by the kidneys. A big share of the soluble substances in urine consists of essential plant nutrients like Nitrogen (N), Phosphorus (P) and Potassium (K) that can be easily reused in agriculture. There is almost a mass balance between nutrient consumption and excretion, but the actual nutrient content in urine is of course dependent on the diet and varies between countries as well as between individuals.

The amount of urine produced per person and day depends on the amount of liquid a person drinks, but usually lies within a range of 0.8 to 1.5 L per day for an adult person and about half as much for children, respectively (WHO 2006). On average, an adult person produces around 500 L (550 kg) of urine per year, thus approximately 4 kg of N, 0.5 kg of P and 1 kg of K per person per year (JOENSSON et al. 2004). Urine can therefore be considered as a nitrogen rich liquid fertiliser. Due to its comparably high N and low organic matter content it is often recommended to complement urine application with other nutrient and organic matter sources.

In respect of the 0.5 kg of phosphorus, and taking into account fertiliser prizes from the Nepalese market in 2008 (35 NRs/kgNPK fertiliser (ratio 20:20:10), GANTENBEIN 2009), this is thus equivalent to 1.2$ per capita per year and 9$ if we consider a family equivalent to 7 adult members.  That does not seem much on a first sight – but it’s the scale that makes the difference. If you take for instance a city with a population of 1.5 million, the value of the generated urine is 1.8 million $ per year.

In larger scale systems where urine is collected from several households, urine should be stored for at least 6 months before considered safe for agricultural use (WHO 2006). You can find more information on the hygienisation of urine through storage in the factsheet regarding storage of urine.

The storage of large quantities of urine can be a difficult logistic problem and should be well organised and prepared. In the view of a large scale application of the stored liquid as a fertiliser (and eventually a commercialisation of the product), at least some samples of different storage containers should be analysed from time to time to guarantee a good hygienisation and fertiliser quality.

Special attention has to be paid to sealing the storage containers: when urea is degraded to ammonium, the pH of the solution rises. Even though higher pH implicates a faster inactivation of pathogenic microorganisms (SCHOENNING 2004) it also means that nitrogen can evaporate as ammonia (JOENSSON et al. 2004).

Because of its high nitrogen content, urine should be applied at a rate corresponding to the desired plant nitrogen requirements. A starting point for dimensioning urine application are local recommendations for use of mineral nitrogen fertilisers.

Urine can be applied neat or diluted with water. The existing recommendations vary widely, depending on the local conditions. A common and often recommended dilution rate is 1:3 (1 part urine with 3 parts of water). It should be considered that dilution increases the volume to be spread and thus labour, transport expense, equipment needed etc. Yet, the advantages of dilution include a noticeable odour reduction and a decreased risk of over-application.

For the best fertilising effect and to avoid ammonia losses to the air, urine should be incorporated into the soil as soon as possible after application, preferably instantly. A low-cost method is the relatively labour-intensive application with watering cans (see picture). Another option is the close to the ground application of urine with slurry spreaders (see picture) or the application of urine with drip irrigation systems. The mix of the urine with flooding irrigation water for rice production has also been tested. When spreading urine, it should not be applied on leaves or other parts of the plants, as this can cause foliar burning.

A good availability of nutrients is particularly important in the early stages of cultivation. Once the crop enters its reproductive stage, it normally stops growing and hardly takes up any more nutrients. Fertilizations should stop after between 2/3 and 3/4 of the time between sowing and harvest. A waiting period of one month between fertilization and harvest should always be observed.

An important challenge for the sustainability of large-scale urine handling systems is to minimise the costs for transport, storage, and application towards the goal that no subsidies are needed. Depending on the acceptance among the population (both farmers and end-product consumers) and the local fertiliser market prices, farmers might be willing to pay for hygienised human urine. In the absence of any alternative treatment or disposal for urine (and excreta), the households or governmental structures might be prepared to contribute to the financing of urine collection, storage and redistribution infrastructure as a sustainable and integrated sanitation and food security approach.

Health risks associated with the use of human urine in plant production are generally low. However, during the source separation, faecal cross-contamination can occur and respective measures to reduce potential health risks to an acceptable minimum following the WHO multi-barrier strategy should always be considered.