Urine Fertilisation (Small-scale)

Urine is a liquid product of the human body that is secreted by the kidneys. 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 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 fertilizer prices from the Nepalese market in 2008 (35 NRs/kg NPK 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. This may not seem a lot, but of course, more money can be saved or income generated from the plants produced.

The guidelines for urine use are based on storage time and temperature (see WHO guidelines on excreta use in agriculture for specific requirements). However, it is generally accepted that if urine is stored for at least 1 month, it will be safe for agricultural application at the household level. If urine is used for crops that are eaten by people other than the urine producer, it should be stored beforehand for 6 months. You can find more information in the factsheet regarding storage of urine. During storage, high pH (above 9), temperature and ammonia are the main factors for inactivating pathogens (SCHOENNING 2004). The rise of pH to above 9 occurs naturally, when urea is degraded to ammonium. At this pH, the initial concentrations of phosphate, magnesium, calcium and ammonia are no longer soluble, but precipitate forming a bottom layer containing phosphor precipitates (struvite), which can be handled as fertiliser together with the rest of the urine. Special attention should however be paid on the ventilation of the urine collection and storage chamber. Because of the high pH, coupled with the high ammonium concentration of urine, there is a risk of losing N in the form of ammonia to the air. As long as the collection and storage chambers are sealed and the contact of the urine with air is reduced to a minimum, neither losses of nutrients nor changes in their availability can occur (JOENSSON 2004).

Another beneficial use of urine is as an additive to enrich compost. Technologies for the production of urine-based fertilizers are currently also under research (e.g., struvite, Emerging Sanitation Technologies).

From normal, healthy people, urine is virtually free of pathogens. Urine also contains the majority of nutrients that are excreted by the body. Its composition varies depending on diet, gender, climate, water intake, etc., but roughly 88% of nitrogen, 61% of phosphorus and 74% of potassium excreted from the body is in urine.

Stored urine should not be applied directly to plants because of its high pH and concentrated form. Instead, it can be:

1) mixed undiluted into soil before planting;

2) poured into furrows, but at a sufficient distance away from the roots of the plants and immediately covered (although this should take place no more than once or twice during the growing season); and

3) diluted several times, whereby it can be frequently used around plants (up to two times weekly).

The optimal application rate depends on the nitrogen demand and tolerance of the crop on which it will be used, the nitrogen concentration of the liquid, as well as the rate of ammonia loss during application. 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 is local recommendations for use of mineral nitrogen fertilisers. As a general rule of thumb, one can assume that 1 m² of cropland can receive 1.5 L of urine per growing season (this quantity corresponds to the daily urine production of one person and to 40-110 kg N/ha). The urine of one person during one year is, thus, sufficient to fertilize 300 to 400 m² of cropland.

A 3:1 mix of water and urine is an effective dilution for vegetables, although the correct amount depends on the soil and the type of vegetables. If diluted urine is used in an irrigation system, it is referred to as “fertigation”. For best fertilizing effect and to avoid ammonia losses to the air, urine should be incorporated into the soil as soon as possible after application, preferably instantly. Equipment that can be used for the application comprises watering cans, dippers, but also empty water bottles cut into half etc. A shallow incorporation is enough, and different methods are possible. One is to apply urine in small furrows that are covered after application. Washing the nutrients into the soil with subsequent application of water is another option. When spreading urine, it should not be applied on leaves or other parts of the plants, as this can cause foliar burning. During the rainy season, urine can also be applied directly into small holes near plants; then it is diluted naturally.

A good availability of nutrients is particularly important in early stages of cultivation. Once the crop enters its reproductive stage it hardly takes up any more nutrients. Fertilizations should stop after between 2/3 and 3/4 of the time between sowing and harvest.

Urine poses a minimal risk of infection, especially when faecal cross contamination during source separation is avoided and it has been stored for an extended period of time. Yet, urine should be carefully handled and should not be applied to crops less than one month before they are harvested. This waiting period is especially important for crops that are consumed raw (refer to WHO guidelines for specific guidance).

Social acceptance may be difficult. Stored urine has a strong smell and some may find it offensive to work with it or to have it nearby. If urine is diluted and/or immediately tilled into the earth, however, its smell can be reduced. The use of urine may be less accepted in urban or peri-urban areas when household gardens are close to peoples’ homes than in rural areas where houses and crop land are kept separate.

Over time, some minerals in urine will precipitate (especially, calcium and magnesium phosphates). Equipment that is used to collect, transport or apply urine (i.e., watering cans with small holes) may become clogged over time. Most deposits can easily be removed with hot water and a bit of acid (vinegar), or in more extreme cases, manually chipped off.