The use of biological waste, such as human and animal faeces, as a nutrient source for crops is widely recognised. However, the potential of urine as a sustainable nitrogen fertiliser remains largely untapped, despite its proven benefits.
Oftentimes, farmers in Nigeria would chase kids who urinate too close to their plants away so as not to kill them with the acidic fluid. Today, scientific research and innovative agricultural initiatives are transforming this perception, positioning urine as a viable, eco-friendly alternative to commercial nitrogen fertilisers.
Experiments and full-fledged initiatives in various countries, such as South Africa, Niger, and the United States, have proven that urine can be an affordable, sustainable, and eco-conscious alternative to the popular synthetic nitrogen-based fertilisers.
Science behind urine fertiliser
Urine contains essential nutrients for plant growth, especially nitrogen, phosphorus, and potassium, often called NPK, which are the main ingredients in many commercial fertilisers. Historical records even indicate that urine has been used to enrich soils for thousands of years, from ancient Rome to China.
Modern science is now refining these practices, with human and animal urine being collected, sanitised, and processed into affordable nutrient-rich fertilisers for farmers. This approach not only recycles valuable resources but also reduces carbon emissions and pollution associated with synthetic fertiliser production and use.
Initiatives like the Urine Nutrient Reclamation Program (UNRP), a programme run by the Rich Earth Institute (REI), a non-profit based in Vermont, USA; the Valorisation of Urine Nutrients in Africa (VUNA) Project and recent scientific trials on farmlands in Niger Republic shows that there is a growing uptake of urine fertilisers by farmers as an alternative to the common synthetic NPK fertiliser.
The initiatives recorded increased productivity for crops such as pearl millet, kale, spinach, maize, and tomatoes on various farms and reduced the use and environmental impact of chemical production as the solution encompasses resource recycling and sustainable practices.
How urine is processed into fertiliser
Turning urine into plant food isn’t as simple as just pouring it on the garden, but with the improvement in science, it is getting easier and more efficient. Transforming urine into safe, effective plant food involves several steps:
- Separate Collection: The first and most important step is keeping urine separate from poop and other wastewater while collecting it. Special “urine-diverting” toilets are often used for this. In some programmes, like the UNRP in Vermont, people collect their urine at home in special containers, and then a truck comes to pick it up. On farms, special collection channels can be set up.
- Treatment and Storage: Once collected, the urine needs to be treated to make sure it’s safe and effective for plants. There are a few ways to do this.
- Sanitisation: One common method is simply storing the urine. If stored for about 2-3 months at typical outdoor temperatures (around 22-24°C), harmful germs (pathogens) are mostly inactivated, making it safe to use.
- Pasteurisation: In this approach, collected urine is heated to a high temperature, like 80°C for 90 seconds, to kill any remaining germs and make it safe for use..
- Nitrification and Distillation: Some advanced methods involve converting the urea in urine into nitrate, a form of nitrogen that plants absorb easily, using tiny microorganisms. This can then be concentrated by boiling, which also gets rid of any pathogens.
- Electrochemical Process: Scientists have also developed a new method using electricity to turn the liquid urea into a solid powder called percarbamide, which is much easier to store and transport. This method is cheap and simple.
- Application: Farmers often spray the liquid urine directly onto their fields. In some variations, it is diluted with water based on the kind of soil it is being applied to.
Sometimes, urine is used alongside other natural fertilisers like animal manure to provide a full range of nutrients.It’s important to apply it at the right time, when plants are actively growing and can soak up the nutrients best. Farmers also check the soil moisture to make sure the urine is absorbed and doesn’t just run off.
Why farmers are using urine fertilisers
Using urine as fertiliser has been proven to be beneficial for crops, farmlands and even the environment. Farmers are particularly drawn to this alternative because of the following benefits:
- Increased Crop Yields: Studies have consistently shown that urine application increases crop yields. Nitrogen recovered from urine significantly benefited a hydroponic tomato farm in Barcelona, and more than doubled the yield of Kale and Spinach farms in Vermont compared to no fertiliser.
In Niger, sanitised human urine increased panicle yield for pearl millet by an average of about 30%, representing an additional 200 to 300 kg per hectare.
Urine-derived fertilisers (struvite and nitrification/distillation products) have also been shown to provide nutrients to plants (like ryegrass and maize) as readily as commercial fertilisers. Ryegrass recovered 72-75% of nitrogen and 26% of phosphorus applied with these urine-based products. - Cost effectiveness: Urine fertilisers can be a cheap and affordable alternative for resource-poor farmers and those who would incur extra cost to procure and transport the expensive synthetic fertilisers to their farms. As evident in the experiment done in Niger, sanitised human urine (locally known as “Oga”) is a “cheap, affordable, and effective solution” and a “low financial input fertiliser option” for resource-poor female farmers, especially when traditional mineral fertilizers are barely affordable.
- Water conservation: The use of urine fertilisers saves water in different ways. One is the reduction of water used in flushing off urine in the toilet or processing it in the waste treatment plants, as it will now be separately collected and reused. The UNRP in Vermont has conserved over 2.7 million gallons (10.2 million litres) of water since 2012 by preventing toilet flushes.
Secondly, urine fertiliser can reduce irrigation need as its liquid form not only provides nutrients to plants, but it can also help moisturise the soil during drought or dry spells. - Reduced Pollution: The use of urine fertilisers also reduces environmental pollution in different ways. Usually, urine, which goes through the regular sewage systems, often ends up in rivers, lakes and other waterbodies, polluting them. The nitrogen and phosphorus components of urine also help algae in water grow even more, which then choke aquatic organisms or block waterways. By diverting urine, we reduce water pollution and keep these nutrients out of waterways.
Another way it reduces pollution is the elimination of nitrogen run-off, which is common in the use of synthetic nitrogen fertilisers. The nitrogen in urine fertilisers is easily and directly absorbed by plants, reducing the chances of nitrogen runoff. - Lower Carbon Emissions: Making traditional chemical fertilisers uses a lot of energy, often from fossil fuels, which creates CO2 pollution. Using urine means we don’t need to make as much of these synthetic fertilisers, which is better for the climate.
Concerns about Urine fertiliser use
While urine fertiliser offers numerous benefits some certain concerns hinder its widespread and sustainable adoption.
- Health and Safety Risks: The potential presence of pathogens and pharmaceutical residues in untreated or inadequately treated urine, and the risk of forming harmful by-products like chlorinated organics during certain electrochemical treatment processes, is a notable concern for farmers.
- Logistical and Technical Challenges: While small-scale operations can be seamless, challenges can arise in the efficient collection and transportation of large volumes of urine. High energy and cost demands of some nutrient extraction technologies, potential system fouling (e.g., from precipitating solids), and the need to modify waste disposal systems can even outweigh the economic and environmental benefits.
- Social Acceptance and Regulatory Barriers: Widespread adoption is hindered by public reluctance, often termed as “ick factor,” and cultural or religious perceptions of human waste. Additionally, there is a lack of clear and supportive regulatory frameworks, as urine is not typically categorised separately from combined wastewater flows, making permitting and scaling difficult.
Urine-based fertilisers present a promising, sustainable alternative to synthetic nitrogen products, offering economic, environmental, and yield benefits for farmers worldwide. As research and infrastructure improve, urine recycling could play a key role in future climate-smart and resource-efficient agriculture.
Adopting urine fertilisers requires overcoming technical, social, and regulatory challenges, but ongoing innovation and successful pilot programs demonstrate strong potential for mainstream agricultural use.
