Farm-Scale Application of Concentrated Urine-Derived Fertilizer: Evaluation of a Roller Pump for Precise and Consistent Side Dressing of Sweet Corn

Diverting human urine from the waste stream and reclaiming it as a fertilizer can simultaneously address issues of 1) dependence of agriculture on unsustainable and expensive sources of fertilizer and 2) pollution of sensitive waterways from excess nutrients. Nitrogen fertilizer is derived from the Haber-Bosh process, which accounts for 1.2% of global energy use and associated greenhouse gas emissions (Dawson & Hilton 2011), while high-N amendments are expensive and supplies are uncertain (Jones & Nti 2022). Phosphate is a finite resource, subject to politically induced price swings, and the Global Phosphorous Research Initiative is predicting a shortage of high-quality rock phosphate within 40 years. 

Just as the supply of nitrogen and phosphorus for agricultural use grows increasingly uncertain, those same nutrients are excessively leached into waterways. Surface waters throughout the Northeast are heavily impacted by nitrogen and phosphorus pollution from both agricultural runoff as well as wastewater effluent. 70% of the nitrogen and 50% of the phosphorus in wastewater effluent is from human urine, and many wastewater plants and septic systems are unable to control this nutrient pollution and are poorly suited to nutrient reclamation. 

The proposed project addresses both issues of fertilizer scarcity and nutrient pollution by improving methods for the application of urine fertilizer in alignment with a circular nutrient economy. The responsible flow of nutrients through a circular nutrient economy honors the holistic connection among land, water, air, and all living beings described in the Northeast SARE’s outcome statement, as it is underpinned by the understanding that Earth’s systems are linked through interdependent exchanges of nutrients. A circular nutrient economy also advances the vision of an accessible, sustainable, and just agricultural system, as it has the potential to provide farmers with a responsibly-sourced, financially accessible, and dependable fertilizer supply. Developing local and affordable sources of fertilizer could help alleviate financial barriers which disproportionately affect farmers of marginalized backgrounds while reducing nutrient loading in communities lacking resources to address polluted waterways. 

The potential to reclaim urine-derived fertilizer within a circular nutrient economy is immense. With 54.5 million people living in the Northeast SARE region, each producing 4 kg of nitrogen in their urine annually (Vinnerås & Jönsson, 2002), there is a maximum potential to source 218 million kg of nitrogen fertilizer each year, (plus P, K and trace nutrients,) which would nearly meet the region’s approximately 280 million kg demand for N fertilizer (US EPA, 2019). While nitrogen is the most significant nutrient that human urine could supply, Rich Earth has also successfully separated phosphorus from urine, producing two products: struvite, and a low-P liquid fertilizer. 

Although still uncommon, urine diversion is gaining traction. Laufen, a high-end porcelain company, is manufacturing a new urine-diverting toilet, and Rich Earth Institute’s spin-off (Brightwater Tools LCC) is now selling urine pasteurizers that will enable farms throughout Vermont to produce state-permitted urine fertilizer. Charcoal filtration can remove pharmaceutical contaminants in urine (Solanki & Boyer, 2017), thereby addressing concerns of some farmers and stakeholders identified in prior research. The practice of urine collection is increasing in the Northeast, with the establishment of the urine-collecting portable toilet company, called Wasted*, in Burlington, VT, and a municipal initiative in Falmouth, MA, aimed at reducing nitrogen emissions to coastal waters. 

With increasing access to urine fertilizer, farmers will need applicator systems tailored to urine fertilization. The Rich Earth Institute has built a hay applicator designed to apply urine in a gentle stream to hayfields (Figure 1). While this gravity-fed system is well-suited for hay application, it does not offer the dosing precision or a high dosing rate required for the cultivation of other crops. Many passes over the hayfield and many refills of the applicator tank are needed with the gravity-fed hay applicator, and these inefficiencies are prohibitive in the adoption of urine fertilization at scale. 

To reduce the labor of fertilization, Rich Earth has applied concentrated urine to sweet corn (Noe-Hays et al., 2024). The urine concentrate reduced the number of tank refills and increased the land area fertilized per tank of urine. Concentrated urine is made at the Rich Earth Institute using freeze-thaw technology developed by Brightwater Tools LCC. If used in conjunction with refined applicator equipment, urine concentrate may offer a fertilization efficiency on par with conventional fertilization practices. 

Ammonia loss through volatilization is another important consideration of urine application technology, especially when using urine concentrate, which is more prone to ammonia volatilization than non-concentrated urine. Volatilization from urine fertilizer has been shown to be reduced by applying urine in a gentle stream close to the soil, or better yet incorporating the urine beneath the soil surface (Noe-Hays, 2018). Rich Earth’s existing prototype row applicator buries urine immediately upon application using a cultivator tine (Figure 2), which was found to effectively reduce signs of volatilization (Noe-Hays et al., 2024).

To address the equipment efficiency needs for the application of urine at scale, this study will develop an applicator with 1) consistent dosing, 2) minimal ammonia volatilization, and 3) efficiency and ease of operation. To achieve a controlled dosing of urine fertilizer, we will use a "roller” pump, also known as a peristaltic pump. Roller pumps are popular because of their low cost, compact size, and easy maintenance. They can be driven by a wheel that contacts the ground, which mechanically links the fertilizer flow rate to the tractor ground speed such that a steady fertilizer volume per acre rate is achieved regardless of tractor speed. To limit ammonia losses, a cultivator tine will bury urine immediately upon application in the same fashion as our row applicator. To achieve a performance comparable to typical fertilizer equipment, the proposed roller pump system will fertilize multiple rows at once, applying urine to an optimal depth and distance relative to crop rows. With these features, we expect this pump system to refine the fertilizer application process and increase farm productivity for farmers interested in adopting urine fertilization practices.

Sources Cited

Dawson, C. J., & Hilton, J. (2011). Fertiliser availability in a resource-limited world: Production and recycling of nitrogen and phosphorus. Food Policy, 36, S14–S22. https://doi.org/10.1016/j.foodpol.2010.11.012

Jones, K., & Nti, F. (2022). Impacts and Repercussions of Price Increases on the Global Fertilizer Market. Foreign Agricultural Service U.S. Department of Agriculture. https://fas.usda.gov/sites/default/files/2022-09/IATR%20Fertlizer%20Final.pdf

Noe-Hays, A. (2018). Practical Strategies for Reducing Ammonia Volatilization from Urine-Derived Fertilizers (SARE ONE18-318). https://projects.sare.org/project-reports/one18-318/

Noe-Hays, A., Schreiber, T., Cavicchi, J., Saveson, G., & Davis, A. (2024). Farm-scale Urine Fertilizer Implementation: Refining Application Methods, Gathering Buyer and Consumer Perspectives, and Producing Farmer Guide (SARE ONE22-426). https://projects.sare.org/?post_type=project_report&p=1072403

Solanki, A., & Boyer, T. (2017). Pharmaceutical removal in synthetic human urine using biochar. Environmental Science: Water Research & Technology, 3(3), 553–565. https://doi.org/10.1039/C6EW00224BUS EPA. (2019, January 30). Commercial Fertilizer Purchased. https://www.epa.gov/nutrient-policy-data/commercial-fertilizer-purchased