Putting the P(ee) in perennial agriculture

Reflections on a workplace urine nutrient reclamation project

Abstract

Phosphorus (P) is a finite resource essential for food production currently lost from fields at an unsustainable rate via runoff and crop harvests. These losses could be addressed by pairing peren­nial crops, which reduce runoff with their deep roots that stabilize the soil, with recovering nutri­ents from human excreta. Urine contains the majority of P and other nutrients that humans excrete and therefore has been the focus of recent nutrient reclamation efforts. Urine fertilizer has yet to be explored for perennials, however, and under­standing the biophysical effects of urine ferti­lizer on soil nutrients and biomass in perennial crops could inform the design of a more circular food system. To that end, we started the first known workplace urine nutrient reclamation pro­ject in the state of Kansas, U.S., to test the feasibil­ity of supplying available soil P from urine to alfalfa (Medicago sativa), a perennial legume forage crop. After one growing season, urine fertilizer had no effect on aboveground biomass but did increase available soil P which otherwise decreased in the control treatments. Urine also increased soil nitrate and sodium compared to the water-only controls. The field study was coupled with a survey of staff members who participated in urine collection to identify opportunities and potential barriers to urine diversion in the U.S. The survey revealed a lack of awareness of both unsustainable P manage­ment and urine recovery as a potential solution, underscoring the need for increased education. Regulatory challenges faced in the second field sea­son also highlighted the need for policy that explic­itly defines urine separately from wastewater in the U.S. We hope that results from this project will make it more feasible to conduct additional studies and circular food system community-based pro­jects on a larger scale going forward.