Methods of production and application of inorganic fertilizers are environmentally harmful. Establishing circular nutrient economies, that reuse “waste”-derived nutrients, can mitigate these issues. Human excreta are an abundant source of plant-available nutrients when safely managed, with urine more nutrient-rich and pathogen-free than feces. Urine-diverting systems source-separate feces and urine, allowing for their distinct treatment. However, urine storage and treatment in these systems is difficult, as urine is difficult to transport, and nitrogen can be lost as ammonia through the activity of ubiquitous urease enzymes. Utilizing biochar as an adsorbent for urine-nutrients may address this challenge by creating a carbon-rich, solid fertilizer product that can be produced on-site. The purpose of this research is to assess the impact of urine-enriched biochar (UEBC) fertilizers made from various types of biochar and urine on tomato growth. A growth trial is being conducted with UEBCs from three types of biochar (550°C sewage sludge, 700°C wood waste, 400°C walnut shell) combined with fresh; stored, covered; and stored, uncovered urine, compared to urine alone and conventional fertilizers. UEBCs were prepared at a 200 g biochar: 1 L urine ratio. UEBCs were applied at 1, 2, 6, and 10% w/w, and urine-only applied at equivalent volumes.
Results/Conclusions
Our preliminary data at week 3 show that UEBCs generally perform better than urine-only treatments with plant height and leaves > 1 cm as growth metrics. Thus far, there is a significant difference in plant growth across treatments with leaves > 1 cm as a growth metric (p = 0.005, α = 0.05, n = 50). No significant difference in germination percentage (p = 0.473, α = 0.05, n = 50) was found across treatments. These preliminary results show that none of the UEBCs, application rates, or urine-only treatments were phytotoxic. We expect that treatment differences will be more pronounced when biomass is harvested. We hypothesize that all amendment types will perform better than unfertilized controls, and that UEBCs will perform better than urine-only treatments. This research has important implications for nutrient recycling solutions in urine-diverting systems. As the world works towards achieving Sustainable Development Goals (SDGs), specifically SDG6, to ensure sanitation for all, urine-diverting and non-sewered approached to sanitation will likely become more widespread. Effective systems for decentralized urine-nutrient recovery coupled with recycling of urine-derived nutrients to agroecosystems will be necessary.
