Lime-treated urine improves sunflower growth without shifting soil bacterial communities

Urine contains high concentrations of nitrogen and phosphorus, which can be utilized as fertilizer in sustainable agriculture, forestry, and landscaping. Before urine application, the nitrogen can be stabilized with calcium hydroxide (lime), which raises the pH and inhibits urea hydrolysis. However, the impact of lime-treated urine on plants and soils remains unclear. Here, lime-treated urine diluted 1:10 with water was applied to soils with sunflowers (Helianthus annuus L.), and growth and soil bacterial diversity was examined at 2 months. We show that lime-treated urine significantly increased sunflower growth up to 85 %, plant biomass up to 151 %, leaf area up to 137 %, and the number of leaves per plant by 2.5 compared to untreated plants. No major differences in bacterial Shannon or Simpson diversity indices were detected between treatment groups, though small shifts in phyla composition were observed, depending on treatment and plant presence. This work demonstrates that recycled urine can effectively be used for the fertilization of non-food crops and landscaping plants.