Physico-chemical Characteristics and Nitrogen Use Efficiency of Nine Human Urine-Based Fertilizers in Greenhouse Conditions

Most of the nutrients in wastewater come from human urine and their recycling for agricultural purposes is very limited. After source separation, urine can be treated to produce various urine-based fertilizers. This study aims to characterize the nitrogen use efficiency of different urine-based fertilizers. Nine urine-based fertilizers were compared together with ammonium nitrate and cattle slurry in a greenhouse pot trial with English rye-grass, (Lolium perenne L.). The detailed physico-chemical characteristics of the fertilizers were analyzed. The biomass production and nitrogen uptake of the plants were measured. The nitrogen use efficiency and the mineral fertilizer equivalent were determined for each fertilizer. The urine-based fertilizers were classified in four types based on their nitrogen forms (ammonia, nitrate, urea, or organic). The mineral fertilizer equivalent of most urine-based fertilizers were above 85% and even higher than 100% for nitrified concentrated and acidified stored urine. The lowest mineral fertilizer equivalent were found for fermented fresh urine and the mixture of fresh urine and woodchips but remained between 65 and 75%. In all cases, the nitrogen use efficiencies of urine-based fertilizers were higher than that of cattle slurry. The differences among the urine-based fertilizers and from the cattle slurry were attributed to the mineral nitrogen content which was much higher in urine-based fertilizers. Indeed, they contain mainly mineral nitrogen. Their content of trace element contaminants is low. Their efficiency as nitrogen fertilizers is high and close to that of mineral fertilizer. However, new valorization pathways from cities to agriculture need to be developed.