High fertilizing value but potentially high volatilization of urine based fertilizers

Human urine contains nutrients that are mainly not recycled in agriculture. It can be collected through source separation and treated to produce “urine-based fertilizers” with various nutrient contents and physiochemical characteristics. We measured ammonia (NH₃) volatilization after the application of several urine-based fertilizers under controlled conditions and of stored urine under field conditions. The nitrogen-use efficiency of four urine-based fertilizers (stored urine from a university, stored urine from a festival, fermented urine and nitrified concentrated urine) was compared under on-farm conditions with ammonium nitrate and bovine slurry in a specific experiment. Stored urine was also compared with ammonium nitrate and seven other organic fertilizers in different experiments under on-farm conditions. Nitrous oxide emissions after the application of two urine-based fertilizers were also measured. NH₃ volatilization from stored urine was high (up to 34% of the total nitrogen under on-farm conditions) compared with the other urine-based fertilizers and ammonium nitrate. Urine-based fertilizers were characterized by a nitrogen fertilizer replacement value (NFRV) greater than 70% and higher than that of all other organic fertilizers used in the experiments (but not significantly different). These differences were mainly explained by the mineral nitrogen content of the fertilizers. The mean NFRV of stored urine over five experiments was 83% (significantly lower than 100%). Nitrous oxide emissions from stored urine, nitrified concentrated urine and ammonium nitrate were low. We concluded that urine-based fertilizers could replace mineral fertilizers if NH₃ volatilization is limited. The constraints linked to the field application of a large volume call for further investigation.