What artificial urine composition is adequate for simulating soil N2O fluxes and mineral N dynamics?

Summary

Artificial urine, an aqueous solution of various nitrogenous compounds and salts, is routinely used in soil incubation studies on nitrous oxide (N2O) emissions and related nitrogen (N) and pH dynamics. There is, however, no consensus on artificial urine composition, and a wide variety of compositions are used. The aim of this study was to test which artificial urine composition is adequate for simulating N2O fluxes, respiration, soil mineral N and pH dynamics of real cattle urine in both short- and long-term incubation studies. Urine solutions of differing compositions were applied to a sandy soil and incubated for 65 days, and results of measurements on N2O fluxes and soil mineral N were analyzed over the first 5 days as well as over the whole incubation period. Results from two real cattle urines with known nitrogenous composition (R1 and R2) were compared with three artificial urine types: (i) urea+glycine (AG), (ii) urea+hippuric acid (AH) and (iii) an artificial urine identical to the nitrogenous composition of real urine R1 (AR). During the first 5 days, only cumulative N2O emissions for AG deviated significantly (P=0.02) from the N2O emissions for real urines, with 0.4% of applied N emitted compared with 0.0% and 0.1% for R1 and R2, respectively. Respiration from R1 was significantly (P