Ammonia (NH3) emissions from swine manure are a major contributor to livestock odor and air pollution. In this study, the urease inhibitor Phenyl- Phosphorodiamidate (PPDA) was applied as a preventive control strategy, and its reduction efficiency was evaluated through both chamber simulations and a pilot-scale pig house experiment. The chamber experiment, conducted from March 17 to May 1, 2023, showed that the treatment group receiving both urea and PPDA (P1) exhibited a 53% lower mean NH3 concentration (51.1±15.1 ppm) compared with the urea-only group (U1, 109.0±34.0 ppm; p < 0.001). The maximum concentration was also reduced by 63.8% (245.1 ppm in U1 vs. 88.8 ppm in P1). Dose-dependent tests revealed that reduction efficiency increased with PPDA dosage (1.0 g, 32.3%; 0.5 g, 27.3%; 0.1 g, 21.1%), but gains plateaued beyond 0.5 g, suggesting economic feasibility at intermediate levels. The pilot-scale experiment, conducted in a mechanically ventilated pig house from May 13 to August 2, 2024, confirmed the short-term effectiveness observed in the chamber tests. During the first application period, the treatment group (P5) maintained approximately 50% lower NH3 concentrations than the control group (C2). However, the effect decreased to less than 5% during the second period, and concentrations converged with or exceeded those of the control group during the finishing stage. This decline was attributed to factors such as insufficient slurry mixing, dosage mismatch due to an increase in body weight, and physicochemical changes in the slurry environment. These findings indicate that PPDA effectively suppresses urea hydrolysis and reduces acute NH3 peaks, thereby functioning as a preventive mitigation strategy. Although its long-term efficacy under field-like conditions was limited, optimization of dosage, re-application intervals, and slurry management could enhance performance. Overall, this study demonstrates the potential of PPDA to shift livestock odor management from conventional end-of-pipe approaches toward preventive control strategies, providing a scientific basis for integrated and sustainable odor mitigation.

Two hundred and twenty three yeast strains were randomly isolated from Korean traditional nuruk. Among them, six urease producing yeast strains (designated JJA, JJB, JJ22, SHA, SHC and SH10) were selected on the Christensen urea agar plates. They showed the same pattern in the PCR-RFLP analysis of the ITS I-5.8S-ITS II region digested with HaeIII and HinF1 restriction endonucleases. Its DNA sequences showed 100% (strains SHA, SHC and SH10) and 99.8% (strains JJA, JJB and JJ22) identity with those of Issatchenkia orientalis type strain ATCC 24210. Phylogenetic analysis resulted in that all the strains were closely related to I. orientalis. Two representative strains, JJ22 and SH10, showing the highest urease activities were selected for further characterization. Their morphological, physiological and biochemical characteristics were also the same as I. orientalis. Therefore, both the two strains were identified as I. orientalis. They could grow at a wide range of temperature between 20-40℃ as well as pH between 2.0 and 10.0. However, a higher level urease activity were obtained at acidic pH than that at alkalic pH. The maximal level of urease activity was obtained at 30℃ (strain SH10) or 35℃ (strain JJ22) and in a liquid medium adjusted to the initial pH 5.0.

To study the effects of an urease inhibitor, N-(n-butyl)-thiophosphoric triamide (NBPT), and a nitrification inhibitor, dicyandiamide (DCD), on nitrogen losses and nitrogen use efficiency, urea fertilizer with or without inhibitors and slowrelease fertilizer (synthetic thermoplastic resins coated urea) were applied to direct-seeded flooded rice fields in 1998. In the urea and the urea+DCD treatments, NH4 + -N concentrations reached 50 mg N L-1 after application. Urea+NBPT and urea+ NBPT+DCD treatments maintained NH4 + -N concentrations below 10 mg N L-1 in the floodwater, while the slow-release fertilizer application maintained the lowest concentration of NH4 + -N in floodwater. The ammonia losses of urea+NBPT and urea+NBPT+DCD treatments were lower than those of urea and urea+DCD treatments during the 30 days after fertilizer application. It was found that N loss due to ammonia volatilization was minimized in the treatments of NBPT with urea and the slow-release fertilizer. The volatile loss of urea+DCD treatment was not significantly different from that of urea surface application. It was found that NBPT delayed urea hydrolysis and then decreased losses due to ammonia volatilization. DCD, a nitrification inhibitor, had no significant effect on ammonia loss under flooded conditions. The slow-release fertilizer application reduced ammonia volatilization loss most effectively. As N03 [-10] -N concentrations in the soil water indicated that leaching losses of N were negligible, DCD was not effective in inhibiting nitrification in the flooded soil. The amount of N in plants was especially low in the slow-release fertilizer treatment during the early growth stage for 15 days after fertilization. The amount of N in the rice plants, however, was higher in the slow-release fertilizer treatment than in other treatments at harvest. Grain yields in the treatments of slow-release fertilizer, urea+NBPT+ DCD and urea+NBPT were significantly higher than those in the treatments of urea and urea+DCD. NBPT treatment with urea and the slow-release fertilizer application were effective in both reducing nitrogen losses and increasing grain yield by improving N use efficiency in direct-seeded flooded rice field.field.