Effects of Yucca schidigera extract on carbon-nitrogen nutrients and trace gaseous emissions during chicken manure storage

 Liquid manure storage represents a critical stage in manure management for mitigating greenhouse gas (GHG) and ammonia (NH₃) emissions while preserving nutrient value. In China, substantial poultry production (173.4 billion birds slaughtered in 2024) generates massive manure volumes, necessitating effective storage-phase mitigation strategies. This study specifically evaluated the impact of Yucca schidigera extract (YSE) on carbon/nitrogen dynamics and gaseous emissions during 30-day static storage of liquid chicken manure, comparing it with a commercial biological deodorant. Fresh layer manure (initial pH 7.09, moisture content 77%, total nitrogen (TN) 2.90 g kg^-1, organic matter (OM) 664.38 g kg^-1) from a Hebei Province farm was used. Three treatments were established in triplicate using 20-L sealed containers (45 cm × 25 cm × 20 cm) equipped with sampling ports: T0 (Control: 100 mL water), T1 (0.5% YSE powder + 100 mL water, w/w fresh weight basis), and T2 (0.1% biological deodorant + 100 mL water, w/w fresh weight basis). YSE (purchased from Xi'an Weiao Biotechnology Co., Ltd.) contained ≥30% saponins (UV method), glycosides, resveratrol, and polyphenols. The biological deodorant contained Bacillus spp., Acetobacter spp., Yeast, and Lactic acid bacteria (>2×10¹⁰ CFU g^-1). Manure temperature and ambient conditions were monitored twice daily. Physicochemical properties (pH, electrical conductivity (EC), moisture content (MC), nitrate-nitrogen (NO₃^--N), ammonium-nitrogen (NH₄⁺-N), TN, OM, C/N ratio) were analyzed on days 0, 9, 19, and 30 using grid sampling (12 locations per container). NH₃ emissions were quantified daily using boric acid trapping and titration with 1% H₂SO₄. GHG fluxes (carbon dioxide (CO₂), methane (CH₄), nitrous oxide (N₂O)) were measured every 2 days (days 0-15) and every 3 days (days 15-30) using static chamber-gas chromatography (Agilent 7890A). Global Warming Potential (GWP, kg CO₂-eq t^-1) was calculated considering CH₄(28×CO₂), direct N₂O (265×CO₂), and indirect N₂O from NH₃ volatilization (0.01×NH₃-N emitted). Data analysis employed one-way ANOVA and LSD tests (SPSS 27.0, significance P < 0.05). Results demonstrated gradual pH increases and MC decreases across all treatments, with no significant inter-treatment differences (P > 0.05). EC decreased significantly over time, with T1 and T2 showing significantly lower values than T0 throughout storage (P < 0.05). By day 30, T1 EC (2261 μS cm^-1) was 29.54% lower than T0 (3017 μS cm^-1). YSE addition significantly altered nitrogen dynamics. T1 exhibited a transient NO₃^--N peak (84.52 mg kg^-1 at day 9) followed by a sharp decline to 27.04 mg kg^-1 by day 30. NH₄⁺-N concentration in T1 decreased significantly more (84.85%, from 23.03 g kg^-1 to 3.49 g kg^-1) compared to T0 (78.01%, from 30.92 g kg^-1 to 6.80 g kg^-1) (P < 0.05). Crucially, TN content at day 30 was significantly higher in T1 (29.48 g kg^-1) and T2 (27.79 g kg^-1) compared to T0 (21.60 g kg^-1), representing increases of 36.43% and 21.69%, respectively (P < 0.05). OM content was also significantly higher in T1 (660.93 g kg^-1) than T0 (616.09 g kg^-1) at termination (increase of 7.28%, P < 0.05). The C/N ratio was consistently lower in T1 than T0. Regarding gaseous emissions, cumulative NH₃ emissions were significantly reduced by 21.60% in T1 and 19.88% in T2 compared to T0 (P < 0.05). T1 also showed a 9.59% reduction in cumulative CO₂ emissions compared to T0, although this difference was not statistically significant (P > 0.05). No significant differences were observed in cumulative CH₄ or N₂O emissions among treatments (P > 0.05). Correlation analysis revealed NH₃ emissions were positively correlated with NO₃^--N concentration (r = 0.78, P < 0.01) and NH₄⁺-N concentration (r = 0.85, P < 0.01), and negatively correlated with TN (r = -0.86, P < 0.01) and OM content (r = -0.93, P < 0.001). CO₂ emissions showed positive correlations with EC (r = 0.72, P < 0.05) and NO₃^--N (r = 0.69, P < 0.05), and a strong negative correlation with OM (r = -0.83, P < 0.01). Total GWP did not differ significantly among treatments (T0: 136.69, T1: 142.75, T2: 121.01 kg t^-1 (CO₂-eq); P > 0.05), with CH₄ contributing 95.52-96.63%. In conclusion, adding 0.5% Yucca schidigera extract effectively mitigated NH₃ emissions (21.60% reduction) and nitrogen loss (36.43% higher TN retention) while enhancing OM preservation (7.28% increase) during static storage of liquid chicken manure. Its efficacy in NH₃ reduction was comparable to a commercial biological deodorant. The primary mechanisms appear linked to YSE's saponins modulating nitrogen mineralization and microbial activity, thereby reducing NH₄⁺-N accumulation and NH₃ volatilization. This study provides a practical, natural additive-based strategy for reducing environmental impact and conserving nutrient value in liquid poultry manure storage systems.