Abatement of greenhouse gases and ammonia from cattle slurry during storage and land spreading: A pilot scale study

Abstract

The storage and spreading of cattle slurry are significant contributors to greenhouse gas (GHG) and ammonia (NH₃) emissions in agriculture, driven by the decomposition of organic matter and volatilization of nitrogen compounds. This study evaluates the impact of hydrogen peroxide and potassium iodide (HK) and its combination with calcium chloride (CaCl₂) (HKC) on mitigating GHG and NH₃ emissions during the manure management chain. Storage trials were conducted at multiple scales (660 L and 20 kg), alongside field trials assessing the effect of treated slurries on emissions during land spreading. Emissions of methane (CH₄), carbon dioxide (CO₂), nitrous oxide (N₂O), and NH₃ were monitored over both the storage and land spreading trials.

Results demonstrated that HK and HKC treatments inhibited CH₄ (HK - 651.41 g m⁻²; HKC – 621.44 g m⁻²; Control – 768.74 g m⁻²) and N₂O (HK – 2.88 g m⁻²; HKC – 1.01 g m⁻²; Control – 7.43 g m⁻²) production compared to control during storage but increased CO₂ (HK – 5140.83 g m⁻²; HKC – 5609.22 g m⁻²; Control – 2474.27 g m⁻²) emissions due to foaming and agitation effects. NH₃ emissions were significantly influenced by the treatments, with HK (168.91 g m⁻²) increasing emissions by 111 % and HKC (102.71 g m⁻²) by 28 %, relative to the control (80.03 g m⁻²). Application of a CaCl₂ spray reduced NH₃ emissions by 49 % in the first 48 h of treatment through surface pH modulation, though this effect was transient. Temperature significantly influenced CH₄ emissions; emissions under high-temperature (HT; 19 °C) (0.085 kg CH₄ kg⁻¹ VS Day⁻¹) conditions were six times higher than under low-temperature (LT; 9 °C) (0.013 kg CH₄ kg⁻¹ VS Day⁻¹) conditions. CH₄ inhibition was more effective at LT (86 % reduction, p < 0.05), highlighting the temperature sensitivity of methanogenic communities. However, no significant differences in cumulative GHG or NH₃ emissions were observed between treatments and controls during land spreading. When storage and spreading results were combined, treatments showed no significant cumulative reduction in GHG emissions compared to controls, highlighting the need for optimization of treatment protocols.

The results indicate that the oxidative treatments (HK & HKC) can suppress methane (CH₄) and nitrous oxide (N₂O) emissions during storage, offering a potential strategy for reducing emissions from livestock waste. Furthermore, the application of CaCl₂ as a surface treatment reduced ammonia volatilization, improving nitrogen retention in slurry, which can enhance its fertilization potential. These findings suggest that oxidative treatments and CaCl₂ spray have potential for reducing emissions during manure storage, particularly under cooler conditions typical of Irish winters. However, the efficacy of these treatments under warmer conditions may require adjustments in application frequency and concentration. Future research should focus on optimizing treatment protocols and assessing the agronomic benefits of treated slurries.