18.104.22.168 Manure management
Animal manures can release significant amounts of N2O and CH4 during storage, but the magnitude of these emissions varies. Methane emissions from manure stored in lagoons or tanks can be reduced by cooling, use of solid covers, mechanically separating solids from slurry, or by capturing the CH4 emitted (Amon et al. 2006; Clemens and Ahlgrimm, 2001; Monteny et al. 2001, 2006; Paustian et al., 2004). The manures can also be digested anaerobically to maximize CH4 retrieval as a renewable energy source (Clemens and Ahlgrimm, 2001; Clemens et al., 2006). Handling manures in solid form (e.g., composting) rather than liquid form can suppress CH4 emissions, but may increase N2O formation (Paustian et al., 2004). Preliminary evidence suggests that covering manure heaps can reduce N2O emissions, but the effect of this practice on CH4 emissions is variable (Chadwick, 2005). For most animals, worldwide there is limited opportunity for manure management, treatment, or storage; excretion happens in the field and handling for fuel or fertility amendment occurs when it is dry and methane emissions are negligible (Gonzalez-Avalos and Ruiz-Suarez, 2001). To some extent, emissions from manure might be curtailed by altering feeding practices (Külling et al., 2003; Hindrichsen et al., 2006; Kreuzer and Hindrichsen, 2006), or by composting the manure (Pattey et al., 2005; Amon et al., 2001), but if aeration is inadequate CH4 emissions during composting can still be substantial (Xu et al., 2007). All of these practices require further study from the perspective of their impact on whole life-cycle GHG emissions.
Manures also release GHGs, notably N2O, after application to cropland or deposition on grazing lands. Practices for reducing these emissions are considered in Subsection 22.214.171.124: Cropland management and Subsection 126.96.36.199: Grazing land management.