Land application of digestate - The Biogas: Science, Production and Applications - page 307

can enhance denitrification in soils and increase N 2 O emissions (Wulf et al.,
2002; Chantigny et al., 2010), with significant N 2 O emissions following land
application of liquid animal manures often observed (Chantigny et al.,
2007). Alternatively, although digestate typically has a higher concentration
of NH 4 + -N, Vallejo et al. (2006) suggested that the easily degradable C in
manure would be decomposed during digestion and the remaining more
stable C would be less likely to stimulate denitrification, resulting in lower
N 2 O emissions. Chantigny et al. (2010) observed denitrification to be in
fact N-limited in clay soils and C-limited in loam soils, suggesting a high
NH 4 + -N content, but low degradable C of digestate could still stimulate
denitrification in clay soils. As discussed earlier in the chapter, nitrification
and denitrification of soils is highly dependent on climatic conditions.
Rochette et al. (2004) reported that manure slurries with high NH 4 + -N
concentrations were easily nitrified in spring when soils were well aerated
and warm, whereas, for fall manure application, wet and cold conditions
limited net nitrification, thereby limiting denitrification and N 2 O emissions.
A few studies have been conducted to compare N 2 O emissions from the
land application of raw manure and digestate. Vallejo et al. (2006) studied
the land application of raw swine manure and digestate on clay loam soils
and determined N 2 O emissions from digestate plots to be 48% lower than
those treated with raw swine manure. In a study conducted by Chantigny
et al. (2007) lower N 2 O emissions were consistently observed over 3 years
from both loam and sandy loam plots that received digested compared to
raw swine manure. A possible explanations could be that some compounds
in digestate have depressive effects on soil nitrifying bacteria, thereby
reducing the supply of nitrate compounds needed for denitrification
(Nyberg et al., 2004) or the C in digestate is not easily degradable and
less likely to stimulate denitrification (Vallejo et al., 2006). Amon et al.
(2006) also reported lower N 2 O emissions from plots receiving digested
dairy manure. However, Wulf et al. (2002) reported similar N 2 O emissions
among digestate and raw dairy manure treated arable soil plots but higher
N 2 O emissions when digestate was applied to grassland soils.
A study conducted in Ontario, Canada, by Agriculture and Agri-Food
Canada (AAFC) and University of Guelph investigated NH 3 and N 2 O
emissions from the land application of raw liquid dairy manure and
digestate on clay-loam soils. Nitrous oxide emissions were measured using
the flux-gradient technique equipped with a closed-path single optical pass
tunable diode laser (TGA-100, Campbell Scientific, Logan) (Fig. 13.2), as
described by Pattey et al. (2006), while NH 3 volatilization was measured by
the relaxed eddy accumulation technique using denuder tubes (Zhu et al.,
2000). Nitrous oxide and NH 3 emission factors for both the fall and spring
land application trials are summarized in Table 13.5. When raw manure and
digestate were surface broadcast in fall 2005, the N 2 O emission factor was

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