Land application of digestate - The Biogas: Science, Production and Applications - page 310

Table 13.6 Odour concentrations for raw manure and digestate using the flux

chamber and wind tunnel methods

Manure type Flux chamber average

odour concentration (OU/m 3 )

Wind tunnel average
odour concentration (OU/m 3 )

Digester 1
Raw manure 2625 898

Digestate 604 111

Digester 2
Raw manure 2429 656
Digestate 762 441
Source: Data collected by University of Guelph and OMAFRA.

discussed earlier, the increased pH and carbonate content in digestate can
stimulate NH 3 volatilization; however, this can be counterbalanced with
reduced NH 3 volatility due to lower digestate viscosity, which increases soil
infiltration (Gerardi, 2003; Chantigny et al., 2004). A study conducted by
Chantigny et al. (2007) demonstrated increased forage dry matter (DM)
yields of timothy when comparing digestate to raw manure application. A
0.2 tonDM/ha and 0.6 tonDM/ha respective yield increase was observed in
loam and sandy loam plots following surface-applied digested liquid swine
manure, compared with plots treated with raw slurry. Measured N uptake in
the timothy crop was also higher in the digested manure plots. The authors
suggested the difference in crop yields was partly due to N loss from the
increased volatilization of NH 3 observed in the plots treated with raw swine
manure. This increased NH 3 loss can be attributed to the slower infiltration
of raw swine manure due to its higher viscosity. In this study the manure
types were not soil incorporated after application. A further study
conducted by Chantigny et al. (2008) demonstrated no significant difference
in corn grain yields between plots treated with raw and digested liquid swine
manure; however, unlike the 2007 study, the raw and digested manures were
surface applied and immediately incorporated to minimize NH 3 volatiliza-
tion.
Field trials were conducted at the University of Guelph in which plots
were land applied with either raw dairy manure or digestate. Each of the
400m 2 sandy loam plots received an application rate of 140 kgN/ha and
were planted with grain corn. Table 13.7 summarizes the seed corn yields
over two years of trials. Fig. 13.3 shows the corn plants at the experimental
plots. The study demonstrated an average 19% increase in corn yield for
plots treated with digestate over two years.
Schro¨ der et al. (2007) investigated the effects of digested cow manure on
cut grassland and reported a 14% higher N fertilizer replacement value (N
needed for plants) in the same year of application when compared with raw
cow manure. Whereas in the subsequent four years when no treatments were

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