Land application of digestate - The Biogas: Science, Production and Applications - page 314

Table 13.8 Flow-weighted mean NO 3 -N concentrations in tile drains
at University of Guelph Campus d' Alfred experimental plots

Mean NO 3 -N concentration
in tile drains (mg/l) Plot treatments

Spring 2009
Raw manure 6.4 ± 1.4

Digestate 8.8 ± 1.7

Control (no treatment) 2.2 ± 0.9

Spring 2010
Raw manure 5.8 ± 2.3

Digestate 6.1 ± 1.9

Control (no treatment) 2.0 ± 0.3

Source: Data collected by University of Guelph.

waters. Differences in mean NO 3 -N concentrations in drainage waters
between raw manure and digestate treated plots were not significant
(p 0.05). The mean drainage NO 3 -N concentrations from the clay plots

were consistently below 10mg/l - much lower than the reported mean
drainage concentrations ranging from 13 to 28mg/l in sandy and silt loam
plots (Jemison and Fox, 1994; Stoddard et al., 2005; Powell et al., 2011).
The impact of land application of digestate on NO 3 -N leaching to tile
drains may be similar to that of raw manure or inorganic fertilizer.
Strategies should be implemented to reduce NO 3 -N drainage losses,
including applying appropriate rates for N application, improving timing of
application, planting cover crops and reducing tillage (Dinnes et al., 2002).

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13.3.6 Bacteria migration to drainage tiles

The land application of agricultural residues can have a direct impact on
bacterial concentrations in groundwater, surface water and soil, where
leachate from manure-amended fields reaching subsurface tile drains has
been shown to have concentrations exceeding background levels (Abu-
Ashour et al., 1994; Jamieson et al., 2002; Unc and Goss, 2004; Goss and
Richards, 2008). The survival of enteric bacteria can be influenced by several
factors, including soil moisture, soil type, pH, temperature and nutrient
availability (Abu-Ashour et al., 1994; Goss et al., 2001; Jamieson et al.,
2002).
The survival of enteric bacteria in manure-amended soils increases with
high moisture content, where moisture retention is linked to soil particle size
distribution and organic matter content (Jamieson et al., 2002). Abu-Ashour
et al. (1994) explain that there is an increased survival of bacteria with
increased organic matter content in soils. Furthermore, finer soils (e.g. clay
and humic substances) increase water retention, which ultimately increases

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