Environmental Engineering Reference
In-Depth Information
also attributed to NH 4 + -N and NO 3 -N via surface runoff and soil
leaching. Due to its high solubility in water, NO 3 -N is the major N species
lost by leaching (Goss et al., 2001). Denitrification further influences N
losses with the production of gaseous N 2 O and N 2 .
Nitrogen loss through NO 3 leaching is an important water quality issue,
where high NO 3 -N concentrations in subsurface waters could lead to
contaminated drinking water sources and have possible negative effects on
human health (Goss et al., 2001; Dinnes et al., 2002; Stoddard et al., 2005).
Leaching of NO 3 -N is dependent on the type of soil amendment and how
its composition affects N transformations in the soil. Studies conducted by
Jokela (1992) and Stoddard et al. (2005) demonstrated lower NO 3 -N
concentrations in leachate from plots that received dairy manure compared
with those treated with inorganic fertilizer. In both studies, average NO 3 -
N concentrations in leachate were typically less than 13mg/l. The authors
indicated the higher organic C from manure may have increased
denitrification or N mineralization was in equilibrium with plant N uptake,
resulting in less NO 3 -N production in soils. However, by the end of the
Stoddard et al. (2005) study, the plots having received manure had higher
leachate NO 3 -N concentrations than the plots treated with inorganic
fertilizer, suggesting that long-term manure use can result in a delayed
NO 3 -N leaching potential due to continued N mineralization from soil
accumulated manure organic matter. Jemison and Fox (1994) demonstrated
the effects of growing season on NO 3 -N leachate concentrations and
found that, during the non-growing months, NO 3 -N concentrations
increased in plots that received dairy manure compared with inorganic
fertilizer plots. The authors suggested N mineralization in the manured plots
led to NO 3 -N production when no plants were available for N uptake.
Nitrate leaching is also affected by rainfall and land application practices.
Powell et al. (2011) reported mean NO 3 -N leachate concentrations were
highest with increased rainfall with negligible concentrations observed at
very low rain events. The authors also reported that when liquid dairy
manure was surface applied and not incorporated, NH 3 losses increased,
which in turn resulted in decreased N availability for leaching. The study
demonstrated no differences in NO 3 -N leaching between surface applica-
tion (no incorporation) and subsurface injection.
Multiple year field studies were conducted at the University of Guelph
Campus d'Alfred (Ontario, Canada) to investigate the effects of land-
applied raw dairy manure and digestate on NO 3 -N leaching to drainage
tiles (1m below soil surface). Each of the 1500m 2 Bearbrook clay plots
received an application rate of 140 kgN/ha and were planted with grain
corn. Table 13.8 summarizes the mean NO 3 -N concentrations in the tile
drains. Figure 13.4 demonstrates the sampling setup for the collection of tile
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