Environmental Engineering Reference
In-Depth Information
TABLE 7.4
Fates of fertilizer N added over 22 years in an Iowa watershed with
continuous corn.
Fate
% of Input
Grain
50
Leaching
16
Runoff
1
Missing (unaccounted for); must be either stored
in the soil or denitrified
31
From
Steinheimer et al. (1998)
.
where this retention is taking place (soil storage, vegetation storage, gaseous loss) there is
a great quantity of “missing” or unaccounted-for N in these balances (
Boyer et al. 2002
).
At the regional scale, it is easy to assume that this unaccounted-for N is being stored in
soil or vegetation somewhere in the watershed, or perhaps being denitrified in wetland
“hotspots” of denitrification (
McClain et al. 2003
). At smaller scales (
Table 7.4
), where it is
possible to account for these possible fates of N with more precision, the “missing N”
represents a fundamental challenge to our understanding of ecosystem N cycles that will
likely continue to be the focus of much research over the next several decades.
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