Agriculture Reference
In-Depth Information
emissions (Butterbach-Bahl et al. 2002, Ambus and Robertson 2006), and changes
in species composition (Bobbink et al. 1998, 2010). Chronic increases in atmo-
spheric N deposition have been shown to decrease plant species diversity even at
moderate levels (e.g., 10 kg N ha
−1
yr
−1
; Stevens et al. 2004, Clark and Tilman
2008). In agricultural systems, N deposition could be considered a free fertilizer
input and, in locations where deposition is high, may need to be considered when
making fertilizer N recommendations.
Between 1989 and 2010, KBS received, on average, 6.3 ± 1.3 kg N ha
−1
yr
−1
via wet precipitation (NH
4
+ NO
3
; NADP/NTN 2011). At sites in Michigan, dry
deposition of N (HNO
3
+ NO
3
+ NH
4
) between 1989 and 2010 was ~one-third that
of wet N deposition (CASTNET 2011). Using this ratio, an annual average total N
deposition (wet and dry) at KBS during this period was ~8.4 kg N ha
−1
yr
−1
. This
estimate is lower than the earlier estimate of 14.2 kg N ha
−1
yr
−1
by Rheaume (1990)
for Kalamazoo County between 1986-1987. The declining trend for wet deposi-
tion of NO
3
−
at KBS (Fig. 9.3) is likely due to the drop in NO
x
emissions following
adoption of air-quality regulations and emission-control technologies (Greaver et
al. 2012; Hamilton 2015, Chapter 11 in this volume).
Nitrogen fertilizer rates for wheat and corn at the MCSE are ~10 to 15 times
higher than atmospheric N deposition levels, so N deposition has little impact in
these systems. In the successional and forested systems, however, the present rate
of atmospheric N deposition represents a 2- to 3-fold increase over preindustrial
levels and likely has profound ecological effects in these N-limited ecosystems
(Galloway et al. 2004, Dentener et al. 2006).
Figure 9.3
. Wet nitrogen (NH
4
-
N, NO
3
-
N) and total wet nitrogen ([NH
4
+ NO
3
]
-
N) deposi-
tion (kg N ha
-1
yr
-1
) at KBS for 1989-2010. Data from NADP/NTN (2011).