Agriculture Reference
In-Depth Information
Nitrogen Loss from Cropping Systems
Hydrologic Losses and Fate
A significant amount of the N fertilizer applied to cultivated crops is lost in agricul-
tural drainage waters, primarily as highly mobile NO
3
−
. Other forms of reactive N in
the soil solution (e.g., NH
4
+
, dissolved organic nitrogen [DON]) are typically pres-
ent in such small quantities that they are unimportant sources of N loss, even in fer-
tilized soils (Hamilton 2015, Chapter 11 in this volume; cf. van Kessel et al. 2009).
Syswerda et al. (2012) estimated NO
3
−
leaching losses from MCSE systems by
combining measured NO
3
−
concentrations in water draining the root zone (sampled
at 1.2-m depth) with modeled rates of water loss. Nitrate losses varied with tillage
and the intensity of management inputs. Among the annual cropping systems, aver-
age annual losses followed the order Conventional (62.3 ± 9.5 kg N ha
−1
yr
−1
) >
No-till (41.3 ± 3.0) > Reduced Input (24.3 ± 0.7) > Biologically Based (19.0 ± 0.8)
management. Among the perennial and unmanaged ecosystems, NO
3
−
losses fol-
lowed the order Alfalfa (12.8 ± 1.8 kg N ha
−1
yr
−1
) = Deciduous Forest (11.0 ± 4.2)
>> Early Successional (1.1 ± 0.4) = Mid-successional (0.9 ± 0.4) > Poplar (<0.01 ±
0.007 kg N ha
−1
yr
−1
) systems (Fig. 9.7).
Figure 9.7
. Nitrate leaching losses (kg NO
3
-
-N ha
-1
yr
-1
) in MCSE systems for 1995-2006.
Mean ± SE (n = 3 replicate locations). Modified from Syswerda et al. (2012).
