Agriculture Reference
In-Depth Information
9
Nitrogen Transfers and
Transformations in Row-Crop
Ecosystems
Neville Millar and G. Philip Robertson
Nitrogen (N) is an essential constituent of both proteins and nucleic acids, crucial
components of all living things. Humans depend on agricultural systems to pro-
vide most of their daily protein, prompting Liebig (1840) to note that agriculture's
principal objective is the production of digestible N. Today's intensive agricul-
ture is built on a foundation of N augmentation via the use of synthetic fertilizers
and cultivation of N-fixing crops on a massive scale. Globally, the addition of
this fixed N to cropping systems is now greater than natural terrestrial N fixation
(Galloway et al. 2004, Vitousek et al. 2013) and is a pervasive and fundamen-
tal feature of modern crop management (Robertson and Vitousek 2009). The net
benefit to humans of this additional N to agriculture is immense—it has enabled
greater food production and unprecedented increases in human population (Smil
2002). At the same time, however, this anthropogenic acceleration of the global
N cycle has caused serious environmental problems including contributing to cli-
mate change and stratospheric ozone depletion, eutrophication and harmful algal
blooms, poor air quality, biodiversity loss, and degradation of drinking water sup-
plies (Galloway et al. 2008).
Here, we summarize findings on the cycling of N in agricultural ecosystems of
the Kellogg Biological Station Long-term Ecological Research site (KBS LTER).
KBS LTER results illustrate a number of opportunities to manage agricultural N in
ways that improve N conservation and reduce the escape of fixed N to the environ-
ment; they also reveal needs for future research to fill knowledge gaps and more
fully document the complex cycling of N in cropping systems that range from con-
ventional to organic and from annual to perennial.
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