Environmental Engineering Reference
In-Depth Information
Downstre
a
m
D
ownwin
d
N
2
O
(Global impact)
N deposition
NO
X
NO
+
-
NH
4
and NO
3
input
to marine
Ecosystems of
the Sierra Madres
-
NO
3
in
surface and
ground Water
Urban
Cropping
systems
Marine
ecosystems
FIGURE 12.3
At the landscape scale, nitrogen moved from farmers' fields to atmosphere, water systems,
oceans, and downwind terrestrial ecosystems.
atmosphere (
Figures 12.3
, 12.4). The integrated story of nitrogen transformations and
transport from land to the sea is told in more detail in
Ahrens et al. (2008)
.
While we pursued these exciting questions about nitrogen cycling and fluxes within the
fields and across the valley, we did not lose sight of our original intention—to identify
management alternatives that made sense for farmers and the environment. In addition to
studying what happens in the farmers' fields, we also measured nitrogen cycling processes
and crop dynamics in a set of comparative treatments that altered the timing and amount
of fertilizer applied. These treatments were constrained by reality—we wanted to test
options that could actually be practiced by farmers. One of the most important early
articles to emerge from this research, published in Science, reported the consequences (in
terms of nitrogen losses) of the mismatch between nitrogen needs of the wheat plant and
the timing of large fertilizer applications by farmers (
Matson et al. 1998
). Its analyses of
nitrogen losses, grain yields and quality, and farm budgets under a variety of alternative
practices suggested that by changing the timing and amount of applications (removing the
preplanting fertilization and applying (less of) it more closely timed to crop demand),
farmers' profits could be increased and the negative externalities of fertilizer losses could
be prevented. It also showed the benefits of a biogeochemist, an agronomist, and an econo-
mist attacking a problem from an ecosystem perspective.
Beyond the Simple Answer
There was just one problem. Despite on-farm trials that generally confirmed our “best
practice,” even progressive farmers seemed unwilling to change application practices. That
led to a series of new questions and hypotheses that engaged the research team for subse-
quent years. Team members David Lobell and Ivan Ortiz-Monasterio used remote sensing
to demonstrate substantial spatial and temporal variability in wheat yields. Their work indi-
cated that high applications of fertilizer in years of optimal weather—which farmers could
not know in advance—could pay off for some farmers (
Lobell et al. 2004
). That result led to
a search for new site-specific measurement technologies that could provide real-time esti-
mates of fertilizer needs during the course of the growing season, a search that ultimately
yielded the use of handheld radiometers to provide in situ information on nitrogen status
