Environmental Engineering Reference
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(a)
(b)
FIGURE 12.4 Irrigation water carried nitrogen from fields (a) and from other land sources to the ocean,
resulting in (b) massive blooms of phytoplankton (here measured by SeaWiFS satellite imagery) that bloomed in
synchrony with irrigation and fertilizer events on land. (From Beman et al. 2005 .)
( Ortiz-Monasterio and Raun 2007 ). At the same time, however, we wondered why, in spite
of climate uncertainties, farmers did not cut back on nitrogen use when fertilizer prices dou-
bled following the removal of subsidies and again when petroleum prices spiked. We
launched a new set of studies on the “knowledge system” of the valley, and uncovered the
important role of credit institutions in controlling the fertilizer decisions made by farmers;
credit union advisors tended to encourage all farmers toward application rates that were
both uniform and very high ( McCullough and Matson 2011 ), and could withhold credit if
these practices were not followed. We realized that, if we hoped to get credit union man-
agers to reduce unnecessary inputs, we needed to engage them in the research itself;
through the influence of Ivan Ortiz-Monasterio and many of the more progressive farmers
of the valley, many of the credit unions became involved to the extent that they helped buy
the new site-specific management technology for their members.
Working in one ecosystem over a decade, of course, leads to an ever-changing set of
questions. At the same time we were working toward improved fertilizer management,
we engaged in research on sustainable use of water resources in the valley, and on the
role of shrimp aquaculture in the loss of ecosystems and ecosystem services. And we
began to worry about agriculture in the context of vulnerability to climate change, ulti-
mately developing an index of vulnerability that suggested who among the farmers and
farms of the valley were most vulnerable (or likely to suffer harm) to climate change and
thus who might benefit most from management assistance ( Luers et al. 2003 ). Research on
these issues and others continue in the valley, thanks in large part to our graduate stu-
dents and the Mexican collaborators on our team.
LESSONS FROM THE YAQUI VALLEY
ECOSYSTEMS STUDY
The fertilizer story is just one part of our interdisciplinary research in the valley, but it
is illustrative. As viewed through this story,
the Yaqui Valley is in transition to
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