Randy, I asked for specific examples of widely grown crops
where the farmers themselves have expressed deep worry
they may soon have to accept lower yields due to serious
and unsolvable problems caused by "mega-ag" practices.

You suggested corn as an example.  However, I am unaware 
of corn farmer groups or their trade associations
who have expressed deep worry over herbicide and insecticide 
resistance problems. Nor can I think of case history 
examples (in modern times) of where the ag chemical/biotech 
industry failed to come up with answers to solve or economically 
manage emerging resistance problems for our widely 
grown crops.

You suggested that growing corn for fuel is unsustainable 
because it takes a calorie of petroleum energy to produce
a calorie of harvested corn grain. But that the net fossil energy 
loss assumption is based on "studies done before 1993 or 
in some combination by the Pimentel and Patzek [Cornell] 
team."
http://www.afdc.energy.gov/vehicles/emissions_balance.html

You suggested overdrafting of our aquifers is an unsustainable
consequence of growing corn, but most corn in the heart of the 
corn belt of the Midwest does not require irrigation or only
minor supplemental irrigation, so overdrafting of aquifers is 
not an issue. Irrigation is essential, however, in the high 
Plains corn growing areas, but aquifer water levels in that
region are a mixed bag; unchanging or rising in about 65% of 
that area and dropping in about 35%
http://en.wikipedia.org/wiki/File:Ogallala_changes_1980-1995.svg  

In sum, I an not convinced that corn (wind pollinated by the
way) is a valid example of a widely grown crop where ongoing 
"mega-ag" practices will end up causing serious and unsolvable
problems that will result in more than minor localized 
yield reductions that will likely be vastly offset by
advances in biotechnology; i.e. Monsanto's pledge to greatly
increase yields of corn, soybeans and cotton the coming decades:
http://monsanto.mediaroom.com/index.php?s=27632&item=76958

Paul Cherubini
El Dorado, Calif.

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