although it is technically off-topic for raw-food, I am submitting
the abstract for a recent study that may be of interest to the list
members. The study suggests that the intensive, industrial, irrigated
agriculture being practiced in California's San Joaquin valley - a major
food source - might not be sustainable, long term.

PNAS | October 25, 2005 | vol. 102 | no. 43 | 15352-15356

Sustainability of irrigated agriculture in the San Joaquin Valley, California
Gerrit Schoups, Jan W. Hopmans, Chuck A. Young , Jasper A. Vrugt, Wesley W.
Wallender, Ken K. Tanji and Sorab Panday

The sustainability of irrigated agriculture in many arid and semiarid areas of
the world is at risk because of a combination of several interrelated factors,
including lack of fresh water, lack of drainage, the presence of high water
tables, and salinization of soil and groundwater resources. Nowhere in the
United States are these issues more apparent than in the San Joaquin Valley of
California. A solid understanding of salinization processes at regional spatial
and decadal time scales is required to evaluate the sustainability of irrigated
agriculture. A hydro-salinity model was developed to integrate subsurface
hydrology with reactive salt transport for a 1,400-km2 study area in the San
Joaquin Valley. The model was used to reconstruct historical changes in salt
storage by irrigated agriculture over the past 60 years. We show that patterns
in soil and groundwater salinity were caused by spatial variations in soil
hydrology, the change from local groundwater to snowmelt water as the main
irrigation water supply, and by occasional droughts. Gypsum dissolution was a
critical component of the regional salt balance. Although results show that the
total salt input and output were about equal for the past 20 years, the model
also predicts salinization of the deeper aquifers, thereby questioning the
sustainability of irrigated agriculture.

http://www.pnas.org/cgi/content/abstract/102/43/15352

Tom Billings