Well, There's Always the Black Death: Rabobank Gloomy on Farm Commodities - except sugar

This morning corn traded down to a new life-of-contract low, $4.35 and attracted some buyers but in the larger scheme of things we are seeing another commodity in oversupply. Here's the last twelve months action:

FinViz

$4.3940 last.
And here's Agrimoney:

Rabobank sounded a bearish note on agricultural commodities - except sugar - cutting price forecasts for many and, for wheat upgrading expectations, but to levels below the futures curve.

The bank cut its forecast for Chicago corn futures in the newly-started October-to-December quarter by up to $0.40 a bushel, warning that the grain faced "an increasingly bearish outlook" thanks to the extra US stocks uncovered in an official report on Monday, and from promising US harvest yields.

"The positive harvest reports bolster expectations that 2013 will indeed by a strong stock-building year," Rabobank, flagging that the extra supplies had already "broken" the cash basis, down $1 a bushel over the past month, on top of the fall in futures.

"As the harvest moves into the Corn Belt over the next three weeks, cash prices are expected to continue to retreat, albeit at a slower pace as producers choose to sell rather than store."

Oilseeds downgrades

For soybeans, the bank cut its price forecasts by up to $0.75 a bushel, citing here too larger-than-expected US inventories at the close of 2012-13, and pressure on values from a US harvest which is beating expectations....MORE

$4.35 is also Rabobank's new Q4 forecast for corn.
If demand doesn't pick up there is one tried and true method to raise prices, kill off the agricultural producers.
From Armstrong Economics:

(click to enlarge)

Possibly related:
Herschel and Me (Sunspots and Wheat)

You can also peruse the work of William Stanley Jevons (he of the paradox):
 "The Solar Period and the Price of Corn" (1875)
"The Periodicity of Commercial Crises and Its Physical Explanation" (1878)
“Commercial crises and sun-spots”, Nature xix

You may want to dip into the big daddy of price series:

"A History Of Agriculture And Prices In England, From The Year After The Oxford Parliament (1259) To The Commencement Of The Continental War (1793)"

by J. E. Thorold‐Rogers, 7 volumes, 1866-1887 which probably influenced Jevons.

Here's another bit o'price series scholarship:

The Price History of English Agriculture, 1209-1914