Good points on the ng/fert correlation. As a commodity there are relationships that appear at times but I don't know that they can be counted on as real or just random occurences.
One interesing statement from POT CEO Bill Doyle is that they are allocating product and are virtually sold out thru 2009. They are the largest company in this arena so until new supply comes on in 2010 or demand for food eases then the prices should hold up.