Lower fertilizer prices this fall suggests that you should be doing some fall broadcast.
Summer and fall 2008 fertilizer prices went to new highs for a number of reasons. This resulted in a major reduction in fertilizer use, especially phosphorous. This reduction in use resulted in phosphorous prices crashing for this summer and fall.
Historically you always paid more for potash per pound of nutrient than phosphorous. I do not remember a year when phosphorous was less money per pound than was potash. That has changed. Phosphorous is now at a value per pound less than the price of a pound of potash.
If history repeats itself this will not last. Growers around the world seeing this lower price will start to buy phosphorous, depleting the supply and then the prices go back up.
Ideally, you have a soil test. Failing that you can put on crop removal rates.
A good crop of corn, beans and wheat will remove about 110 pounds per acre of phosphorous over the three-year cycle. BF