How much fertilizer to use?

I've got 1 row of pumpkins, it's 600 feet long. 300 plants total, and they're planted on a gradual slope (not on flat ground). They are about the size of a saucer or dinner plate. Some of the leaves are turning yellow, the others are sort of pale green. I have a 600 foot drip tape, and the water supply is from a 55 gallon drum at the top of the slope. I hook the drip tape up to the drum, and the water flows and drips the entire length of the patch. How much actual nitrogen (urea or ammonium sulfate or both) should I put in the 55 gallon drum?