A better chum than what you describe is cottonseed cake, rabbit pellets or cattle range cubes. Each of these are readily available from feed stores. The range cubes and cottonseed cake are chunks of solid feed that have a plesant aroma and are heavier than the water, so they sink. They attract catfish by the aroma of the high-protein cottonseed. The rabbit pellets are compressed chunks of alfalfa hay, one of the strongest catfish attractants.
Many people bait a hole by sinking bales of alfalfa hay. The catfish will make all but the wire disappear within a week, so you need to add bales weekly to maintain the hole. Check your state's game laws for legality...
Chum works for firing up the bite if the fish are there. Don't depend on the chum to bring fish in.
The chum on the trotline is probably a wasted effort. Instead, if the trotline is not in heavy current and shallow water, cast the chum along the length of the line.
I occasionally use soured grain chum here on the Arkansas River in Oklahoma, but only in backwater areas with little or no current. If you try to chum in the current, the chum will be quickly dissapated and washed away.
When I do chum with soured grain, I use milo, wheat, corn, soybeans, oats... whatever is available for free, spilled at the commodity elevator. (The operator lets me clean it up for him to help him control rodents.)
Throw two or three old tomato cans full of chum in a semi-circle around the area you want to fish, then immediately move to another spot, repeating the chumming. Repeat in a third spot, then return to the first chummed spot and begin fishing. If you have no bite within 15 minutes, move to the second chummed spot. If no bite, go to the third. Repeat the circle once, then start over at least 100 yards away.
If the fish bite, then slow down, throw out an additional can full of chum to fire them up again. If you catch dinks, then they abruptly stop biting, STAY THERE. Bigger fish have probably moved in and run off the dinks. Hang onto your rods.