You can ask the trucker to find out if the houses are cleaned after each flock, once a year, etc. The university can run an analysis or the broiler producer should areald have it. If you let it stack and go through a heat, the odor will decrease and the weed seeds will be less. Usually, with annual cleanout, the N-P-K will be something like 45 pounds N, 60 pounds P2O5 and 45 pounds K2O. But it varies so a test report is useful. I'd skip the sawdust routine unless you have a windrow machine. If they use alum or PEL in the houses to control moisture, the P2O5 can be a good bit lower. 4 tons would be a mighty dose. The price sounds a little high but trucking is a big player.