National Farm Building Code of Canada lists the bulk density of many materials including:
Hay (air dried)
- baled 160 kg/cu.m (10 pounds per cubic foot)
- chopped 160 kg/cu.m (10 pounds per cubic foot)
- long 80 kg/cu.m (5 pounds per cubic foot)
- wafered 325 kg/cu.m (20 pounds per cubic foot)
I'm not sure what they mean by long or wafered hay.
Also, there is a statement in the NFB that floor loading for stored products shall not be less than 5.0 kPa (105 psf) and for areas of the floor used by farm machinery traffic shall not be less than 7.0 kPa (145 psf). Also design for case of 23 kN (5167 lbs) point loads per wheel for farm equipment. There is another clause that the design live load shall be increased by 50% for areas where equipment is loaded or unloaded.