A bushel is 1.25 cubic feet.
I suppose that, 200 years ago, corn soybeans and wheat were bought and sold by measuring the wagons.
No one does that today.
A bushel of corn is converted to 56#
Most corn weighs more like 58#
A bushel of soybeans is converted to 60#
Most soybeans weigh more like 58#
A bushel of wheat is converted to 60#
Most wheat weighs 60#
Test weight is used as a measurement of quality.
Test weight could be used as a measurement of quantity.