grain ready for grinding, grain
稞 centers on grain that has been harvested and is ready for processing, specifically grinding. It refers to grain in a prepared state rather than growing in the field.
稞 combines 禾 (grain plant) with 果, which likely contributes the sound and may suggest the result or fruit of the grain harvest. The exact historical development is uncertain.
The grain plant 禾 stands beside 果 (fruit/result), like grain that has reached its final ready-to-grind stage.
For カ, imagine a car full of grain ready for grinding: car -> カ, and the grain is loaded up.