chaff, rice hulls, (kokuji)
粭 centers on the waste left after processing rice: chaff and rice hulls. It is a kokuji, created in Japan for this specific agricultural byproduct.
粭 is a Japanese kokuji, combining 米 (rice) with 合 (fit, join) to represent the chaff or hulls that come together during rice processing. The exact historical origin is uncertain beyond this component combination.
Rice 米 that is gathered together 合 after threshing is just the leftover chaff and hulls.
For すくも, imagine scooping up chaff: 'scoop mo' sounds like すくも, and you scoop the hulls away from the rice.
—