We investigated difference in effects between periodic and one-time application of digested slurry (PDS and 1DS, respectively) to wet rice fields by a slurry irrigation system using controlled pot cultivation and actual wet rice field tests. Fertilizer application rates were 120 kgN/ha for PDS and 220 kgN/ha for 1DS. Both experiments gave similar results for growth duration and nitrogen (N) use efficiency. During the tillering stage, plants after PDS had lower stem number and SPAD values (chlorophyll content of leaves) than plants after 1DS, but the values increased during the panicle initial stage and were higher than 1DS during the ripening stage. PDS exhibited significantly higher levels of N uptake, agronomic efficiency, and fertilizer N recovery efficiency than 1DS.