Response of Rice to Small Differences in Length of Day

Abstract

THE natural annual variation in length of day in Malaya is from 41 min. in the north (lat. 6° N.) to 8 min. in the south (Singapore; lat. 1° 20′ N.). The monthly differences in length of day in the principal rice-growing areas lie between 1 and 3 min. It has been recognized in reports of rice sowing date experiments in Ceylon1,2 in Indonesia3 and in Japan4, that observed differences in time of emergence and maturation of the ear are possibly due to these small monthly differences in length of day. It has also been suggested that a decreasing length of day will advance flowering while an increasing length of day will delay flowering of rice3,5.