Impact of photoperiod on seasonal sowing in rice

Abstract

One late-winter variety ofindica rice was sown on the 1st of every month during the period from August 1964 to July 1965. In each month, a set of plants were subjected at the age of 28 days to 8 hr photoperiod for 21 days, and grown thereafter in natural daylength along with untreated controls till flowering and subsequent harvest. Production of tillers, leaves and plant height were significantly reduced by the short-day treatment. The vegetative growth period of the variety was greatly altered by the date of sowing. Control plants remained vegetative till they received in nature a critical nightlength of not less than 11 hr 26 min and an optimum temperature for the pigment (phytochrome) conversion. Thus plants sown during the months February to July came to ear emergence in the following October, plants of August and September sowing came to ear emergence in November, plants sown in October came to ear emergence in December, plants sown in November and December came to ear emergence in March and plants sown in January came to ear emergence in April. The 8 hr photoperiod induced a markedly earlier flowering in the treated plants in all the months of sowing. Grain yield was higher in the control plants than that of the treated plants in all the monthly sowings, while late sowings remarkably reduced the grain yield in the control plants.