Growth and Phenological Responses of Rice to Artificial Light at Night

Abstract

An experiment was undertaken at the Regional Agricultural Research Station, Pilicode, to study the effects of artificial light at night (ALAN) on the growth and phenology of rice. The experiment was laid out in a split-plot design, in which the absence and presence of artificial night illumination were considered main-plot treatments and five rice varieties, viz. ‘Rakthashali’, ‘Karuthanjavara’, ‘Chempav’, ‘Uma’ and ‘Jeerakasala’ were used as subplot treatments. Biometric observations were recorded on plant height, tiller number and panicle number. Crop phenological observations, such as duration to booting, heading and maturity, were also noted. The experiment was conducted over two seasons, and in both seasons, the variety ‘Karuthanjavara’ remained in the vegetative stage throughout the experimental period. Although ‘Chempav’ and ‘Jeerakasala’ reached the heading stage, they failed to achieve proper grain filling and did not produce quality seeds. In general, ALAN considerably increased the number of days required to reach the booting stage and extended the total crop duration, while reducing the duration from heading to harvest maturity compared to the non-ALAN-exposed plots. Among the five varieties evaluated, only ‘Rakthashali’ and ‘Uma’ produced harvestable grains under ALAN stress, although their crop duration was longer. ALAN also adversely affected early vegetative growth, resulting in reduced plant height and lower tiller production. One month after transplanting, the mean plant height in the ALAN-exposed main plot was 70.1 cm in autumn and 93.9 cm in summer, compared to 84.7 cm and 98.0 cm in the non-ALAN-exposed main plot. Similarly, the mean number of tillers in the ALAN-exposed plot was 6.4 in autumn and 17.9 in summer, whereas the non-ALAN-exposed plot recorded 15.5 and 28.4 tillers, respectively. In addition, panicle production was lower in the ALAN-exposed plots than in the non-ALAN plots. The ALAN-stressed main plot produced 23.4 panicles in autumn and 17.7 in summer, whereas the non-ALAN-exposed plot recorded 34.4 and 20.7 panicles, respectively. The study revealed that certain rice varieties are sensitive to extended photoperiods and confirmed that the transition from the vegetative to the reproductive phase in rice requires exposure to short-day conditions and relatively longer nights. This research highlights the negative impact of ALAN on rice growth and phenology. Even if improved cultivars tolerate minor night-light stress, extended exposure disrupts flowering schedules, grain filling and total yields in rice-based cropping systems.