In rainfed lowland,
rice crop undergoes submergence for 10-15 days during the vegetative and reproductive
stages of crop growth. Most of the rice varieties are unable to withstand complete
submergence for more than a week. More than 16% of lowland rice is adversely
affected by excess water stress with a time scale from a few days to 2 weeks. Upon
complete submergence, the rice plants have to adapt themselves to two drastic
environmental changes: the transformation of the aerobic environment to the hypoxic
environment during the period of submergence followed by retransformation of the
hypoxic environment to the aerobic environment
when the floodwater recedes. The turbidity, turbulence, pH, and temperature of floodwater and the stage of
submergence are the main factors that affect crop growth. The major problems
associated with submergence are reduced PAR and underwater photosynthesis, leaf
senescence due to more ethylene production under submergence, cell wall damage
and lodging, reduce tiller and leaf numbers, deposition of silts on the leaf
surface in case of turbid water, reduced plant population and difficulties in
crop establishment. Suitable management practices are recommended to cope with
the submergence. Resilient varieties like Swarna-SUB1, IR64-SUB1, Samba
Mahsuri-SUB1, CR1009-SUB1 can withstand submergence better than its parent
cultivar. Agronomic
approaches such as using higher seed rates, better seeding methods, skipping
basal N application, post submergence application of N (both foliar and soil
application), application of 20% more P and K and soil application of sodium silicate,
foliar application of orthosilicic acid have been found to increase the
productivity of both sub 1 introgressed
and non-introgressed HYV subjected to submergence of 14 days duration.
