Phenology in rainfed lowland rice

This paper reviews the factors determining flowering time and phenology requirement in rainfed lowland rice. Recent developments in understanding of the temperature and photoperiod effects on flowering time of rice resulted in phenology models that can predict flowering time accurately in the irrigated field. However, in the rainfed lowland ecosystem drought and low soil fertility commonly delay flowering time. Genotypes with a long delay are often those with a large yield reduction under the adverse conditions. In rainfed lowland rice, there may not be standing water at the appropriate time for transplanting and the use of old seedlings for transplanting on a later date results in delay in flowering. Optimum time of flowering for high yield is often related to water availability, and early flowering cultivars are favoured in areas where the probability of occurrence of late season drought is high. However, short duration cultivars are less tolerant to stress such as early season drought if the stress develops during the vegetative stage. The variation in water availability in paddies would cause genotype phenology-environment interaction for yield. Further understanding of water balance in the rainfed lowlands would assist determination of the optimum phenology groups for different regions of the rainfed lowland system. (C) 1999 Elsevier Science B.V. All rights reserved.