Grain-filling process in lowland rice (Oryza sativa L. 'PSB Rc18') under water deficit is enhanced by nitrogen fertilization

A 3 x 4 factorial pot experiment was conducted to characterize the effects of nitrogen (N), water deficit (WD), and their interaction on grain development and grain yield of PSB Rc18, a popular lowland rice cultivar in the Philippines. Nitrogen fertilizer was administered at different phenological stages: before transplanting + tillering (N-0); before transplanting + tillering + flagleaf emergence (N-1); before transplanting + tillering + flagleaf emergence + anthesis (N-2). On the other hand, water deficit (psi = -10 kPa) was imposed 10 days before and until anthesis (WD,), during and until 10 days after anthesis, DAA (WD2), and 10-20 DAA (WD3), with the control (WD0) having 1-2 cm ponded water until 2 weeks before harvest. Panicles were tagged at anthesis, and sampled at 5-day interval until physiological maturity to determine the grain-filling rate and grain-filling duration under various treatment combinations. Results showed that, in general, N fertilization under WD improved grain-filling by delaying the attainment of maximum grain-filling rate by 5-10 days, hence longer grain-filling duration up to 5 days. Availability of current and stored assimilates and their rapid translocation to the grains improved spikelet fertility resulting to heavier grains and higher yield by 15%.