Agronomic practices to enhance crop establishment, grain yield and weed suppression in flooded-direct seeded rice

The ability of rice to germinate and develop seedlings under water logged conditions is defined as anaerobic germination tolerance of rice (AG-tolerance) and can be combined with direct seeded rice (flooded-DSR) to suppress weeds and to increase crop stand in flood prone rice growing areas. However, success of flooded-DSR depends on agronomic practices that are being carried out. Therefore, two experiments were conducted at the Rice Research and Development Institute, Batalagoda, Sri Lanka to evaluate flood water heights at sowing and seeding rate on crop establishment, panicle density and grain yield and weed biomass in flooded-DSR. In experiment 1 (Maha 2014/15 and Yala 2015), two water levels (5 cm, saturated) and three seeding rates (60, 80, 100 kg/ha) were evaluated. The experiment 2 was conducted in Maha 2015/16 and Maha 2016/17 to evaluate three water levels (5 cm, 2.5 cm, saturated), and three different seeding rates (100, 125, 150 kg/ha). In all experiments, crop establishment reduced substantially in 5 cm flooding compared to saturated condition. When weeds were controlled, panicle density and grain yield increased in saturated condition compared to 5 cm flooding while under no weed control, 2.5 cm flooding gave the highest panicle density and grain yield with reduction of weed growth by 31-58% compared to saturated condition. Seeding rates ≤ 80 kg/ha reduced panicle density and grain yield under flooding. However, seeds sown >125 kg/ha rates had no effect to increase panicle density or grain yield. Therefore, adjusting flood water height at 2.5 cm at sowing and using 100 kg/ha seeding rate can optimize crop establishment, panicle density and grain yield with considerable reduction in grasses and sedges in flooded-DSR.