EFFECTIVENESS OF NITROGEN AND POTASSIUM FERTILIZER APPLICATION ON LODGING HABIT AND YIELD ATTRIBUTES OF T. AMAN RICE IN GANGES TIDAL FLOOD PLAIN

A two factor (N and K) experiment was conducted at Dumuria Upazila, Khulna, from June to December 2010 to evaluate the performance of different N and K doses in T. Aman rice. cv. Moulata on calcareous Silty Clay Loam soil of Bajoa soil series developed on Ganges tidal flood plain (AEZ 13). Four nitrogen rates (N₁ = N control, N₂ = 25 kg N ha^-1, N₃ = 50 kg N ha^-1 and N₄ = 75 kg N ha^-1); and four potassium rates (K₁ = control, K₂ = 10 kg K ha^-1, K₃ = 20 kg K ha^-1 and K₄ = 30 kg K ha^-1) were selected as the treatments. The experiment was laid out in a Split Plot Design allotting N rates in the main plots and K rates in the subplots with three replications. Therefore, the total number of plots was 48 (4 × 4 × 3) and area of unit plot was 10 square meter (4 m x 2.5 m). In the study it was found that, lodging of T. Aman rice at maturity stage was increased with rising N content and decreasing K rate. N₃ K₃, N₁ K₄, N₂ K₃, N₂K₄, N₃K₄, showed statistically identical and lower lodging habit (lodging score 1.33-1.67). Fifty kg N ha^-1 application with 0 and 10 kg K ha^-1 gave the higher number of lodged plants. Fifty kg N ha^-1 and 75 kg ha^-1 gave higher plant height, number of effective tillers hill^-1, panicle length and filled grain panicle. Among 4 K treatments K3 and K₄ produced statistically higher plant height and 1000-grain weight, number of effective tillers hill^-1, panicle length and lower number of sterile spikelet´s panicle^-1. All the N × K showed statistically significant effect on all the yield and yield contributing parameters in the study. Numerically, N₄K₄ produced the highest plant height, 1000-grain weight and straw yield. The highest number of effective tillers hill^-1, panicle length and harvest index were produced by N₃K₃. N₃K₄ gave the highest filled grains panicle^-1 and the lowest sterile spikelet´s panicle^-1 at harvest. N₄K₄ and N₃K₃ gave the highest straw yield and harvest index, respectively. N and K application showed significant effect on grain yield of T. Aman rice. Later two higher N rates produced higher grain yield (3.60 t ha^-1). N application did not show significant effect on grain yield of T. Aman rice beyond 50 kg N ha^-1. Grain yield was significantly increased with the increased K dose and highest (4.18 t ha^-1) one was given by K₃ and the lowest grain yields were given by control plots of N and K.  In case of interaction 20 kg K ha^-1 with 50 and 75 kg N ha^-1 gave the higher (3.83 – 4.08 t ha^-1) grain yield. But the highest one was obtained from the interaction N₃K₃ whereas the lowest (2.52 t ha^-1) grain yield was given by N₁K₁. Over fertilization might reduce grain yield by giving excess vegetative growth and lodging.