Abstract
Grain filling rate, yield and 1000 grain weight are very important traits to determine the different nitrogen levels of response for different rice varieties. This study will investigate the rate of grain filling, grain yield and 1000 grain weight, and some quality parameters of one elite breeding line (At 08 1078) and standard variety (At 362) grown at five different nitrogen (N) levels (0, 50, 100, 150 & 200 kg N ha-1) under irrigated water condition in the low country dry zone of Sri Lanka. A split-plot experimental design was used in this experiment with three replicates. The gross plot and net plot area were 18 m2 and 12.96 m2 of each experimental unit. Main plots were separated by a ridge (40cm in width). The thousand-grain weight of each experimental unit from heading to harvesting was recorded at the 4-day interval to inspect the grain filling rate. Irrespective of the variety, grain filling commenced after four days from the day of heading and the rate of grain filling depended on the rate of nitrogen application on each experimental unit. Rice fertilized with ≥100 kg N ha-1 had a high grain filling rate and the period of grain filling increased in both varieties. Application of 100 kg N ha-1 was recognized as the optimum level for grain filling. Further increment of soil nitrogen (150 or 200 kg N ha-1) has not significantly affected the grain filling rate of the paddy. In addition, the significant highest grain yield, grain hardness, brown rice content, grain length and width were recorded at 100 kg N ha-1. It can be concluded that the N level of 100 kg N ha-1 was found for yield response and grain filling to be the best rate for both elite line At 08 1078 and the variety At 362.