Growth Performances and Grain Yield Response of Rice Varieties (<em>Oryza sativa</em> L.) Established at Different Seed Broadcasting Rates in Irrigated Fields of Low Country Dry Zone of Sri Lanka

Abstract

Seed broadcasting rate has an enormous influence on rice plant density and the competition of the crop stands, tiller number, time taken to maturity and grain yield. Relatively low plant densities due to inappropriate sowing methods are the most significant aspects of agronomic restrictions for obtaining higher grain yields and weed competitiveness. A research study was conducted in Maha 2019/20 and Maha 2020/21 seasons to study the effect of different seed broadcasting rates on the yield and weed competitiveness of rice. The experiment was established with 3 different seed broadcasting rates 100, 150 and 200 kg ha -1 for the rice variety At 362 (Long grain) and 75, 112.5 and 150 kg ha -1 for the rice variety At 307 (Intermediate grain). The experiment was conducted under the irrigated condition of the low country dry zone of Sri Lanka in imperfectly drained reddish brown and low humic gley soils at the Rice Research Station (RRS), Ambalantota. Parallel to the research field experiment, recommendation and farmer practiced seed broadcasting rates (100 and 150 kg ha -1 ) were evaluated at farmers' fields using rice variety At 362. Grain yield, plant height, tiller count, filled and unfilled grain per panicle, spikelet count per panicle, 1000 grains weight and weed performance were determined. Results of this experiment have shown that elevated seed rates beyond 100 kg ha -1 do not improve the tiller count, effective panicles or the grain yield of two rice varieties At 362 and At 307. Diseases like sheath blight may affect the rice crop more severely causing significant yield losses in favourable weather with increased populations (150 kg ha -1 ). Therefore, a 100 kg ha -1 seed broadcasting rate can be recommended as the best seed rate for farmer field cultivation where better weed management practices are adopted. Finally, the results of this experiment reconfirmed that exceeding the recommended seed broadcasting rates of 100 kg ha -1 or 75 kg ha -1 for At 362 or At 307 respectively will not be effective to get a higher yield response from paddy under irrigated conditions in the dry zone. Recommended seed application rate of 100 kg ha -1 for long grain rice and 75 kg h -1 for intermediate grain rice in the paddy farming system had been recorded as cost effective seed broadcasting rates.