Effect of planting distance on the performance of different upland rice varieties (Oryza sativa L.) grown organically under lowland conditions

Abstract

The effect of planting distance on the performance of different upland rice varieties grown organically under lowland conditions was investigated. Result revealed that among the tested varieties, Glutinous rice demonstrated superior performance in plant height, culm diameter, number of spikelets, panicle length, panicle weight, biomass, and 1000-seed weight. The optimal planting distance for maximizing yield was found to be 20 x 20 cm, as it resulted to improve spikelet count, panicle length, panicle weight, filled grains, and biomass across seasons while red rice and Glutinous rice had higher numbers of filled grains, NSIC 22 produced the most spikelets without necessarily achieving the highest yield. In addition, the 15 x 15 cm spacing performed well in productive tillers and 1000-seed weight. While the broadcast method consistently resulted in the lowest yields, making it unsuitable for organic lowland rice farming. Seasonal variations also played a crucial role, with the dry season producing higher growth and yield across most parameters due to favorable environmental conditions, whereas the wet season led to increase the unfilled grains, likely due to excessive rainfall and disease susceptibility. Additionally, the significant interaction was found between planting distance and variety highlighted the importance of selecting the right combination to optimize productivity. Overall, Glutinous rice was the best-performing variety, 20 x 20 cm which showed the most suitable planting distance, and the dry season was the most favorable for organic lowland rice production. Further studies should explore the long-term effects of different planting distances on soil fertility and pest resistance in organic farming systems.