The determination of desired plant density in soils with different fertility in a region for mechanized rice cultivation

Physicochemical characteristics of soil, especially organic matter and soil texture, affect the optimal plant density in rice (Oryza sativa L.). A split-plot field experiment was done based on a randomized complete block design (RCBD) in four replications in Amol (Northern Iran) on the coastal strip of the Caspian Sea. The experimental treatments, that is, soil fertility (infertile, semi-fertile, and fertile) as the whole-plot factor and plant density (low, medium, and high by 15.2, 19.6, and 27.8 plants m⁻², respectively) as the split-plot factor, were studied over 2 years (2022 and 2023). The results indicated the greatest and smallest number of days from planting to tillering and from tillering to flowering for infertile soil, respectively. The maximum root fresh weight was measured during the tillering stage for infertile soil, whereas for fertile soil, the highest root fresh weight was recorded throughout the phases of panicle initiation and flowering. The greatest root length was measured at the tillering stage for 2022 in high-density infertile soil. The lowest number of panicles m⁻² and the percentage of full spikelets were obtained from infertile soil. The highest grain yield was obtained from high-density fertile soil. In mechanized rice cultivation, high density is suggested for fertile and semi-fertile soils and low density for infertile soil.