Effect of planting arrangement and seedling age on grain yield and radiation use efficiency of local and improved rice (Oryza sativa L.) cultivars in Khouzestan province, Iran

Solar radiation affects crop growth and development. Dry matter production by crops has often a positive relationship with radiation absorption by canopy and radiation use efficiency. Therefore, to evaluate radiation use efficiency of rice cultivars, a field experiment was carried out as split-split-plot arrangements in randomized complete block design with three replications in pilot plots in Qaleh-Tal district of Khuzestan province, Iran, in 2019-2020 and 2020-2021 growing seasons. Three rice cultivars; Champa, Anbouri and Danial were assigned to main plots, three planting arrangement; 15 cm × 15 cm, 15 cm × 20 cm and 15 cm× 30 cm, were randomized in sub-plots and seedling age at three levels; 30, 40 and 50-day old seedlings, in sub-sub-plots . Results showed that highest grain yield (9466 kg.ha-1) was recorded for cv. Danial in the 15 cm× 15 cm planting arrangement of 30-day seedling age treatment. The highest leaf area index (5.8) was achieved for cv. Champa in 30-day seedling age treatment. The highest crop growth rate (33.3 g.m-2 .day-1) observed for cv. Danial in 15 cm × 15 cm planting arrangement and 30-day seedling age treatment. The highest (1.95) and lowest (1.22 g,MJ-1) radiation use efficiency (RUE) were obtaibed in 30 and 50-day old seedlings, respectively. The increase of seedling age from 30 to 50 days led to incraese of light extinction coefficient from 0.06 to 0.10. The results of this experiment showed that 30-day old seedling at 15 cm × 15 cm planting arrangement treatment is more suitable for improving grain yield of rice cultivars in the target areas considering the low light extinction coefficient and high radiation use efficiency.