Effect of temperature associated with levels of bulk density on rice seedling emergence

Summary

A laboratory study was conducted to find out the effect of temperatures on rice seedling emergence under different levels of bulk density. The temperatures ranging from 10 to 40°C in increments of 5°C were maintained constant with ±1°C accuracy. The bulk density levels were 1.3, 1.5, 1.7, and 1.9 g cm⁻³. Aluminum cylinders with top open and bottom provided with a removable 20-mesh brass screen, were used as soil containers. The moisture content in soil was always above field capacity which could be accomplished by placing the cylinders in a tray in which water level was maintained constant to 5 cm depth.

Seedling emergence counts were taken till the 10th day of seeding. At the end of the experiment, observations on root and shoot elongations were recorded. Emergence was maximum at 25 and 30°C under 1.3 and 1.5 g cm⁻³, and decreased at 35, 20, and 15°C. As compared to the lower bulk densities, the reduction in emergence under 1.7 g cm⁻³ was smaller at 25 and 30°C than at 35°C. This was ascribed to greater seedling vigour at 25 and 30°C, as could be inferred from larger root and shoot elongation. The reduction in emergence at lower temperatures (20 and 15°C) might be due to delay in time of germination as well as less seedling vigour. The soil under 1.9 g cm⁻³ was sufficiently dense that the seedlings could not emerge except a few ones at 25 and 30°C.