HYPOCOTYL ELONGATION AND SWELLING OF COTTON AS AFFECTED BY SOIL-TEMPERATURE, MOISTURE, AND PHYSICAL IMPEDANCE

Hypocotyl elongation and swelling affect the time required for a seedling to emerge and the potential emergence force of the seedling against soil impedance. This study was conducted to evaluate effects of soil physical condition on hypocotyl elongation and swelling of cotton [Gossypium hirsutum L.] seedlings. Effects of soil temperature, moisture, and physical impedance on hypocotyl growth were investigated by applying a constant downward force on the hypocotyls at different temperature and moisture conditions under controlled environments. Average hypocotyl elongation in a 3-d period decreased with increasing downward force from 9.7 cm under no load to 1.8 cm under a 180-g load. Hypocotyl elongation increased with increasing soil temperature from 22 to 32-degrees-C and soil water potential from -300 to -10 J kg-1. The swelling index, calculated by dividing the fresh weight of the hypocotyl by its length, increased quadratically with increasing downward load. Total fresh weight decreased with increasing downward load and decreasing soil moisture. Hypocotyl swelling generated potential emergence forces exceeding downward loads in the tested range, 0 to 1.8 N. The potential emergence force was lower and the response to greater downward load was reduced at a soil water potential of -300 J kg-1.