Hypocotyl and Radicle Elongation of Cotton as Affected by Soil Environment1

Abstract Cotton ( Gossypium hirsutum L.) seedling growth during emergence was studied under controlled conditions to estimate the main and interacting effects of soil temperature, moisture, and physical impedance on hypocotyl and radicle elongation. This information additionally provided a data base for the development of an elongation model for an emerging cotton hypocotyl which is not included in this report. Soil temperature increasing from 15.6 to 32.2 C resulted in more rapid and greater total elongation of hypocotyls and radicles. Increasing physical impedance decreased elongation of both hypocotyls and radicles, with hypocotyls being the most sensitive. Decreased hypocotyl elongation was consistently noted with increasing soil moisture tension; however, radicle elongation tended to be greater at 3.0 bars than for .3 bar. A marked temperature‐moisture interaction was evident for hypocotyl and radicle elongation at 37.8 C which is near the hot null temperature (40 C) for cotton. However, this interaction did not exist at 15.6 which is near the cold null (14 C). A relative slow‐down in hypocotyl elongation rate between 2.5 and 5.0 cm occurred at 37.8 C and .3 bars soil moisture, and at 32.2 C and 3.0 bars.