Germination and emergence of cotton seed were studied in the laboratory in constant temperatures and in a Soil Temperature Simulator (STS). Variables evaluated were soil moisture saturation, soil at a constant temperatures, soils under a cyclic temperature and cotton seed quality.

Seeds from commercial lots representing six varieties of cotton, Gossypium hirsutum L. , were screened and six lots were selected to represent varying seed quality levels. These six lots were subjected to four different constant temperature treatments, 30 C, 25 C, 20 C and 15 C. Constant temperature emergence tests were conducted at four levels of soil, or meda, moisture saturation, 40, 60, 80 and 98%. Four replications of 50 seed were planted in 20 x 27 x 9.5cm plastic crispers containing non sterile builders sand. Constant temperature tests were conducted in lighted, temperature controlled rooms. After testing at constant temperatures, three lots were selected to represent high, medium and low quality seed for evaluation in the STS at cyclic temperature schemes. Cyclic temperature schemes were selected to imbibe seed at low temperatures followed by favorable temperatures and imbibing at higher temperatures then lowering temperatures.

The results of constant temperature tests indicate that: (a) low temperature stress adversely effected cotton seedling emergence regardless of quality; (b) low quality cotton seed were more adversely affected by low temperature stress than high quality seed; (c) detrimental effects of low temperatures increased as soil moisture saturation increased; (d) seedling emergence decreased as temperature dropped to 20 C or lower and soil moisture saturation increased above 60%.

Results from cyclic temperature tests indicated that: (a) imbibing seed at 10 C resulted in more adverse affects than imbibing at 25 C, regardless of seed quality; (b) holding seed at 10 C for periods exceeding 24 hours resulted in reduced seedling emergence as compared to holding seed at 10 C for 24 hours then increasing substrate temperature; (C) increasing substrate temperature after 48 hours of exposure to 10 C did not reverse damaging effects of low temperatures; (d) increasing substrate moisture saturation increased sensitivity of seed to adverse effects of low temperatures; (e) high quality seed were less effected by low temperatures at all levels of moisture saturation than were low or marginal quality seed; (f) imbibing seed at 25 C reduced the adverse effects of low temperatures.