Effects of changes in soil temperature on seedling emergence and phenological development in field-grown stands of peanut (Arachis hypogaea)

We investigated the effects of soil temperature on seedling emergence and phenological development in field-grown stands of peanut (Arachis hypogaea). The rate of seedling emergence increased by about 1.4 calendar-days for every 1 degreesC rise in soil temperature. When seeds were exposed to a mean soil temperature of 23.4 degreesC, an air thermal time (Q(a)) of 49 degree-days (degreesC d) was required for seedling emergence to start, and emergence was completed within 117 degreesC d. With a cooler soil (18.1 degreesC), seedling emergence began at 96 degreesC d and was completed by 237 degreesC d. There were no significant differences among temperature treatments in the soil thermal time (Q(s)) required for emergence. The rates (d(-1)) of leaf appearance, branching, flowering, pegging and podding were positive linear functions of soil temperature. For the phenological events of 50% seedling emergence, leaf appearance, branching, flowering, pegging, and podding, the base temperature (T-b) of the soil was 9.9, 10.3, 9.7, 10.4, 10.7, or 11.1 degreesC, respectively, and the Q(s) was 125, 270, 556, 588, 667, or 833 degreesC d, respectively. The mean T-b for the development of all phenophases studied was 10.4 (+/-0.5) degreesC. Strong positive correlations (r greater than or equal to 0.95) were noticed among the rates of development of the phenophases observed. Rising air thermal times (134-1147 degreesC d) increased the number of main stem leaves (L-f) but decreased the ratio of the number of main stem leaves to the total number of leaves (L-f:TLv) on the plant. Plants grown in warmer soil produced more leaves on their branches than on the main stem, resulting in a lower L-f:TLv ratio. (C) 2002 Elsevier Science B.V. All rights reserved.