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

Abstract

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 °C rise in soil temperature. When seeds were exposed to a mean soil temperature of 23.4 °C, an air thermal time ( Q a) of 49 degree-days (°C d) was required for seedling emergence to start, and emergence was completed within 117 °C d. With a cooler soil (18.1 °C), seedling emergence began at 96 °C d and was completed by 237 °C 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 °C, respectively, and the Q s was 125, 270, 556, 588, 667, or 833 °C d, respectively. The mean T b for the development of all phenophases studied was 10.4 (±0.5) °C. Strong positive correlations ( r≥0.95) were noticed among the rates of development of the phenophases observed. Rising air thermal times (134–1147 °C 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: TL v) 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: TL v ratio.