Premature Flowering in Soybean Yield Reductions at Nonoptimal Planting Dates as Influenced by Temperature and Photoperiod1

Publisher Website
Google Scholar
Abstract
The optimum time for soybean [Glycine max (L.) Merr.] planting in the southeastern USA is from early May to early June. Planting at other times has consistently resulted in seed yield losses which have been blamed on premature flowering induced by short photoperiods. Objectives in this study were to characterize the photoperiod response of soybean cultivars commonly grown in the southeastern USA, determine if daylength differences between optimal and nonoptimal planting dates in the southeastern USA are great enough to cause premature flowering, determine the interaction of photoperiod and temperature factors on the length of the vegetative stage, and evaluate the ability of delayed flowering genotypes to avoid yield losses at nonoptimal planting dates. The studies were conducted in both growth chambers (to provide daylengths of 12 to 16 h and temperatures of 21 to 30°C) and in the field (Aquic Fragiudalf soil). Group V cultivars had smaller increases in vegetative period as daylength increased and had a longer daylength beyond which flowering did not occur compared to Group VI, VII, and VIII cultivars. The critical daylength using constant photoperiod durations for achieving an adequate vegetative period was determined to be between 14 and 14½ h in ‘Forrest’, ‘Centennial’, and ‘Tracy‐M’, while ‘Bedford’, ‘Davis’, ‘Ransom’, ‘Bragg’, and ‘Braxton’ had a critical photoperiod between 13½ and 14 h. Based on these studies, daylength encountered by soybeans planted early (e.g., early April) is short enough to cause premature flowering. Daylength encountered by some cultivars planted late (e.g., mid‐June) is not short enough to cause premature flowering. However, daylength is short enough to cause premature flowering in most cultivars at a July planting date. Field data supported these predictions. Evaluation of delayed flowering genotypes in photoperiod and field studies showed promise for avoidance of yield losses caused by short‐day induced premature flowering. Temperature photoperiod interaction studies showed that warm temperature (27°C) compared to cold temperature (21°C) decreased the time to first flowering and had its greatest effect under short rather than long days. This effect was greater in Group VI and VII cultivars compared to Group V cultivars.