El Niņo-Southern Oscillation Effects on the Yield Difference Between Early and Late Maturity Varieties of Winter Wheat in the Southeastern USA.

The winter wheat growing season in the southeastern USA goes from late fall to late spring, the period when the climate in this region is strongly influenced by El Niño Southern Oscillation (ENSO). The ENSO-based interannual climate variability could influence different responses in growth, maturity, and yield of wheat varieties. This study examined if the yield difference between early and late maturity groups of winter wheat varieties planted in this region is associated with ENSO-based climate. Data on yield and planting and heading dates were obtained for a number of wheat varieties grown at four locations in Georgia during 1975-2012. Wheat varieties were classified according to heading date into early and late maturity groups. The yield differences between maturity groups and among ENSO phases were examined using the Wilcoxon test. Results showed that the effect of ENSO on winter wheat yield could vary depending on whether the variety grown was early- or late-maturity and whether the location planted was northern or southern Georgia. During La Niña, early group outyielded late group in southern locations, but no differences were observed in northern locations. During El Niño, in contrast, differences were observed only in northern locations where late group outyielded early group. Among all ENSO phases, La Niña was associated with the greatest yield across all locations especially for early group. For late group, however, no yield difference among ENSO phases was found at most locations. During El Niño, the yield difference between early and late groups increased with increase in latitude, favoring late maturity as moved toward north. During La Niña, in contrast, the yield difference increased with decrease in latitude. These findings could potentially be helpful to wheat growers of this region in optimizing decisions regarding planting date and variety selection to reduce the risks related to climate variability.