Modifications of Optimum Adaptation Zones for Soybean Maturity Groups in the USA

Soybean cultivars are generally adapted within a narrow north‐south geographical zone for full‐season growth due primarily to photoperiod response. The areas of adaptation were empirically defined more than three decades ago and re‐examination is needed. The accuracy of adaptation area determination can be improved by utilizing updated information, including changes in production practices and new technologies. The objective of this paper was to use current soybean yield data from experiments conducted across soybean producing states in the US to develop optimum zones of adaptation for soybean maturity groups (MGs) in the continental US. Data from state soybean variety trials conducted in 1998‐2003 were obtained from 139 locations, and were used to create regional adaptation map using ArcGIS. The MG 0 cultivars are adapted best to the region north of latitude 46°N, whereas succeeding groups are adapted further south. Each of the MGs 0 to III is adapted best within approximately two degrees latitude covering an area equivalent to 220 km wide from north to south. The zones of adaptation for MGs IV, V, and VI are wider than those for the earlier maturing cultivars. Overall, the regions of adaptation for the early‐maturing cultivars (MG 0 to III) have not changed; however, the adapted zones for MGs IV, V, and VI are much broader than previously thought. Groups VII and VIII, which dominated production areas in the South decades ago are now planted on a limited basis.