Crossing latitude introduction delayed flowering and facilitated dry matter accumulation of soybean as a forage crop

Grain soybean (Glycine max (L.) Merr.) shows potential as a forage crop following its introduction from low to high latitudes due to in its growth phenotype. However, the application of this approach is impeded by the diverse ecological types of soybean, their adaptability to the introduction, and the uncertainty surrounding the growth phenotype post-introduction. This study introduced 24 grain soybean varieties from low-latitude regions (22–31°N) to the high-latitude northwestern Loess Plateau (39°N) between 2018 and 2019. The growth phenotypes were observed, and their forage productivity potential was assessed. All varieties displayed delayed flowering following cross-latitude introduction, with the vegetative growth phase of some varieties even exceeding their entire growth duration at their origin. Rapid dry matter accumulation rates indicated growth adaptation performance and formed the basis for soybean forage yield. Varieties from the tropical South China region exhibited significant yield advantages, with dry matter yields of 8.97–14.68 t ha^–1 and crude protein yields of 1.44–2.51 t ha^–1. Varieties HX3 and GX7 from this region demonstrated optimal growth adaptability and productivity in the cross-latitude environment, achieving the highest dry matter yields of 14.68 and 13.86 t ha^–1, respectively. As a result, HX3 and GX7 are recommended for local farming systems to provide high-quality forage. The cross-latitude introduction of soybean is proposed as a viable and efficient strategy for forage improvement and application.