Impact assessment of main stem elongation and wind speed on lodging of soybean cultivar ‘Miyagishirome’

As soybean lodging leads to yield losses, predicting the occurrence of lodging is an important measure. Lodging is affected by main stem length and weather factors. However, the effect of main stem elongation between growth stages on lodging is unknown. The objective of this study was to analyze the effects of main stem elongation and weather factors on lodging and to present a simplified lodging model for the establishment of future lodging prediction methods. Data obtained in 2018, 2020, and 2021 in experimental plots with different cultivation management (n = 32) were used. The test cultivar was ‘Miyagishirome’, a major cultivar in Miyagi Prefecture with a tendency to lodging. The lodging angle was measured at the beginning pod stage (R3) and the full maturity stage (R8); lodging at R3 was classified as ‘Early lodging’ and at R8 as ‘Late lodging’. Multiple regression analysis for Early lodging showed that main stem length was not significant, only wind speed was significant at the 0.1% level. For Late lodging, the effect of main stem elongation from the sixth leaf stage (V6) to the blooming stage (R1) was significant, producing the highest R2 value (0.81) for the multiple regression model. This model included the full seed stage (R6) main stem length and wind speed as an explanatory variable. The results indicated that Early lodging was strongly influenced by wind speed, whereas Late lodging was strongly influenced by main stem elongation (especially from V6 to R1):. Early lodging is difficult to predict but Late lodging is predictable from main stem elongation after V6.