Dynamics in elongation and dry weight of internodes in sweet sorghum plants

Sweet sorghum (Sorghum bicolor (L.) Moench) has been recognized as a potential energy crop due to high dry biomass yield and sugar content in its stems, which are composed of nodes and internodes. In this study, a field experiment with middle and late maturity types was conducted to investigate dynamics in length and diameter, elongation, and dry weight of elongated internodes (EIs) in sweet sorghum plants. The EI thermal time duration varied from 151.5 to 399.7 growing degree days (GDD) for the two cultivars in the two years. Simple linear regression models were developed to describe the relationship between node and EI numbers (correlation coefficient (R ²)=0.93**, root mean square error (RMSE)=0.80), and between the dry mass content per unit length (DML) and EI order (R ²=0.90**, RMSE=0.11gcm ^-1). The stem dry weight on the maturity date was simulated as the sum of the products of the DML and the maximal length of all EIs (R ²=0.84**, RMSE=9.0). The change in thermal time of an internode elongation start with the EI order was simulated using the cubic equation (R ²=0.97**, RMSE=0.019). A revised logistic equation was used to simulate the dynamics in the internode elongation with GDD after the EI divided into five groups (EIG) (R ² varied between 0.93** and 0.98**; RMSE between 0.28cm and 1.45cm). The models validation exhibited highly significant correlation coefficients between observed and simulated values for all the developed models. The findings will afford insight into growth and development and will facilitate the construction of an integrated sweet sorghum model.