Effect of silicon fertilizer treatment on nodule formation and yield in soybean (Glycine max L.)

Silicon application (Si) is considered beneficial for plant growth and development in both monocotyledons and dicotyledons, however its effect on root development and nodule formation in soybean is poorly understood. For this reason, we examined the effects of Si application on soybean (Glycine max L.) growth and its yield in field conditions. On 4 m × 5 m plots, we applied 0.08 kg/m² of commercial Si fertilizer incorporated into the soil at the time of planting and 2.0 mM of sodium metasilicate for foliar spraying when the plants reached V5 growth stage. Then, we measured various parameters of shoot and root morphology of the soybean plants during 2018 and 2019. In particular, image-based machine learning method was conducted to identify nodule formation. On Si application to the soil and leaves, we found an increase in nodule number and nodule size over the two years. Furthermore, root morphological traits were significantly changed in Si-treated soybean plants compared to control plants, including the root projected area, average root diameter, and average root link diameter. In the shoots, the net photosynthesis (P_N), transpiration rate (E), and stomatal conductance (g_s) were also higher in Si-treated soybean plants than control plants. Finally, the yields of the Si-treated soybean plants were 21 % and 19 % higher in 2018 and 2019, respectively, than the control plants. Therefore, the improved photosynthesis and root morphological traits resulting from Si application led to an increased yield in soybean.