Effects of Coated Fertilizer Application on Seed Protein Content of the Soybean Variety ‘Tsukuizairai’

Abstract

The lower seed protein content of soybean variety ‘Tsukuizairai’ is a defect in tofu processing. This study aimed to determine the possibility of increasing the seed protein content of ‘Tsukuizairai’ via applying a coated nitrogen fertilizer to provide nitrogen. In experiment 1, the type of coated fertilizer for increasing the highest seed protein content was investigated by using coated fertilizers with different nitrogen leaching times. Four plots, the control, 40-day plot, 60-day plot, and 80-day plot were prepared in this experiment. The control was applied only basal dressing (N:P₂O₅:K₂O=3:10:10 g m^-2), and the 40-day plot, 60-day plot, and 80-day plot were applied basal dressing and coated fertilizer, LP coat S40, S60 and S80, respectively. The amount of applied nitrogen of coated fertilizer was 10 g m^-2 in all plots. In this experiment, the above-ground growth and seed yield did not differ significantly with the plot.However, the seed protein content could be increased from 35.0% to 39.7-40.6% to the same level as those of ‘Enrei’ and ‘Tachinagaha’ in all coated fertilizer plots. In experiment 2, to investigate the quality of coated fertilizer to increase seed protein content, we prepared a control, 3 g plot, and 5 g plot, which were applied 0, 3 and 5 g m^-2 nitrogen in coated fertilizer, respectively. In this experiment, the protein content of ‘Tsukuizairai’ could be increased to the same level as that of ‘Tachinagaha’ by applying either 3 g or 5 g nitrogen per m². These results suggest that the application of a coated fertilizer can increase the protein content of ‘Tsukuizairai’ and improve its suitability for tofu processing.