Development of New Cropping Types, Evaluation of Pod Thickening Characteristic, and Stabilization of Seed Production in Green Soybean Cultivar ‘Niigata Kei 14 Gou’ Bred in Niigata Prefecture

A new cultivar of green soybean, ‘Niigata Kei 14 Gou’, was developed in Niigata Prefecture to meet the demand of earlier supply of “Chamame”, a special group of soybean cultivars that has a pleasant aroma. In order to evaluate a wider range of cropping types for this cultivar, we conducted experiments from sowing in late April to late July to determine the range of possible sowing periods that can ensure a stable yield. The results showed that the yield was only 40% when sown in late July, while yields equivalent to those of the standard cropping type were achieved when sown up to late June. There were no significant differences in plant growth in any of the tested cropping types, indicating that the same cultivation management could be applied through the practical cropping period. It was found that the thickness of pods, which is widely recognized as a reliable indicator in predicting the harvesting time, could be accurately estimated using the cumulative average temperature after flowering for all cropping types. It was also possible to estimate the thickness of pods of the whole plant by measuring only those attached to the uppermost node of the main stem, allowing for quick and efficient measurements in fields. In response to an increasing demand for stable seed production of this cultivar, we showed that the optimal sowing period for obtaining high-quality seeds was from early to mid-August.