Technical development of nodule formation to enhance nitrogen supply to the maturing stage of soybean seed

通过栽培技术提高固氮活性是提高日本大豆产量的潜在目标之一。在本研究中，我们提出了一种新的栽培技术--“裂缝施肥”。这是一种利用大豆开花期前深松形成的不规则形状的土壤裂缝，并将根瘤菌、肥料和土壤改良剂引入深层土壤的技术。裂隙施肥后3~6周的固氮活性显著增强，根系下部的根瘤数也显著增加。这些结果表明，新开发的裂缝施肥技术有可能控制大豆的结瘤，即结瘤的时间和位置，以及提高固氮活性。

Enhancement of nitrogen fixation activities by a cultivation technique is one of the potential targets to improve soybean yield in Japan. In this study, we proposed a new cultivation technique termed"crack fertilization". It is the technique to utilize the irregularly shaped soil cracks formed by subsoiling just before the flowering stage of soybean, and introduce root nodule bacteria, fertilizers, and soil amendments to the deep subsoil layer. Nitrogen fixation activities at three to six weeks after the crack fertilization were significantly enhanced, and nodule number was also significantly increased at the lower portion of the root system. These results indicated that the soybean nodulation control, i.e. timing and position of nodulation, as well as the enhancement of nitrogen fixation activities were possible by the newly developed crack fertilization technique.