Abstract
Enhancement of nitrogen fixation activities by a cultivation technique is one of the potential targets to improve soybean yield in Japan. A cultivation technique named “crack fertilization” is described and the nodulation control by this technique is analyzed by experiments in two fields with different soil and environmental conditions, and a root box experiment. Crack fertilization is a technique that utilizes the irregularly shaped soil cracks formed by subsoiling just before the flowering stage of soybean, and introduces root nodule bacteria, fertilizers, and so on to the deep subsoil layer. Production of ureide-form nitrogen at six weeks after the crack fertilization (only nodule bacteria application to the subsoil layer) was 1.4 times higher than the control in the Hikone field. Acetylene reduction activity at four or eight weeks after the crack fertilization (application of both nodule bacteria and low level of fertilizer to the subsoil layer) tended to be higher than in the control in both fields. In the root box experiment, nodule number was four times higher than that in the control at the lower portion of the root system, where modified crack fertilization treatment was conducted, and the acetylene reduction activity was increased significantly by the treatment. These results indicated that the soybean nodulation control, i.e., timing and position of nodulation, as well as the enhancement of nitrogen fixation activity could be achieved by this crack fertilization technique.
