TRANSPLANTATION AS A SOYBEAN FIELD TECHNIQUE TO MODIFY ROOT NODULE OCCUPANCY

Field studies of symbiotic interactions between soybean (Glycine max [L.] Merr.) and Bradyrhizobium japonicum (Kirch.) Jordon are often limited by an inability of specific inocula to compete successfully with indigenous bradyrhizobia for root nodule sites. The objective of this note is to describe and evaluate a transplantation technique for modifying soybean root nodule occupancy under field conditions. Pre-nodulated seedlings were prepared under greenhouse conditions in containers designed for the generation of transplants. The inoculation procedures used ensured that all nodules initiated prior to transplanting contained only selected strains of B. japonicum. The seedlings were transplanted to field microplots when approximately 3 wk old and subsequently allowed to develop normally. The transplanted seedlings exhibited high rates of survival and excellent yield potentials. Control of nodule occupancy on tap roots and adjoining portions of major lateral roots was nearly complete for several weeks after transplanting.