Thiram produces effects in between these two groups. Planter box treatments using dry materials or auger treatments with liquids, fresh or frozen materials are both acceptable if they give good coverage of all seed. Competition is possible from native strains of Rhizobium bacteria which are less efficient than commercial inoculum. Nodules from initial inoculation tend to be located on the main top root near the surface, while native strains tend to grow on the branches away from the seed zone. Native strains also siphon off nutrients from the host, lowering the N-fixing ability of more efficient strains.
Native strains are sometimes much better at infecting roots and can limit inoculation effectiveness.
It is important to inoculate with the best strains whenever soybeans are planted, especially the first time, or in long rotations. However, because of competition from aggressive strains, the effectiveness of the inoculated strains will be reduced. In the central US soybean belt, it is uncommon for soybeans to respond to pre-plant fertilizer N applications. However, North Dakota soybeans are grown in a very different soil environment. Research at NDSU has shown that as soil salt and carbonate levels increase, nodule infection is reduced.