Presence of Bradyrhizobium sp. under Continental Conditions in Central Europe

Soil samples from different locations with varied soybean cultivation histories were taken from arable fields in 2018 in East Germany and Poland (Lower Silesia) to evaluate the specific microsymbionts of the soybean, Bradyrhizobium japonicum, one to seven years after inoculation. Soybeans were grown in the selected farms between 2011 and 2017. The aim of the experiment was to investigate whether there is a difference in rhizobia contents in soils in which soybeans have been recultivated after one to seven years break, and whether this could lead to differences in soybean plant growth. The obtained soil samples were directly transferred into containers, then sterilized soybean seeds were sown into pots in the greenhouse. After 94 days of growth, the plants were harvested and various parameters such as the nodular mass, number of nodules, and dry matter in the individual plant parts were determined. In addition, the relative abundances of Bradyrhizobium sp. in soil samples were identified by sequencing. No major decline in Bradyrhizobium sp. concentration could be observed due to a longer interruption of soybean cultivation. Soil properties such as pH, P, and Mg contents did not show a significant influence on the nodule mass or number, but seem to have an influence on the relative abundance of Bradyrhizobium sp. The investigations have shown that Bradyrhizobium japonicum persists in arable soils even under Central European site conditions and enters into an effective symbiosis with soybeans for up to seven years.