Presence of Bradyrhizobium sp. under Continental Conditions in Central Europe

Abstract

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.

Effects of <em>Bradyrhizobium japonicum</em> on Nitrogen Content in Soybean Leaves and Seeds Cultivated on Acidic Soils

“…However, the results found by Zamukulu et al (2018) in South Kivu in DR Congo and Ahmed et al (2006) in Pakistan found that yield and nodulation increased with increasing doses of mineral nitrogen fertilizer indicating a positive relationship between soil N and nodulation. The difference observed between our results and those obtained by certain authors such as Voisin et al (2013) and Griebsch et al (2020), could be explained by the fact that these different studies were described under different conditions. Indeed, Mendes et al (2003) report that the soybean response to nitrogen depends on several factors such as the efficiency of the Bradyrhizobium strain, the soybean variety and the initial soil nitrogen in the event of nitrogen supply in the form of mineral fertilizer.…”

“…For soil N at site 1 and 2, it correlated positively with yield and number of nodules (P <0.05). These results seem to be in contradiction with those found in Europe by Griebsch et al (2020) who found no relationships between N supplied alone as inorganic fertilizer on nodulation and yield except when supplied in combination with P. Furthermore, Voisin et al (2013) found that N supplied as mineral fertilizer slowed down nodulation and a lower yield than the control. However, the results found by Zamukulu et al (2018) in South Kivu in DR Congo and Ahmed et al (2006) in Pakistan found that yield and nodulation increased with increasing doses of mineral nitrogen fertilizer indicating a positive relationship between soil N and nodulation.…”

“…The studies by Kosslak and Bohlool (1985) and Lawson et al (1995) report that nodule formation decreases with decreasing pH. More recently, in a study conducted in Germany and Poland by Griebsch et al (2020), it was proved that pH significantly affected the relative abundance of Bradyrhizobium sp and this is attested by Albareda et al (2009) and Gazdag et al (2015) who report that Bradyrhizobium sp prefer soil with neutral or slightly acidic pH. All of these studies, like many others, evaluated the influence of soil acidity on the nodulation and abundance of Bradyrhizobium sp.…”

Does a Soybean Intercrop Increase Nodule Number, N Uptake and Grain Yield of the Followed Main Crop Soybean?

“…It had been already shown that Bradyrhizobium japonicum is able to survive for a long time under Central European soil and climatic conditions [13,34,35]. Madrzak et al, (1995) and our own preparatory work also demonstrated that rhizobia were present in Central Europe, even though soybeans have not been grown before [12,36]. Further, Narozna et al, (2015) and McDermott and Graham (1989) demonstrated that Bradyrhizobia have low mobility in soil [13,37].…”

“…In this context, various preparations are available on the market, in liquid or powder form, as well as the already fully inoculated seed. Various studies have already demonstrated the presence of soybean-specific bacteria after a long time in Central European soils where seed inoculated soybean had been cultivated many years before [11][12][13]. Previous reports have indicated a strong to moderate correlation between intensity of nodulation and the associated nitrogen fixation and, thus, a higher grain yield or grain N content [14,15].…”