Effect of inoculation of soybean seeds with Bradyrhizobium japonicum on plant development, nodulation and seed yield under conditions of Central North Bulgaria

Soybean is a crop with a great importance, as a source of vegetable protein and oils. In a period of three consecutive years 2018-2020, the plant growth, nodulation capacity and yield parameters of ten selected soybean cultivars were monitored under the field conditions of Central North Bulgaria, the region of town Pavlikeni. The widely established agrotechnology of crop-ping soybean in Bulgaria was applied in combination, with additional inoculation of seeds with Bradyrhizobium japonicum before sowing. Selected elite Bulgarian cultivars from different maturity groups with high income for the Bulgarian agriculture were tested together, with three foreign cultivars, which are part of the recent soybean breeding program. The aim is to study the respond of morphological parameters related to the plant growth, nodulation and yield to additional Rhizobium inoculation for each cultivar. The results demonstrated that cultivars Rosa and Srebrina expressed better capacity to produce seeds (respec-tively, 189 and 205 seeds per plant after inoculation, vs 135 and 150 from control plants), as a result of better development of branches, fruiting nods and pods in the condition of additional inoculation. Better nodulation was demonstrated by foreign cul-tivars Romantica, Atlanta and Saikai in comparison with the Bulgarian cultivars adapted to the soil microbiota. The cultivars Avigeya, Daniela and Pavlikeni seed inoculation before sowing supports the overcoming critical climatic conditions. These results provide a base to promote these cultivars to Bulgarian farmers, intended to produced soybean especially in a regions without soybean history.