Variety-Specific Soybean Yield with Respect to Nitrogen-Fixing Symbiosis on the Northern Boundary of the Crop’s Geographical Range

Abstract

The effects of inoculating nitrogen-fixing symbionts on soybean yield were tested in the experimental field of the Krasnoyarsk State Agrarian University, 50 km north of Krasnoyarsk. Strain 634 was tested in 2017–2018 on the Zaryanitsa variety. Strain 634 and Spontaneous, discovered in Krasnoyarsk forest steppes, were tested in 2019 on the precocious Zaryanitsa and Eos varieties (Siberian ecotype). Treating Zaryanitsa soybean with Strain 634 induced a yield of 0.197 kg/m2 compared to the control yield of 0.167 kg/m2 (p = 0.037). The number of nodules peaked in Zaryanitsa inoculated with the biological Spontaneous: 104 nodules per root. Spontaneous reduced the height of Zaryanitsa plants (p = 0.0606) but increased the seed weight (p = 0.0282). Eos was inoculated with two strains; compared to the controls, it had lower productivity metrics such as the number of branches (p = 0.0771), beans (p = 0.0483), seeds (p = 0.0142), and seed weight (p = 0.0381). However, the preservation rates were 16% higher in case of Strain 634, 22% in case of Spontaneous. Factor analysis (varimax rotation) identified two factors: one comprised the indicators related to the development of photosynthesis organs (the number, weight, and area of leaves) and to nodulation (the number, weight, and moisture of nodules). The other one comprised the yield structure components and the number of plants per unit of area. Eos yield rose by 0.02 kg/m2 and 0.048 kg/m2 when inoculated with Strain 634 and Spontaneous, respectively.