Symbiotic activity and productivity of soybean in the Western Forest Steppe
Authors: Kozyrskyi D. V. , Sydorak I. Ya. 
Published: December 2024

Purpose. To determine the effect of seed inoculation and foliar application of fertilisers on the growth and development of soybean.
Methods. Field research was carried out in 2019–2021 in the fields of the Kozatska Dolyna 2006 LLC (Khmelnytskyi Region). Experiments were carried out according to the following design: factor A: inoculation of seeds: 1) without inoculation, 2) inoculation with the biopreparation Rizoactive; factor B: foliar feeding: 1) without foliar feeding, 2) foliar feeding with Fulvohumin; factor C: soybean varieties: 'Samorodok' (control), 'Rohiznianka', 'Triada', 'Orfei', 'Evridika', 'Aratta', 'Azymut', and 'Avrora'.
Results. Foliar application of Fulvohumin contributed to obtaining 4.09 more nodules per plant. At the same time, inoculation with Bradyrhizobium japonicum strains eko/001, eko/002, and eko/003 contributed to an increase in the number of nodules by 8.35 (29.5 nodules per plant in the control treatment). That is, in areas where soybean is grown quite often, a certain indigenous type of microorganisms is supported in the soil, capable of inoculating plants during soybean cultivation; however, the use of pure, dedicated strains of microorganisms is a more effective way of increasing the efficiency of symbiotic interactions. In the case of seed inoculation with Rizoactive and foliar application of Fulvohumin, the best conditions for the formation of nodules were formed by varieties 'Azymut' (1.30 g/plant), 'Orfei' (1.31 g/plant), and 'Rohiznianka' (1.32 g/plant). Therefore, the improvement of the physiological state of plants with foliar application of Fulvohumin contributed to a general increase in the weight of nodules by 0.20 g/plant. However, inoculation with strains of Bradyrhizobium japonicum eko/001, eko/002 and eko/003 was more effective, because, due to the displacement of indigenous strains of microorganisms an increase in the weight of nodules of 0.36 g/plant was obtained. Based on the analysis of the factors of influence, it was determined that seed inoculation is a driver of changes in the number of colonies of active nodule bacteria on soybean roots (50%), even under the strong influence of the weather conditions of the growing season (33%). The importance of inoculation in the beginning of photosynthesis with the use of Bradyrhizobium japonicum strains eko/001, eko/002 and eko/003 is obvious. The mass of active nodules on plant roots is even more dependent on seed inoculation (57%), which supports the assumption that local native species are not able to cooperate with soybean plants as effectively as specially selected strains of nodule bacteria. On average, according to the experiment, the yield of soybean seeds in 2019 was 3.41 t/ha, in 2020, it was 3.10, in 2021, it was 3.92, and in 2022, it was 3.20 t/ha. The all-year leader in grain yield was the 'Aurora' variety. However, in 2019, 'Triada' showed good results, in 2020 – 'Azymut' and 'Triada', in 2021 – 'Triada', and in 2022 – 'Orfei', 'Azymut' and 'Triada' showed good results. This indicates the individual varietal response to growing conditions and the importance of technology adaptation for certain varieties and their in-depth verification in the area of ​​distribution regarding the possibility of forming a high yield level.
Conclusions. The correct choice of mineral nutrition for soybean provided general stimulation of plant development and the subsequent formation of the legume-rhizobial relationship and its functioning from the point of view of assimilation of nitrogen from the atmosphere. This emphasises the role of small doses of starter nitrogen fertilisers from the standpoint of better crop development, especially when combined with foliar feeding of plants during the growing season. Even with the maximum need of plants for nutrients at the time of the formation of beans and seeds, and filling grain, their good start at the beginning of the growing season provided an advantage due to better rooting, development, and work of the leguminous rhizobial apparatus, etc. And therefore, against the background of the main fertilizer N30Р60K60, foliar application of Fulvohumin in combination with soybean seed inoculation contributed to the formation of a high level of productivity. All varieties increased their productivity in these treatments: 3.70 t/ha in 'Evridika', 3.76 t/ha in 'Aratta', and 4.02 t/ha in 'Orfei', while the highest indicators over the years of research were recorded in 'Azymut' (4.11 t/ha), ‘Triada’ (4.12 t/ha), and ‘Avrora’ (4.16 t/ha).