## 3 Results
(**A**)—Total number of heterotrophic bacteria, (**B**)—The number of molds, (**C**)—The number of Actinobacteria; 1—control variant (without undersown crops, without PGPR), 2—red clover catch crop, 3—red clover and Italian ryegrass catch crop, 4—Italian ryegrass catch crop, 5—control variant (without undersown catch crops) + PGPR, 6—red clover catch crop + PGPR, 7—red clover catch crop + Italian ryegrass + PGPR, 8—Italian ryegrass catch crop + PGPR. Although the count of this group of microorganisms varied considerably in individual years of the experiment, it always increased significantly after the application of PGPR (_Bacillus subtilis_, _Bacillus amyloliquefaciens_, _Pseudomonas fluorescens_), i.e., in variants 5-8. In 2019, the greatest count of these microorganisms was observed after the application of the PGPR together with the catch crops (red clover and Italian ryegrass--variant 7). In 2021, the greatest count was noted after the application of the PGPR only (variant 5), whereas in 2020--after the application of the PGPR together with the Italian ryegrass catch crop (variant 8)--the counts of these microorganisms in the aforementioned variants were, respectively, 197%, 67%, and 97% greater than the count in the control variant. Like the total bacterial count, the count of molds in the soil under the spring barley also varied and depended on the applied treatments. In the first year of the experiment their count was greater in the variants in which both the catch crops and PGPR had been applied (Figure 1B). In 2020 and 2021, there were significantly greater counts of molds than in the control variant when only the catch crops had been applied. On the other hand, when the PGPR inoculants were applied alone (variant 5), they reduced the count of molds significantly (Figure 1B). The chart shows the counts of actinobacteria in individual years of the experiment. In 2020, their count was high--it ranged from 350 to 450 cfu 104 g\({}^{-1}\) dm soil (Figure 1C). In 2019, their count was lower--it ranged from 50 to 137 cfu 104 g\({}^{-1}\) dm soil. During the three years of the experiment the count of actinobacteria in variants 5-8 was significantly lower than in the control variant as well as in the variants where the PGPR consortium had been applied alone or in combination with the catch crops. In 2019, the lowest count of actinobacteria was observed in variant 7, where the catch crops of red clover and Italian ryegrass had been combined with the bacterial consortium. In 2020, the lowest count of actinobacteria was found in variant 5, where the bacterial inoculant had been applied alone. In 2021, the lowest count of actinobacteria was noted in variant 8, where the catch crop of ryegrass had been combined with the PGPR (Figure 1C). The analysis of the biochemical activity of the soil (the activity of dehydrogenases, acid phosphatase, and catalase) and the biological index of fertility (BIF) showed that these biological parameters were significantly higher in 2019 than in 2020 and 2021 (Figure 2). In 2019, the activity of dehydrogenases in the soil under barley ranged from 0.0143 umol TPF g\({}^{-1}\) dm soil:24 h\({}^{-1}\) to 0.1378 umol TPF g\({}^{-1}\) dm soil:24 h\({}^{-1}\). In 2020, the activity of this enzyme was much lower--it ranged from 0.0014 to 0.0072 umol TPF g\({}^{-1}\) dm soil:24 h\({}^{-1}\) (Figure 2A). The analysis of the dehydrogenase activity showed that in 2019 and 2021 it tended to increase in the variants where the catch crops had been applied simultaneously with the PGPR. In those years the highest metabolic activity of the enzyme was observed in variant 7, where red clover and Italian ryegrass had been applied in combination with the PGPR. The acid phosphatase activity in the soil under spring barley was similar to the dehydrogenase activity.