The effect of inoculation with Azospirillum brasilense strain 410 on spring barley cv. nosivsky development and yield

Aim. To study the efficiency of inoculating spring barley with Azospirillum brasilense 410. Methods. 1) A field ex- periment on turfpodzolic sandy soil with different mineral fertilization regimes; 2) A greenhouse experiment on sand as substrate, with isotope dilution analysis using 15N; 3) A lysimetric experiment in a stationary lysimetric installation. Furthermore, chromatography to determine nitrogenase activity of bacteria in the root zone of plants, agrochemical, and statistical methods. Results. Under field conditions, the inoculation with A. brasilense 410 promoted a significant increase (37–103 %) in the nitrogenase activity in the “soil-plant” system without any mineral fertilization and (espe- cially) where N60P60K60 was used. A high fertilizer level (N120P120K120) lead to a long-term inhibition of the nitrogenase activity. In both cases (plants with and without inoculation with A. brasilense 410) this fertilization level showed an increase in the nitrogenase activity only at the end of the vegetation period. The highest increase in yield (0.7 t/ha, 27 %) in yield following A. brasilense strain 410 inoculation, occurred in plots with N60P60K60 fertilization; the least increase in yield (0.33 t/ha, 16.5 %) was observed in plots receiving no fertilizers. The pre-sowing inoculation led to an increase in the protein content of 0.3–1.0 % in the barley grain, especially when receiving high fertilization levels, enhancing its value for the use in cereals and feeds, but decreasing its value for its use in brewing. The green- house experiment with 15N established an increase 77.1 % in the nitrogen intake into the plants due to the activation of the nitrogen-fixation process and enhanced 29.5 % nitrogen consumption from fertilizers. The lysimetric studies demonstrated that inoculation of spring barley cv Nosivsky with A. brasilense 410 limited the vertical migration and leaching of nitrogen by 27–30 %, potassium by 13–30, calcium by 32–51 %, manganese by 33–100 %, and water-sol- uble organic matter by 46–75 %. Conclusions. The pre-sowing inoculation of spring barley cv. Nosivsky seeds with A. brasilense 410 intensifies nitrogen consumption by plants within 29.5 % due to active nitrogen-fixation and a better utilization of N from mineral fertilizers. The barley yield increase with 0.7 t/ha was in our limited experiment, using one cultivar roughly equivalent to the increase after mineral fertilization with N60P60K60. Thus, pre-sowing inoculation with A. brasilense 410 may lead to substantial reduction of the use of mineral fertilisers in practice.