Effect of Azotobacter salinestris on soil microbiological parameters and cucumber yield in integrated and organic farming systems

The aim of this study was to evaluate the effect of Azotobacter salinestris bacteria applied in the form of Rhizosum N plus preparation on the yield of cucumber cv. Gala F1 grown in organic and integrated systems. In addition, the effect of this preparation on soil microbiological parameters – Pseudomonas spp. and Azotobacter spp. number, dehydrogenases activity, biodiversity (Shannon coefficient) and microbial activity (AWCD) analyzed by BIOLOG tests – were studied.

In both cropping systems, the experiment included three treatments: control (full nitrogen fertilization); half dose of nitrogen fertilization; Rhizosum N plus preparation + half dose of nitrogen fertilization. The Rhizosum N plus formulation was applied at a rate of 25 g/ha as a spray on plants at the stage of 2–4 proper leaves. Cucumbers were harvested and segregated into the following fractions: canned, pickling and overgrown. Soil microbiological analyses and leaf analyses for Azotobacter spp. abundance were performed in three terms.

It was found that the abundance of Azotobacter spp. bacteria on cucumber leaves increased after spraying with Rhizosum N plus. The bacteria maintained a high abundance at least until 14 days after application. The preparation Rhizosum N plus had a slight effect on the increase of Pseudomonas bacteria number in the soil. No changes were found in dehydrogenases activity or in the biodiversity and functional activity of microorganisms in the soil in the treated combinations. In both cultivation systems, it was shown that the application of Rhizosum N plus had a positive effect on the yield of cucumbers. First of all, it accelerated fruit setting, which resulted in a higher yield at the first harvest. In addition, a positive effect on pickling and canning fractions was observed – a higher yield was obtained in the treatment with Rhizosum N plus + 1/2 N than in the “1/2 N fertilization” treatment.

These findings show that foliar spraying of Azotobacter salinestris in cucumber cultivation could be a sustainable way to promote plant growth and improve soil microbiological diversity.