Influence of bio-inoculants (earthworms and nitrogen-fixing bacteria) on rhizosphere microflora of alfalfa

Kostadinka Nedyalkova, Galina Petkova, Hristo Valchovski, Radka Donkova

Abstract: The impact of bio-inoculants on soil environment is insufficiently studied in our country. The present work is based on a pioneer investigation on earthworm inoculation in Chromic-Vertic Luvisol in pot experiment with alfalfa. In addition to the main subject, we aimed to study the influence of inoculation with the three main ecological groups of Lumbricidae and with nitrogen-fixing bacteria on rhizosphere microflora of alfalfa. Single inoculations with endogeic, anecic and epigeic earthworms, and with the symbiotic nitrogen-fixing bacteria Rhizobium meliloti strain 116 were performed. Mixed inoculation with endogeic, anecic and epigeic individuals, and another with endogeic, anecic and
epigeic earthworms+ Rhizobium meliloti 116 were also set. Analyses of rhizosphere soil were made at the beginning of the experiment (first alfalfa cut) and at the end (fourth alfalfa cut). Microbial counts were presented as CFU/g soil. It was found that bio-inoculants had markedly positive effect on the amount of heterotrophic bacteria at the beginning, as well as at the end of the experiment. Inoculation impact on the amount of actinomycetes, microscopic fungi and cellulolytic microorganisms in the investigated stages was characterized by specificity but, in general, a decreasing trend prevailed. Amongst the single earthworm inoculations, endogeic earthworms showed significantly positive effect on most microbial groups (heterotrophic bacteria, microscopic fungi and cellulolytic
microorganisms). Both mixed inoculations increased basal soil respiration at the end of the experiment.

Keywords: alfalfa; earthworms; inoculation; Rhizobium meliloti; soil microflora

Date published: 2019-04-09