The effect of inoculation with Azotobacter chroococcum on microorganisms in rhizosphere and sugar beet yield in organic farming

Abstract

The effect on sugar beet yield parameters and microbiological soil sta­tus was studied using two techniques of sugar beet inoculation with strains of Azotobacter chroococcum. Cultivar 'Drena' was used in the study, and field trial was set under the conditions of organic farming system in Bački Petrovac. A mixture of three strains of Azotobacter chroococcum was used as microbial fertilizer. Inoculation was performed by: (A) incorporation of strains into soil before sowing; and (B) repeated incorporation of strains into soil two weeks after sowing. PGP characterization of the strains confirmed the ability of producing indole-3-acetic acid (IAA) from 12.63 μg ml-1 to 14.95 μg ml-1, nitrogen fixation, and P-solubilization. Positive effects on the number of azotobacter and free nitrogen fixers in rhizosphere were obtained by inoculation, as well as positive effects on the tested sugar beet yield parameters. The largest increase in root yield, yield of crystal sugar, and yield of polarised sugar compared with the control was obtained by repeated soil inoculation, ranging from 22 to 23%.

Ispitan je efekat dva načina inokulacije šećerne repe sa sojevima Azotobacter chroococcum na parametre prinosa šećerne repe i mikrobiološki status zemljišta. U ispitivanjima je korišćena sorta Drena, a eksperiment je postavljen u sistemu organske proizvodnje u Bačkom Petrovcu. Kao mikrobiološko đubrivo korišćena je smeša tri soja Azotobacter chroococcum. Inokulacija je izvršena na dva načina: (A) inkorporacija sojeva u zemljište pre setve, (B) ponovljena inkorporacija sojeva u zemljište dve nedelje nakon setve. PGP karakterizacijom korišćenih sojeva utvrđena je sposobnost produkcije indol-3-sirćetne kiseline (IAA) od 12.63 μg ml-1do 14.95 μg ml-1, azotofiksacije i fosfosolubilizacije. Inokulacijom je dobijen pozitivan efekat na broj azotobaktera i slobodnih azotofiksatora u rizosferi, kao i na ispitivane parametre prinosa šećerne repe. Najveće povećanje prinosa korena, prinosa kristalnog i polarizacionog šećera dobijeno je na varijanti ponovljene inokulacije zemljišta i kretalo se od 22 do 23% u odnosu na kontrolnu varijantu.