Evaluation of the effect of a dual inoculum of phosphate-solubilizing bacteria and Azotobacter chroococcum, in crops of creole potato (papa “criolla”), “yema de huevo” variety (Solanum phureja)

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Abstract

Four isolates of PSB (Pseudomonas cepacia, Xanthomona maltophilia, Enterobacter cloacae and Acidovorans delafieldii, formerly called P. delafieldii) and four strains of Azotobacter chroococcum, isolated in a previous work were chosen. They did not show antagonism among themselves, by means of in vitro tests made on GISA medium (PSB-Azotobacter modified medium). A dual inoculum was made with the 8 isolates in 4.6 L of sterile GISA broth, which was under continuous air flow. This dual inoculum was taken to a field sample where seeds of “criolla” potato, yema de huevo variety (Solanum phureja) were cultivated. After120 days from inoculation, statistical analyses showed that as for stem height, dry weight of the root, number of tubers and soil available phosphorus, there were significant differences among the various treatments. As for all other variables, there were no observable differences among them. With the a posteriori test of Tukey, it was possible to determine that with chemical fertilization — with or without dual inoculum, — the stem height, the fresh weight of plants, fresh weight of leaves and tubers, the results were significantly greater than with the other treatments. The dry weight of roots, and the soil available N, showed better results with the inoculation of 50% of the inoculum plus 50% of chemical fertilizer. The number of tubers showed better results with 100% of fertilizer. A dual inoculum of PSB and Azotobacter chroococcum like the one used in this research, will maintain production (ton/ha) of “criolla” potato, Yema de Huevo variety (Solanum phureja), at a level matching that of crops with 100% NPK fertilization only, and at the same time, will contribute to the reduction of costs (in nearly 7.4%), a fact that represents favorable implications at both, economical and environmental levels.