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)

Abstract

Four isolates of Phosphate-Solubilizing Bacteria (PSB) (Pseudomonas cepacia, Xanthomonas maltophilia, Enterobacter cloacae and Acidovorans delafieldii, formerly called P. delafieldii) and 4 of Azotobacter chroococcum, isolated from previous studies (Martínez, A and Moreno, A, 1996; Cuenca, D and González, A, 1996) were chosen. These strains did not show antagonism among themselves, when tested in vitro 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 test where seeds of “creole” potato (Solanum phureja) var. ‘Yema de Huevo’, were planted in a field plot with 15 beds (1.20 m x 25 m each) divided into 5 treatments with 3 replications each (T1: negative control – water only; T2: NPK 10:30:10 100%; T3: NPK 10:30:10 50% + 20 L/Ha of the dual inoculum; T4: 20 L/Ha of the dual inoculum and T5: NPK 10:30:10 50%). One hundred twenty days later, statistical analyses showed that as for stem height, root dry weight, 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 a Tukey test, it was possible to determine that with chemical fertilization, with or without dual inoculum, stem height, plant fresh weight, fresh weight of leaves and tubers, the results were significantly greater than with the other treatments. Root dry weight and the soil available N showed better results with the inoculation of 50% of the inoculum + 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 crop production (Ton/Ha) of “creole” potato, at a level matching that of potato fields fertilized with 100% NPK only. At the same time, this will contribute to reduction of costs (in nearly 7.4%), representing favorable economical and environmental implications.