Interaction Between Phosphate Solubilizing Bacteria And Rhizobium Of Alfalfa And The Effects Of Their Inoculum On Alfalfa Growth And Quality

Interaction among three phosphobacteria strains and one Rhizobium strain isolated from root nodule of alfalfa (Medicago sativa) and characteristics of antagonism, solubilizing phosphorus property, secreting indole acetic acid (IAA) and salt tolerance were studied in the present paper, and the effects of their inoculum on alfalfa growth and quality were researched as well. The results obtained as follows:1. There was no antagonism among three phosphobacteria strains and one Rhizobium strain.2. The phosphorus-solubilizing ability of bacteria was different with single strain treatments (Jm170, Jm92, Lx191, S7) and strain combination treatments (Jm170+S7, Jm92+S7, Lx191+S7, Jm170+Jm92, Jm170+Jm92+Lx191, Jm170+Jm92+S7, Jm170+Jm92 +Lx191+S7). Available phosphorus content of all the strain combination treatments were significantly increased compared to single strain treatments (P<0.01), and available phosphorus content of treatments, Jm170+S7, Jm92+S7 and Lx191+S7 were higher than the sum of the two strains incubated alone in combination, enhaning 14.71%, 9.72% and 17.06% respectively. In all combination, the total phosphorus content of Jm170+S7, Jm92+S7 and Lx191+S7 was higher than sum of the total phosphorus content of two strains incubated alone in combination, the total phosphorus content of them were enhanced 8.34%, 7.03% and 12.26% respectively compared to sum of the total phosphorus content of two strains incubated alone in combination after each liquid medium supernate boiled.3. pH values of liquid medium supernates were differently influenced by the four strains cultured separately and together, pH values of phosphorus solubilizing bacteria incubated solely were lower than Rhizobium incubated solely. pH values of Jm170+S7, Jm92+S7 and Lx191+S7 were lower than those of two strains cultured solely in combinations. Compared to pH values of strains incubated solely in combinations, the pH values of Jm170+Jm92+S7 and Jm170+Jm92+Lx191+S7 were ascended or debased.4. Effects of the four strains incubated solely and together on total organic acids content of liquid medium supernatants were different, compared to PSB incubated solely, the total organic acids content of Jm170+S7, Jm92+S7 and Lx191+S7 were respectively enhanced 68.77%, 26.4% and 53.01%, but total organic acids content of each combination were lower than sum of organic acids content of each strain in combination.5. IAA concentrations of the four strains were different incubated solely and together. Differences of IAA concentrations of PSB were significant(P<0.01). Except Jm92+S7 by using PC reagent colorimetry. IAA concentrations of Jm170+S7 and Lx191+S7 were significantly enhanced compared to the sum of two strains incubated alone in combinations (P<0.01), moreover, the IAA concentrations of combinations were increased 13.90% and 12.06% respectively. Change tendency of IAA concentrations was similar to that of PC reagent, but IAA concentrations were higher than that of PC reagent by using S2 reagent colorimetry. The IAA concentrations of single strain and mixed strains were different because of existing Tryptophan or not, it indicated that Tryptophan as synthesis precursor played a certain role in the course of IAA secretion.6. Salt-tolerance of single strain and mixed strains were varied. Single strain (Jm170,Jm92,Lx191,S7) and strain combination (Jm170+S7,Jm92+S7,Lx191+S7,Jm170+ Jm92+S7,Jm170+Jm92+Lx191+S7)grew well on the 1%NaCl solid culture medium, they could not grow under 7% NaCl. The growth of various strain and mixed strains were changed under 3% and 5% NaCl. As far as the whole, the salt tolerances of mixed strains were better than that of single strain.7. The inoculum was made with mixture of organic fertilizer and peat by 1:2 proportion as carrier,and the quality of inoculum was tested.The result showed that quantities of aim bacteria in solid single and compound inoculum were over 108/g after storage for 30, 60, 90, 120, 150 or 180 days at room temperature, then it dropped rapidly with contamination. It indicated that the storage expiration of the single and compound inoculum should not more than 6 months.8.The effects of different inoculum applications on the growth of alfalfa were varied. Treatment of compound inoculum +half amount calcium superphosphate fertilizer is the best one, followed by total amount calcium superphosphate fertilizer, single inoculum + half amount calcium superphosphate fertilizer, total amount urea + total amount calcium superphosphate fertilizer.9.Single and compound inoculum could improve the quality of alfalfa to a certain extent, there were no effective differences among single inoculum treatments, but separate treatment in the individual index performed similar to total P fertilizer treatment.There were also no effective differences between compound inoculum treatment and total P fertilizer treatment, but the effects of individual treatments were better than that of total P fertilizer treatment.10.Synthesizing the effects of inoculums on growth and quality of alfalfa, Jm170, Lx191 and S7 were better in the single inoculum treatments .Their effects were inferior to total P fertilizer or better than total P fertilizer, but they had certain growth promoting effect . Jm170+S7, Jm191+S7, Jm170+Jm92+S7 and Jm170+Jm92+Lx191+S7 were bettter in the compound inoculum treatments, the effects of them were similar to total P fertilizer or better than total P fertilizer. It indicated that these compound inoculum treatments in the study could replace total P fertilizer in alfalfa production.