Vesicular arbuscular mycorrhizae (V AM), the symbiotic root infecting fungi, are Known to increase crop growth and yield through enhanced nutrient uptake. These fungi are of particular interest in soil microbial interactions, since they actively affect the composition of microbial populations and are in turn influenced by them in the context of mycorrhiza formation and function. Furthermore, such selective' interactions between establishment of microorganisms and VAM fungal species is reflected in plant growth and nutrient uptake. In the present study the test crop species mungbean [Vigna radiate (L.) Wilczek] was inoculated in different combinations with two species of VAM fungi namely Glomus mosseae (Nicol. and Gerd) Gerd and Trappe and G. fasciculatum (Thexter sensu Gerd.) Gerd. and Trappe; two strains of root nodulating symbiotic nitrogen fixing bacteria viz. Bradyrhizobium japonicum TAL.-102 and n. japonicum MN-S; and EM (Effective microorganisms), a mixture of 80 species of coexisting beneficial microorganisms. These microbial interactions were studied under various regimes of organic and inorganic soil amendment viz. farmyard manure (FYM), green manure (GM), and half (1/2 NPK) and full (NPK) doses of chemical fertilizers. Two harvest at 40 and 75 days intervals after sowing were scheduled corresponding with flowering and maturity stages, respectively. The functional compatibilities of the introduced microbial inocula were assessed in terms of nodulation. nitrogen fixation. growth, yield, mycorrhizal colonization and nutrient uptake response of the host plant both in sterilized pot soil and under field conditions. Symbiotic efficiency was dependent on the particular combination of Glomus species and Bradyrhizobium strain reflecting selective and specific compatibilities between the two types of symbionts, and also between them and their. host plant. The specific compatibility between the two types of symbionts, however, was found to vary with soil amendments. Furthermore, the host plant response to various mycorrhizal and rhizobial inoculation combinations was different in sterilized soil and under field conditions. A highly variable response to EM application was recorded in different soil amendment systems.
The following specific observations were recorded in the sterilized pot soil trials and under field conditions.
In general, though not always, in pot trials, the local B. japonicum strain MNS was superior to exotic strain TAL-102 in nodule characteristics in all the four soil amendment systems. Host plant nodulation response to inoculation of either of the two B. japonicum strains under field conditions was very poor in all but 1/2NPK amendment.
In combination with the two mycorrhizal species, B. japonicum strain MN-S was more efficient in N fixation in organic manure and TAL-102 in chemical fertilizers amendments, in pot trials. Maximum increase of 257% N content was obtained by G. mosseae + TAL-102 inoculation in 1/2NPK followed by 162% in GM amendment due to U mosseae + MN-S inoculation. However, under field conditions highest shoot N content response to various B. japonicum strains and Glomus species inoculation combinations was recorded in FYM and NPK amendments.
G. fasciculatum was more efficient in P uptake than G. mosseae in pot trials. G fasciculatum + MN-S was found to be the best microbial combination for P uptake in all the four soil amendment systems. Effectiveness of introduced VAM species in P uptake was diminished under field conditions.
In pot trials. shoot biomass, grain yield, mycorrhizal colonization and spore population, and shoot N, P and K contents were generally higher in organic manures amended soils than those where chemical fertilizers were applied. Under field conditions, root and shoot biomass, nodule number and grain yield were higher in FYM as compared to other soil amendments.
In FY M and GM amendments, nodule biomass produced in different combination treatments of B. japonicum strains and Glomus species was positively and significantly correlated with shoot biomass, acetylene reduction activity (ARA) and shoot N content at flowering stage. in pot trials. Such correlations were entirely lacking in chemical fertilizers amendment systems. Under field conditions there was not any significant association of nodulation with shoot biomass. ARA and N content in any of the four soil amendment systems.
In pot trials, grain yield response to different combinations of Glomus species and B. japonicum strains inoculation was highest in NPK followed by in 1/2 NPK soil amendment where 170-320% and 1-160% increase in yield over corresponding control treatments, respectively, was recorded. In FYM and (GM amendments, grain yield response to different inoculum combinations was comparatively lower than in chemical fertilizers amendments where 1-70% and 1-35 % increase in yield was recorded, respectively. G. mosseae + MN-S inoculation proved to be the best inoculum combination in FYM and 1/2NPK, and G. fasciculatum + MN-S in GM and NPK amendments. Under field conditions, grain yield was significantly enhanced by G. mosseae + MN-S in FYM and GM, and by G. fasciculatum + T AL-102 and G. Mosseae + TAL-102 in 1/2NPK and NPK amendments.
EM application significantly increased nodule number in plants inoculated with TAL-102 in combination with either of the two Glomus species, both in FYM and GM amended soils. Similarly in NPK amendment, EM application significantly improved nodule number in G. mosseae+TAL-102 inoculated plants. There was a parallel increase in shoot N content due to EM application in these treatments. Under field conditions, generally nodulation showed insignificant or negative response to EM application in different amendment systems. Shoot N content generally showed a significantly positive response 10 EM application in all except GM amendment.
In pot trials variable effect of EM application on grain yield was observed in different soil amendments. EM application significantly enhanced grain yield (14%) in un-inoculated control treatment in GM amendment. In 1/2NPK amendment, G. Mosseae + TAL-102 and G. fasciculatum + MN-S inoculated plants showed a positive response to EM application resulting in a significant increase of 72 and 108% in grain yield, respectively. In NPK amendment, a significant increase of 73% in grain yield was recorded due to EM application in G Mosseae + MN-S inoculated plants. Under field conditions, EM application in GM amendment generally suppressed crop growth and yield while a significant increase in the studied parameter was recorded due to EM application in un-inoculated control treatments in FYM and NPK amendments, and in G. mosseae + T AL-102 inoculated plants in FYM.
The present study concludes that the maximum benefits from symbiotic microorganisms can be exploited by using specific microbe-microbe and microbe soil amendment combinations. The highest grain yield in mungbean under field conditions can be obtained by inoculating appropriate V AM species along with B. japonicum strain MN-S in organic manure amended, and B. japonicum strain. TAL-102 in chemical fertilizers amended soils. In addition, host plant N-content can be improved by EM application in FYM and chemical fertilizers amended soils.