A Study on soybean cultivar and rhizobium strain interaction related to biological nitrogen fixation in different soils

Since, symbiotic effectiveness is affected by three important factors such as bacteria genotype, plant cultivar and environmental conditions (e.g. soil properties). In this research, simple and interaction effects of the first two factors about symbiosis of three soybean cultivar, which are most commonly cultivated soybean, with several commercial strain of bacteria with three different soils is investigated. For this purpose five Bradyrhizobium japonicum commercial strains (Rhizoking, Helinitro, Goldoat, Biodoz and CB 1809) were taken from soil and water rea search institute. Based on assurance of bacteria strains purity and ineffectiveness with cultivars, for comparison of strains symbiotic effectiveness with soybean cultivars and the best strain selection performed a factorial experiment with RCBD in 24 treatments and 4 replication. The seeds of soybean cultivars were cultivated in Growth chamber under Leonard jar system. The treatment used were 3 levels of soybean cultivar, 5 levels of Bradyrhizobium strains and 3 levels of Nitrogen (0, 35 and 70 PPM). Plants were fed with Brought on and Dil worth solution (1970) for 75 days. Then, plants were harvested and dried. Selective parameters were analysed by MSTATC program. The results indicated that, all bacteria stains were highly effective as far as symbiotic effectiveness is concerned. Eventually Rhizoking, Gold coat and Helinitro stains selected for soybean inoculation. Provided for pot culture, two soil samples from soybean original planting area (in the subregion of Gorgan and Sari cities) and another sample from Karaj countryside were taken with moderate, high and zero symbiont indigenous bacteria levels respectively. For study of interaction and simple effects of Bacteria strain and soybean cultivar in each soil; a factorial experiment with RCBD in 4 replication performed. Factors were contained soybean cultivar (three levels) and three Bacteria strain with a blank treatment for inoculation. In this respect homogenized soil samples were distributed in pots and with consideration of treatment every seed inoculated with 1 ml of special strain inoculum (at Mcfarland's standards no.3). During four months the pots moisture were kept at about Fc 80% with distilled water. Then in reproductive stage 6 (R6) eleven parameters of plant growth in every soil were measured and analysed individually. The results indicated that in Karaj soil considered parameters of Sahar cultivar is higher that other cultivars. In addition all inoculate treatment showed a considerable yield increase in investigated parameters than blank (non inoculated). Results of inoculation with Go and Ri strains were similar but the yield of He strain inoculation was lower. Interaction of cultivar and Bacteria strain was significant too. Calculation of Nitrogen percent (N%) derived from air in this soil for soybean cultivars in symbiosis with Bacteria strains, by using Nitrogen difference method, indicated 80%-9 of plant nitrogen demand were supplied by symbiosis. In Gorgan soil (with intermediate indigenous bacteria level), the soybean cultivar effect on investigated characteristic was signified completely. The best cultivar was Sahar too. The effects of inoculation and also interaction of bacteria strain and soybean cultivar were not significant. In Sari soil (with high indigenous Bacteria level) The cultivar effect (in all measured characteristic) and strain effect (at major of measure characteristic) was significant. Interaction of cultivar and strain on investigated characteristic didn't show to be significant. In this soil, the best bacteria strain for inoculation was Gold coat strain and the best soybean cultivar was Sahar. In general, we can conclude that, in soils without indigenous symbiont bacteria and low nitrogen level, the use of effective and active strain of bacteria inoculum for nitrogen fixing ability and yield enhancement is necessary. In soils with high nitrogen and indigenous bacteria level use of inoculum of strains with high competitiveness and effectiveness can have positive effect on Growth indexes. At last, it is necessary to say that, in application of every kind of bacteria strain as inoculum and also proper plant cultivar for increasing yield, climatic and environmental conditions must be seriously considered