The inoculation of the legume seed material with active nitrogen fixing bacteria strains before sowing has a significant role for the increase of the legume yield. Inoculation can improve crop yields in cases where appropriate rhizobia are not present in the soil or the soil contains a significant proportion of non-nodulating or ineffective nitrogen-fixing strains. The aim of the investigation was to detect the effectiveness of Rhizobium leguminosarum strains in field beans at different soil microbiological activity. The experiment was conducted at the Institute of Soil and Plant Sciences of the Faculty of Agriculture of the Latvian University of Agriculture from the 5th of June till the 17th of October 2008. The field bean (Vicia faba. L) cultivars - 'Ada', 'Lielplatones', Rhizobium leguminosarum bv. vicia strains No. 110; 408; 501 and 2 types of soils (with different microbiological activity) were used in vegetation pot experiment. The highest shoot dry matter was observed in cultivars cultivated in soil with higher microbiological activity. The highest pod dry matter was observed in cultivars cultivated in soil with higher microbiological activity. The highest total nitrogen amount was in field beans cultivated in soil with lower microbiological activity. Rh. leguminosarum strain resistance to streptomycin decreases with the plants age, from anthesis forward in both soil types and both cultivars. The fingerprinting showed significant difference between Rh. leguminosarum strains.

The vegetation pot experiment was conducted at the Institute of Soil and Plant Sciences of the Faculty of Agriculture of the Latvia University of Agriculture. The aim of the experiment was to investigate the effectiveness of five Rhizobium legumonosarum strains stored in the period from the 18th of August till the 20th of October 2006 in the collection of the Latvia University of Agriculture. Three of the five mentioned Rhizobium legumonosarum strains were included in the international Rhizobium database IBP World Catalogue of Rhizobium collections. Taking into consideration the results of the experiment it has been pointed out that all Rhizobium strains were active and inoculated plants formed nodules on the roots. Inoculation with Rhizobium strains increased the proportion between shoots and roots' weight. It has been found that the dry matter content of the inoculated plants increased in comparison with the untreated ones. In addition, negative correlation between the dry matter and the protein content has been observed.

Legumes (Leguminosae) are one of the most widely grown crops in the world after cereals (Poaceae). They are not only an important source of protein in food and feed, but also a significant component of different agrosystems. The N2 fixation by legumes is of great importance in nutrient management and sustainable economy of nitrogen. Legume productivity largely depends on a successful formation of symbiosis between the plant and soil microorganisms. The most important among those are rhizobia and mycorrhiza fungi. The field experiment was carried out at the Institute of Soil and Plant Sciences, Latvia University of Agriculture in 2014 to evaluate the influence of double inoculation using rhizobium leguminosarum and mycorrhiza fungi preparation on yield formation of broad bean V. faba L. var. major Harz ‘Bartek’. The bean seeds were treated with rhizobia and/or mycorrhiza fungi before sowing. Seeds were treated with rhizobia by soaking in bacteria suspension for 30 minutes directly before sowing. Mycorrhiza fungi preparation was added in soil under seeds before sowing. Plant height, fresh and dry weight and the weight of nodules were measured at the beginning of broad bean flowering (BBCH 60-61). rhizobium leguminosarum response to double inoculation differed between the strains. Rhizobium leguminosarum strain RL407, isolated from Vicia faba, was shown to be the most appropriate strain used for inoculation of broad bean seeds. Bean seed double inoculation increases the protein content significantly comparing to single inoculation using mycorrhiza fungi preparation.