The effect of inoculating Bradyrhizobium liaoningense on growth, chlorophyll concentration, nodulation and yield of soya beans

Abstract

Soya bean is important staple food crops in Western Kenya. Legumes play a significant role in agriculture by fixing nitrogen. Currently Kenya is experiencing low yield of soya beans. Approximately 0.8 t/ha is under production and this is due to low soil fertility. This has posed a threat to agricultural productivity. Symbiotic rhizobia inoculation increases crop yields through biological nitrogen fixation. However, the potential of Bradyrhizobium liaoningense in improving yield and productivity of soya beans has not been documented. Rhizobia bacteria are known to improve growth and yield of several other crops but the effect of inoculating soya beans with B. liaoningense on growth, chlorophyll concentration, nodulation and yields has not been determined. This study was conducted at Maseno University under greenhouse conditions. Previously purified local isolates of B. liaoningense (S3) from wild soya beans plants were used to inoculate the soya bean seeds. 4.5 litre plastic pots were filled with 7kg of top soil. Ten seeds of Soya beans coated with Bradyrhizobium liaoningense inoculants were sown in each pot except the control. The seeds were treated with the isolates inoculants as: un-inoculated (control), 1.07x107 cfu/ml, 1.19x107 cfu/ml, 1.31x107 cfu/ml and 2.67x107 cfu/ml inoculation of B. liaoningense. The experiment was laid out as Completely Randomised Design (CRD). The treatments were replicated three times. After two weeks of germination, the seed lings were thinned to three plants per pot. Watering was done daily with 200 ml of water per pot up to the end of the experiment. Data on plant height, number of leaves, leaf area, shoot and root fresh weight and dry weight, chlorophyll concentration, number of nodules and number of pods were determined. Data was subjected to Analysis of Variance (ANOVA). Treatments means were separated using Fisher’s Least Significant Difference at (P = 0.05). Soya bean growth, chlorophyll concentration, number of nodules and number of pods after inoculation treatments were significantly different among the treatments (P ≤ 0.05). Plant height, number of leaves and leaf area were highest in 2.67 x 107 cfu/ml of B. liaoningense inoculation followed by 1.31x 107 cfu/ml inoculation, 1.19x107 cfu/ml, 1.07x107 cfu/ml and lowest in un-inoculated. Inoculation at 2.67 x 107 cfu/ml significantly increased soya bean root and shoot fresh weight and dry weights. Chlorophyll concentration was found to be highest in 2.67 x 107 cfu/ml treatment and lowest in un-inoculated control treatment. Inoculation at 2.67 x 107 cfu/ml increased the number of nodules of soya beans. Number of pod per plant were highest at 2.67 x 107 cfu/ml treatment and lowest in un-inoculated (control treatment). These findings showed that B. liaoningense inoculation was effective in enhancing growth, chlorophyll synthesis, formation of root nodules and pods in soya beans. From the study it can be recommended that B. liaoningense from wild soya bean may be used as a biofertiliser to improve productivity of soya beans by smallholder farmers in Kenya.