School of Agriculture and Biotechnology
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Item Bradyrhizobium inoculation has a greater effect on soybean growth, production and yield quality in organic than conventional farming systems(2021-06-22) Gitonga, Nicholas Mawira; Njeru, Ezekiel Mugendi; Cheruiyot, R. C.; Maingi, JohnGlobally, organic farming and bradyrhizobia inoculation are gaining popularity as agronomically and environmentally sound soil management strategies with great potential to alleviate declining soil fertility, maintain environmental quality and enhance soybean production. However, the role of bradyrhizobia in organic farming system is poorly understood. Field experiment was conducted to evaluate the effects of bradyrhizobia inoculation and organic farming on growth parameters and yield quality of soybean varieties: SC squire, SB19 and Gazelle. The experimental treatments included native bradyrhizobia, commercial Bradyrhizobium japonicum, mixture of native + commercial bradyrhizobia and uninoculated control. The experimental design was a split-split plot, with three replications. The results demonstrated significant improvement in soybean nodule dry weight (NDW), shoot dry weight (SDW) and seed dry weight (SEDW) following bradyrhizobia inoculation. Remarkably, organic farming significantly out-performed conventional systems in nodulation, SDW and SEDW. Moreover, seed nutrient content differed depending on farming system; where nitrogen, phosphorus, potassium and organic carbon were higher in organic farming. Soybean varieties differed significantly on SDW, NDW and SEDW; where SC squire performed better than SB19 and Gazelle. The results demonstrate the importance of organic farming and bradyrhizobia inoculation in enhancing soil fertility, yield production and quality, a key step towards sustainable food production.Item Enhancing Tripartite Symbiosis between Soybean, Bradyrhizobia and Arbuscular Mycorrhizal Fungiunder Contrasting Farm Management Practices in Tharaka-Nithi County-Kenya(Kenyatta University, 2021-05) Gitonga, Nicholas MawiraOrganic farming is gaining popularity as agronomically and environmentally sound soil management strategy with the potential to enhance soil microbial diversity and fertility, environmental quality and sustainable crop production. However, the role of bradyrhizobia and arbuscular mycorrhizal fungi (AMF) in organic farming systems is poorly understood. Field experiments were carried out to evaluate the effects of organic farming and bradyrhizobia inoculation on soybean nodulation, AMF root colonization, growth, production and yield quality. Greenhouse and laboratory experiments sought to determine the effects of bradyrhizobia and/or AMF inoculation and dual inoculation in promoting root colonization and nodulation, determine soil mycorrhizal inoculum potential (MIP), evaluate the abundance and effectiveness of native bradyrhizobia and determine the morphological and genetic diversity of native bradyrhizobia isolates under different farm management practices. Field experimental treatments included native bradyrhizobia, commercial Bradyrhizobiun japonicum, a mixture of native and commercial Bradyrhizobium japonicum and control. Promiscuous soybeans varieties SB 19 and SC squire as well as non-promiscuous Gazelle were used as test plants. All field experiments were carried out in split-split plot design. In the greenhouse, AMF and bradyrhizobia were inoculated and dual inoculated on SC squire soybeans. The AMF inoculants used were Funneliformis mosseae and Rhizophagus irregularis while bacteria involved commercial bradyrhizobia and native bradyrhizobia. Greenhouse experiments were set out using completely randomized design. The native bradyrhizobia were isolated and characterized. Deoxyribonucleic acid (DNA) from nodule isolates was extracted using Gene Jet DNA extraction kit. Polymerase chain reaction (PCR) targeting 16S rDNA gene was carried out using universal primers P5-R and P3-F. Polymerase chain reaction product purification and sequencing was carried out in MacrogenNetherlands. Sequencing was done using the same primers. Non molecular data obtained was analyzed using analysis of variance (ANOVA). Means that were significantly different at p< 0.05 were separated using Tukey’s HSD test. Field experiment results demonstrated significant improvement of soybean nodule dry weight (NDW), shoot dry weight (SDW) and seed dry weight (SEDW) due to inoculation. Bradyrhizobia inoculation increased soybean seed yields by between 29-59% of its potential yield. Remarkably, organic farming significantly (p=0.001) out-performed conventional systems in SDW, NDW, SEDW and AMF root colonization. Moreover, seed nutrient significantly differed in organic and conventional farming where, seed nitrogen, phosphorus, potassium and organic carbon were higher in organic farming. Soybean varieties differed significantly on SDW, NDW and SEDW, where SC squire performed better compared to SB 19 and Gazelle. Greenhouse results showed bradyrhizobia and AMF dual inoculation significantly enhanced AMF root colonization, NDW and SDW compared with individual bradyrhizobia, AMF or control. Moreover, organic farming significantly (p=0.001) increased SDW, NDW and AMF root colonization compared to conventional farming. Organic farming had a significant effect (p = 0.001) on soil MIP. Based on molecular analysis, isolates were bradyrhizobia and matched with Bradyrhizobium japonicum among other species. There was little or no genetic differentiation of isolates with the highest molecular variation (91.12%) within the populations and 8.88 % among populations. The results demonstrate the importance of organic farming and dual inoculation in sustainable crop production. The highly potential native bradyrhizobia isolates (GRPc and GRPk) and exotic AMF should be xix popularized and commercially ultilized by farmers to alleviate declining soil fertility and increase food production with minimum expenses.Item Dual inoculation of soybean with Rhizophagus irregularis and commercial Bradyrhizobium japonicum increases nitrogen fixation and growth in organic and conventional soils(AIMS Agriculture and Food, 2021) Gitonga, Nicholas Mawira; Koskey, Gilbert; Njeru, Ezekiel Mugendi; Maingi, John M.; Cheruiyot, RichardSoil amendment with beneficial microorganisms is gaining popularity among farmers to alleviate the decline ofsoil fertility and to increase food production and maintain environmental quality. However, farm management greatly influence soil microbial abundance and function, which overly affects crop growth and development. In this work, greenhouse experiments involving soybeans were conducted to evaluate the effects of bradyrhizobia and arbuscular mycorrhizal fungi (AMF) dual inoculation on nodulation, AMF root colonization, growth and nutrient acquisition under contrasting farming systems. The experimental treatments were AMF and/or bradyrhizobia inoculation and dual inoculation on SC squire soybean variety. The exotic AMF inoculants used were Funneliformis mosseae (BEG 12) and Rhizophagus irregularis (BEG 44) while bacteria were commercial Bradyrhizobium japonicum (USDA110) and native bradyrhizobia isolates. Experiments with soil samples from organic and conventional farms were set out using a completely randomized design with three replicates. The results demonstrated that bradyrhizobia and AMF dual inoculation consistently and significantly enhanced soybean nodule dry weight (NDW), shoot dry weight (SDW) and AMF root colonization compared with individual bradyrhizobia, AMF and non-inoculated control. Moreover, organic soil significantly (p = 0.001) increased soybean SDW, NDW and AMF root colonization compared to conventional soil. Remarkably, shoot nutrients content differed in organic and conventional farming where, shoot nitrogen, phosphorus, potassium and organic carbon were 479 AIMS Agriculture and Food Volume 6, Issue 2, 478–495. higher in organic farming than the latter. Among individual inoculants, Rhizophagus irregularis outperformed Funneliformis mosseae, while commercial Bradyrhizobium japonicum showed higher performance than native bradyrhizobia. Our results demonstrated the importance of organic farming, AMF and bradyrhizobia dual inoculation in enhancing soybean growth and nutrient acquisition. However, field trials should be assessed to determine the good performance of bradyrhizobia and AMF dual inoculation in organic farming before being popularized and adopted by farmers as a sustainable agronomical management strategy to increase soil fertility and food productivity.