| dc.description.abstract | Organic 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
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popularized and commercially ultilized by farmers to alleviate declining soil fertility
and increase food production with minimum expenses. | en_US |