Abstract
Organic farming systems are gaining popularity as agronomically and environmentally sound soil management strategies with potential to enhance soil microbial diversity and fertility, environmental quality and sustainable crop production. This work aimed at understanding the effect of organic and conventional farming on the diversity of soybean nodulating bradyrhizobia species. Field trapping of indigenous soybean Bradyrhizobium was done by planting promiscuous soybeans varieties SB16 and SC squire as well as non-promiscuous Gazelle in three organic and three conventional farms in Tharaka-Nithi County of Kenya. After 45 days of growth, 108 nodule isolates were obtained from the soybean nodules and placed into 13 groups based on their morphological characteristics. Genetic diversity was done by polymerase chain reaction (PCR) targeting 16S rDNA gene using universal primers P5-R and P3-F and sequencing was carried out using the same primer. High morphological and genetic diversity of the nodule isolates was observed in organic farms as opposed to conventional farms. There was little or no genetic differentiation between the nodule isolates from the different farms with the highest molecular variation (91.12%) being partitioned within populations as opposed to among populations (8.88%). All the isolates were identified as bradyrhizobia with close evolutionary ties with Bradyrhizobium japonicum and Bradyrhizobium yuanminense. Organic farming systems favor the proliferation of bradyrhizobia species and therefore a suitable environmentally friendly alternative for enhancing soybean production.
Highlights
Human population has risen steadily over time, soils lost fertility and arable land are scarce leading to increased pressure on agricultural systems to provide food for the ever-increasing population
The objectives of this study were to (i) assess the morphological characteristics of soybean nodulating indigenous bradyrhizobia isolated from nodules under organic and conventional farming in Eastern Kenya and (ii) evaluate the genetic diversity of indigenous bradyrhizobia nodulating soybean
The physicochemical properties of the soil varied depending on farm management practice
Summary
Human population has risen steadily over time, soils lost fertility and arable land are scarce leading to increased pressure on agricultural systems to provide food for the ever-increasing population This has led to drastic land-use changes that involve intensive agricultural practices that has affected biodiversity driven ecosystem processes on the local and global scale (Foley et al, 2005). The adverse effects of prolonged use of inorganic agrochemicals in conventional farming system have led to increased demands to make agricultural systems more sustainable by reforming agricultural practices. These concerns and negative impacts posed by conventional farming gave birth to organic farming
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