Trapped Field Research Articles

Trapping a magnetic field of 14.8 T using stacked coated conductors of 12 mm width

We fabricated a compact (13 12 12.5 mm3) trapped-field magnet by stacking 200 pieces of EuBa2Cu3O7 coated conductors (CCs) with BaHfO3 nanorods as artificial pinning centers. It was magnetized by field-cooling method using a 18 T superconducting magnet, and the maximum field of 14.8 T was trapped at 10 K at a field-ramp rate of 0.1 T min−1. At higher temperatures, although the trapped field was decreased, we could trap the field with much faster ramp rate. In order to understand these results, we also performed calculations of the trapped field based on characteristics of the CC. The calculated trapped field value was larger than the experimental value at 10 K. This discrepancy can be understood by considering the reduction of the effective size of the stacked CCs due to the existence of extended regions of irregular flux penetration called ‘flux jets’.

The mechanical characteristics and control of high temperature superconducting magnetic docking mechanism

The space docking mechanism is one of the important ways to set up a space station, which is an important platform to explore the space. The traditional docking mechanism has achieved a series of docking missions, but it has the problems of large impact and plume pollution, which has the risk to affect the normal work of high precise instrument and equipment installed on spacecraft. In order to solve the drawback of the traditional docking mechanism, the high temperature superconducting magnetic docking mechanism (a novel docking mechanism) consisting of a high temperature superconductor (HTS) bulk installed on a target spacecraft module and an electromagnet installed on a tracking spacecraft module is proposed to be designed based on the flux pinning effect of a HTS. The diamagnetic and trapped magnetic field characteristics of a HTS can be considered to propose an equivalent method of processing HTS (equivalent processing method). Moreover, the equivalent processing method is verified by way of experiment. The mechanical characteristics of the high temperature superconducting magnetic docking mechanism in the case of different parameters are studied using the equivalent processing method. Based on the mechanical characteristics, the dynamic model of the novel docking mechanism is established in order to analyze the dynamic response in the case of different control laws. Furthermore, the docking performance of the high temperature superconducting magnetic docking mechanism is evaluated based on three indicators, that is, maximum overshoot, peak time, and adjustment time.

Modeling of the dynamics of a superconducting maglev in the mixed state

We studied the levitation of a YBa2Cu3O7 (YBCO) melt-textured superconducting specimen above a closed path of permanent magnets. The superconductor was magnetized with an auxiliary permanent magnet before brought to the path of magnets. This way, the superconducting levitation in the mixed state was achieved. The vertical and horizontal forces acting on the superconductor were calculated by means of two models. One model considers that the superconductor is in the Meissner state and assumes that it is possible to take into account the demagnetizing field by using a single average parameter. The second model considers that the superconductor with trapped field behaves as a permanent magnet with a uniform magnetization. The total force on the superconductor in the mixed state is result of the superposition of these two contributions. In order to validate the model, the height of levitation and the frequency of horizontal oscillations were measured. Both variables were then calculated with the model fed with experimental information. The calculated values were in agreement with the measured ones.

Flow boiling characteristics of minichannel heat sink with artificial conical cavities array under electric field

Three kinds of minichannel heat sinks with artificial conical cavities array formed by ultrafast laser were designed and manufactured to explore flow boiling heat transfer performance of surface with artificial cavities under electric field. Using R141b as the working fluid, the effect of cavity parameters (diameter and density) and electric field (U′=400 V, 600 V, and 800V) on heat transfer coefficient and flow instability at heat flux ranges from 1.93 kW/m2 to 25.11 kW/m2 were experimentally studied. Field trap effect on heat transfer surface with artificial conical cavities under electric field was further developed. The synergy effect of electric field and artificial cavity on enhancing flow boiling heat transfer was found. The mechanism of this can be attributed to field trap effect and enhancing disturbance effect of boundary layer around heat transfer surface. Visualization shows lots of small bubbles generating from bottom of artificial conical cavity, and process of bubble from nucleation to detachment in artificial conical cavity was discussed. The results show that the maximum heat transfer enhancement ratio of 1.99 appears at heat flux of 7.72 kW/m2 for MCH-2 with an applied voltage of 800 V, and the standard deviation of total pressure drop for MCH-2 with electric field reduces about 31% comparing to MCH-1 without electric field. Flow instability has been improved for minichannel with artificial cavities array under electric field, due to more uniformly distributed artificial cavities and more unified artificial cavity structural sizes.

Arbuscular mycorrhizal status of Erythrina brucei in different land use types in Ethiopia

Erythrina brucei is a leguminous tree commonly used in agro-forestry practices in southern and southwestern Ethiopia. It has desirable agro-forestry attributes that make it a good candidate for agro-forestry systems. However, there is a scarcity of information regarding species diversity and spore density of arbuscular mycorrhizal fungi (AMF) associated with E. brucei growing in different land use types. Therefore, this study was initiated to determine species diversity and richness in trap cultures of AMF associated with E. brucei growing in different geographic locations in various land use types of Ethiopia. Soil samples were collected from various E. brucei growing areas with different land use patterns. Trap culture was established using a portion of each soil sample by planting E. brucei as the host plant. AMF spore extraction was carried out in field and trap culture soils, and AMF species identification was done using spore morphology. Erythrina brucei root colonization with AMF structures was studied using trap culture, and AMF spore density in both field and trap culture soil samples was determined. A total of 11 AMF genera and 33 AMF species were recovered. The highest number of genera was recovered from forest land use type at Rebu Gebeya, followed by Adiskdam, live fence land use type. Glomus and Acaulospora were the dominant AMF genera covering 73% of the samples and contained 10 and 9 AMF species, respectively. All the soil samples contained indigenous AMF spore populations regardless of their origin and land use types. The highest mean AMF spore density in a field soil sample was recorded at a farmland in Bodite (280 spores 100 g−1 of dry soil), while the lowest was from Hossana (172 spores 100 g−1of dry soil). However, the highest mean AMF spore density in trap culture was detected from a farm land at Humbo (715 spores 100 g−1 of dry soil) and the lowest from Dhakallo (217 spores 100 g−1 of dry soil). Direct extraction of AMF from field soil samples showed lesser AMF spore density compared with trap culture in the same soil sample. All E. brucei root segments were colonized with the AMF structures, and the colonization status ranged from 34.4% to 49.1%. Both geographic location and land use type significantly affected AMF species richness (p < 0.05). Undisturbed land use types were characterized by high species richness. The soil pH and available phosphorus were negatively correlated to AMF spore density (p < 0.05), but AMF root colonization did not show any significant correlation. Moreover, significant correlations were also not observed between spore number and root colonization, and available phosphorus and root length colonization. We conclude that diverse and dominant AMF genera inhabited the rhizosphere of E. brucei, which can be used for the enhancement of host plant growth. To explore AMF species diversity and richness across geographic location and land use types in detail enhanced area coverage and the combination of both direct field soil and trap culture techniques are recommended.

Trapped field evaluation of ring-shaped GdBCO bulk magnet excited by pulsed field magnetization

Recently, physical and mechanical properties of REBCO bulk are improved, and, accordingly, various practical applications are considered. As one of them, a portable bulk NMR system has been developed, and, then, the improvement of the system for practical use are progressing. In that system, 6 stacked bulks were magnetized by a superconducting magnet for NMR, resulting that the magnetic field of 4.74 T and inhomogeneity of 6.9 ppm were achieved. In this paper, we fabricated the bulk magnet with the room-temperature bore specialized in pulsed-field magnetization. The ring-shaped bulk was activated by pulsed-field magnetization, and, magnetic fields on the bulk surface and in the room-temperature bore of bulk magnet were evaluated. In the bore, the trapped field was approximately 0.79 T and homogeneity was over 150000 ppm.

Characterization of High-Temperature Superconductor Bulks for Electrical Machine Application.

High-temperature superconducting (HTS) bulks can be used in electrical applications. Experimental characterization of large-size HTS bulks is a tricky issue. The relevant parameters for their application were directly measured in this study. This paper has three main aims. Firstly, features of YBaCuO bulks are presented. Secondly, an electrical motor application is developed using magnetic field shielding and trapping. Thirdly, the HTS bulks are characterized. Several classical methods were used, which are mainly magnetic methods only available for small samples. The complete penetration magnetic field and the critical current density were found to be the main parameters relevant for applications. An innovative entire HTS bulk characterization method is presented. This characterization method is useful for end users and engineers to better implement HTS bulks.

Characterization of Magnetic Field in the Bitter-Like HTS Magnet Magnetized By Multiple Excitation Methods

High temperature superconducting (HTS) bulks stacked by the RE (RE = rare earth) Ba-Cu-O tape have been demonstrated to trap field as permanent magnets. A Bitter-like HTS magnet stacked by the REBCO annuli was investigated to realize its ability to operate with the persistent current mode without joint resistance and current lead. However, the magnetic field generated by the Bitter-like HTS magnet was relatively small and increased rapidly to the saturation value during the short period. To further analyze the characterization of the magnetic field in the Bitter-like HTS magnet under various excitation methods, the inner multiple pulsed fields and field cooling methods, as well as the zero-field cooling method, were performed by experiments in the LN <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sub> bath (77 K). It can be observed that the magnetic field of the HTS magnet passed through a low induction zone and linearly increased to a saturated value magnetized by the inner multiple pulsed fields. Moreover, a finite element method was also developed for the HTS magnet to pursue the distributions of the magnetic field and current density during the excitation process.

Experimental realization of an all-(RE)BaCuO hybrid trapped field magnet lens generating a 9.8 T concentrated magnetic field from a 7 T external field

In this work, we have verified experimentally an all-(RE)BaCuO hybrid trapped field magnet lens (HTFML) using only one cryocooler and a special technique named the ‘loose contact method’. In the experimental setup, only the inner magnetic lens was tightly connected to the cold stage and cooled at all times, and the outer trapped field magnet (TFM) cylinder was loosely connected to the cold stage before the magnetizing process by introducing a gap between the outer TFM and cold stage of the cryocooler. As a result, the superconducting state for zero-field cooled magnetization of the inner magnetic lens and the non-superconducting (normal) state for field-cooled magnetization of the outer TFM cylinder can co-exist at the same time. A maximum concentrated field of B c = 9.8 T was achieved for the magnetizing process with an applied field of B app = 7 T in the present HTFML, consistent with the numerical estimation in our previous conceptual study. These results validate the HTFML concept as a compact and desktop-type magnet device that can provide 10 T-class magnetic field enhancement from the viewpoint of the magnetizing method. However, during magnetization with a higher B app of 10 T, thermal instability of the outer stacked TFM cylinder caused flux jumps to occur, resulting in mechanical fracture of multiple bulks. These results suggest that the further development of a practical cooling method that can realize a stable and controllable cooling process for each part of the HTFML is necessary based on fundamental studies relating to the thermal stability of the large stacked TFM cylinder.

Electromagnetic properties of curved HTS trapped field stacks under high-frequency cross fields for high-speed rotating machines

Superconducting electric propulsion systems, characterized by high power densities and efficiencies, provide a possibility to zero carbon emission for future aviation. Stacks of high temperature superconducting (HTS) coated conductors (CCs) have become an alternative for high field magnets applied to superconducting machines, given their excellent field trapping ability and thermal stability. High-frequency ripple fields always exist in high-speed electric machines. Most research work regarding HTS trapped field stacks (TFSs) was focused on their magnetization methods and amplitude of trapped flux density; however, their performance in the high-frequency environment remains unclear. Despite several numerical models established for flat HTS TFSs, a comprehensive analysis of curved ones is still lacking, which possess geometrical applicability for cylindrical rotating shafts. Aimed at exploring the electromagnetic properties of curved HTS TFSs applied to high-speed rotating machines, a 3D numerical model considering both the multilayer structure and the Jc (B) dependence of HTS CCs has been built. Current and magnetic flux density distributions, as well as loss properties of a curved HTS TFS have been studied in detail, under perpendicular and cross fields with varying frequencies ranging from 50 Hz to 20 kHz. Results have shown that, the widely adopted two-dimensional-axisymmetric models are inapplicable to study the electromagnetic distributions of TFSs because of the emergence of the electromagnetic criss-cross defined in this paper. High-frequency ripple fields can drive induced current towards the periphery of the HTS TFS due to the skin effect, leading to a fast rise of AC loss and even an irreversible demagnetization of the stack. This paper has qualified and quantified the high-frequency electromagnetic behaviours of curved HTS TFSs, providing a useful reference for their loss controlling and anti-demagnetization design in high-speed propulsion machines.

Direct evidence of microstructure dependence of magnetic flux trapping in niobium

Elemental type-II superconducting niobium is the material of choice for superconducting radiofrequency cavities used in modern particle accelerators, light sources, detectors, sensors, and quantum computing architecture. An essential challenge to increasing energy efficiency in rf applications is the power dissipation due to residual magnetic field that is trapped during the cool down process due to incomplete magnetic field expulsion. New SRF cavity processing recipes that use surface doping techniques have significantly increased their cryogenic efficiency. However, the performance of SRF Nb accelerators still shows vulnerability to a trapped magnetic field. In this manuscript, we report the observation of a direct link between flux trapping and incomplete flux expulsion with spatial variations in microstructure within the niobium. Fine-grain recrystallized microstructure with an average grain size of 10–50 µm leads to flux trapping even with a lack of dislocation structures in grain interiors. Larger grain sizes beyond 100–400 µm do not lead to preferential flux trapping, as observed directly by magneto-optical imaging. While local magnetic flux variations imaged by magneto-optics provide clarity on a microstructure level, bulk variations are also indicated by variations in pinning force curves with sequential heat treatment studies. The key results indicate that complete control of the niobium microstructure will help produce higher performance superconducting resonators with reduced rf losses1 related to the magnetic flux trapping.

Influence of RE-Based Liquid Source (RE = Sm, Gd, Dy, Y, Yb) on EuBCO/Ag Superconducting Bulks

One of the common approaches to improve the microstructure of rare-earth-barium-copper-oxide-based superconducting ceramics is an addition of a liquid source under the precursor bulk during top-seeded melt growth or top-seeded infiltration growth. The additional liquid source partially negates the change in elemental composition due to the loss of the liquid phase, which otherwise occurs. The focus of this contribution is to study the effects of various RE <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sub> O <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">3</sub> -Ba <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">3</sub> Cu <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">5</sub> O <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">8</sub> -BaO <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sub> (RE = Sm, Gd, Dy, Y, Yb) liquid sources on the properties and microstructure of single-domain EuBCO/Ag bulks. The samples were prepared with a height of 16 mm and a diameter of 28 mm (as grown). This allowed us to study the diffusion of rare earth elements from the liquid source into the final bulk in detail. Samples were characterized by XRD, SEM, and EDS. The phase composition was studied in detail using Rietveld refinement. The influence on key superconducting properties was also examined. The addition rare earth liquid phase has significantly improved the trapped field homogeneity. Dy <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sub> O <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">3</sub> has yielded the highest trapped field among the studied rare earth elements. This research is significant in the field of high-performance superconducting ceramics since it allows for a better understanding of the role of the additional liquid phase during the TSMG process, the influence of different rare earth elements, and most importantly the impact of these techniques on the superconducting bulks.

All-Fiber Hollow Bessel-Like Beam for Large-Size Particle Trap

A 32 μm large-size microparticle is trapped by an all-fiber hollow Bessel-like beam. In order to realize the proposed high-order Bessel-like beam, we fabricate the optical fiber probe by splicing an annular core fiber with a step-index multimode fiber. We grind the fiber tip into a truncated cone shape to converge the hollow Bessel-like beam to obtain a large focal area. Simulation and experimental results show that the trapping field introduced by the Bessel-like beam provides a relatively strong optical force and has the capability of 3-D capture of a large particle (whose diameter is 32 μm). These highly integrated fiber tweezers provide hollow Bessel-like beams with strong optical force and large trapping area, which can be promisingly applied in biomedical and integrated optical research.

Investigation of the Magnetizing Performance of a REBCO Bulk Magnet Excited by Pulsed Field Magnetization Using Cross-Shaped Iron Yokes

We study to improve a trapped field of REBCO bulk excited by pulsed field magnetization (PFM). In PFM, a soft-iron yoke is used in order to expose the bulk to a large amount of magnetic flux for a long time. We paid attention to the soft-iron yoke and investigated the influence of its size and shape on the magnetizing performance. Our previous study estimated trapped-field performance when using disk-, ring-, and cross-shaped yokes and found that the cross-shaped yoke was the best. In this paper, we report our investigation of the influence of the width and arrangement of a cross-shaped yoke on magnetizing characteristics. When performing PFM experiments using yokes with 15 mm wide and 10 mm wide and arranging the growth sector region and the growth sector boundary, we obtained almost the same results. When comparing the total magnetic flux per unit weight, those values of 10 mm wide cross-shaped yoke were approximately 27% higher than those of 15 mm wide one.

Electrophysiological and Behavioral Responses of Holotrichia parallela to Volatiles from Peanut.

Simple SummaryThe dark black chafer, Holotrichia parallela, which is widely distributed all over the world, is an economically important pest in agriculture and forestry. In the north part of China, this beetle causes serious damage to the peanut plant. Much attention has been paid to olfactory perception of volatile compounds from supplemental nutrition hosts by H. parallela prior to sexual maturation. However, volatile compounds attractive to this beetle from the peanut plant have not been identified yet. In this study, we collected the volatile compounds from peanut seedlings by dynamic headspace adsorption and identified twelve electrophysiologically active compounds responsible for the attraction of H. parallela to the peanut. Among the eight chemically identified compounds, β-caryophyllene and hexanal significantly attracted both sexes of H. parallela when tested individually in the field. A blend of β-caryophyllene and hexanal at a ratio of 2:1 was most attractive to the beetles. The addition of the remaining compounds to the binary mixture did not increase the attractiveness. The findings of this study reveal that β-caryophyllene and hexanal can be potentially used for development of effective attractants for management of H. parallela.Holotrichia parallela (Coleoptera: Scarabaeidae: Melolonthinae) is a notorious pest of many crops, especially peanuts. In this study, volatiles from peanut plants were analyzed using both gas chromatographic-electroantennographic detection (GC-EAD) and gas chromatography/mass spectrometry (GC/MS) techniques, and tested for adult attraction with field trapping bioassays in Hebei Province, China. GC-EAD analyses indicated that H. parallela antennae strongly responded to twelve GC peaks, including eight identified compounds, (Z)-β-ocimene, hexanal, 6-methyl-5-hepten-2-one, nonanal, dihydromyrcenol, linalool, β-caryophyllene, methyl salicylate, and four unidentified compounds. When tested individually in field conditions from 24 to 31 July, 2020, β-caryophyllene and hexanal significantly attracted both sexes of H. parallela, whereas all other compounds were unattractive. A blend of β-caryophyllene and hexanal at a ratio of 2:1, close to the natural ratio of these two compounds from the intact peanut plant, was most attractive to the beetles. The remaining identified compounds, (Z)-β-ocimene, 6-methyl-5-hepten-2-one, nonanal, dihydromyrcenol, linalool, and methyl salicylate had no synergistic effects on H. parallela attraction when tested in combination with the blend of β-caryophyllene and hexanal. These results demonstrated that β-caryophyllene and hexanal in the volatiles from peanut plants have strong attraction to H. parallela. These two compounds have the potential to be used for monitoring H. parallela and its management programs.

Modelling of protons spectra encountered in space using medical accelerator and its microdosimetric characterization

Radiation environments in space are mainly composed of protons coming from the Galactic Cosmic Rays (GCRs) pervading the universe, the Solar Particle Events (SPEs) resulting from solar flares and coronal mass ejections, and the two Van Allen Belts surrounding the Earth due to the presence of the geomagnetic field trapping charged particles. Their wide spectra of energies up to hundreds of GeV imply diverse radiobiological effects to astronauts and radiation damage to electronics in the spacecraft. Even if lower in abundance, heavy ions such as He, C, O, Si, Fe are present in space and constitute an even bigger hazard due to their high penetrability and high linear energy transfer (LET). Most irradiation facilities available for research and testing worldwide provide usually only monoenergetic beams of high-energy protons or other heavier particles limiting studies of radiobiological effects and effects on electronics to a set of discrete energies.This paper introduces a procedure where a proton fluence spectra of interest for space radiation protection, previously generated by Monte Carlo simulations was delivered using a clinical proton therapy accelerator.Particularly, it reports the first results of modelling a proton radiation field in space in the energy range from 70 to 230 MeV during a single experimental session by programming a treatment planning system (TPS) to deliver required proton irradiation energies. Moreover, the angular distribution of the proton irradiation field has been varied to reproduce the isotropic exposure experienced by humans in space. The obtained proton radiation field was characterized using a 3D sensitive volume SOI microdosimeter developed by the Centre for Medical Radiation Physics (CMRP), University of Wollongong, Australia.

Visualization of the Field Penetration at the Shielding Current Break and Its Restoration in the Pulse Magnetized YBCO Ring

The Hall scanning method was used to measure the distribution of the trapped magnetic field above the melt grown high temperature superconducting (YBCO) ring at various modes of the pulsed field magnetization. The scan detects the ring’s sector with a small trapped magnetic field after pulse with a short duration (14 ms) of sufficient amplitude (μ0На > 0.86 T). The residual field in the entire ring hole is also very low. Under these conditions of magnetization, the screening current is observed to break down in a certain region of the ring. This sector of the current break (SCB) arises as the result of the local overheating and the destruction of superconductivity. But in the rest (larger) part of the ring, the trapped magnetic field is significant since high current densities remain due to its weak heating. If descending time of the magnetizing field is increased from 7 ms to sufficiently large values > 100 ms, then the SCB has time to cool and the irregularity of the trapped magnetic field in the SCB disappears.

Modeling of vortex dynamics in HTSs with defects under the impact of pulsed magnetic field

By means of the Monte Carlo method, a numerical study of the vortex system in a high-temperature superconductor under the impact of pulses of magnetic field has been conducted. Various shapes and amplitudes of pulses have been considered. Samples with random and regular distributions of three different numbers of defects have been compared from the viewpoint of efficiency of flux trapping. The low-temperature behavior of vortices and their penetration into samples have been shown to be independent of the pulse shape but strongly dependent of the type of pinning distribution. Saturating dependences of density of trapped magnetic flux on the pulse amplitude have been obtained. The samples with random pinning demonstrated higher efficiency of flux trapping at lower pulse amplitudes, and the samples with a triangular lattice of defects—at higher amplitudes. If the amplitude exceeded the saturation field of both samples, the trapped field was almost equal. The increasing number of defects has lead to an increase in trapped field within the considered range of concentrations.

Dark-level trapping, lateral confinement, and built-in electric field contributions to the carrier dynamics in c-plane GaN/AlN quantum dots emitting in the UV range

c-plane GaN/AlN quantum dots (QDs) are promising zero-dimensional quantum nanostructures that exhibit single photon emission properties up to room temperature and even above. In this context, it is of prime interest to gain a deeper insight into the recombination dynamics of photogenerated electron–hole pairs captured by such dots. Hence, in this work, we study the time-resolved photoluminescence (PL) properties in the low injection regime and at cryogenic temperatures of c-plane GaN/AlN QD ensembles emitting above the bulk GaN bandgap in order to properly understand the nature of the recombination channels behind the observed non-exponential decay time profiles. Such decays reveal the existence of a relaxation channel competing with the radiative recombination one. It is thus observed that for the former process the dynamics is independent of the dot height, which is attributed to a reversible nonradiative transfer that could be mediated by a spin-flip process to a dark-level state. The radiative recombination process is recognizable thanks to the characteristic dependence of its lifetime with the emission energy, which is well accounted for by the built-in electric field inherent to quantum nanostructures grown along the c axis and the variations in the lateral confinement at play in such QDs. Those conclusions are drawn from the analysis of the time evolution of the PL spectra by means of a simple analytical model that enables to exclude any screening of the built-in electric field.

Genetic and Morphological Diversity of Indigenous Bradyrhizobium Nodulating Soybean in Organic and Conventional Family Farming Systems

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.