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The effect of inoculants was confirmed to improve the mass effect of ferritic spheroidal graphite iron castings with heavy sections. In the first series of tests, primary inoculation was performed simultaneously with the spheroidizing treatment, followed by the addition of post-inoculant, and the effectiveness of this method was evaluated in the terms of nodule count and mechanical properties. Post-inoculation is the common term for inoculation after initial treatment. In the first series of tests, six inoculants were evaluated in separately cast test samples, for the second part of the evaluation, Fe–Si–Ca–Zr and Fe–Si–Ca–Ba① were selected. In the second series of tests, these inoculants were used and evaluated by cast on test samples with the wall thickness of 40 and 70 mm. The results showed that possibly the change to Fe–Si–Ca–Zr provided the greatest increase in the nodule count. Tensile properties of samples post-inoculated Fe–Si–Ca–Zr showed almost the same values for tensile strength, proof stress, and elongation at 40 mm and 70 mm wall thickness. In impact tests, differences in absorbed energy were observed in samples with a wall thickness of 70 mm, with Fe–Si–Ca–Zr having the highest absorbed energy. Therefore, the Fe–Si–Ca–Zr inoculant is effective post-inoculation for reducing mass effect. Also, the factors were discussed through electron probe micro analyzer (EPMA) analysis of inoculant. [ABSTRACT FROM AUTHOR]

High silicon solid solution-strengthened ductile iron exhibits advantageous combinations of static strength and ductility due to elevated silicon contents. However, the Charpy impact toughness decreases rapidly with increasing silicon content. In particular, the transition temperature between ductile and brittle fracture behaviour is shifted significantly to higher temperatures. Therefore, the optimum adjustment of the graphite phase is of major importance in order to achieve sufficient toughness properties. So far, little is known about the influence of the graphite phase on the toughness properties of high-silicon ductile iron. In the present study, the graphite particle distribution was therefore systematically varied for ductile iron grade EN-GJS-500-14. The effect of the graphite nodule count in the range from 77 to 273 1/mm2, and the influence of the average particle size and particle distance on the Charpy impact energy and the characteristics of the resulting transition curves were investigated by means of statistical analyses. The results that were obtained indicate that the ductile-to-brittle transition temperature in Charpy impact tests can be reduced by about 22 °C by increasing the average nodule count by 100 1/mm2. Additionally, both the lower and upper shelf energies are raised by increasing the nodule count by 100 1/mm2. Based on these results, it becomes apparent to producers that the inoculation technology for toughness-stressed components needs to be specifically considered and adapted. [ABSTRACT FROM AUTHOR]

Samples of ductile iron alloyed with 0.88 % Ni with a nodule count of 606, 523, and 290 nod/mm2 were obtained from sand cast plates of different thickness in the range from 8.46 to 25.4 mm. The effect of the nodule count was evaluated during the austempering process held at 285°C and austempering times of 15, 30, 45, 60, 70, and 90 min. The volume fraction of high carbon austenite increased when the nodule count increased, however, the carbon content of the high carbon austenite kept almost constant. The process window was narrow, requiring a lower austempering time when the nodule count increased. The combination of a higher nodule count and low austempering temperature allowed obtaining a fine ausferritic microstructure which led to higher Brinell hardness and tensile strength. The process window was determined by XRD measurements and it was in good agreement with the microstructural and hardness evolution as the austempering time increased.

In order to elucidate the mechanism of nodule count increase by Bi, we analyzed spheroidal graphite cast iron with increased nodule count by Bi addition. In the Scanning Electron Microscope - Energy Dispersive X-ray Spectrometry (SEM-EDS) analysis, Bi was identified to be present near the center of the spheroidal graphite. The center of this spherical graphite was pretreated by Focused Ion Beam (FIB) micro sampling method to prepare analytical sample and analyzed by Transmission Electron Microscope - Energy Dispersive X-ray Spectrometry (TEM-EDS). As a result, it was found that Bi exists as BiLaCeSb oxide on the outer periphery of the graphite core centered on (MgCa) S. To verify the effect of the BiLaCeSb oxide on the increase in nodule count, we first used mechanical alloying to prototype a BiLaCeSb oxide having the same composition as that observed via TEM-EDS. This oxide was then added to the molten spheroidal graphite cast iron. As a result, nodule count did not increase with the addition of the prototype BiLaCeSb oxide alone, but when the prototype BiLaCeSb oxide and FeSi inoculants were mixed and added, the nodule count increased more than when only the FeSi inoculants was added. From these results, it is considered that the effect of increasing nodule count by Bi addition is that Bi acts on graphite nucleus as an oxide. [ABSTRACT FROM AUTHOR]

The effect of the casting modulus on the distribution and features of graphite in hypo-eutectic ductile iron unalloyed and alloyed with nickel (0.88 wt %) was studied. The cooling rate of the casting plates of 25.4, 12.7 and 8.5 mm in thickness with a casting modulus of 6.87, 4.46 and 3.31 mm, respectively promotes several microstructural changes, such as cementite precipitation and a noticeable nodule count increment. The nickel addition suppressed the cementite formation and improved the nodule count and nodularity for the three casting modulus evaluated. The nickel addition increased the nodule count in 69, 67 and 128 % for the modulus of 3.31, 4.46 and 6.87 mm, respectively, regarding the unalloyed ductile iron. It was found that the biggest casting modulus produced the biggest nodules with the lowest nodule count for both ductile cast irons. Further to the improvements in the graphite features, the nickel addition allowed to keep almost constant the yield and tensile strength ratio for the different casting modulus.

The solidification of spheroidal graphite cast iron (SGI) plays an important role in production of sound quality castings. However, owing to the complex solidification behaviour of SGI, prepouring melt quality evaluation technique such as thermal analysis is used to predict quality of liquid metal by analysing the cooling curve pattern. In this study, an attempt has been made to investigate the role of speed of recalescence (SOR) in nucleation of graphite during solidification of SGI. Cooling curve analysis of liquid samples was carried out at different inoculation degrees. Recalescence and SOR data were obtained from thermal analysis, whereas nodule counts were obtained from microstructural examination of respective sample. It was observed that recalescence and nodule counts (nucleation sites) have a statistically significant inverse linear relationship; with the increase in recalescence, the nodule count was found to get reduced. However, the multiple values of nodule count at same recalescence degree were to be understood, which was clearly justified by SOR studies. After analysing the SOR vs nodule count relation, almost each SOR value corresponds to different nodule counts and the relation was statistically more significant. This infers that for an in-depth nodule count estimation, SOR analysis will be more helpful as compared to ∆Tr; hence, it is envisaged that speed of recalescence is true indicator of graphite nucleation as compared to recalescence in SGI. [ABSTRACT FROM AUTHOR]

Silicon promotes nodule formation in legume roots which is crucial for nitrogen fixation. However, it is very time-consuming and laborious to count the number of nodules and to measure nodule size manually, which led nodule characterization not to be study as much as other agronomical characters. Thus, the current study incorporated various techniques including machine learning to determine the number and size of root nodules and identify various root phenotypes from root images that may be associated with nodule formation with and without silicon treatment. Among those techniques, the machine learning for characterizing nodule is the first attempt, which enabled us to find high correlations among root phenotypes including root length, number of forks, and average link angles, and nodule characters such as number of nodules and nodule size with silicon treatments. The methods here could greatly accelerate further investigation such as delineating the optimal concentration of silicon for nodule formation.

The effect of biochar alone or co-applied with triple superphosphate on rhizosphere soil characteristics, nodule formation, phytoconstituents and antioxidant property of cowpea (Vigna uguiculata) is yet to be adequately examined in sub Saharan Africa. A field experiment was conducted where cowpea (Vigna unguiculata) was grown in a tropical sandy loam soil amended with biochar at 1.5 t ha−1 and 2.5 t ha−1 solely or together with inorganic phosphate fertilizer (Triple superphosphate), applied at a rate of 60 kg P ha −1. At 50% flowering, changes in selected rhizosphere soil properties (pH, total nitrogen, available phosphorus, soil organic carbon, cation exchange capacity), nodule count, phytochemicals (phenols, flavonoids, alkaloids, tannins, saponins) and antioxidant property of cowpea roots and leaves were determined by standard laboratory procedures. Differences between means of the measured parameters were established using ANOVA, and relationships among the parameters were explored using Pearson correlation (p < 0.05). Addition of biochar solely or in combination with TSP significantly (p < 0.05) increased soil pH, total nitrogen, available phosphorus, soil organic carbon, cation exchange capacity and root nodule count. Flavonoids, phenols, alkaloids, saponin, tannin contents and antioxidant activity in the roots and leaves were significantly (p < 0.05) higher in the amended soils compared with the unamended soil. Similarly, soil flavonoids, phenols, alkaloids and antioxidant activity were significantly higher in amended soils compared with control. Significant, positive inter and intra correlation with varying strength was found between soil properties, nodule number and phytoconstituents. This is an indication that biochar can be co-applied with triple superphosphate to sustain soil fertility, improve nodulation and enhance concentrations of phytoconstituents in soil, cowpea roots and leaves.

Silicon promotes nodule formation in legume roots which is crucial for nitrogen fixation. However, it is very time-consuming and laborious to count the number of nodules and to measure nodule size manually, which led nodule characterization not to be study as much as other agronomical characters. Thus, the current study incorporated various techniques including machine learning to determine the number and size of root nodules and identify various root phenotypes from root images that may be associated with nodule formation with and without silicon treatment. Among those techniques, the machine learning for characterizing nodule is the first attempt, which enabled us to find high correlations among root phenotypes including root length, number of forks, and average link angles, and nodule characters such as number of nodules and nodule size with silicon treatments. The methods here could greatly accelerate further investigation such as delineating the optimal concentration of silicon for nodule formation. [ABSTRACT FROM AUTHOR]

We have studied the problems and improvement on producing large casting with solid solution strengthened ferritic spheroidal graphite cast irons (hereafter Hi–Si). As the matrix of Hi–Si material becomes hardened with silico-ferrite, hardness, tensile strength and yield strength increase. But elongation and impact value decrease conversely. If silicon content increases or if the cooling rate decreases due to heavy section, as silicon segregation progresses, the elongation and impact value are remarkably reduced. When increasing the graphite nodule count with optimum inoculation and setting chiller, the segregation of silicon decreases and then the mechanical properties are recovered. In addition, when Hi–Si reaches around 400 °C, its elongation decreases largely, which is called 400 °C embrittlement. This high-temperature embrittlement can be prevented with setting the ratio of Mg/P less than 1.5 and reducing the free Mg, because the grain boundary fracture occurs due to the free Mg not fixed as Mg3P2 at the grain boundary. [ABSTRACT FROM AUTHOR]

This paper attempts to investigate the effect of preconditioning and inoculation on nodule count and their size distribution to eliminate shrinkage porosity in spheroidal graphite (SG) iron castings. Studies were conducted on various heats of SG iron prepared for differential case casting with and without the addition of 0.1% Al, Zr, Ca-FeSi alloy as preconditioner and Ca-Ce-FeSi alloy was used as an inoculant. It was found that the combined effect of preconditioning and inoculation significantly improves nodule count and nodule size distribution which subsequently reduces the number of castings containing shrinkage porosity. The shrinkage quantity (Q) was found to reduce from 10 to 2.4%. Graphite nodule count and their size distribution were found to be important factors for controlling shrinkage porosity, and it was observed that preconditioning substantially improves the percentage of small size (5-15 µm diameter) graphite nodules. Higher nodule count reduces chances of shrinkage but simply having higher graphite nodule count of similar size does not help in minimising or elimination of shrinkage, it is necessary to have nodules of different sizes in a significant proportion. [ABSTRACT FROM AUTHOR]

In this study, the effect of inoculant composition and nodularisation treatment temperature on recalescence temperature (TER) and undercooling temperature (TEU) in SG iron has been studied by using thermal analysis. 0·1, 0·2 and 0·3 wt-% of three types of inoculants Ca,Ce,Al-FeSi, Ca,Sr,Al-FeSi and Ca,Ba,Al-FeSi were used as so called stream inoculation. Ca,Ce,Al-FeSi was found to be the most potent one in reducing both recalescence (∆T r ) and eutectic undercooling (∆T). The nodule count has also been found higher in Ca,Ce,Al-FeSi inoculated SG iron samples compared to other two inoculants. It has been observed that higher the nodule count lower is the ∆T r and ∆T and vice versa. The recalescence and shrinkage relationship of 24 heats of differential case castings has been established; it was observed that the number of castings containing shrinkage in respective heats increase as the recalescence and nodularisation treatment temperature increases. [ABSTRACT FROM AUTHOR]

Copyright of Journal of Polytechnic is the property of Journal of Polytechnic and its content may not be copied or emailed to multiple sites or posted to a listserv without the copyright holder's express written permission. However, users may print, download, or email articles for individual use. This abstract may be abridged. No warranty is given about the accuracy of the copy. Users should refer to the original published version of the material for the full abstract. (Copyright applies to all Abstracts.)

Image analysis has become an increasingly important analytical tool to facilitate the determination of nodularity and nodule count in ductile iron. This paper summarizes the image analysis results obtained by several laboratories on identical samples having different nodularity and nodule count. The parameters studied include; the number of particles analyzed, the effect of the trap size and varying the shape factor. [ABSTRACT FROM AUTHOR]

In this work, a theoretical model is proposed for heterogeneous nucleation on substrates whose size distributions can be described by the Weibull statistics. In particular, the proposed model suggests that the size distribution for the various nucleation sites is exponential in nature. Measurements of grain count were carried out on experimental AI-T3Sİ and AI-5-OCu single phase alloys inoculated using an AI-5Tİ-1B master alloy. In addition, experimental nodular and flake graphite iron castings were processed under various metallurgical conditions. In single phase alloys, the area of the equiaxed dendritic grain count was estimated from the electron backscattering diffraction analysis, whereas the graphite nodule and graphite eutectic cell count were estimated on polished cast iron surface sections by stereological means. In addition, maximum undercoolings were determined by thermal analysis. The experimental outcome indicates that the grain count can be properly described by a proposed exponential function of the maximum undercooling at the onset of alloy solidification. Finally, the magnitudes of the nucleation parameters were experimentally determined in this work. [ABSTRACT FROM AUTHOR]

Copyright of Technical Journal / Tehnički Glasnik is the property of Polytechnic of Varazdin and its content may not be copied or emailed to multiple sites or posted to a listserv without the copyright holder's express written permission. However, users may print, download, or email articles for individual use. This abstract may be abridged. No warranty is given about the accuracy of the copy. Users should refer to the original published version of the material for the full abstract. (Copyright applies to all Abstracts.)

The present investigation was carried out to study the effect of manganese and copper addition, singly as well as in combination, on the microstructure, micro-segregation, and mechanical properties of ductile irons. Alloy A (3.18C, 2.64Si, 0.45Mn), alloy B (3.35C, 2.51Si, 0.82Mn), alloy C (3.16C, 2.80Si, 1.08Mn, 0.56Cu), and alloy D (3.18C, 3.00Si, 1.04Mn, 1.13Cu) were melted and cast in the form of Y-block test pieces. The cast microstructures varied from ferrito-pearlitic in alloys A, B, and C to pearlitic in alloy D. However, on XRD analysis and SEM examination, the presence of martensite patches was also detected. There was a marginal decrease in nodule count in alloy B. In alloys C and D, nodule counts were higher, but the proportion of ferrite decreased drastically. Alloy D was found to be the strongest (UTS ≈ 800 MPa, El = 5%) with alloys A and C coming next in strength; while alloy B was weakest of the four. The presence of martensite patches in association with pearlite appears to be responsible for low toughness of these alloys. Microprobe analysis shows some silicon segregation near the graphite nodules and practically little segregation of manganese. Elemental mapping by FE-SEM does not indicate any manganese segregation. [ABSTRACT FROM AUTHOR]

The surface decarburisation produced during the austenitising stage of ductile iron parts constitutes an issue that needs to be addressed in many manufacturing processes. This work examines the role that nodule count and other variables play on decarburisation onset and decarburised layer thickness. Specimens with noticeable different nodule counts were employed to perform the experiments. The results showed that the thickness of the decarburised layer markedly decreases as nodule count increases, and that the decarburised layer depth increases as the austenitising holding time increases. On the other hand, the austenitising temperature has little influence on the decarburisation process. An equation able to calculate the decarburisation onset, the austenitising holding time and the decarburised layer thickness was developed. This equation yields accurate estimations for austenitising ductile iron parts with prior ferritic matrixes, and is further applicable to a wide range of nodule counts, which even comprise those proper of thin wall ductile iron parts. [ABSTRACT FROM AUTHOR]

The present work focuses on the fatigue propagation of long cracks in ferritic ductile iron parts of varied thickness. Samples were taken from thin wall ductile iron plates and standard 'Y' blocks with nodule counts ranging from 250 to 2200 nod/mm2 and ferrite grain sizes from 70 to 150 μm. Fatigue crack propagation threshold ΔK th and Paris law constants C and m were measured, and the influence of the microstructure refinement (established through nodule count and grain size) on the characteristics of the fatigue fracture surface was analysed. The results show that, once the crack is initiated, the fatigue crack growth threshold diminishes as the microstructure is refined, while the rate of growth remains practically unaltered. The crack path preferentially intersects graphite nodules and is mostly transgranular through the ferrite grains. Nevertheless, at low levels of ΔK, a low percentage of intergranular fracture was also observed. [ABSTRACT FROM AUTHOR]

The present work gives a detailed analysis into one of the most important quality parameters in cast iron, namely the eutectic cells or nodule count. The analysis is based on theoretical fundamentals of cast iron solidification. Expressions are derived and used to relate either the number of cells or the nodule count to factors of technological importance. It is found that such factors are intrinsically related to the chill tendency, pre-shrinkage expansion, shrinkage porosity, shrinkage depression and graphite type. Also, it is shown that the resultant mechanical properties of cast iron are strongly influenced by the foundry practice. In particular, it is established that the eutectic cell density or the nodule count is a quality factor reflecting the physical-chemical state of the liquid cast iron at a given cooling rate. In turn, this determines the graphite nucleation potential of cast iron which can be used to incorporate all of the technological factors associated with melt preparation. [ABSTRACT FROM AUTHOR]

Abstract: Surface characteristics of thin wall ductile iron (TWDI) parts, such as residual stresses, distortion and dimensional changes produced during casting and heat treatment, are relevant variables when it comes to production processes design. This work focuses on the effect of nodule count on residual stresses (RS) and of TWDI plates distortion. As-cast, ferritised and austempered samples were employed. The role played by two typical austempering temperatures (280 and 360°C) and three significantly different nodule counts (265, 1200 and 1700nodules (nod)/mm2) are discussed by establishing microstructural changes, i.e., microstructure fineness, retained austenite volume fraction (V γ %), and austenite carbon content (C γ %). Besides, residual stresses profiles below the surface and dimensional changes are determined. Results show that all samples display compressive RS on the surface and neighbouring layers. Samples with high nodule count austempered at 280°C lead to higher compressive RS and distortion as well as to an increase in the RS field below the surface. As-cast and ferritised plates exhibit noticeably lower compressive RS values. [Copyright &y& Elsevier]

The graphite nodule density and size distribution are two very important parameters in the characterization of the microstructures of ductile iron. Various amount of cerium element (Ce) (from 0.005% to 0.020%) were added into ductile iron cast in sand moulds to investigate the effect of Ce concentration on graphite nodule count and size distribution. The addition of Ce has a significant effect on solidified microstructures of ductile iron. Increasing of Ce concentration from 0.005% to 0.014%, an obvious increase in nodule graphite amount is achieved and graphite size becomes finer. When the addition level of Ce reaches 0.018% or 0.020%, spheroidal graphite begins to coarsen, resulting in the decrease in graphite amount and formation of the some non-spherical graphite. An evident nucleus and faceted crystals inside a nodule are clearly distinguished and the thin flakes that constitute the nodule are observed from the SEM photograph. EDX-analysis of nucleus of the spheroidal graphite shows that it is composed of sulfur, cerium, magnesium and trace calcium. The 3-D nodule count of ductile iron is 11.7 × 103/mm3 with 0.005% Ce addition. The value is 45.8 × 103/mm3 with Ce addition up to 0.014% and the majority of diameter is less than 30 µm. However, with 0.018%Ce residual, the nodule count decreases to 29.0 × 103/mm3. The value is close to that of 0.018%Ce when Ce concentration is 0.020%, and the majority of diameter is less than 40 µm. The results indicate that the graphite nodule count reaches the maximum and mean diameter reaches the minimum with 0.014%Ce residual existing in ductile iron. [ABSTRACT FROM AUTHOR]

In the first phase of the AFS-sponsored research project on "Restoring Techniques for "Monday Morning Iron", the investigation focused on the extent to which prolonged holding of the base iron in an induction furnace affected the quality of ductile iron. The objective in Phase II was to find a way to increase the nucleation potential of iron having a high chilling tendency. The technique consisted of adding SiC, SiCa, crystalline graphite, etc., to a base iron in the furnace before the Mg-treatment with the aim to supply the iron with active elements considered suitable sites for graphite nodule nucleation. The results of this investigation demonstrated that SiC is the most efficient addition to increase the iron nucleation potential. Based on these results, tests were run under commercial foundry operating conditions. This report presents and discusses the results of investigation performed in the MTL laboratory with detailed analysis of chilling tendency, microstructure and shrinkage propensity on test samples from both base and final ductile irons. [ABSTRACT FROM AUTHOR]

In the present work the predictions based on a theoretical analysis aimed at elucidating of eutectic cell count or nodule count N were experimentally verified. The experimental work was focused on processing flake graphite and ductile cast irons under various inoculation conditions in order to achieve various physicochemical states of the experimental melts. In addition, plates of various wall thicknesses s, were cast and the resultant eutectic cell or nodule counts were established. Moreover, thermal analysis was used to find out the degree of maximum undercooling for the graphite eutectic ΔTm. A relationship was found between the eutectic cell or nodule count and the maximum undercooling ΔTm. In addition, it was also found that N can be related to the wall thickness of plate shaped castings. Finally, the present work provides a rationale for the effect of technological factors such as the melt chemistry, inoculation practice, and holding temperature and time on the resultant cell count or nodule count of cast iron. In particular, good agreement was found between the predictions of the theoretical analysis and the experimental data. [ABSTRACT FROM AUTHOR]

In the present work the predictions of a proposed analytical theory were compared with the experimental outcome on metallographic determinations of eutectic cell count N and nodule count Nn. Accordingly, processing of flake graphite and ductile cast irons was carried out under various inoculation conditions in order to achieve a range of physicochemical states for the experimental melts. In addition, plates of various wall thicknesses s were cast and the resultant eutectic cell and nodule counts were established. Moreover, thermal analysis was employed for determinations of the maximum degree of undercooling for the graphite eutectic ΔTm. A relationship was found between the eutectic cell N or the nodule count and ΔTm. In addition, it was found that N and Nn can be related to the casting modulus M and hence to s in plate shaped castings. Finally, the present work provides insights into the effect of technological factors such as the melt chemistry, the inoculation practice and the holding temperature and time on the resultant N and Nn values. In general, it was found that the predictions of the present analysis are in good agreement with the experimental outcome. [ABSTRACT FROM AUTHOR]

Abstract: Thin wall ductile iron castings are being used in the industry as a way to improve the strength to weight ratio of machine parts. The high cooling rate, suffered by thin wall parts during the solidification process, promotes several microstructural changes, such as, carbide precipitation and a noticeable nodule count increment. The present work, studies the effect that the increase in nodule count has on the rolling contact fatigue resistance of ductile iron with different matrix microstructures. Ductile cast iron test samples, with nodule counts ranging between 150 and 1400nod/mm2 were obtained. The samples were then heat treated in order to obtain three sets of different ADI grades and also a quenched and tempered set. The rolling contact fatigue properties were evaluated by using a flat washer type test rig. Different relations of the contact area versus the nodule size were obtained by using three different counterparts. The results show that an increase in the nodule count promotes a noticeable increase in the rolling contact fatigue life, being more important for the quenched and tempered samples. The relation between contact area surface and nodule size was the main variable influencing the rolling contact fatigue life. [Copyright &y& Elsevier]

The transformation of austenite to ferrite and graphite or to pearlite in spheroidal graphite cast iron depends on a number of factors, among which are the nodule count and the cooling rate. In this study, the pearlite fraction decreased as the nodule count increased for a given cooling rate. Furthermore, as the cooling rate increased, the fraction of pearlite increased. Both effects were more sensitive at low nodule count. The effects of altering these parameters on the relative amount of pearlite and ferrite in the matrix of a copper-molybdenum (Cu-Mo) spheroidal graphite cast iron were addressed using heats carried out in an induction furnace, and the melts were treated with magnesium ferrosilicon in a ladle. To vary the nodule count, the melts were inoculated with two different amounts of ferrosilicon. Pouring was performed into sand molds of cylindrical cavities with different section size in order to achieve various cooling rates. Both the nodule count and the cooling rate affected the relative amount of ferrite and pearlite in the matrix. [ABSTRACT FROM AUTHOR]

The effect of biochar alone or co-applied with triple superphosphate on rhizosphere soil characteristics, nodule formation, phytoconstituents and antioxidant property of cowpea ( Vigna uguiculata ) is yet to be adequately examined in sub Saharan Africa. A field experiment was conducted where cowpea ( Vigna unguiculata ) was grown in a tropical sandy loam soil amended with biochar at 1.5 t ha -1 and 2.5 t ha -1 solely or together with inorganic phosphate fertilizer (Triple superphosphate), applied at a rate of 60 kg P ha -1 . At 50% flowering, changes in selected rhizosphere soil properties (pH, total nitrogen, available phosphorus, soil organic carbon, cation exchange capacity), nodule count, phytochemicals (phenols, flavonoids, alkaloids, tannins, saponins) and antioxidant property of cowpea roots and leaves were determined by standard laboratory procedures. Differences between means of the measured parameters were established using ANOVA, and relationships among the parameters were explored using Pearson correlation (p < 0.05). Addition of biochar solely or in combination with TSP significantly (p < 0.05) increased soil pH, total nitrogen, available phosphorus, soil organic carbon, cation exchange capacity and root nodule count. Flavonoids, phenols, alkaloids, saponin, tannin contents and antioxidant activity in the roots and leaves were significantly (p < 0.05) higher in the amended soils compared with the unamended soil. Similarly, soil flavonoids, phenols, alkaloids and antioxidant activity were significantly higher in amended soils compared with control. Significant, positive inter and intra correlation with varying strength was found between soil properties, nodule number and phytoconstituents. This is an indication that biochar can be co-applied with triple superphosphate to sustain soil fertility, improve nodulation and enhance concentrations of phytoconstituents in soil, cowpea roots and leaves., (© 2020 The Author(s).)