Mo In Soil Research Articles

Assessing Adsorption Behavior of Molybdenum in Soils: An Emerging Metal Contaminant

Molybdenum (Mo) is an essential micronutrient for most living organisms but also an emerging contaminant in the environment. A narrow range exists between critical requirements for plants (0.5 mg kg-1) and threshold toxicity of molybdenum (10 mg kg-1) to ruminants, considered as “molybdenosis”. Adsorption is one of the most important chemical processes in soils that affect the mobility of metals/contaminants in soil. To evaluate the sorption behaviour of molybdenum in soils, twenty bulk surface soil samples (0–15 cm) with diverse physical and chemical properties were collected from different parts of India. A laboratory experiment was conducted to study the sorption behaviour of Mo in soil under two temperature (20 and 30○ C) conditions. Five graded Mo concentrations (1, 2, 5, 10, 20, and 50 mg L-1) were prepared using (NH4 ) 6 Mo7 O24 in a 0.005 M Ca(NO3 ) 2 background solution. Maximum adsorption of Mo was observed in the soils where pH ranges from 4-5, while in alkaline soils (pH > 8) negative adsorption phenomena were found. Freundlich isotherm fitted better than Langmuir isotherm in a wide range of soil’s pH. A highly significant negative correlation was observed between soil pH and adsorption parameters, while a significant positive correlation was found between SOC and adsorption parameters. The thermodynamic parameters i.e., free energy (∆G○ ), enthalpy (∆H○ ), and entropy (∆S○ ) were determined using sorption data in two different temperature conditions. It was observed that molybdenum sorption in soil is a spontaneous endothermic reaction. This study highlighted the role sorption mechanism in the evaluation of mobility and availability of molybdenum in different soil chemical environments.

Enrichment mechanisms of Mo in soil in the karst region Guangxi, China

Soils developed in karst regions have naturally high background values of molybdenum (Mo) due to geological factors. However, the enrichment mechanism of Mo in these soils are not fully understood, making it challenging to assess their ecological risk and utilize Mo-rich land resources. To shed light on this issue, this study collected and analyzed data from the 1:50,000 geochemical survey in Guangxi, including 536,503 sets of soil data and 3043 sets of rock data, as well as 40 sets of carbonate rock-soil from typical karst regions. The results showed that soil Mo enrichment is highly correlated with the distribution of carbonate rocks in karst regions. The carbonate rocks in these regions contain Mo ranging from 0.03 to 1.06 mg·kg−1 (with a mean of 0.22 mg·kg−1). In comparison, the soil Mo derived from carbonate rocks can reach up to 6.00 mg·kg−1 (with a mean of 2.75 mg·kg−1), representing an average enrichment of soil Mo that is 24 times higher compared to the carbonate parent rock. The enrichment of soil Mo in karst regions is primarily controlled by secondary enrichment during the weathering process of carbonate. During the insoluble residue accumulation process, the dissolution of carbonate leads to a dramatic reduction in bedrock volume, and the adsorption of clay minerals and Fe minerals in insoluble residues plays an essential role in Mo enrichment during these stages. During the soil-forming stage of the insoluble residue, most Mo leaches into the water body due to the mineral transformation of insoluble residue. Consequently, as Fe–Mn nodules in soils become more enriched with increasing weathering intensity, some Mo is absorbed and passivated by iron and manganese oxides (hydroxides). Accordingly, the contribution of Fe–Mn nodules and the degree of leaching were closely related to the enrichment of soil Mo in karst regions. This study provides insights into the enrichment mechanisms of Mo in soils developed in karst regions, which will help to evaluate their ecological risk in these environments.

Source identification and spatial distribution of heavy metals in soil of central urban area of Chongqing, China

ABSTRACT To understand the characteristics of heavy metal pollution in soil and identify the source of heavy metals, 342 surface soil samples were collected in Chongqing, China. The contents of 11 heavy metals (i.e., arsenic (As), cadmium (Cd), chromium (Cr), lead (Pb), copper (Cu), zinc (Zn), nickel (Ni), mercury (Hg), antimony (Sb), manganese (Mn), and molybdenum (Mo)) were determined. The Principal Component analysis/absolute Principal component fraction (PCA/APCS) receptor model, the classified regression (CATREG) model, and the hot spot model were employed to analyze the data. The contents of As, Cd, Cr, Pb, Cu, Zn, Ni, Hg, Sb, Mn, and Mo in soil were 5.80, 0.13, 76.56, 25.55, 23.99, 75.58, 30.50, 0.05, 0.64, 573.32, and 0.56 mg·kg−1, respectively. The results of principal component analysis showed that the main heavy metal elements under the first principal component load were Cu, Ni, Zn, Mn, Cr, Pb, and Cd. The second principal component is mainly loaded with Mo, As, Hg, and Sb. The results of classified regression analysis showed that population density mainly affected Cu (0.54), soil mainly affected Ni (0.41), Sb (0.49), Zn (0.47), and Mn (0.21), and water quality mainly affected As (0.45) and Mo (0.37). Air quality mainly affected Cd (0.33) and Cr (0.37), traffic activity mainly affected Hg (0.31), and slope mainly affected Pb (0.31). The research results can be used to trace the environmental sources of soil heavy metals, fundamentally prevent and repair soil heavy metal pollution, and protect urban soil environmental quality.

Application of land snail Helix lucorum for evaluation of genotoxicity of soil pollution

Application of native species as sentinels allows environmental scientists to determine real genotoxic impact of environmental pollutants. The present study aims at investigating the DNA damage in the land snail Helix lucorum as a biomarker of soil pollution. For this reason, the genotoxic impact of contaminated soil on H. lucorum, collected from different polluted areas, was investigated using the comet assay in haemocytes and digestive gland cells. An increase in DNA damage was found in the snails sampled from polluted sites compared with the reference one. Strong correlations between DNA damage in haemocytes and digestive gland cells with the level of contamination indicate pollution-induced genotoxic effects in both tissues. At the same time, the digestive gland was more sensitive towards pollutants compared with haemolymph. A direct relationship between concentrations of Cu, As and Mo in soil and the number of damaged cells for hаemolymph and digestive gland tissue was found. However, the data obtained reflect the total genotoxicity of all pollutants in the studied areas. Significant correlations between the DNA damage measured by the comet assay and metal contents in soil indicate that it is a suitable biomarker in ecotoxicological studies. Our results indicate the effectiveness of H. lucorum in biomonitoring of environmental pollution.

Molecular speciation of Mo (VI) on goethite and its implications for molybdenum and its isotopic cycle in ocean

Sorption of Mo to goethite and related iron (hydr)oxides plays an important role in controlling the mobility of Mo in soil and aquatic environments. We first performed ab-initio molecular dynamics (MD) simulations of Mo complexation at the goethite {1 0 1}-water interface. We find that molybdenum adsorbed on goethite mainly exists as the inner-sphere tetrahedral bidentate and monodentate corner-sharing complex, instead of the previous argued bidentate edge-sharing or outer-sphere complex. Different from previous literature, we didn’t find any distorted octahedral structure of Mo on goethite. The predicted Mo-Fe distances of bidentate and monodentate corner-sharing complex based on ab-initio MD is 3.53 and 3.38 Å, respectively, which are consistent with the fitted Mo-Fe distances: 3.40 ± 0.15 Å and 3.41 ± 0.1 Å from EXAFS.We measured the adsorption of Mo (VI) on goethite (α-FeOOH) at different initial concentration and pH from 3 to 11 under N2 atmosphere and constructed a surface complexation model that is consistent with the molecular speciation based on ab-initio MD, XANES, EXAFS and reported in-situ ATR-IR analysis (Davantes and Lefevre, 2015, 2016). Application of SCM for Mo on goethite assuming iron oxides as the principal component of ferromanganese crust (containing average 276 mg/kg Mo) will have ∼0.3 μg/l Mo in seawater in equilibrium. The observed ∼10 μg/l Mo in seawater (c a. 400–800 yr) is between 0.3 (adsorption equilibrium by marine goethite) and 23 μg/l (adsorption equilibrium by marine birnessite, Kashiwabara et al., 2011), suggesting that molybdenum in seawater has reached equilibrium with ferromanganese crust, and goethite (57%) probably plays a more important role than birnessite (43%) in regulating molybdenum abundance in the ocean, which has not been fully recognized in past.Observed molybdenum isotopic fractionation between seawater and ferromanganese crust excesses the experimental molybdenum isotopic fractionation range during adsorption by birnessite and goethite (Goldberg et al., 2009). Based on reported experimental molybdenum isotopic fractionation values and our SCM prediction, the molybdenum isotopic fractionation δ98/95Mo value should vary between 1.6 and 2.3‰, which is lower than the observed range between seawater and ferromanganese crust: 2.7–3.2‰ about 1‰, suggesting the disequilibrium of molybdenum isotopic fractionation in ocean. To clarify the discrepancy, this study highlights the necessity of clarifying the molybdenum source in hydrogenic and hydrothermal ferromanganese crusts before understanding molybdenum isotopic fractionation between seawater and ferromanganese crust.

Molybdenum Fertilization Improved Antioxidant Capacity of Grazing Nanjiang Brown Goat on Copper-Contaminated Pasture.

Copper (Cu) is an essential trace element, but excessive Cu intake can induce poor performance and Cu poisoning and result in various health problems. Cu and molybdenum (Mo) antagonize each other in vivo. Therefore, Mo can reduce the absorption and utilization of Cu. The aims of this study were to investigate the impacts of Mo fertilization on antioxidant capacity of grazing Nanjiang brown goat on Cu-polluted meadow and explore the control methods of Cu pollution in natural pasture. Fertilization and grazing experiments were carried out in Liangshan Yi Nationality Prefecture of the Western Sichuan Plateau, Sichuan Province, Southwest China. Cu-polluted meadows of 12 hm2 were fenced, and randomly divided into two groups (3 replications/group, 2 hm2/replication), control group and treatment group, fed with basic diets supplemented with 0 and 3 kg Mo/hm2 [ammonium molybdate tetrahydrate, (NH4)6Mo7O24·4H2O], respectively. In the current study, 36 healthy Nanjiang brown goats (1 year old, 32.8 ± 1.1 kg) were randomly divided into two groups (3 replications/group, 6 goats/replication) and assigned to the experimental pastures. The grazing experiment lasted for 60 days. The results showed that the concentration of Mo in soil in treatment group was 96.28 mg/kg, far exceeding the normal levels. At days 30 and 60, the levels of Hb, RBC, and PCV in blood in treatment group and the activities of serum SOD, GSH-Px, T-AOC, CAT, and Cp were higher than those in control group (P < 0.01). The MDA content in treatment group was lower than that in control group (P < 0.01). The contents of Cu in blood and liver in treatment goats were lower than those in control animals (P < 0.01). The contents of Zn and Mo in blood and liver in treatment goats were higher than those in control animals (P < 0.01). The Mn content in liver in treatment group was higher than that in control animals (P < 0.01). These results indicated that fertilization of (NH4)6Mo7O24 not only markedly influenced the mineral contents in blood and liver, but also extremely improved antioxidant capacity of grazing Nanjiang brown goat from fertilized pastures and relieved the damage caused by Cu pollution.

Seasonal Dynamics of Copper Deficiency in Wumeng Semi-Fine Wool Sheep.

A study of the seasonal dynamics of copper (Cu) deficiency and its effects on the antioxidant system in Wumeng semi-fine wool sheep in Weining county was conducted. In addition, the concentrations of mineral elements in soil, grass, and blood of affected and healthy Wumeng semi-fine wool sheep were determined, and blood indices were measured. The results showed that Cu contents in soil, grass, and sheep blood from the experimental pasture were significantly lower than those from the control pasture (P< 0.05), while the Mo content in the samples from the experimental pasture were higher than those from the control pasture (P< 0.05). Hb, RBC, PCV, and MDA values in the blood of affected sheep were significantly higher than those of healthy sheep, the content of TP was significantly lower (P< 0.05), and the activities of CAT, GSH-Px, CP, SOD, POD, and TP in the blood of affected sheep were lower than those in healthy sheep (P< 0.05). A comparison of different months showed that the Cu content in soil was higher in November than in June and September. Hb, RBC, PCV, WBC, and the content of MDA in the blood of affected sheep was higher in November than in June and September; however, the change in CP, CAT, GSH-Px, POD, and TP showed the opposite trend. The content of Cu and Mo in soil, grass, and blood showed seasonal changes. Therefore, it is concluded that the seasonal dynamics of Cu deficiency in Wumeng semi-fine wool sheep in Weining was due to the content of Mo and Cu in soil and grass in different seasons, and high Mo concentration in grass affected Cu deficiency in sheep. The function of the antioxidant system of Wumeng semi-fine wool sheep was reduced as a result.

Soil micronutrient availability to crops affected by long-term inorganic and organic fertilizer applications

The effects of mineral and organic fertilization on the contents of Fe, Cu, Zn, Mn, B and Mo in soil and in the soil solution as well as on availability of these elements for crops were investigated in the long-term field trial. The highest contents of Zn, Fe, Mn and Cu in soil and soil solution were observed in the treatment with the lowest pH (NPK). In this same combination the content of B and Mo was the lowest. The concentration of Zn, B and Fe in the soil solution significantly increased under farmyard manure application. Liming significantly decreased contents extractable by 1 mol/L HCl forms of Mn and Zn and significantly increase the content of Mo in the soil. Regardless of fertilization applied, microelement concentrations in the soil solution are sufficient for fulfilling nutritional needs of plants cultivated during the trial.

Contamination investigation and risk assessment of molybdenum on an industrial site in China

Because certified reference standards on molybdenum (Mo) in soil are not available, and drafted risk assessment procedures in China have not included Mo. Assessment of the potential risks posed by Mo in soil and groundwater is the key to establishing the extent of the contamination and deriving achievable remedial targets, should remediation deemed to be necessary. This paper reports the first investigation of Mo contamination in soil and groundwater from an incandescent light-bulb manufacturing facility in China. Though the plant was built in 1971, the contamination of Mo in the site received little attention until the 1994 and 2008 monitoring campaigns; soil Mo concentrations ranged from not-detectable to 15mg/kg in 1994, and from 0.25 to 252mg/kg in 2008. In addition, groundwater Mo concentrations ranged from not-detectable to 362μg/L in 1994, and 1 to 32, 500μg/L in 2008. Simulation by Visual MINTEQ software showed that Mo speciation in the groundwater would be limited to MoO42−. Detailed site investigation showed that the high concentrations of Mo in groundwater could be adequately explained by the predominant presence of anionic MoO42− at the measured average soil pH of 8.65, and given the small adsorption coefficient 112L/kg for Mo onto field soil samples. A modified three-step sequential extraction procedure showed that residual percentages of soil Mo at this industrial site ranged from 69.8 to 81.0%, indicating that Mo in the soil was mostly present in the mineral lattice. Bounding of Mo onto the mineral lattice is not available to living organisms and thus the risk from soil contamination was considered minimal.A conceptual site model developed for quantitative risk assessment indicated that the main exposure pathways would be consumption of the groundwater by local residents, and lateral Mo migration to bounding rivers. Only non-carcinogenic risk was assessed, because Mo has no known carcinogenic effect on living organisms, as indicated from the toxicity data for Mo. Among the 35 assessment locations, Mo in 14 locations was determined to pose unacceptable non-cancer risk for on-site children, with a hazard quotient from 1.2 to 433 when children directly drink groundwater. In addition, Mo in groundwater which is transported off-site by lateral migration will pose unacceptable non-cancer risks for off-site children, with a hazard quotient of up to 45.8 from direct water drinking. Although Mo concentrations in the bounding rivers ranged from 4 to 6,053μg/L, toxicity data indicated that the ecological risk is minimal for aquatic biota in the surface water. A site-specific target level for Mo in groundwater was established as 75.1μg/L. Further work will be conducted regarding remediation feasibility at this site; permeable reactive barriers may be an effective option given the predominant distribution of Mo in the groundwater in the site.

Deževniki kot kazalniki onesnaženosti tal

The metal levels were determined in soil samples in earthworms collected in the vicinity of the abandoned lead smelter (the Upper Meža Valley, Žerjav) andthe largest thermal power plant in Slovenia (the Šalek Valley, Veliki Vrh),near Velenje - Celje road (Črnova) and at the reference area (the Logar Valley, Polanc) with the aim to investigate the transfer of metals from soil to earthworms and to assess the bioindicative potential of earthworms. Our study revealed the following: (i) the highest levels of metals were determinedin earthworms from the most polluted area (Žerjav) and the lowest inearthworms from the reference location (the Logar Valley); (ii) earthworms bioaccumulated Cd, Hg and Zn at all locations, bioaccumulative factors (BCF) of these three metals ranged between 1.18 - 29.2 (Cd), 1.68 - 21.0 (Hg) and 1.10 - 5.57 (Zn), respectively; (iii) earthworms are good bioindicator of polluted soil, since the correlations between Zn, Cd, Cu, Pb, Hg and Mo in soil and in earthworms were established.

Application of orientation biogeochemical exploration method in the vicinity of Ildong Fe-Pb-Zn skarn deposits in Korea

Orientation biogeochemical exploration was applied in the vicinity of Ildong Fe-Pb-Zn skarn deposits in Korea. Sampling was conducted along four traverse lines and control areas. A total of 12 rock, 64 soil and 320 plant samples (including three species such as Daimyo oak leaves/branches (Quercus dentata), Ash tree leaves/branches (Fraxinus rhynchophylla Hance) and Japanese red pine leaves (Pinus densiflora Siebold & Zucc.)) were collected and analysed. The content of Cu, Pb, Zn, Mn, Cd, As and Mo in soil from target areas (n = 56) were 2.0–4.5 times higher than those from control areas (n = 8). However, there were no specific contrasts of element content in plant samples (each n = 56) except both for Pb in Q. dentata leaves (0.45–54.93 mg/kg Pb) and branches (0.73–25.89 mg/kg Pb) and Cd in P. densiflora leaves (0.06–4.08 mg/kg Cd). The biological absorption coefficient for each plant sample was low, except for Cd and Mo, which shows 0.214 and 0.149 respectively in P. densiflora. Also, element content in soils and P. densiflora leaves is positively correlated and these geochemical variations of Cd and Mo show similar trends. Therefore, P. densiflora leaves showed the possibility of Cd and Mo indicator in these types of deposits.

Effects of Treated Municipal Wastewater on Soil Chemical Properties and Heavy Metal Uptake by Sorghum (sorghum bicolor L.)

In order to investigate the effect of treated municipal wastewater on soil chemical properties and heavy metal uptake by sorghum an experiment was carried out in the Institute of Agriculture at Zabol University, Iran 2007 in a randomized complete block design with four replications. The treatments were managed for irrigation; with well water during entire period of growing season as control (T1); wastewater during the first half of growing season (T2); wastewater during the second half of growing season (T3); wastewater and well water alternately (T4) and wastewater during entire period of growing season (T5). The results have indicated that irrigation with wastewater lead to significant increase in N, P, K, Ca, Na, Mg, SAR, EC, O.C% than control treatment (p ? 0.05). In addition, the increases of Zn, Fe, Mo in soil, and Cu, Fe in sorghum plant were statistically significant in comparison with control treatment (p?0.01). The highest transfer coefficient was observed for Mo and Pb (1.28, 1.02), and the lowest for Cu (0.077 which highlight the high absorption power of sorghum toward these elements.

Predicting molybdenum toxicity to higher plants: Estimation of toxicity threshold values

Four plant species (oilseed rape, Brassica napus L.; red clover, Trifolium pratense L.; ryegrass, Lolium perenne L.; and tomato, Lycopersicon esculentum L.) were tested on ten soils varying widely in soil properties to assess molybdenum (Mo) toxicity. A larger range (66-fold–609-fold) of added Mo concentrations resulting in 50% inhibition of yield (ED 50) was found among soils than among plant species (2-fold–38-fold), which illustrated that the soils differed widely in the expression of Mo toxicity. Toxicity thresholds based on soil solution Mo narrowed the variation among soils compared to thresholds based on added Mo concentrations. We conclude that plant bioavailability of Mo in soil depends on Mo solubility, but this alone did not decrease the variability in observed toxicity enough to be used in risk assessment and that other soil properties influencing Mo toxicity to plants need to be considered.

MOLYBDENUM AVAILABILITY IN ANDISOLS AND ITS EFFECT ON BIOLOGICAL PARAMETERS OF SOIL AND RED CLOVER (TRIFOLIUM PRATENSE L.)

Greenhouse experiments were conducted to evaluate the effect of different rates of molybdenum (Mo, 0-0.58 mg kg−1) on the yield and quality of Trifolium pratense L. (red clover), nitrogenase, and some biological parameters (microbial biomass, L-asparaginase activity, and L-glutaminase activities) in four Andisols. The effect of lime and phosphorus on Mo availability under laboratory conditions was also evaluated. Preliminary laboratory incubation studies showed that the concentration of available Mo in soil increased significantly with the addition of phosphorus, lime, and Mo but less than that found in greenhouse experiments. In red clover, the critical range of Mo concentration to be considered deficient appeared to be 0.4-0.5 mg Mo kg−1 of dry matter. Dry matter production and red clover protein content increased significantly as Mo concentration increased in the shoots (from 0.5 to 1.0 mg Mo kg−1 dry matter). The nitrogenase activity and the number and weight of the nodules were significantly influenced by the concentration of available Mo in the soil. In general, 50 to 100 μg kg−1 of available Mo were necessary to maintain or increase the biological fertility in soils, as estimated by the measurement of several fertility-linked soil parameters, although exceeding 200 μg Mo kg−1 had a detrimental effect on microbial biomass, L-asparaginase activity, and L-glutaminase activity.

Transport of molybdenum in a biosolid-amended alkaline soil

The transport of molybdenum (Mo) in a biosolid-amended, alkaline, agricultural soil was examined in the research reported herein. Batch-equilibrium and miscible-displacement experiments were conducted to examine the transport of Mo in soil with and without 10% by weight biosolid amendment. The results of geochemical modeling, conducted using PHREEQC, indicated that no mineral dissolution or precipitation reactions were expected for the system under the prevailing conditions. Sorption equilibrium coefficients ( K d ) obtained from moment analysis of the Mo breakthrough curves were similar to those calculated from the results of the batch-equilibrium experiments. Mo sorption was greater for the biosolid-amended soil ( K d of 1.3 versus 0.35). Sorption of Mo was shown to be linear, rate limited, and reversible for both unamended and amended soil. The results suggest that Mo associated with biosolid-amended soils is relatively bioavailable and mobile.

Molybdenum Metabolism in Plants

Abstract: Among the micronutrients essential for plant growth and for microsymbionts, Mo is required in minute amounts. However, since Mo is often sequestered by Fe‐ or Al‐oxihydrox‐ides, especially in acidic soils, the concentration of the water‐soluble molybdate anion available for uptake by plants may be limiting for the plant, even when the total Mo content of the soil is sufficient. In contrast to bacteria, no specific molybdenum uptake system is known for plants, but since molybdate and sulfate behave similarly and have similar structure, uptake of molybdate could be mediated unspecifically by one of the sulfate transporters. Transport into the different plant organs proceeds via xylem and phloem. A pterin‐bound molybdenum is the cofactor of important plant enzymes involved in redox processes: nitrate reductase, xanthine dehydrogenase, aIdehyde oxidase, and probably sulfite oxidase. Biosynthesis of the molybdenum cofactor (Moco) starts with a guanosine‐X‐phos‐phate. Subsequently, a sulfur‐free pterin is synthesized, sulfur is added, and finally molybdenum is incorporated. In addition to the molybdopterin enzymes, small molybdopterin binding proteins without catalytic function are known and are probably involved in the storage of Moco. In symbiotic systems the nitrogen supply of the host plant is strongly influenced by the availability of Mo in soil, since both bacterial nitrogenase and NADPH‐dependent nitrate reductase of mycorrhizal fungi are Mo enzymes.

Effect of pH of ammonium oxalate extracting solutions on prediction of plant available molybdenum in soil

Abstract Molybdenum (Mo) is an essential element of plants and animals and is of concern from human nutrition and environmental standpoints. Rational applications to soil of Mo in fertilizers, sewage sludges, or other soil amendments requires information of the concentrations of Mo in soils and plants. Two greenhouse experiments were conducted at Lexington, Kentucky, using surface samples of 12 soils (11 soil types) derived from diverse parent materials in Kentucky with soil pH ranging from 5.18 to 7.46. Molybdenum (Na2MoO4.2H2O) was added at rates equivalent to 0, 0.3, and 0.6 mg Mo kg‐1 soil. Tobacco (Nicotiana tabacum L., cv. Ky14) and soybean [Glycine max. (L.) Merrill cv. McCall] were grown to provide plant Mo data for Mo soil test correlations and comparisons. The primary purpose of these investigations was to determine the effect of pH of NH4‐oxalate extractant solution on the relationship of soil Mo and Mo uptake by tobacco and soybeans, and to evaluate the automated KI‐H2O2 procedure for use in determining Mo in soil extracting solutions. The mean dry weight and Mo concentration of tobacco and soybean were increased by applications of Mo fertilizer to soil in the greenhouse. Dry matter of tobacco was increased 11 to 25% and concentration of Mo from 40 to 82% by each increment of added Mo fertilizer. The results of this study suggest that many soils in Kentucky are not meeting the requirements for Mo sufficiency for tobacco and soybean plants. The average amount of soil Mo extracted by NH4‐oxalate decreased with increasing pH of extractant. Regression estimates for the relationship of Mo uptake by tobacco or soybean and extractable soil Mo show that the slope and the coefficients of determination increased with pH of NH4‐oxalate solution from pH 3.3 to 6.0 and then decreased again at pH 6.4. The greatest amounts of variation in Mo uptake by plants (67% and 20%, respectively, for tobacco and soybean) were accounted for by the soil Mo data at pH 6.0. Soil Mo values for the NH4‐oxalate extractant (pH 6.0) were related to values for anion exchange resin extractant (r2 = 0.61**), but not soil pH. However, values for anion exchange resin were more closely related to Mo uptake by tobacco (r2 = 0.86**) and soybean (r2 = 0.60**) than were values for NH4‐oxalate (r2 = 0.65** and r2 = 0.27**, respectively). Results of this study indicate that the automated KI‐H2O2 method used previously in analysis for plant Mo can be used to analyze Mo in soil extracts. Other instrumentation such as GFAAS and ICP may be effective in the analysis of extracts obtained by the NH4‐oxalate (pH 6.0) or by anion exchange resin procedures when the Mo concentration of extracts falls within the detection limits of the instrument.

Survey of molybdenum fertility status in Maryland coastal plain soils for tobacco production

Abstract Coastal Plain soils in southern Maryland are typically acid (pH = 5.0±0.5) with low organic matter (1.2±0.5%), clay (2.8 to 9.8%), CEC (2.4 to 6.8 meq 100/g), and total Fe contents (4.5 to 34.9 g/kg). The objectives of this investigation were to assess the status of plant available molybdenum (Mo) in these soils by examining the extractable Mo levels in Ap horizon soil samples and tissue Mo contents in cured tobacco collected across a five‐county region. Seventy soil samples representing 11 soil series and 198 composite samples of tobacco served as the basis for the surveys. Plant available Mo in soil, estimated using a solution containing 0.18M ammonium oxalate and 0.1M oxalic acid as the extractant, ranged from 0.02 to 0.53 (ig/g and averaged 0.08 μg/g Mo. Three of the 11 soil series examined and 30% of the total soil samples exhibited extractable Mo levels ≤ 0.03 μg/g therefore may have less than adequate available Mo for tobacco. Cured leaf Mo contents ranged from non‐detectable to 7.95 μg/g ...

Formation of Calcium and Magnesium Molybdate Complexes in Dilute Aqueous Solutions

AbstractIn order to increase our understanding of the chemistry of Mo in soil, waste‐affected soil, and waste‐disposal environments, it is imperative to understand the processes controlling the aqueous and solid‐phase distribution of Mo. Recent research shows the importance of alkaline earth metal ion pairs with molybdate in aqueous solutions. However, ion association constants for these species have not been rigorously determined. The objectives of this study were to measure conditional ion association constants (log cQ) for the formation of Ca and Mg molybdate ion pairs. Potentiometric titrations were performed at pH 7 and 25 °C in NaNO3 ionic media. The logcQ values were converted to the zero‐ionic‐strength molar reference state (log Q) using the Davies equation. The mean log Q and standard free energy of formation (ΔGof) values for the formation of CaMoO04 are 2.57 ± 0.08 and −1405.19 ± 1.60 kJ mol−1, respectively. The mean log Q and ΔGof values for the formation of MgMoO04 are 3.03 ± 0.13 and −1309.08 ± 2.06 kJ mol−1, respectively.

Interaction of phosphorus and molybdenum and the availability of zinc, copper, manganese, molybdenum and phosphorus in waterlogged rice soil

Laboratory incubation experiments were conducted with low-land rice soil to study the effect of applying three different levels of molybdenum (0, 2.5 and 5.0 ppm) and phosphorus (0, 100 and 200 ppm), in all possible combinations, on the changes in available Mo, P, Mn, Zn and Cu in soil. The results showed that application of Mo at both the levels increased the content of extractable Mo and P but decreased those of Cu and Mo in soil whereas application of Mo at higher level only increased the content of extractable Zn in soil. Application of P at both the levels decreased the content of extractable Mo, Mn and Cu but increased that of P whereas it showed an inconsistent effect on the extractable Zn content in soil. The P × Mo interaction effect was found to be beneficial for the content of P, Mo and Zn only. During the initial period of incubation all elements except Cu recorded an increase but with the progress of incubation period the content of all the elements except Mn gradually declined.