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A major environmental problem with aluminum is its toxicity to plants growing in highly weathered acid soils. Aluminum is one of the more abundant elements in soils, making up approximately 7% of the solid matter in an average soil. The solubility of aluminum in soils is initially controlled by minerals that are present that have the highest solubility. Pedogenic processes slowly remove the more soluble minerals, so that the more stable ones supporting the lowest activity of aluminum ultimately control its solubility. The widespread presence of aluminosilicates in soils is accompanied by a reciprocal solubility relationship between aluminum, silica. The presence of hydroxy-interlayered vermiculite in a number of these soils suggests that an amorphous aluminum hydroxide phase forming in the interlayer could also be an active component in these systems, since some of the data fall only slightly below this solubility line.

Fertilizer-applied Nitrogen (N) may be lost from the soil by various mechanisms, i.e., runoff, leaching, denitrification, and volatilization. The latter process is of primary concern in calcareous soils of arid and semi-arid regions, especially when urea is used. In this field study from northern Syria, urea alone, urea with either an incorporated urease inhibitor, phenylphosphorodiamidate, or an experimental bran-wax coating were evaluated on wheat for two cropping seasons at two experimental stations with varying average seasonal rainfall (340 mm, 270 mm). Loss of N was assessed with 15N by mass balance, i.e., the amount of N applied minus the crop N uptake and N remaining in the soil. Crop yields and N uptake were related to seasonal rainfall. Losses of N, apparently as volatilized NH3, were relatively low at both sites, i.e., 11–18%. However, compared to the unmodified urea, neither the incorporated urease inhibitor nor the bran-wax coating had any effect on yields, N uptake or N loss. While urea hydrolysis is normally rapid, it may be delayed by dry conditions at the soil surface; similarly, unusually cold periods may delay nitrification following hydrolysis. Thus, under the cool-season conditions of rainfed cropping in the Middle East, efficient use of urea is not likely to be achieved by modification of the urea but by conventional management practices that ensure pre-plant soil incorporation or topdressing during early spring rains.

Reports on the solubility of Fe during fluctuating redox conditions in soils and sediments are often difficult to interpret. This study was undertaken to examine the solubility relationships of Fe in suspensions of amorphous Fe(OH) 3 , Fe 2 O 3 (hematite), and soils subjected to changing redox conditions. A decrease in pe + pH was accomplished by the addition of organic matter and H 2 (g) in soils, and by H 2 (g) with a Pt catalyst in Fe(III) oxide suspensions. Addition of H 2 (g) and a Pt catalyst to Fe(III) oxide suspensions resulted in their dissolution and subsequent precipitation of two distinct Fe 3 O 4 products. With small additions of O 2 (0.2 mL of air), equilibrium was maintained with Fe 3 O 4 (magnetite). X-ray diffraction confirmed its presence. When large amounts of atmospheric O 2 (g) were added (15 mL of air), the precipitate designated Fe 3 O 4 (amorp) was formed with a mean log of the equilibrium constant based on activities (K°) of 40.65 ± 0.11. X-ray diffraction showed this predpitate to be amorphous. This precipitate controlled Fe solubility within the pe + pH range of 4.0 to 12.7. In soil suspensions subject to changing redox, the Fe 3 O 4 (amorp) precipitate and Fe(OH) 3 (amorp) appear to control Fe solubility. Crystalline Fe(III) oxides including Fe 2 O 3 (hematite) and FeOOH(goethite) can only control Fe solubility under more highly stable, oxidizing conditions. Only with prolonged and intensive reduction is Fe 3 O 4 (magnetite) expected to form and control Fe solubility.

Many soils used for tree fruit production before 1968 contain elevated Pb concentrations resulting from use of lead arsenate pesticides. The chemical form of Pb in these soils may influence its bioavailability and the need for and type of remediation actions. The competitive chelation method was used to determine the single-ion activity of Pb 2+ in aqueous suspensions of 11 lead arsenate contaminated soils and, for comparison, three Pb-enriched roadside soils. The activity of Pb 2+ ranged from 10 -9.37 to 10 -7.21 , consistent with values published elsewhere, and was inversely related to pH. The soils appeared to fall into two solubility groups, one where Pb 2+ activity was consistent with control by a Pb-phosphate mineral, possibly Pb 5 (PO 4 ) 3 OH or Pb 3 (PO 4 ) 2 , and a second group where Pb 2+ activity was consistent with control by Pb(OH) 2 . Both groups contained calcareous soils. Adding monocalcium phosphate to two of the soils from the higher Pb solubility group shifted one soil to the lower solubility group but had no effect on the second soil. The experimental results suggest that Pb solubility in lead arsenate contaminated soils is not appreciably higher than in soils contaminated by Pb from gasoline and that phosphate amendment may not always reduce soil Pb solubility.

The solubility of Fe in soils is largely controlled by Fe oxides; ferrihydrite, amorphous ferric hydroxide, and soil-Fe are generally believed to exert the major control. Fe(III) hydrolysis species constitute the major Fe species in solution. Other inorganic Fe complexes are present, but their concentrations are much less than the hydrolysis species. Organic complexes of Fe including those of organic acids like citrate, oxalate, and malate contribute slightly to increased Fe solubility in acid soils, but not in alkaline soils.

We selected thermodynamic data for 45 fluorine minerals and solution species that may play important roles in the fluorine chemistry of soils. Equilibrium reactions and stability constants for these minerals and species were calculated and used to develop stability diagrams in soils.Aluminum fluorid

Thermodynamic data were used to develop equilibrium reactions and constants for 83 selenium (Se) minerals and solution species that relate to soils. The solubilities of the metal-selenate minerals are very high in well-aerated soils and are not expected to persist in these systems. The solubilities

Numerous workers have examined the weathering products of soil minerals and have proposed empirical weathering sequences. The present paper outlines the development of a thermodynamic model that predicts in a systematic way several mineral transformations that can occur in soils. According to this model, the stability of primary minerals increases in the order: Na-glass, K-glass, pyroxene, analcime, anorthite, low albite, muscovite, microcline, and quartz. The stability of secondary clay minerals depends on soluble silica. At pH 6 with high silica (≃ 10⁻³M) the order of increasing stability is: chlorite, halloysite, gibbsite, illite, dickite, beidellite, kaolinite, and montmorillonite; at low silica (≃ 10⁻⁵M) the order is: chlorite, halloysite, illite, beidellite, montmorillonite, dickite, kaolinite, and gibbsite. The stability of both primary and secondary minerals increases with pH. The observed weathering of volcanic ash agrees well with the predictions of this model. The model makes use of important thermodynamic data accumulated for soil minerals and helps to pinpoint deficiencies in these data. The need to examine the kinetics of mineral transformations in soils in greater detail also becomes obvious from this model.

A modification of the EDTA method of determining ion activities in soil developed by Norvell was used to measure the solubility of various ferric hydroxides. The solubility products of jarosite (KFe₃(SO₄)₂(OH)₆) and amorphous Fe(OH)₃ were also determined on a natural jarosite nodule taken from an acid sulphate soil. For amorphous ferric hydroxide and lepidocrocite, the method gave pK° values of 39.02 ± .35 and 42.48 ± .23, respectively. Hematite and goethite were too inert to yield reproducible solubilities. For a mixture of jarosite and ferric hydroxide, the respective pK° values were 98.56 and 39.93. These values were used to develop an Eh-pH stability diagram that helps to explain the occurrence of jarosite under acid oxidizing conditions in soils.

Tests were made to determine the effects of grinding, type of extraction vessel, type of shaker, speed of shaking, time of shaking, time of filtering, soil to solution ratio and other variables on DTPA‐extractable Zn, Fe, Mn, and Cu from soils. Time of grinding, force of grinding, and the quantity of soil being ground greatly affected the amount of extractable Fe. At the lower grinding force, the quantity of soil being ground only slightly affected extractable Fe, but at the higher grinding force, more Fe was extracted from the smaller sized samples especially at the longer grinding period. Extractable Zn was also increased by longer grinding time and greater grinding force, but increases were much less than increases for Fe. Increasing grinding time tended to increase extractable Mn. The effects of grinding on Cu was inconclusive. Increasing the ratio of extractant to soil increased the amount of extractable Fe from soils and tended to increase Zn, Mn, and Cu but to a lesser extent. Both shaker ...

One solution to the management of retorted shale (spent oil shale) is to establish a satisfactory vegetative cover over retorted shale disposal piles. However, the high alkalinity of these waste materials severely hampers direct revegetation efforts. A sample of Lurgi-Ruhrgas (Lurgi) retorted shale was recarbonated to lower its high alkalinity, by exposing it to 0.04 MPa CO₂(g) and moisture for 4 d. A preliminary greenhouse experiment was conducted to examine the uptake of microelements by tall wheatgrass [Agropyron elongatum (Host) Beauv.] grown on this recarbonated shale. Exposing spent Lurgi shale to pressurized CO₂(g) and moisture lowered the pH from 11.6 to 8.6 and increased the electrical conductivity (EC) from 4.7 to 15.8 dS/m. Lowering the pH through recarbonation increased ammonium bicarbonate-diethylenetriaminepentaacetic acid (AB-DTPA) extractable Fe, Zn, Cu, Mo, and Ni, while extractable B, Sr, Cr, and Mn were decreased. Wheatgrass seeds failed to germinate in spent Lurgi shale, which had no soil cover. Plant growth decreased in the recarbonated shale compared to retorted shale with a soil cover due to higher salinity. Plant tissue grown on the recarbonated shale accumulated lower concentrations of As, Se, Ba, Cd, Sr, and Ti than did plants grown on spent Lurgi shale with a soil cover. Boron concentrations ranged from 7.2 to 13.0 mg/kg in plant tissue, with the lowest concentrations coming from the recarbonated shale. Fluoride concentrations in plant tissue increased with recarbonation but were below the toxic level. Plant uptake of Mo increased with recarbonation. The Cu/Mo ratios of the tall wheatgrass were below 2:1 in all treatments except the control. This preliminary study shows that recarbonated spent shales can be revegetated directly without a soil cover but that some leaching may be advantageous.

Adsorption and precipitation of Cd/sup 2 +/ in soil suspensions were investigated as possible factors controlling Cd/sup 2 +/ levels in soils. Both adsorption of Cd/sup 2 +/ onto soils surfaces and possibly precipitation of cadmium minerals were evident in this study. At low cadmium levels solubility relationships in soils are best described by adsorption and fit the empirical Freundlich adsorption isotherm. Based on current thermodynamic data the solid phases CdCO/sub 3/ and Cd/sub 3/(PO/sub 4/)/sub 2/ most likely limit Cd/sup 2 +/ activities in soils. Under alkaline conditions, Cd/sup 2 +/ activity decreased approximately 100-fold for each unit increase in pH. CdCO/sub 3/ precipitated in sandy soils having low cation exchange capacity (CEC), low organic matter, and pH values >7.0. DTPA-extractable cadmium levels in soils were highly correlated (r = 0.96) with Cd concentrations in corn (Zea mays L.) seedlings grown in soils amended with Cd solutions, sewage sludge, or Cd-spiked sewage sludge. Increasing Cd additions to the soil increased plant Cd regardless of the form of Cd added. Addition of inorganic Cd to the soil increased the Cd concentration of corn seedlings more than equivalent Cd additions in the form of sewage sludge or Cd-spiked sludge.

Summary Soil samples obtained from genetic horizons of an upland and acid sulphate soil of Sierra Leone, were equilibrated with 0.01 M CaCI using a 1:2 soil to solution ratio. Al3+ activity was estimated from total Al measured in the equilibrium extract, by accounting for hydrolysis and the formation of other complex species. The Al3+ activity was pH-dependent, but the Al(OH)3 ion product was I'airly constant throughout the upland soil profile; Al3+ activity was near that expected for equilibrium with kaolinite and quartz. In the acid sulphate soil alunite appeared to control the activity of Al3+.

Four divalent Mn phosphate compounds were prepared and identified. The compound, Mn3(PO4)2 . 3H2O slowly transformed to Mn5H2(PO4)4 . 4H2O, when the solid was left in contact with the mother liquor. Dissociation constants were determined for the following reactions: where log K° is the log of the equilibrium constant, (K°). The mineral Mn(H2PO4)2 . 2H2O (manganese [II] di-[dihydrogen phosphate] dihydrate) was identified, but its solubility constant was not determined because of high ionic strength corrections. X-ray diffraction patterns, densities, and refractive indices were determined for the four minerals. Additional Index Words: Chemical formation, manganese precipitates, manganese(II) hydrogen phosphate, trimanganese diphosphate, pentamanganese dihydrogen tetraphosphate, manganese(II) di-(dihydrogen phosphate). View complete article To view this complete article, insert Disc 4 then click button8

Corn (Zea mays L.) ‘Pioneer-3932A’ was grown in the greenhouse on a loamy sand amended with cadmium, cadmium-spiked sewage sludge, and sewage sludge. Soil pH was adjusted to approximately 5.7, 6.7, and 7.8, and phosphorus was applied at 0, 200, and 400 µg/g soil. Soil treatments were applied 0, 8, and 16 weeks prior to planting, and the plants were grown for 5 weeks. Increasing the pH of the soil amended with inorganic cadmium (CdSO₄) decreased the Cd concentration of corn seedlings by approximately 67%. The Cd concentration was reduced approximately 47% for a similar increase in pH on soil amended with Cd-spiked sludge. The Cd concentration of corn seedlings was significantly reduced by the addition of P. Increasing incubation time decreased the availability of added inorganic Cd, but increased the availability of Cd applied with sewage sludge. Increasing the amount of Cd added to the soils increased the Cd concentration of the corn seedlings regardless of the form of Cd used. Cadmium concentrations in the corn seedlings were significantly correlated with DTPA-extractable soil Cd. Solubility measurements of Cd in the acidified soils showed undersaturation with respect to all known Cd minerals, whereas in soils above pH 7.25 the Cd solubility was limited by CdCO₃ at a CO₂ level of 0.003 atm or higher and showed the expected hundredfold decrease in solubility for each unit increase in pH. The minerals Cd₃(PO₄)₂ and Cd(OH)₂ are much too soluble to account for the precipitation of Cd in these soils.

The solubility of iron in soils is controlled by Fe(OH)3(soil)in well‐oxidized soils, by Fe3(OH)s(ferrosic hydroxide) in moderately oxidized soils, and by FeCO3(siderite) in highly reduced soils. The Fe(III) hydrolysis species Fe(OH)2 +, and Fe(OH)3° are the major solution species of inorganic Fe, but they are maintained too low to supply available iron to plants. Iron is absorbed by plants as Fe2+ and must be in the general range >10–7.7 M to avoid iron deficiency. The redox of soil‐root environments must be

Western wheatgrass (Agropyron smithii Rybd. 'Arriba') and fourwing saltbush (Atriplex canescens (Pursh) Nutt.) were sampled from oil shale revegetation plots in northwestern Colorado. Plants were growing on two types of retorted shales: TOSCO II, produced by the Tosco Corporation; and USBM, produced by the U.S. Bureau of Mines. Various treatments included leaching and different depths of soil covering over the retorted shales. Plant samples were analyzed for B, Mo, As, Se, and F on a dry-weight basis. Plant samples with elevated Mo concentrations were also analyzed for Cu. Boron in western wheatgrass from the TOSCO retorted shale ranged from 85 to 202 ppm, compared with ranges of 4 to 15 ppm B in plants from the soil control. Analysis of variance indicated significant differences in B content due to site, aspect, type of retorted shale, and amount of soil cover over retorted shale. The concentration of B in western wheatgrass growing on retorted shales, especially TOSCO retorted shale, could affect plant growth. Fourwing saltbush samples, growing on USBM retorted shales, contained levels of Mo averaging 28 ppm, and low-to-moderate Cu content (4.8-6.8 ppm). This combination could make this species unacceptable as forage for ruminants. The concentrations of As (0.03-0.44 ppm),more » Se (0.02-0.94 ppm); and F (0.5-10.0 ppm) in the plant species investigated in this study were below limits usually set for either plant or animal toxicities and appear to be of little environmental significance.« less

Dosage du fer, molybdene, plomb, nickel, cobalt, cadmium, chrome, mercure, selenium, arsenic et bore dans la vegetation poussant sur un sol contamine par des schistes bitumineux

The major cause of iron deficiency in plants is the insolubility of Fe (III) oxides in soils. Minimum solubility occurs in the pH range of 7.4 to 8.5 where the dominant solution species Fe(OH)3° is present at approximately 10‐10.4 M. The critical level of soluble iron for plants is approximately 10‐8 M, so the ferric oxides are too insoluble to supply adequate iron to plants unless modifying factors intervene. Major factors that modify iron solubility relationships in soils include oxidation‐reduction processes and the presence of chelating agents. Reduction processes near respiring plant roots enable ferric chelates to dissociate and Fe3+ to reduce to Fe2+. It is necessary for Fe2+ to increase above the critical level to supply adequate iron to plants. Competition of metal ions for chelating agents gives rise to many nutrient interactions. Redox relationships also affects metal solubility relationships in soils. When combined these factors greatly affect iron availability to plants. Important nu...

The concentration of ferric ion and the ion product of ferric hydroxide in the Weld loam (Aridic Paleustoll) were estimated from equilibria of EDTA (ethylenediaminetetraacetic acid) chelates. Additions of ferric chloride to the Weld loam raised the solubility of soil iron at least seven‐fold. The (Fe3+)(OH‐)3 ion product increased from approximately 10‐39.2 to at least 10‐38.4 after ferric chloride was added. The solubility of soil iron decreased slowly with time after fertilization. After one month the (Fe3+)(OH‐)3 ion product had fallen to 10‐39.1, virtually the same level as in the unamended soil. The results are consistent with the hypothesis that iron oxides of high specific surface or poor crystalinity control the solubility of ferric ion in soil solution. 1. This paper was presented, edited, and accepted as part of the International Symposium on Iron Nutrition and Interactions in Plants, which was published in the Journal of Plant Nutrition 5 (4 to 7), 1982. Due to error in editorial handl...

Theoretical calculations were used to develop an electron titration curve for a hypothetical soil to show the characteristic redox poises (pe + pH values) maintained by various manganese and iron minerals. An experimental electron titration of soil was made by adding either oxidant or reductant and measuring the pe + pH after 7 days and after 14 days. The resulting redox poises were compared with theoretically developed poises. The results show that many redox-related mineral transformations occur slowly and that poorly defined, mixed valency solids often result. Nevertheless, the present study demonstrates how redox poises are controlled by mineral transformations that can be identified. Redox solubility diagrams show how Mn 2+ and Fe 2+ solubilities can be predicted from pe + pH measurements.

The pH and redox relationships of a rice soil subjected to alternate flooding and drying were measured during the growth of three successive rice crops in the greenhouse. The objective was to explain why greater nitrogen losses occur under alternating flooding and drying than under continual submergence. At 2 cm below the soil-water interface the pH dropped from 8.3 to approximately 7.0 in 40 days and remained there through 120 days. The redox (pe + pH) dropped from 16 to 4 under the same conditions. When alternate flooding and drying were imposed, the pH fluctuated from 8.0 during drying to near 7.6 during submergence while pe + pH shifted from 16 during drying to approximately 8 during flooding. Both pH and pe + pH dropped slightly with depth into the sediment reflecting greater accumulation of CO2 and depletion of O2. The findings in this study support the hypothesis that alternate flooding and drying causes the redox of rice soils to pass through the pe + pH range of 13 to 15 where theoretical considerations show that NO(g) is most stable and can function as a viable intermediate reaction product of denitrification in soils.

The Mo concentration in water, soils, and alfalfa (Medicago sativa) was monitored for 1 growing season. The concentration of Mo in irrigation water in this area ranged from 27 to 213 ppB. A significant increase of Mo concentration in alfalfa and available soil Mo was observed at 1 site irrigated with water containing 213 ppB Mo, and the Mo concentration in the alfalfa increased during the growing season from 4.3 to 7.2 ppM which is below the 10 ppM level considered toxic to livestock. Plant Mo was highly correlated (r = 0.94) with resin-extractable Mo in a greenhouse experiment using soils from 3 of the field sites. Field results were less satisfactory (r = 0.51), partially due to limited indigenous levels of Mo in the soils. A simulation model was used to assess the potential hazards of irrigating with water containing from 0 to 600 ppB Mo. The model indicates that a level of 400 ppB Mo in irrigation water applied to soil with 40 percent retention of Mo in an available form would result in toxic levels of Mo in plants within 3 yr. The impact of Mo on the Brighton area during 1 growing season was minimal inmore » relation to uptake of Mo by plants.« less

Barbotage de CO 2 a travers deux schistes distilles. Transformations minerales accompagnant ce barbotage. Solubilite de B, Mo et F avant et apres la recarbonatation

A general approach is developed by which the equilibria between chelating agents and metal ions in soils can be predicted from formation constants. Mole-fraction diagrams are derived for EDTA (ethylenediaminetetraacetic acid) and DTPA (diethylenetriaminepentaacetic acid) in soils when the competing cations are either Fe, Ca, and H, or Zn, Fe, Ca, and H. These diagrams give the specific metalligand complexes that form in soils and show how the concentration of each complex changes with pH. Evidence is presented to support the hypothesis that Zn reacts with amorphous SiO2 in soils to form ZnSiO3. The concentration of Zn in equilibrium with solid phase ZnSiO3 and amorphous SiO2 is approximately 10M at pH 6, and decreases 100-fold for each unit increase in pH. This concentration of Zn is approximately 100,000 times lower than that in equilibrium with ZnO or ZnCO3. Additional