Desorption of myo‐inositol hexakisphosphate and phosphate from goethite by different reagents

Inositol phosphates are abundant organic phosphates found widely in the environment. The sorption and desorption of organic phosphate (P_o) are important processes in controlling the mobility, bioavailability and fate of phosphorus (P) in soil and sediment. The desorption characteristics of myo‐inositol hexakisphosphate (IHP) and inorganic phosphate (P_i) from goethite were studied by pre‐sorption of IHP or P_i followed by desorption by KCl, H₂O, and citrate. Batch experiments and in situ attenuated total reflectance Fourier transform infrared (ATR‐FTIR) spectroscopy were used to investigate the desorption of IHP/P_i. The desorption percentage of IHP/P_i by citrate was much higher than that by H₂O/KCl. The desorption of P by citrate was mainly achieved through ligand exchange, and the desorption increased with decreasing pH. Desorption by H₂O was slightly greater than that by 0.02 M KCl because the electrostatic repulsion between the P molecules is larger in H₂O. Due to the higher affinity of IHP for goethite than that of P_i, the maximum desorption of IHP was lower than that of P_i. Desorption curves (desorption concentration in solution vs. sorption density) of IHP or P_i on goethite by KCl or H₂O was well fitted by an exponential equation, while those by citrate were well fitted by a linear equation. The desorption amounts of P in the first cycle account for more than 58% of the total desorption followed by substantial decreases in the second and third cycles. There was a re‐sorption of P_i from solution in the late stage of desorption by KCl and H₂O, resulting in a sharp decrease in desorption. Re‐sorption of IHP did not occur, which is probably due to its poor diffusion into goethite. The initial desorption rate of P_i with KCl and H₂O decreased with increasing pre‐sorption time, whereas that of IHP was opposite. This study indicates that strong sorption on and weak desorption of IHP from iron (hydr)oxides may explain the accumulation of IHP in soils.     

Inhibition of acidification of kaolinite and an Alfisol by aluminum oxides through electrical double‐layer interaction and coating

Soil chemical properties are affected significantly by surface charge characteristics of the soil. Interaction between oppositely charged particles in variable‐charge soils plays an important role in variation of soil electrochemical properties. In this study, the effects of Al oxides on surface charge and acidity properties of kaolinite and an Alfisol during electrodialysis were investigated. The results indicated that Al oxides, when mixed into kaolinite or the Alfisol, decreased the effective cation exchange capacity (ECEC) and exchangeable acidity and inhibited the decrease in pH. Gibbsite had less effect than γ‐Al₂O₃ and amorphous Al(OH)₃ in reducing the ECEC and acidity of kaolinite and the Alfisol; γ‐Al₂O₃ and amorphous Al(OH)₃ displayed comparable effects. However, this effect is inconsistent with the order of the surface positive charge per unit mass that the Al oxides carried. Their effect on the ECEC of kaolinite and Alfisol varied irreversibly with ionic strength of the bathing solutions. X‐ray diffraction spectra indicated that amorphous Al(OH)₃ and γ‐Al₂O₃ were more effective than gibbsite in decreasing peak intensity of electro‐dialyzed kaolinite when mixed with these Al oxides at the same rate. The results demonstrated that Al oxides could decrease the effective negative charge and inhibit acidification of kaolinite and an Alfisol through diffuse‐double‐layer overlapping between oppositely charged particles and coating of Al oxides on these materials. Both mechanisms intensified with increasing rate of added Al oxides, which can therefore act as anti‐acidification agents in variable‐charge soils.     

Copper retention by Danish Spodosols in relation to contents of organic matter and aluminum,iron, and manganese oxides

Abstract

The importance of various soil components on copper (Cu) retention by Spodosois was investigated. Copper sorption and extraction were conducted on samples from the B horizon from six Danish Spodosois. The investigation was conducted on untreated samples, on hydrogen peroxide‐treated samples (to remove organic matter), on oxalate‐treated samples [to remove amorphous to poorly crystalline aluminum (Al) and iron (Fe) oxides], on hydroxylamine‐treated samples [to remove manganese (Mn) oxides]. Subfractions treated with hydrogen peroxide (H₂O₂) were further treated with oxalate and citrate‐bicarbonate‐dithionite (CBD). Sorption of Cu from an initial 10^‐6 M solution after 48 hours was determined in the pH range 3 to 7 using 0.1M sodium nitrate (NaNO₃) as the background electrolyte. The pH‐dependent sorption curve (sorption edge) was shifted to a higher pH with decreasing Al oxide content in the soils, and for the treated sample after removal of organic matter and Al and Fe oxides. A negligible effect was seen after removal of the Mn oxides because of their low abundance. Extraction of sorbed Cu at pH 4 to 6 with 0.1M nitric acid (HNO₃) for 24 hours confirmed the sorption results, in inasmuch as removal of the Al (and Fe) oxides increased Cu extractability. Therefore, it was concluded that in the soils investigated, Cu retention is mainly determined by the oxalate‐extractable Al fraction with a minor contribution due to crystalline Fe oxides.     

Association of the Fungicide Propiconazole with Size Fractionated Material from a Silty Clay Soil – S.E. Norway

Eroded soil material may be an important transporting agent for pesticides that are strongly sorbed to soil. The abilityof the fungicide propiconazole to interact with colloidal andparticulate materials has been studied by means of sorptionand desorption experiments. Size separation of silty clay soilfrom Mørdre, Norway and subsequent characterization showedthat different size fractions of soil possessed different physical and chemical properties and, therefore, different capacity to associate with propiconazole. A large part of the soil organic carbon was associated with coarser material (2–0.02 mm), which also showed higher affinity towards propiconazole than for smaller size fractions (<20 and <2 μm). Similar K _oc values (2306 and 2244) for the size fractions <2 and <20 μm indicate that organic carbon played a dominant role in the sorption of propiconazole. Furthermore, organic carbon associated with these size fractions seemed to have similar properties withrespect to binding of propiconazole. Although, poor in organiccarbon (0.4%), the smallest size fraction (<2 μm) had higher sorption capacity for propiconazole compared to the medium size fraction (<20 μm). Higher sorption for the smallest size fraction (<2 μm) is probably due to higherspecific surface area, cation exchange capacity and content of Fe/Al oxides (free, organically bound and amorphous oxides) than the other size fractions. Results from the desorption experiments indicate that a part of propiconazole associates with sites in the soil material that resist desorption. Fluvialsediments originating from propiconazole treated fields may, therefore, represent potential reservoirs of propiconazole.Treatment with H₂O₂ modified the sorption/desorptioncharacteristics of the soil beyond that which could be expectedsimply by the removal of organic material. The pH values for all the size fractions decreased, and the specific surface areaof the medium sized fraction (<20 μm) increased from 14 to 19 m² g^-1 after the treatment with H₂O₂,probably due to disruption of the aggregate structure. Carrying out fractionation and separation procedures, it is important to be aware of physical and chemical changes that areintroduced during the different steps. An effort should be made to develop fractionation methods that keep the original characteristics of the soil material as intact as possible.     

The influence of aminopolycarboxylates on the sorption of copper (II) cations by (Hydro)oxides of iron,Aluminum, and manganese

The influence of some complexing agents of (poly)aminopolycarboxylic acids (diethylenetriaminopentaacetic acid (DTPA), ethylenediaminotetraacetic acid (EDTA), nitrilotriacetic acid (NTA), and iminodiacetic acid (IDA)) on the sorption of Cu²⁺ by crystal and amorphous (hydr)oxides of Fe(III), Al(III), and Mn(IV) that are widespread mineral components of soils was studied. The obtained results are considered in terms of complex-formation in the solution and on the sorbent’s surface. The effect of the complexing agents on the metal sorption (mobilization/immobilization) is determined by (1) the stability, structure, and sorption capability of compexonates formed in the solution; (2) the acidity, and (3) the nature of the sorbent. The desorption effect on Cu²⁺ cations was found to change in the following sequence of complexing agents: EDTA > DTPA ? NTA > IDA. The high-dentate complexing agents (EDTA, DTPA) had the greatest impact on ?u²⁺ cations bound with crystalline (hydr)oxides of Fe, Al, and Mn. The low denticity of the complexing agents (IDA, NTA) and binding of ?u²⁺ with amorphous sorbents leads to the weakening of desorption. The decrease in acidity promoted the mobilization of the metal under the influence of complexing agents; the increase in acidity caused its immobilization. The growth in the mobility of heavy metals bound with soil (hydr)oxides of Fe, Al, and Mn due to the complexing agents entering the surface and ground water is considered a factor of ecological risk.     

The effect of pH on zinc transformation in autoclaved soils treated with pyrophosphate

Abstract

Zinc solubility in soils can be affected by both pH and pyrophosphate (PP), yet the reaction of PP is influenced by pH, thus there is a need to evaluate pH effect on Zn transformation in soils treated with PP. Samples of three autoclaved soils, a Dalhousie (DT) clay, a St. Bernard (ST) loam, and an Uplands (UT) sand were equilibrated first with PP (0.0 and 9.0 P mM), then with Zn (0.0, 0.5, 1.0 Zn mM) and followed by 0.03 M KC10₄ solutions at the initial pH of 4.5, 6.0, and 7.5 with constant ionic strength. The first equilibration was for PP sorption, the second for Zn sorption and PP desorption, and the third for Zn desorption and further PP desorption. And finally, Zn of selected samples were extracted with 0.5 M KNO₃ (exchangeable Zn, Zn_KNO3), 0.5 M NaOH (organic and Fe oxides associated Zn, Zn_NaOH) solutions, and concentrated HNO₃+H₂O₂ (residual Zn, ZnHNO₃).

Increases in pH reduced PP sorption in the UT and the ST soils while high or low pH values tended to reduced it in the DT soil, indicating a competition between PP and OH ions for sorption sites. Zinc sorption was linearly related to solution pH, the slopes varied from 0.10 to 1.06, lower values were associated with PP addition, with low Zn rate, with finer textured soils, with high contents of Fe and Al materials, and with high pH buffer capacity. The values of Zn desorption and Zn_KN03 were greater at low than high pH while the reverse was true for Zn_NaOH. The pH effects on Zn sorption‐desorption and fraction distributions were less significant in soil with than without PP. The overall effect of high pH and the presence of the sorbed PP was the increased Zn specific sorption, compared to the pH or PP effect alone.     

Phosphorus remediation by acid mine drainage floc and its implications for phosphorus environmental indices

Purpose

Acid mine drainage (AMD) and phosphorus pollution are grave environmental concerns. Iron- and aluminum oxide-rich waste resulting from AMD treatment, variously called floc, sludge, or ochre, needs quick disposal. Fe and Al oxides have great affinity for phosphorus. AMD floc needs be characterized for its relative affinity for inorganic and organic P and subsequently for its implications in the validity of degree of P saturation (DPS) like environmental indices.

Materials and method

Phosphorus sorption on ammonia-treated floc (AF) and lime-treated- (LF) and sodium hydroxide-treated AMD floc (SF) was examined by using a range of concentrations of inorganic P (IP) and organic P (OP, inositol hexaphosphate (IHP), or phytate, the predominant OP form in manures and soils).

Results and discussion

AMD floc was highly effective, in the order AF > SF > LF, in attenuating solution P. IHP-P attenuation was 2.5–3 times IP attenuation under high P loadings. Phosphorus remediation differences across the floc types seemed to be due to differences in their surface area and porosity. A comparison between inorganic and organic P attenuation ability of the flocs suggested against blanket use of an arbitrary α value in computing DPS. Factor α in the DPS index represents the maximum number of moles of P sorbable on one mole of amorphous Fe + Al. Value of α (0.81) in OP sorption was highly different from the α value in IP (0.28) in the IP sorption. This vast difference suggests against arbitrary choices of α value in computing the DPS index.

Conclusions

AMD flocs can effectively attenuate P, especially manure P. Relative abundance of type or sources of P needs to be considered in the computation of such soil P indices that are solely based upon the amount of P associated with amorphous phases of Fe and Al oxides.     

Specific sorption of antimony (III) by the hydrous oxides of Mn,Fe, and Al

The hydrous oxides of Mn, Fe, and Al avidly sorbed Sb from μM Sb(OH), solutions, with uptake levelling off as initial Sb concentration increased. Capacity values decreased along the sequence MnOOH > Al(OH)₃ > FeOOH. The amount sorbed by each substrate decreased gradually at pH values > 6. Addition of 0.4M CH₃COONa to the aqueous phase (to minimise retention of weakly bound Sb) had little effect on MnOOH uptake capacity (～160 mmol, kg^?1 at pH < 7) but retention dropped rapidly at higher pH. With the other two substrates (pH 6–7) the calculated capacity values for specific Sb sorption were ～ 45 mmol kg^?1 FeOOH and ～ 33 mmol kg^? Al(OH)₃; about a third of the total capacity values. On these substrates specific Sb sorption tended to peak in the pH 7 to 8 region. The pH response pattern was modified using Sb tartrate sorbate solutions. Factors influencing Sb sorption included substrate surface charge, chemical form of Sb and surface interactions. Formation of a sparingly soluble metal coating was indicated by the uptake plateaus observed when increasing amounts of solid were added to Sb solutions containing acetate.     

Poorly crystalline iron and aluminium oxides contribute to the carbon saturation and sorption of dissolved organic carbon in the soil

Soil carbon (C) saturation implies an upper limit to a soil's capacity to store C depending on the contents of silt + clay and poorly crystalline Fe and Al oxides. We hypothesized that the poorly crystalline Fe and Al oxides in silt + clay fraction increased the C saturation and thus reduced the capacity of the soil to sorb additional C input. To test the hypothesis, we studied the sorption of dissolved organic carbon (DOC) on silt + clay fractions (<53 µm) of highly weathered oxic soils, collected from three different land uses (i.e., improved pasture, cropping and forest). Soils with high carbon saturation desorbed 38% more C than soils with low C saturation upon addition of DOC, whereas adsorption of DOC was only observed at higher concentration (>15 g kg^?1). While high Al oxide concentration significantly increased both the saturation and desorption of DOC, the high Fe oxide concentration significantly increased the desorption of DOC, supporting the proposition that both oxides have influence on the DOC sorption in soil. Our findings provide a new insight into the chemical control of stabilization and destabilization of DOC in soil.     

Comparison of different models for phosphate sorption as a function of the iron and aluminium oxides of soils

Phosphate sorption on topsoil and subsoil samples from different soils located in the eastern part of Germany was studied. Two models were fitted to sorption data obtained after 4 and 40 d of gentle shaking. The models differ with respect to the fractions of iron and aluminium (hydr)oxides that are considered and whether the phosphate initially sorbed in the soil is taken into zccount. Oxalate-extractable P, (P_ox), appears to be a major part of the total soil P. The total P sorption measured, F, was predominantly related to the amounts of amorphous iron (Fe_ox) and aluminium (Al_ox). A significant relation between crystalline iron (Fe_d– Fe_ox) and total P sorption was not found. Reversibly adsorbed phosphate (P_i), measured after 40 d reaction time, was a function of clay content and content of amorphous iron and aluminium (hydr)oxides.     

Crystallization of single and binary iron‐ and aluminum hydroxides affect phosphorus desorption

In acidic soils, phosphorus availability is affected by its strong affinity for mineral surfaces, especially Fe‐ and Al‐hydroxides. Plant roots have developed adaptive strategies to enhance the availability of phosphorus, including producing and exuding low molecular weight organic acids with a high affinity for phosphorus that competes with high molecular weight organic ligands formed during humification and mineralization. The aim of this study was to characterize the kinetics and mechanism of phosphorus desorption from Fe‐ and Al‐hydroxides of variable crystallinity, as well as binary Fe:Al‐hydroxide mixtures. Long‐term desorption experiments (56 days) were conducted with CaCl₂, CaSO₄, citric acid, and humic acid as competitive sorptives. CaCl₂ and CaSO₄ were selected as general inorganic sorptives and citric and humic acids were selected as organic ligands produced by organisms in the rhizosphere or following humification. The cumulative phosphorus desorption increased following the order CaCl₂ < CaSO₄ < humic acid < citric acid. Amorphous ferrihydrite and Fe‐rich Fe:Al‐hydroxides exhibited much less desorption when exposed to inorganic solutions than the crystalline and Al‐rich Fe:Al‐hydroxide mixtures. Models of the desorption data suggest phosphorus desorption with citric acid is diffusion‐controlled for ferrihydrite and Fe‐rich amorphous Fe:Al‐hydroxides. When humic acid was the sorptive, metal‐organic complexes accumulated in the solution. The results suggest organic compounds, especially citric acid, are more important for liberating phosphorus from Fe‐ and Al‐minerals than inorganic ions present in the soil solution.     

Oxidation and sorption of arsenite by manganese dioxide as influenced by surface coatings of iron and aluminum oxides and calcium carbonate

Manganese dioxide (birnessite) was coated with two levels of Fe and Al oxides and CaCO₃, and the influence of these coatings on the surface features and the reactivity of MnO₂ with respect to the oxidation and sorption of As(III) (arsenite) was examined. For all untreated and coated MnO₂ samples, the depletion (oxidation plus sorption) of As(III) by the samples follows first-order kinetics. The rate constants are smaller for the samples with the high levels of coating of Fe and Al oxides and CaCO₃ on MnO₂ than they are for the untreated MnO₂ and the MnO₂ with the low levels of coating. The extent of masking of the electron-accepting sites on the MnO₂ for converting the toxic As(III) to the less toxic As(V) significantly varies with the kinds and levels of coatings. Coatings of Fe and A1 oxides and CaCO₃, on MnO₂ distinctively affect the sorption of As. Manganese oxide evidently catalyzes the sorption of As by Al oxide through oxidation of As(III) to As(V). The relative affinities of the oxides of Mn, Fe, and Al and CaCO₃, toward As(III) and As(V) account for the coating effects.     

Retention of cobalt by an oxisol in relation to the content of iron and manganese oxides

Abstract

The study aims at determining the cobalt retention properties of various soil components. Therefore, cobalt (Co) sorptions and extractions were carried out using an Oxisol sample before (untreated) and after successive removal of organic matter and active manganese (Mn) oxides (H₂O₂‐treated) and iron (Fe) oxides (H₂O₂+CBD‐treated). A synthetic goethite was included for comparison. Sorption of the four sorbents was determined over a range of Co concentrations (initially 10^‐8 M to 10^‐4 M), pH values (3 to 8) and reaction times (2 hours to 504 hours). The Co species sorbed was Co(ll), since oxygen exclusion during sorption had no effect on the amount sorbed. The pH‐dependent sorption curve (sorption edge) was shifted to lower pH at decreasing initial Co concentration and increasing reaction time. The displacements, in particular of the sorption edges corresponding to the lowest initial Co concentrations, to successively higher pH following removal of Mn oxides, organic matter and Fe oxides could be attributed to sorption onto sites of decreasing Co affinity [Mn oxides (and organic matter) > Fe oxides > kaolinite]. Extractions of sorbed Co at pH 5.5–7.5 with 2 M HCI showed that the extractability decreased with increasing sorption time and decreasing initial Co concentration. The untreated and H₂O₂‐treated soil samples retained sorbed Co at least as firmly as the synthetic goethite, whereas the H₂O₂+CBD‐treated sample (kaolinite) was clearly less effective. The results emphasized the importance of the soil Mn and Fe oxides for Co retention in soils but also the necessity of taken interior sorption sites into consideration.     

Retention of dissolved organic matter by illitic soils and clay fractions: Influence of mineral phase properties

The dependency of the retention of dissolved organic carbon (DOC) on mineral phase properties in soils remains uncertain especially at neutral pH. To specifically elucidate the role of mineral surfaces and pedogenic oxides for DOC retention at pH 7, we sorbed DOC to bulk soil (illitic surface soils of a toposequence) and corresponding clay fraction (< 2 μm) samples after the removal of organic matter and after removal of organic matter and pedogenic oxides. The DOC retention was related to the content of dithionite‐extractable iron, specific surface area (SSA, BET‐N₂ method) and cation exchange capacity (pH 7). The reversibility of DOC sorption was determined by a desorption experiment. All samples sorbed 20–40 % of the DOC added. The DOC sorption of the clay fractions explained the total sorption of the bulk soils. None of the mineral phase properties investigated was able to solely explain the DOC retention. A sorption of 9 to 24 μg DOC m^–2 indicated that DOC interacted only with a fraction of the mineral surface, since loadings above 500 μg m^–2 would be expected for a carbon monolayer. Under the experimental conditions used, the surface of the silicate clay minerals seemed to be more important for the DOC sorption than the surface of the iron oxides. The desorption experiment removed 11 to 31 % of the DOC sorbed. Most of the DOC was strongly sorbed.     

Selenite adsorption by a variety of oxides

Abstract

Selenite adsorption by a variety of oxides consisting of iron (Fe), aluminum (Al), titanium (Ti), manganes (Mn), and silicon (Si), and by two humic acids were investigated in order to grasp selenite behavior and fixation mechanisms in soil. It was found that selenite was apparently adsorbed even by the Mn oxides on which surface negative charge was dominant in normal pH range (pH <4). No selenite adsorption was observed in the silicon dioxide (SiO₂) and the two humic acids. A sequential extraction of adsorbed selenite with competitive anions showed the differences of binding force or stability of adsorbed selenite among the minerals. While the goethite fixed selenite strongly, selenite adsorbed on the Mn oxide was easily released to the liquid phase with other anions, such as phosphate. Each mineral had its inherent characteristic in ligand exchange reactions accompanied with selenite sorption. Selenite sorption by the Mn and the Ti oxides resulted in large increase of surface negative charge, while only a little increase in the Fe and Al oxides. Proton consumption with selenite sorption was extremely smaller for the Mn oxide than for the others.     

Speciation and sorption structure of diphenylarsinic acid in soil clay mineral fractions using sequential extraction and EXAFS spectroscopy

Purpose

The mobility of arsenic (As) in soils is fundamentally affected by the clay mineral fraction and its composition. Diphenylarsinic acid (DPAA) is an organoarsenic contaminant derived from chemical warfare agents. Understanding how DPAA interacts with soil clay mineral fractions will enhance understanding of the mobility and transformation of DPAA in the soil-water environment. The objective of this study was to investigate the speciation and sorption structure of DPAA in the clay mineral fractions.

Materials and methods

Twelve soils were collected from nine Chinese cities which known as chemical weapons burial sites and artificially contaminated with DPAA. A sequential extraction procedure (SEP) was employed to elucidate the speciation of DPAA in the clay mineral fractions of soils. Pearson’s correlation analysis was used to derive the relationship between DPAA sorption and the selected physicochemical properties of the clay mineral fractions. Extended X-ray absorption fine structure (EXAFS) L_III-edge As was measured using the beamline BL14W1 at Shanghai Synchrotron Radiation Facility (SSRF) to identify the coordination environment of DPAA in clay mineral fractions.

Results and discussion

The SEP results showed that DPAA predominantly existed as specifically fraction (18.3–52.8%). A considerable amount of DPAA was also released from non-specifically fraction (8.2–46.7%) and the dissolution of amorphous, poorly crystalline, and well-crystallized Fe/Al (hydr)oxides (20.1–46.2%). A combination of Pearson’s correlation analysis and SEP study demonstrated that amorphous and poorly crystalline Fe (hydr)oxides contributed most to DPAA sorption in the clay mineral fractions of soils. The EXAFS results further demonstrated that DPAA formed inner-sphere complexes on Fe (hydr)oxides, with As-Fe distances of 3.18–3.25 Å. It is likely that the steric hindrance caused by phenyl substitution and hence the instability of DPAA/Fe complexes explain why a substantial amount of DPAA presented as weakly bound forms.

Conclusions

DPAA in clay mineral fractions predominantly existed as specifically, amorphous, poorly crystalline, and crystallized Fe/Al (hydr)oxides associated fractions. Amorphous/poorly crystalline Fe rather than total Fe contributed more to DPAA sorption and DPAA formed inner-sphere complexes on Fe (hydr)oxides.

     

广东主要母质发育水稻土对硅的吸附特性

Silicate adsorption in eight paddy soils developed from four different parent materials in Guangdong Province, China was examined to obtain fundamental knowledge of silicate adsorption to improve the efficacy of silicate fertilizer use in these areas. A correlation analysis showed that silicate adsorption did not obey the Langmuir equation （r = -0.664- 0.301） but did obey the Freundlich and Temkin equations （P〈0.01, r = 0.885-0.990）. When the equilibrium silicate concentration （Ci） was less than 45 mg SiO2 kg^-1, the adsorption capacity was in the following decreasing order of paddy soils： basalt-derived 〉 Pearl River Delta sediment-derived 〉 granite-derived 〉 sand-shale-derived. Stepwise regression and path analysis showed that for the investigated paddy soils amorphous MnO and Al2O3 were the two most important materials that affected silicate adsorption. Moreover, as Ci increased, amorphous Al2O3 tended to play a more important role in silicate adsorption, while the effects of amorphous MnO on silicate adsorption tended to decrease.     

Behavior of soil boron and boron uptake by M.26 apple rootstock as affected by application of different forms and nitrogen rates

Abstract

The changes in availability and uptake of boron (B) by M.26 apple rootstocks as affected by applications of different forms and rates of nitrogen (N) were examined. The study was carried out in a greenhouse using soil with low contents of organic matter, clay, calcium carbonate, NH₄‐oxalate soluble aluminum (Al) and iron (Fe), NH₂OH·HCl extractable manganese (Mn), poor cation exchange capacity and low pH. Soil N application was in the form of urea, calcium nitrate, ammonium sulphate, or ammonium nitrate at rates of 0, 17, 34, and 51 mg N kg^?1. After 1, 3, and 5 days of N application, soil B fractions were determined: B in soil solution, B specifically and non‐specifically adsorbed on soil surfaces, B occluded in Mn oxyhydroxides, and B occluded in crystalline Al and Fe oxides. The results showed that N as calcium nitrate and ammonium nitrate increased B both in soil solution and non‐specifically adsorbed on soil surface and decreased B concentration on Al and Fe oxides. This indicates that N‐NO₃ inhibited B sorption on Fe and Al oxides. Maximum B desorption from Fe and Al oxides was obtained within one day after N‐NO₃ was supplied. Nitrogen application as calcium nitrate and ammonium nitrate increased availability and uptake of B by plant roots. Thus, it was concluded that apple trees planted on coarse‐textured soils where risk of B deficiency is high, calcium nitrate or ammonium nitrates would be appropriately to apply to keep B more available.     

Reductive dissolution of crystalline and amorphous Fe(III) oxides by microorganisms in submerged soil

Summary Reduction of Fe(III) of amorphous and crystalline Fe(III) oxides to Fe(II) in flooded soils was studied using ⁵⁹Fe(OH)₃ and ⁵⁹Fe₂O₃. The results indicated that Fe(III) in the amorphous oxide was readily amenable to microbial reduction in anaerobic soil condition whereas Fe(III) in the crystalline oxide was not. Following soil submergence, the native as well as the applied crystalline Fe(III) oxides were rapidly converted into the amorphous form. The transformation of the crystalline oxides to the amorphous form appears to be a prerequisite for the reduction of Fe(III) of the oxide. This transformation, probably through hydration, is also mediated by microorganisms.     

Nitrate Sorption in a Mexican Allophanic Andisol using Intact and Packed Columns

Abstract

Contamination of groundwater by nitrate is a worldwide environmental issue. A better knowledge of nitrate sorption characteristics by soils contributes to efficient fertilizer use and prevents aquifer contamination. In volcanic soils, nitrate sorption is induced by variable charges due to the presence of amorphous materials and aluminum (Al) and iron (Fe) oxides. Anion transport in packed and intact columns was investigated in a Mexican Allophanic Andisol, under different permanent flow regimes in unsaturated conditions and several NO₃ ^?‐N and Br^? input concentrations. In the packed columns, the NO₃ ^?‐N adsorption in the soil was nonlinear. In the intact columns, the retardation coefficient variation was directly correlated to the increase of amorphous material with depth. The presence of preferential flow in the intact columns significantly increased the mobility and velocity of nitrate moving through the columns, whereas in the packed columns, NO₃ ^?‐N fate was only affected by soil chemical composition and mineralogy.