Transformations and Availability of Iron to Wheat as Influenced by Phosphorus and Manganese Fertilization in a Typic Haplustept Soil

An investigation was conducted using Typic Haplustept, sandy loam soil, to investigate the interactive effects of phosphorus (P) and manganese (Mn) fertilization on native iron (Fe) pools in soil and their availability to wheat (cv. PBW-343) crop. Phosphorus fertilization moved Fe from residual mineral fraction of Fe to manganese oxides (MnOX), organic matter (OM), amorphous (AMPOX), and crystalline (CRYOX) Fe and Al oxide fractions. However, Mn application decreased specifically adsorbed (SAD)–Fe and CRYOX–Fe but increased OM–Fe and mineral fraction of Fe. Available Fe in soil decreased as Olsen P and P:Mn ratio increased in the soil. Higher Olsen P (>60 mg P kg^?1soil) reduced mean Fe uptake by shoot. P content and P:Mn ratio in soil as well as in root and shoot were inversely related to Fe concentration in both the plant parts. The role of soil Fe associated with oxides and organic matter was found most notable in Fe nutrition of wheat.     

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.     

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.     

Molybdenum Determination in Mehlich‐1 and Mehlich‐3 Soil Test Extracts and Molybdenum Adsorption in Brazilian Soils

Abstract

The extractant Mehlich‐1 is routinely used in Brazil for determination of soil nutrients, whereas Mehlich‐3 has been suggested as a promising extractor for soil fertility evaluation. Both were used for extraction of molybdenum (Mo) in Brazilian soils with Mo dosage by the KI+H₂O₂ method. The Langmuir and Freundlich isotherms were used to study soil Mo adsorption. Mehlich‐1 extracted more Mo than Mehlich‐3 in soils with high contents of organic matter, clay, and iron (Fe) oxides. Mehlich‐3 and Mehlich‐1 extractions correlated positively and significantly with amorphous Fe oxides, crystalline Fe oxides, and organic matter. Molybdenum recovering rates correlated to crystalline Fe oxides and clay contents but not to organic matter, pH, and Mo adsorption capacity. Amorphous and crystalline Fe oxides, clay, and organic matter were responsible for most of the Mo adsorption. The Langmuir isotherm described better the Mo adsorption to soil amorphous Fe oxides and organic matter than the Freundlich isotherm.     

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.     

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.

     

Aluminum and iron(III) species in the soil solution including organic complexes with citrate and humic substances

The solubility of Al and Fe in soil is of relevance for their toxicity and availability, respectively, to plant roots. Humic substances as the main part of stable soil organic matter and citrate which is often excreted by P deficient plants are strong complexants of Al and Fe(III). Therefore, equations were developed to calculate the Al and Fe(III) species distribution in the soil solution in the presence of humic substances and citrate as organic ligands. Calculations in the pH range 4.0–7.0 showed that at higher pH humic-Al complexes were the most important species whereas AlOH-citrate^? dominated between pH 4.0 and 5.4. Free monomeric Al and AlSO₄⁺ were of minor relevance. Iron(III) species calculations showed that humic-Fe complexes were the main species in the pH range 4.0–7.0. But if mugineic acid, a Fe complexing phytosiderophore released into the rhizosphere by graminaceous plant species, was present in the soil solution (10^?6 M), Fe-mugineic acid complexes accounted for most of the Fe in solution. Fe-citrate^? was relevant at lower pH but contributed little to Fe(III) species at pH > 6.0. The results demonstrate the strong importance of the considered organic ligands for Fe and Al in the soil solution.     

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.     

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.     

淹水条件下施加石灰和有机质对酸性土壤性质和磷吸附的影响

每公斤土加入2克碳酸钙和(或)三叶草的5个老成土和1个氧化土,在淹水培育45天后风干,结果发现:(1)淹水土壤风干,其pH比淹水时低,但仍比未淹水的高;(2)淹水降低了土壤中0.5MCuCl₂提取的铝量,石灰和三叶草处理使3个轻质土中的铝量进一步降低,但3个粘质土则呈现相反的趋势;(3)改良剂使3个轻质土吸附的磷减少,而使3个粘质土吸附的磷增加。前者增加的原因是因为通过还原作用和氧化作用形成了较多的活性表面,而后者的减少则可能是粘粒表面所形成的水化氧化物胶膜堵塞了原有的吸附位,从而使吸附位减少(4)改良剂对磷解吸的影响,是降低了3个轻质土的磷解吸,而增加了3个粘质土的磷解吸;(5)经淹水风干处理土壤的磷吸附量与草酸盐提取的铁、铝、锰及CuCl₂溶液提取的铝有很高的相关性,表明控制淹水土壤磷吸持的土壤组分,不仅包括无定形铁,而且也包括羟基铝聚合物。     

Characterization of iron oxides in Fe-rich concretions from an imperfectly-drained Greek soil: a study by selective-dissolution techniques and X-ray diffraction

Fe-rich concretions commonly occur in Greek soils with alternating drying and waterlogging periods. This study was conducted to characterize the iron oxides in Fe-rich concretions from the upper solum of an Alfisol with seasonal perched water table by the combination of selective dissolution and X-ray diffraction (XRD) techniques. The results showed that more than 75% of the total iron (Fet) was associated with the crystalline and the amorphous Fe oxides, indicating a strong accumulation of free iron oxides (Fed) in concretions. Amorphous iron compounds (Feo) was present at high concentrations and fluctuated with profile depth. The active Fe ratio (Feo/Fed) values that ranged from 0.35 to 0.41 reflected an association of poorly crystalline goethite with some ferrihydrite. The XRD data showed that the Fe-rich concretions consisted of quartz, feldspars, illite and gypsum. The mineralogy of iron oxides in concretions was determined by comparison of XRD patterns for dithionite-citrate-bicarbonate (DCB) treated (deferrated) and untreated (non-deferrated) samples. Poorly crystalline goethite as demonstrated by broad lines in the diffraction patterns and ferrihydrite were the iron oxides detected in the concretions. This mineral assemblage appears to be related to the pedoenvironmental conditions in which the concretions were formed and indicates that the mechanisms governing the formation of crystalline Fe oxides from ferrihydrite are retarded by the presence of crystallization inhibitors.     

Phosphorus sorption by Andepts from the Southern Highlands of Papua New Guinea

P sorption curves (18 hours, 0.01 M CaCl₂) were determined for various A, AB, B and C horizons of six Andepts. Two of these soils were formed in alluvially sorted and redeposited volcanic ash. P buffer capacity (PBC) and equilibrium solution P concentration (EPC) were derived from the curves. PBC was high for all samples indicating large sorption capacities. Soils formed in alluvial ash had lower PBC than those developed in airfall ash. In the latter soils, PBC was affected by degree of weathering. Multiple regression indicated that most variation in PBC was accounted for by citrate-dithionite minus pyrophosphate extractable Al, oxalate minus pyrophosphate extractable Al, and pyrophosphate extractable Fe. This suggests that allophane, crystalline and non-crystalline aluminium hydrous oxides, and Fe associated with organic matter, account for the predominant P-sorbing sites. The low EPC figures, which were correlated with Olsen extractable P, indicate potential P deficiency as a limitation to crop production.     

消落带土壤铁的形态变化及其对有效磷的影响

Fe3+还原为Fe2+的过程中会增加磷酸铁的溶解,影响磷的化学行为及有效性。本文采用室内模拟试验研究了三峡库区消落带土壤铁的形态变化及其对有效磷的影响。消落带旱地和水田土壤经淹水和落水处理后,活性铁、水溶性铁增加,其他各形态铁变化较小。旱地土壤在不同的有机质和淹水落水处理下,其活化铁、游离铁、络合铁、水溶性亚铁、和交换性亚铁均为淹水处理高于落水处理,其中活性铁在各处理间呈现出显著性差异,其他则各处理间差异均未达到显著性水平;水田下层活性铁高于上层,且落水处理间呈显著差异。氧化铁及亚铁之间总处于不断的相互转化中,活性铁、络合铁和有机质正相关。旱地土壤中的有效磷各处理间差异显著,水田有效磷淹水处理高于落水处理。     

The influence of weathering processes on labile and stable organic matter in Mediterranean volcanic soils

The relationship and mechanisms among weathering processes, cation fluxes, clay mineralogy, organic matter composition and stability were studied in soils developing on basaltic material in southern Italy (Sicily). The soils were transitions between Phaeozems and Vertisols. Intense losses of the elements Na, Ca and Mg were measured indicating that weathering has occurred over a long period of time. The main weathering processes followed the sequence: amphibole, mica, volcanic glass or if ash was the primary source → smectite → interstratified smectite–kaolinite → kaolinite. Kaolinite formation was strongly related to high Al, Mg and Na losses. The good correlation between oxyhydroxides and kaolinite in the soils suggests that (macro)aggregates have formed due to physical or electrostatic interactions between the 1:1 clay minerals and oxides. The stability of organic matter was investigated with a H₂O₂-treatment that assumes that chemical oxidation mimics the natural oxidative processes. The ratio of C after the H₂O₂ treatment to the total organic C ranged from 1–28%. No correlation between clay content and organic matter (labile or stable fraction) was found. The refractory organic fraction was enriched in aliphatic compounds and did not greatly interact with the kaolinite, smectite or poorly crystalline Fe or Al phases. A part of this fraction (most probably proteins) was bound to crystalline Fe-oxides. In contrast, the oxidisable fraction showed a strong relationship with poorly crystalline oxyhydroxides and kaolinite. Surprisingly, smectite did not contribute to the stabilisation of any of the organic C fractions. The stabilisation of organic matter in the soils has, therefore, two main mechanisms: 1) the protection of labile (oxidisable with H₂O₂) organic matter, including also aromatic-rich compounds such as charcoal, by the formation of aggregates with oxyhydroxides and kaolinite and 2) the formation of a refractory fraction enriched in aliphatic compounds.     

有机肥(物)对土壤中磷的活化作用及机理研究──Ⅰ.有机肥(物)对土壤不同形态无机磷的活化作用

采用逐级去磷的土壤研究在好气与淹水条件下猪粪、稻草和纤维素对土壤中不同形态磷的活化作用。结果表明,在好气条件下,猪粪、稻草和纤维素均能对土壤中各种形态的无机磷起活化作用,其效果为猪粪＞稻草＞纤维素。在淹水条件下,有机肥则表现为明显增加土壤对磷的固定,这主要是土壤中的铁氧化物强烈吸附磷所致。但当土壤去除Fe－P和O－P后,有机肥则能对土壤磷起明显的活化作用。采用人工合成磷酸铁加入去磷、去铁氧化物土壤的试验表明,有机肥对磷酸铁的活化率可高达30％。由于土壤中存在的铁氧化物对活化的磷起掩盖作用,因此,有机肥对土壤磷,尤其对Ca₂－P、Ca₈－P、Al-P和Fe－P的实际活化作用有可能比测定值还要高。     

有机肥(物)对土壤中磷的活化作用及机理研究──Ⅰ.有机肥(物)对土壤不同形态无机磷的活化作用

采用逐级去磷的土壤研究在好气与淹水条件下猪粪、稻草和纤维素对土壤中不同形态磷的活化作用。结果表明,在好气条件下,猪粪、稻草和纤维素均能对土壤中各种形态的无机磷起活化作用,其效果为猪粪＞稻草＞纤维素。在淹水条件下,有机肥则表现为明显增加土壤对磷的固定,这主要是土壤中的铁氧化物强烈吸附磷所致。但当土壤去除Fe－P和O－P后,有机肥则能对土壤磷起明显的活化作用。采用人工合成磷酸铁加入去磷、去铁氧化物土壤的试验表明,有机肥对磷酸铁的活化率可高达30％。由于土壤中存在的铁氧化物对活化的磷起掩盖作用,因此,有机肥对土壤磷,尤其对Ca2－P、Ca8－P、Al-P和Fe－P的实际活化作用有可能比测定值还要高。     

Accumulation of organo‐metallic complexes in laterites and the formation of Aluandic Andosols in the Nilgiri Hills (southern India): similarities and differences with Umbric Podzols

We have investigated the speciation and distribution of iron (Fe) and aluminium (Al) between minerals and organic species in A and B horizons of two Aluandic Andosols with X‐ray diffraction, thermal analyses, visible diffuse reflectance and Fourier transform infrared (FTIR) spectroscopies, together with selective and total chemical extractions. The two Aluandic Andosols of the Nilgiri Highlands (south India) have formed at the expense of intensively weathered lateritic formations of the Eocene. Data revealed that Al and Fe were predominantly stored in end‐weathering products of laterites, mainly as gibbsite and Fe (hydr)oxides in B horizons of the Aluandic Andosols. These secondary minerals are gradually replaced by organo‐metallic complexes in the topsoil A horizons exhibiting andic properties. We then indicate that formation of the organo‐metallic complexes results from weathering of the dominant crystalline Al‐ and Fe‐(hydr)oxides mediated by the organic ligands and complexation of the polyvalent metals following the accumulation of organic matter. Such weathering and complexation mechanisms are therefore similar to those recently ascribed to deferralitization and the formation of freely drained Umbric Podzols (Humus‐Podzols) in the upper Amazon Basin. In the present case, large supplies of both Al‐ and Fe‐bearing minerals provide large metal:carbon ratios that prevent the mobility of the organo‐metallic complexes and induce the formation of Aluandic Andosols rather than Podzols.     

Farm-scale variations in soil color as influenced by organic matter and iron oxides in Japanese paddy fields

To understand how soil color is influenced by soil components at the farm scale, we evaluated spatial variation in soil color and related soil properties in Japanese paddy fields. After harvest of rice, 246 surface soil samples were collected in 10-m grids from five contiguous irrigated paddy fields, each with an area of about 0.5 ha. The samples were analyzed to determine color parameters (L*, a*, and b*), and contents of total C, total N, Fe oxides, sand, and loss-on-ignition. The results obtained were modeled and mapped geostatistically. All color parameters indicated strong spatial dependence with long ranges (>85 m). In contrast, total C and N showed short ranges (about 40 m). The contents of Fe oxides, sand, and loss-on-ignition showed intermediate ranges (50–85 m). The ranges of these properties and their distribution patterns suggested that the contents of total C and N were influenced by long-term application of manure and that sand content was influenced by topography and past land consolidation. Further soil color analysis after removal of organic matter or silt plus clay particles revealed that soil organic matter, texture, and Fe oxides affected soil color parameters in a complex manner. Prediction of total C from soil darkness was hindered by the presence of silt plus clay particles containing Fe oxides. On the other hand, citrate-dithionite extractable Fe was estimated accurately from the b* value (yellowness), which can be useful for predicting the occurrence of akiochi (autumn decline) disease of rice at the farm scale.     

DISTRIBUTION OF PYROPHOSPHATE-EXTRACTABLE IRON AND ORGANIC CARBON IN SOILS OF VARIOUS GROUPS

Potassium pyrophosphate (0.1m ) removes very little Fe from crystalline Fe oxides at pH 10, but peptizes finely divided hydrous amorphous oxides and organic matter in soils. Fe and C contents of extracts from each horizon of twenty-six British soil profiles show distinctive patterns, independent of the residual dithionite-soluble Fe. Thus extracts of humus Fe podzols have maximum Fe and C in the B horizon, peaty gley podzol has maximum Fe in the B horizon but maximum C in the surface. These groups are differentiated from non-podzols which have maximum pyrophosphate extractable Fe and C in the surface horizon, decreasing with depth. Intermediate patterns help to quantify differences in soils of classes having properties of more than one soil group.