Significance of hydrous iron oxides in enhancing P sorption of soils with the addition of sodium hydrosulfite (Na2S2O4)

Phosphorus sorption (P_sor) of soils is affected by redox conditions. It has been shown that P_sor of lowland soils at a pH value of about 4.3 increases when a small amount of sodium hydrosulfite (Na₂S₂O₄) is added and decreases when an excess amount of (Na₂S₂O₄) is added to the mixture of a soil and P solution. Hydrous Fe-Al oxides, manganese dioxide (MnO₂) exchangeable Ca, models of reactive components with P in soils, were examined to identify the factors responsible for the increase of P_sor in lowland soils when a small amount of Na₂S₂O₄ was added. For clarifying the contribution of the hydrous Fe-Al oxides, goethite and 7 hydrous Fe-Al oxides (Fe/Al atomic ratio: 1/0, 5/1, 2/1, 1/1, 1/2, 1/5, and 0/1) were used. The P_sor of all these materials increased when they were treated with a small amount of Na₂S₂O₄ although the increase was the smallest for the hydrous Al oxide among the 7 oxides. Thus, the hydrous Fe oxides, and Al oxide to a smaller extent, play an important role in the increase in P_sor of the lowland soils treated with a small amount of Na₂S₂O₄ The P_sor of the hydrous Fe oxides was not appreciably affected by the addition of MnO₂. The increase in P_sor of the Ca-saturated Hachirogata soil was almost the same as that of the Nasaturated Hachirogata soil, indicating that exchangeable Ca did not affect appreciably the increase of P_sor in reduced soils at a pH value of about 4.3.     

Interference by organic complexation of Fe and A1 on the SO2-4 adsorption in Spodic B horizons in Sweden

The relations between pH, different fractions of Fe and A1 and Na₄P₂O₇-soluble C and the amount of adsorbed SO^2-₄ were assessed by analysing 63 soil samples from 14 podsolized soils in Sweden. The amount of adsorbed SO^2-₄ was significantly better correlated with the calculated amount of the inorganic fraction of Fe and A1 oxides obtained by subtracting Na₄P₂O₇-soluble Fe and A1 from oxalate-soluble Fe and Al than with the oxalate extraction alone. There was a close correlation between C and organically-bound S in the Na₄P₂O₇ extract which shows that the C:S ratio of the extracted fulvic acids is about constant in the soils studied. It was found that, as the proportion of organically-complexed Fe and Al increases, the ability of the soil to adsorb SO^2-₄ decreases. The amount of adsorbed SO^2-₄ expressed on the basis of the amounts of oxalate-soluble Fe and Al was generally smaller in areas with low S deposition (< 60 mmol m^-2 a^-1). The ratio between pyrophosphate-soluble C and oxalate-extractable Fe and Al was negatively correlated with pH in water. It was concluded that Fe and Al associated with organic matter cannot adsorb SO^2-₄ and that the degree of this association is pH dependent. These observations have important implications regarding the effects of anthropogenic acidification.     

Effect of iron oxide on phosphate sorption by calcite and calcareous soils

Pure calcite (AR grade CaCO₃) was treated with ferrous perchlorate solution to give a surface coating of iron (Fe) oxide. Maximum sorption (x_m) of phosphate (P) by the calcite increased from 18.2 to 160 mg P kg^?1 as the amount of coating increased from 0.00 to 16.0 g Fe₂O₃, kg^?1 CaCO₃. Evidence for Fe oxide coatings on carbonate minerals in two Sudanese soils was obtained by optical microscopy and electron-probe microanalysis. The relative contributions of carbonate and Fe oxide minerals, and Fe oxide coatings to P sorption in these soils were calculated, based on an assumed model of oxide distribution. Separate-phase Fe oxide was the major contributor (30–40%) to P sorption in the soils; the Fe oxide coatings on carbonate minerals were only minor contributors (< 6%), and the contribution of uncoated carbonate minerals was found to be negligible (<1 %). These results suggest a very minor role for carbonate minerals, even when coated with Fe oxide, in the sorption of P by these calcareous, Sudanese soils.     

Origin and properties of humus in the subsoil of irrigated rice paddies

Stability of humus in the plow layer soil is considered to affect the quantity and quality of dissolved organic matter leached from the plow layer soil. Therefore, a model experiment was conducted to analyze the effect of soil reduction under submerged conditions on the stability of humus in the plow layer soil. The changes in the stability of humus in the plow layer soil during submerged incubations with and without rice straw application were evaluated based on the changes in the binding type of humus. Binding type of humus in the plow layer soil was analyzed by successive extractions of organic matter with water, 0.25 M Na₂SO₄, 0.1 M Na₄P₂O₇ (pH 7.0), 0.1 M Na₄P₂O₇ (pH 10.5), and 0.1 M Na₄P₂O₇ (pH 10.5) with NaBH₄. Amounts of Fe, Mn, and Mg in each fraction were also determined to estimate the relationships between humus and metals.

The successive extraction of humus indicated that the amount of organic carbon which was extractable with the (NaBH₄ +0.1 M Na₄P₂O₇) solution decreased while that of the 0.1 M Na₄P₂O₇ (pH 7.0}-extractable organic carbon increased during submerged incubation with rice straw application. The origin of the increase in the amount of organic carbon in the Na₄P₂O₇ (pH 7.0)-extractable fraction during submerged incubation was investigated further by another incubation experiment using ¹³C-glucose as a reducing agent. Atom- 13C% analysis showed that the contribution of organic carbon derived from compounds other than glucose to the increase in the contents of humic acids and fulvic acids in the Na₄P₂O₇ (pH 7.0)-extractable fractions was ca. 80%. Therefore, it was concluded that the binding type of humus changed from (NaBH₄ + Na₄P₂O₇)-extractable to Na₄P₂O₇ (pH 7.0)-extractable humus under reducing conditions. Since the amounts of organic carbon and Fe increased in the Na₄P₂O₇ (pH 7.0)-extractable fraction and decreased in the (NaBH₄ +0.1 M Na₄P₂O₇)-extractable fraction simultaneously, iron reduction was presumably associated with the change in the binding type of humus in submerged paddy soil.     

Effect of Thiobacillus,sulfur, and phosphorus on the yield and nutrient uptake of canola and the chemical properties of calcareous soils in Iran

This factorial experiment consists of four levels of sulfur+Thiobacillus and three levels of triple superphosphate arranged in a completely randomized block design in three regions. With an increased sulfur+Thiobacillus and phosphorus (P), grain yield, phosphorus, iron (Fe), and zinc (Zn) uptake of canola increased in Qom and Mazandaran. Combined treatments of S₂₀₀₀T₄₀ and P_100% showed these properties most. In Safiabad, S₁₀₀₀T₂₀ resulted in a significant increase of P, Fe, and Zn uptake of canola, and no significant effect was found on the grain yield. The highest Fe and Zn concentrations in Qom soil was measured in S₂₀₀₀T₄₀. In Safiabad, maximum Fe concentration in soil was registered by S₁₀₀₀T₂₀ and P_65%. The minimum soil pH of Qom and Mazandaran was recorded by S₁₀₀₀T₂₀ and S₂₀₀₀T₄₀, respectively. The effect of sulfur and Thiobacillus on nutrients uptake and canola yield was good and indicates its potential for alleviating the impacts of calcareous soils.     

Comparative evaluation of methods employing alkali and sodium pyrophosphate to extract humic substances from peat

Abstract

Humic substances from two different types of peat ‐ Sphagnum and Carex ‐ were obtained by using either alkali extractants, O.IM NaOH, O.IM KOH, and 0.25M KOH, or solvents containing sodium pyrophosphate (O.IM Na₄P₂O₇, or O.IM NaOH/Na₄P₂O₇). The alkalis released considerably greater amounts of humic substances from the Sphagnum peat than the extractants containing pyrophosphate, whereas the opposite occurred in the Carex peat, the two greatest yields being obtained with 0.25M KOH in Sphagnum peat and with O.IM NaOH/Na₄P₂O₇ in Carex. As shown by the spectroscopic and chemical analyses, humic acids released from both peats by extractants containing Na₄P₂O₇ are generally more oxidized than those obtained by any of the alkali solutions. Also, humic acids extracted from the Sphagnum peat by any of the solvents generally exhibit lower molecular sizes, more pronounced aliphatic characteristics, and a higher degree of oxidation than those extracted from the Carex peat.

Results of gel permeation chromatography indicate that humic acids obtained from Sphagnum peat by either O.IM NaOH or O.IM KOH extraction show a similar distribution of molecular sizes with a predominance of compounds with a molecular weight greater than 50,000, whereas the use of 0.25M KOH enhances the release of partially degraded humic substances. Also, humic acids extracted from the same peat with 0.1M Na4P2O7 show a considerable amount of molecules of low molecular weight, but much fewer of these compounds are obtained when 0.1M NaOH/Na₄P₂O₇ extraction is employed. In Car ex peat, molecular size distribution does not seem to depend on the type of extractant used for solubilization of their humic acids.     

Phosphate fixation by ando soils different in their clay mineral composition

The phosphate fixation capacity at pH 4.5 and an equilibrium concentration of 250 mM phosphate was measured. The soil samples were divided into five groups according to their clay mineralogical composition. The first group soils contain opaline silica and allophanelike constituents, and some unidentified minerals, the second opaline silica and crystalline layer .i1icates, the third opaline silica and crystalline layer silicates with additional allophanelike constituents or aluminarich gel-like materials, the fourth allophanelike constituents, allophane and imogolite and the fifth crystalline layer silicates, allophanelike constituents and alumina-rich gel-like materials, plus some halloysite-like minerals, respectively. The first group soils had phosphate fixation capacities of 3,000 to 8,000, the second group soils 1,000 to 3,000, the third group loib 2,000 to 13,000, the fourth group soils 8,000 to 15,000 and the fifth group soil. 5,000 to 12,000 mg P₂O₅/100 g oven-dry soil, respectively. The fourth group soils in which allophane and imogolite predominated showed the highest phosphate fixation capacity.

The fractions which dissolved from almost all soil samples by treatments with 6% H₂O₂ Na₂S₂O₄-NaHCO₂-Na citrate and 2% Na₂CO₃ were estimated to have very high phosphate fixation capacities (8,000 to 19,000 mg P₂O₅/100 g dry-matter), and there was not much difference among the soil samples examined. Iron and aluminum combined with humus, allophanelike constituents, alumina-rich gel-like materials and halloysite-like minerals in addition to allophane and imogolite contribute to the phosphate fixation of Ando soils.     

Dilute acid-soluble phosphorus in fresh air-borne tephras and fixation with an increase in active aluminum and iron

Fresh rhyolite-to-andesite tephras ground to less than 0.15 mm particles contained dilute acid-soluble phosphorus (P) as in the case of cultivated upland soils in Japan. The amount of P determined by Truog extraction (Truog P) ranged between 119 and 784 mg P₂O₅ kg^-1 in 12 rhyolite-to-andesite tephras, and that determined by a modified Bray P₂ extraction method (modified Bray P₂) ranged between 133 and 812 mg P₂O₅ kg^-1. In contrast, the Truog P-content in fresh basaltic andesite-to-basalt tephras was only 3.4–23 mg P₂O₅ kg^-1, and the modified Bray P₂-content was in the range of 41–185 mg P₂O₅ kg^-1, although the total P-content of the two tephra groups was in almost the same range.

Among 12 rhyolite-to-andesite tephras, those from Mt. Usu that erupted in 1977 and from Mt. Pinatubo that erupted in 1991 were selected for detailed studies. Fine particle size fractions of these tephras showed higher Truog P values than the coarse ones. The Truog P values further increased in the heavy fraction with a particle density of 2.8 or greater. In this heavy fraction, apatite was detected by energy dispersive X-ray (EDX) analysis, indicating the contribution of the mineral to the high Truog P. Dilute sulfuric acid treatment of the tephras at 80°C for 15 d followed by neutralization increased the amount of active Al and Fe and decreased the Truog P values of these tephras. These results suggested that the amount of apatite rapidly decreased with weathering in volcanic ash soils.     

红壤中铝的形态

以改进的连续分级提取方法,用１ｍｏｌ／Ｌ,ＫＣｌ,０．２ｍｏｌ／Ｌ,ＨＣｌ,０．１ｍｏｌ／Ｌ Ｎａ４Ｐ２Ｏ７（ｐＨ８．５）,ＤＣＢ溶液,０．３３ｍｏｌ／Ｌ,柠檬酸钠和０．５ｍｏｌ／Ｌ ＮａＯＨ为提取剂,把红壤中可提取的非晶态铝区分为交换态铝,肿附态无机羟基铝,有机配合态铝,氧化铁结合态铝,层间铝和非晶态铝硅酸盐。     

Linear and Cyclophosphates as Sources of Phosphorus for Corn

Abstract

Cyclophosphates are not adsorbed by soil constituents and can be mobile in the soil profile. Mobile phosphorus (P) sources are of interest in soil science and for agronomic practices. Cyclotri (Na₃P₃O₉; C3P), and cyclotetraphosphate (Na₄P₄O₁₀; C4P) were compared to linear, ortho‐, pyro‐, and tripolyphosphate in four soils with different chemical, physical, and biological properties to determine their mobility and availability to corn (Zea mays, L.) in laboratory and greenhouse experiments. Cyclophosphate (C3P and C4P) hydrolysis products were evaluated by ion chromatography after incubating for 6 to 192 h with 100 and 200 µg P g^?1 soil. Phosphorus distribution and mobility, and plant availability and uptake with time, were determined in 45‐cm columns for four soils. Cyclophosphates sorbed less and moved deeper in all soils compared to the linear phosphates. The results showed that after 24 h a large proportion of cyclophosphates (34% of C3P and 37% of C4P) remained unhydrolyzed in Falba sandy acid soil. Split application of C3P and C4P at planting and at booting stage increased corn yield in sandy acid soil. Results of this experiment suggest that P deficiency after plant establishment can be corrected with cyclophosphates in soils with a low potential for cyclo‐P hydrolysis.     

The influence of vegetation and soil type on the speciation of iron in soil water

Soluble organic matter derived from exotic Pinus species has been shown to form stronger complexes with iron (Fe) than that derived from most native Australian species. It has also been proposed that the establishment of exotic Pinus plantations in coastal southeast Queensland may have enhanced the solubility of Fe in soils by increasing the amount of organically complexed Fe, but this remains inconclusive. In this study we test whether the concentration and speciation of Fe in soil water from Pinus plantations differs significantly from soil water from native vegetation areas. Both Fe redox speciation and the interaction between Fe and dissolved organic matter (DOM) were considered; Fe – DOM interaction was assessed using the Stockholm Humic Model. Iron concentrations (mainly Fe²⁺) were greatest in the soil waters with the greatest DOM content collected from sandy podosols (Podzols), where they are largely controlled by redox potential. Iron concentrations were small in soil waters from clay and iron oxide‐rich soils, in spite of similar redox potentials. This condition is related to stronger sorption on to the reactive clay and iron oxide mineral surfaces in these soils, which reduces the amount of DOM available for electron shuttling and microbial metabolism, restricting reductive dissolution of Fe. Vegetation type had no significant influence on the concentration and speciation of iron in soil waters, although DOM from Pinus sites had greater acidic functional group site densities than DOM from native vegetation sites. This is because Fe is mainly in the ferrous form, even in samples from the relatively well‐drained podosols. However, modelling suggests that Pinus DOM can significantly increase the amount of truly dissolved ferric iron remaining in solution in oxic conditions. Therefore, the input of ferrous iron together with Pinus DOM to surface waters may reduce precipitation of hydrous ferric oxides (ferrihydrite) and increase the flux of dissolved Fe out of the catchment. Such inputs of iron are most probably derived from podosols planted with Pinus.     

Humus composition and humification degree of humic acids of alpine meadow soils in the northeastern part of the Qinghai–Tibet Plateau

The characteristics of humus composition are important for understanding the mechanism of carbon storage in the Qinghai–Tibet Plateau. The aim of this study was to characterize the quality of soil organic matter (SOM) in this region. Soil samples from four soil profiles in fenced study sites in the alpine grassland were collected at altitudes of 4200, 4000, 3800, and 3400 m, along the southwest facing slope in the Qilian Mountains. The humus composition and humification degree of the humic acid (HA) were determined by two methods: (1) extraction with 0.5% sodium hydroxide (NaOH) followed by 0.1 M sodium pyrophosphate (Na₄P₂O₇) (OH-PP method); and (2) treating once with 0.1 M hydrochloric acid (HCl) followed by extracting with 0.5% NaOH (Cl-OH method). Physico-chemical analysis revealed higher exchangeable cation content and higher base saturation ratios could be related to slightly acidic to neutral soils, which could be regarded as calcium (Ca)-rich soils. The amounts of combined-form HAs obtained by HCl pretreatment (HA_Cl – HA_OH; ?HA_Cl) were remarkably higher than those extracted with Na₄P₂O₇ (HA_PP), indicating that the combined form of HAs is mainly Ca. In addition, the proportion of HA_PP in the total HAs extracted with both NaOH and Na₄P₂O₇ (HA_OH + HA_PP) obtained in the OH-PP method increased with soil depth and decreasing elevation, indicating that HAs associated with aluminum (Al) and iron (Fe) were distinguished in the subsoils of lower elevation. Therefore, the formation of the organo-mineral complex may contribute to stabilizing SOM in the Qinghai–Tibet Plateau. Moreover, Type A-HA with the highest degree of humification was obtained from the deeper horizons with the Cl-OH method and almost all horizons by extraction with Na₄P₂O₇ in the OH-PP method. Further studies using various spectroscopic analyses are necessary to elucidate the chemical properties of SOM in this region.     

A Hybrid Approach for PAHs and Metals Removal from Field-Contaminated Sediment Using Activated Persulfate Oxidation Coupled with Chemical-Enhanced Washing

The aim of this study was to investigate the removal of both polycyclic aromatic hydrocarbons (PAHs) and heavy metals from field-contaminated sediments by activated persulfate oxidation. Various chemicals, including hydroxypropyl-??-cyclodextrin (HPCD), S,S-ethylenediaminedisuccinic acid (EDDS), tetrasodium pyrophosphate (Na₄P₂O₇), and hydrochloric acid (HCl), were applied individually before or after activated persulfate oxidation to enhance the co-removal of both types of pollutants. It was found that the organic removal efficiency was not significantly enhanced by increasing the concentration of HPCD from 2.5 to 5.0?mM. The removal efficiency of heavy metals was not improved even at an excess amount of EDDS after activated persulfate oxidation. However, the addition of EDDS acted as the Fe²⁺ carrier for activated persulfate oxidation. In addition, no significant enhancement of heavy metal removal was observed by increasing the concentrations of Na₄P₂O₇ and HCl from 0.01 to 0.1?M after activated persulfate oxidation. However, comparing 0.1?M HCl with 0.1?M Na₄P₂O₇, HCl was shown to be more effective in promoting the removal of organic pollutants. With further adjustments on the experimental conditions, the highest removal amount of metals and PAHs was achieved by adding 2?M of HCl with 3?days mixing, followed by Fe²⁺-activated persulfate oxidation (PS/Fe²⁺ molar ratio at 4:1) for further 6?h mixing. The removal efficiency of low and high molecular weight PAHs was about 70 and 20?%, respectively, while the removal efficiency of metals was 70, 100, 40, 65, 65, 80, and 100?% for Cr, Cu, Hg, Mn, Ni, Pb, and Zn, respectively.     

Differential response of mineral-associated organic matter in tropical soils formed in volcanic ashes and marine Tertiary sediment to treatment with HCl,NaOCl, and Na4P2O7

Quantitative knowledge of the amount and stability of soil organic matter (SOM) is necessary to understand and predict the role of soils in the global carbon cycle. At present little is known about the influence of soil type on the storage and stability of SOM, especially in the tropics. We compared the amount of mineral-associated SOM resistant to different chemical treatments in soils of different parent material and mineralogical composition (volcanic ashes – dominated by short-range-order aluminosilicates and marine Tertiary sediments – dominated by smectite) in the humid tropics of Northwest Ecuador. Using ¹³C isotope analyses we traced the origin of soil organic carbon (SOC) in mineral-associated soil fractions resistant to treatment with HCl, NaOCl, and Na₄P₂O₇ under pasture (C₄) and secondary forest (C₃). Prior to chemical treatments, particulate organic matter was removed by density fractionation (cut-off: 1.6 g cm^?3). Our results show that: (1) independent of soil mineralogical composition, about 45% of mineral-associated SOC was resistant to acid hydrolysis, suggesting a comparable SOM composition for the investigated soils; (2) oxidation by NaOCl isolated a SOM fraction with enhanced stability of mineral-bound SOM in soils developed from volcanic ashes; while Na₄P₂O₇ extracted more SOC, indicating the importance of Al-humus complexes in these soils; and (3) recently incorporated SOM was not stabilized after land use change in soils developed from volcanic ashes but was partly stabilized in soils rich in smectites. Together these results show that the employed methods were not able to isolate a SOM fraction which is protected against microbial decay under field conditions and that the outcome of these methods is sensitive to soil type which makes interpretation challenging and generalisations to other soils types or climates impossible.     

Comparison of chemical fractionation methods for isolating stable soil organic carbon pools

Stable soil organic matter (SOM) is important for long‐term sequestration of soil organic carbon (SOC), but the usefulness of different fractionation methods to isolate stable SOM is open to question. We assessed the suitability of five chemical fractionation methods (stepwise hydrolysis, treatment with H₂O₂, Na₂S₂O₈, NaOCl, and demineralization of the NaOCl‐resistant fraction (NaOCl + HF)) to isolate stable SOM from soil samples of a loamy sand and a silty loam under different land use regimes (grassland, forest and arable crops). The apparent C turnover time and mean age of SOC before and after fractionation was determined by ¹³C and ¹⁴C analysis. Particulate organic matter was removed by density fractionation before soils were exposed to chemical fractionation. All chemical treatments induced large SOC losses of 62–95% of the mineral‐associated SOC fraction. The amounts of H₂O₂‐ and Na₂S₂O₈‐resistant SOC were independent from land use, while those of NaOCl‐ (NaOCl + HF)‐ and hydrolysis‐resistant SOC were not. All chemical treatments caused a preferential removal of young, maize‐derived SOC, with Na₂S₂O₈ and H₂O₂ being most efficient. The mean ¹⁴C age of SOC was 1000–10000 years greater after chemical fractionation than that of the initial, mineral‐associated SOC and mean ¹⁴C ages increased in the order: NaOCl < NaOCl + HF ≤ stepwise hydrolysis ≪ H₂O₂≈ Na₂S₂O₈. None of the methods appeared generally suitable for the determination of the inert organic matter pool of the Rothamsted Carbon Model. Nonetheless, our results indicate that all methods are able to isolate an older, more stable SOC fraction, but treatments with H₂O₂ and Na₂S₂O₈ were the most efficient ones in isolating stable SOM.     

Iron oxides serve as natural anti-acidification agents in highly weathered soils

Purpose

The effect of Fe oxides on the natural acidification of highly weathered soils was investigated to explore the natural acidification process in variable charge soils

Materials and methods

A variety of highly weathered soils with different Fe oxide contents were collected from the tropical and subtropical regions of southern China to investigate the soil acidity status. Electrodialysis experiments were conducted to simulate natural acidification process and promote accelerated acidification in a variety of systems such as relatively less weathered soils, mixtures of goethite with montmorillonite or kaolinite, an Alfisol, a limed Ultisol, and Fe oxides coated montmorillonite. The objective was to gather evidence for the occurrence of Fe oxide inhibited natural acidification in highly weathered soils.

Results and discussion

Highly weathered soils with free Fe₂O₃?<?100?g/kg (17 soils) had an average pH?=?4.64?±?0.06, while the soils with free Fe₂O₃?>?100?g/kg (49 soils) had an average pH?=?5.25?±?0.04. A significant linear relationship was found between the soil pH and Fe oxide content of these soils. Similar results were obtained in electrodialysis experiments, i.e., in soils that underwent accelerated acidification. A negative correlation was found between the Fe oxide content and exchangeable acidity or effective cation exchange capacity, respectively. In another set of experiments, goethite slowed down acidification in experiments conducted with this Fe oxide and montmorillonite, or kaolinite, or an Alfisol, or a limed Ultisol. The overlapping of the electrical double layers on the positively charged Fe oxide particles and negatively charged minerals may have caused the release and subsequent leaching of the base cations, but inhibited the production of exchangeable acidity cations. In addition, when montmorillonite or Fe oxide-coated montmorillonite were electrodialyzed in another set of experiments, exchangeable acidity of the former was much greater than that of the latter, suggesting that the positively charged Fe oxide coatings on montmorillonite have partially neutralized the permanent negative charge on montmorillonite surfaces, decreasing exchangeable acidity.

Conclusions

Fe oxides may function as natural ??anti-acidification?? agents through electric double-layer overlapping and coating of phylliosilicates in highly weathered soils.     

Comparison of the effects of nano-iron fertilizer with iron-chelate on growth parameters and some biochemical properties of Catharanthus roseus

Nanofertilizers, which supply nutrients to the plant, are used to replace conventional fertilizers. Iron (Fe) is one of the essential elements for plant growth and plays an important role in the photosynthetic reactions. To study the effects of nano-iron fertilizer on Catharanthus roseus, plants were treated with different concentrations (0, 5 10 20, 30, and 40 mM) of iron oxide nanoparticles (Fe2O3) for 70 days. Fe₂O₃ nanoparticles increased growth parameters, photosynthetic pigments, and total protein contents in the treated plants significantly. The maximum amounts of growth parameters, photosynthetic pigments, and protein contents were obtained with 30 µM Fe₂O₃ and minimum values of these parameters were found with 0 µM Fe₂O₃. The highest value of total alkaloid content was obtained in 0 µM Fe₂O₃ and the lowest value was observed in control plants. Iron oxide nanoparticles increased potassium, phosphorus, and iron absorption but did not show a significant effect on sodium content.     

Influence of chemical properties of soils on methane emission from rice paddies

Abstract

The relationships between methane (CH₄) emission from flooded rice paddies and soil chemical properties were investigated using eight different soils in a pot experiment. Since CH₄ is produced in paddy soil microbiologically when reducing conditions are sufficiently developed, the amounts of oxidizing agents including free iron (Fe)(III), amorphous Fe(III), easily reducible manganese (Mn), nitrate (NO₃ ^‐), and sulfate (SO₄ ^2‐), and indexes of reducing agents including total carbon (C), total nitrogen (N), and easily decomposable C, were measured as possible decreasing and increasing factors in CH₄ emission. The seasonal variations in CH₄ emission rates were similar in pattern among the soils used. However, the amount of emitted CH₄ varied largely, with the maximum total CH₄ emission (from a brown lowland soil, 1,535 mg pot^‐1) being 3.8 times that of the minimum (from a gley soil, 409 mg pot^‐1). No correlation was found between the total CH₄ emission and any single factor investigated. However, a statistically significant equation was found through multiple regression analysis: r=‐2.24x10² a+2.88b+6.20x10²; r ²=0.821; P<0.01; where Y is the amount of emitted CH₄ (mg pot^‐1), a is the amount of amorphous Fe(III) (mg pot^‐1), b is the amount of easily decomposable C (mg pot^‐1), and r ² is a multiple correlation coefficient adjusted for the degree of freedom. The amendment of ferric hydroxide [Fe(OH)₃] to a gray lowland soil significantly decreased the CH₄ emission from 1,099 to 592 mg pot^‐1. This measured amount agreed well with that estimated from the above equation, 554 mg pot^‐1.     

A rapid method for the determination of fixed ammonium in soil

Abstract

Five different procedures for the oxidation of organic carbon were compared in order to determine the most suitable method for use as a pretreatment before the determination of fixed NH₄‐N in soils. Three of the procedures involved a method based on the use of a solution containing 0.1M Na₄P₂O₇, 0.1M NaCl, and 6% H₂O₂, applied for three different periods of time, 10 days, 20 days, and whatever number of days are required until frothing no longer occurs. This third period of time is designated as NF (no frothing). The remaining two procedures involved a method based on the use of a 3M NaOCl solution applied for two different periods of time, 3‐cycles and 5‐cycles.

Two of the procedures, the NF treatment with H₂O₂+NaCl+Na₄P₂O₇ and the 5‐cycle treatment with NaOCl, were found to give the must efficient removal of organic C. The amount of residual N in the soil after the NF treatment was highly correlated with the amount of residual N in the soil after the 5‐cycle treatment. It is concluded that the 5‐cycle treatment is as effective as the NF treatment for the oxidation of organic C in the soil before carrying out the determination of fixed NH₄‐N. The 5‐cycle treatment has the advantage of being a faster and simpler analytical procedure than the NF treatment.     

Extractability and adsorption of sulphate in soils

Virtually all of the indigenous sulphate (SO₄) in a range of UK soils with moderately high pH values (> 6) was found to be present in the soil solution and, as a consequence, was highly susceptible to leaching. For acid soils containing adsorbed SO₄, the extractability of SO₄ in NaCl and CaCl₂ solutions was dependent on both the ionic strength and cation species. Addition of small amounts (<～ 10^?2M) of either NaCl or CaCl₂ actually decreased the amount of SO₄ extracted, but SO₄ extractability increased sharply with concentrations of NaCl or CaCl₂ higher than about 0.1 M. At a similar ionic strength, more SO₄ was extracted by NaCl than CaCl₂. Sequential extraction with 1 M NaCl removed essentially all of the absorbed SO₄. The release characteristics of SO₄ were very different to those of phosphate and this difference in behaviour is not easily reconciled with the view that SO₄ is chemisorbed, as is phosphate. Except for a few acid soils with high oxide contents, the capacity of the soils to adsorb added SO₄ was quite small. None of the soils with pH values higher than 6 adsorbed a significant amount SO₄. The results raise questions regarding the efficiency of SO₄-containing fertilizers in correcting and preventing S deficiency in situations where leaching is important.