影响土壤中铬, 锰的氧化还原反应的环境因素

Disposal of chromium(Cr) hexavalent form,Cr(VI),in soils as additions in organic fertilizers,liming materials or plant nutrient sources can be dangerous since Cr(VI) can be highly toxic to plants,animals,and humans.In order to explore soil conditions that lead to Cr(VI) generation,this study were performed using a Paleudult(Dystic Nitosol) from a region that has a high concentration of tannery operations in the Rio Grande do Sul State,southern Brazil.Three laboratory incubation experiments were carried out to examine the influences of soil moisture content and concentration of cobalt and organic matter additions on soil Cr(VI) formation and release and manganese(Mn) oxide reduction with a salt of chromium chloride(CrCl 3) and tannery sludge as inorganic and organic sources of Cr(III),respectively.The amount of Cr(III) oxidation depended on the concentration of easily reducible Mn oxides and the oxidation was more intense at the soil water contents in which Mn(III/IV) oxides were more stable.Soluble organic compounds in soil decreased Cr(VI) formation due to Cr(III) complexation.This mechanism also resulted in the decrease in the oxidation of Cr(III) due to the tannery sludge additions.Chromium(III) oxidation to Cr(VI) at the solid/solution interface involved the following mechanisms:the formation of a precursor complex on manganese(Mn) oxide surfaces,followed by electron transfer from Cr(III) to Mn(III or IV),the formation of a successor complex with Mn(II) and Cr(VI),and the breakdown of the successor complex and release of Mn(II) and Cr(VI) into the soil solution.     

Characteristics of free sesquioxides and humic acids in soil distributed under Warm-temperate forest climate in Nyu mountains,Fukui Prefecture,Central Japan

The activity and crystallinity ratios of free iron oxides, and the ΔlogK and RF values of humic acids were analyzed in five soil types in the Nyu mountains, Fukui Prefecture, to examine the relation between the zonality of soils and the bioclimatic conditions under the Warm-temperate deciduous broad-leaved forest climate. The characteristics of free iron oxides and humic acids were as follows: The Dark red soil, Kunimidake series was a Dark Red soil under the Cool-temperate deciduous broad-leaved forest climate; the Dry brown forest soil (reddish), Tega series was a Yellow-Brown Forest soil under the Warm-temperate deciduous broad-leaved forest climate; the Dry brown forest soil, Takasu-1 series and the Yellow soil, Yada series were Yellow-Brown Forest soils under the Warm-temperate lucidophyllous forest climate; and the Red soil, Oshibayama series and the lower parts of the Tega series were paleo-red soils. These results indicated that zonal soils under the Warm-temperate deciduous broad-leaved forest climate were Yellow-Brown Forest soils in the Nyu mountains, Fukui Prefecture. The Dark red soil, Kunimidake series corresponded to a Hyperdystri-Rhodic Cambisol of World Reference Base for Soil Resources, WRB (FAO, ISRIC, and ISSS: World Soil Resources Reports 84, 1998). The Dry brown forest soil (reddish), Tega series, the Dry brown forest soil, Takasu-1 series, and the Red soil, Oshibayama series were compared with the Hyperdystri-Chromic Cambisol (WRB). The Yellow soil, Yada series was a Hypereutri-Chromic Cambisol (WRB).     

Density fractionation of organic matter in dolomite‐derived soils

Dolomite (CaMg(CO₃)₂) constitutes half of the global carbonates. Thus, many calcareous soils have been developing rather from dolomitic rocks than from calcite (CaCO₃)‐dominated limestone. We developed a physical fractionation procedure based on three fractionation steps, using sonication with subsequent density fractionation to separate soil organic matter (SOM) from dolomite‐derived soil constituents. The method avoids acidic pretreatment for destruction of carbonates but aims at separating out carbonate minerals according to density. The fractionation was tested on three soils developed on dolostone parent material (alluvial gravel and solid rock), differing in organic‐C (OC) and inorganic‐C (IC) concentrations and degree of carbonate weathering. Soil samples were suspended and centrifuged in Na‐polytungstate (SPT) solutions of increasing density, resulting in five different fractions: two light fractions < 1.8 g cm^–3 (> 20 μm and < 20 μm), rich in OC and free of carbonate, and two organomineral fractions (1.8–2.4 g cm^–3 and 2.4–2.6 g cm^–3), containing 66–145 mg g^–1 and 16–29 mg g^–1 OC. The organomineral fractions consist of residual clay from carbonate weathering such as clay minerals and iron oxides associated with SOM. The fifth fraction (> 2.6 g cm^–3) was dominated by dolomite (85%–95%). The density separation yielded fractions differing in mineral compositions, as well as in SOM, indicated by soil‐type‐specific OC distributions and decreasing OC : N ratios with increasing density of fractions. The presented method is applicable to a wide range of dolomitic and most likely to all other calcareous soils.     

Chemical properties of Niger floodplain soils,eastern Nigeria,in relation to mineralogy

The agricultural potentials of the floodplain soils of river Niger have been less exploited due to lack of information on their chemical and mineralogical characteristics. We studied five soil profiles within the floodplain to determine the levels of plant nutrients and relate them to their clay mineralogy and total element. The soils flooded for eight months of the year are low in pH and plant available nutrients while the dominant clay mineral is kaolinite. Kaolinite and interlayered vermiculite were negatively correlated with all the exchangeable bases, CEC and available P, indicating the negative contribution of these clay minerals to the plant nutrient reserve of these soils. Illite correlated positively with Na⁺ and K⁺ (r=0.51; 0.50), while smectite correlated significantly with Na, K, Ca and CEC. Also positive significant correlation existed between illite/smectite and Na⁺, K⁺, Mg²⁺, CEC and base saturation thus confirming the positive role of smectite and illite to the plant nutrient reserve in the soils. Kaolinite and CaO could be used for the prediction of exchangeable K (R²=0.62, 0.78 respectively). Although the level of nutrient cations are low, the depositional effect of the river and traditional cultivation practices can boost crop yield especially paddy rice.     

Explaining soil organic matter composition based on associations between OM and polyvalent cations

Site conditions and soil management determine the content and the composition of soil organic matter (SOM). Organic matter (OM) is characterized by functional groups, which preferentially interact with polyvalent cations and soil minerals. These interactions could perhaps explain the site‐specific composition of bulk SOM and a pyrophosphate‐soluble OM fraction (OM‐PY) using basic soil properties. The objective of this study was to test a simplified model for the interactions between OM and polyvalent cations (i.e., Ca, Mg, Al, Fe, and Mn) by using data from soils from long‐term field experiments. The model considered (1) OM–cation, (2) OM–cation‐mineral, and (3) OM–mineral associations and assumed that the availability of the cation's coordination sites for the interaction with OM depends on these three types of associations. The test was carried out using data (topsoil) from differently fertilized plots from three long‐term field experiments (Halle, Bad Lauchstädt, Rotthalmünster). The composition of SOM and OM‐PY was characterized by the relationship of the ratio of the C=O (i.e., here indicating both carbonylic and carboxylic groups) versus C–O–C absorption band intensities obtained from the Fourier transform infrared (FTIR) spectra with the content of exchangeable, oxalate‐, and dithionite‐extractable polyvalent cations. The assumed associations between the OM and cations and the availability of the coordination sites explained most of the variations in the C=O/C–O–C ratios of the SOM, and fewer variations in the OM‐PY, when using the site‐specific exchangeable and oxalate‐extractable cation contents. The C=O/C–O–C ratios of the OM‐PY were site‐independent for samples from plots that regularly received farmyard manure. The results suggested that a simplified model that considers the polyvalent cation content weighted by the number of coordination sites per cation according to the type of association could be used to improve the explanation of site‐specific differences in the OM composition of arable soils.     

无定型氧化铁对土壤中阿特拉津吸附-解吸的影响

选取人工合成的无定型氧化铁(AHOsFe)纯矿物,以及两种典型土壤(黑土和砖红壤)的原土(S1和S2)和AHOsFe包被土壤(AHOsFe-S1和AHOsFe-S2)为研究材料,采用批量平衡法,研究AHOsFe对土壤中阿特拉津(AT)吸附—解吸行为的影响及其机理。研究结果表明,各吸附剂对AT的吸附均能采用Freundlich方程进行较好地拟合(r≥0.996,p0.01),AHOsFe对AT具有较强的吸附性能和较高的吸附非线性,AHOsFe包被黑土和砖红壤后,两种土壤对AT的吸附能力(Kd值)分别增加56.3%和43.8%。各吸附剂对AT均存在解吸迟滞效应,两种土壤及被AHOsFe包被后,其对AT的解吸迟滞系数(HI)在AT低初始浓度时随浓度的增加而降低,而在AT高初始浓度时随浓度的增加略有增加,AHOsFe对AT的HI则随AT初始浓度的增加而增加,说明不同吸附剂在AT不同初始浓度时的解吸迟滞机制不同。与土壤相比,AHOsFe对AT具有较强的解吸迟滞效应,但AHOsFe包被土壤后,却降低了土壤对AT的解吸迟滞效应。     

不同林地类型土壤团聚体稳定性与铁铝氧化物的关系

[目的]探究浙江省凤阳山保护区内土壤铁铝氧化物对土壤团聚体稳定性的影响机理,为该区恢复与保护土壤资源提供理论依据。[方法]以浙江省凤阳山保护区内黄棕壤地带4种林分类型(阔叶混交林、针阔混交林、杉木林、竹林)为对象,测定不同土层(0—10cm,10—20cm,20—30cm)水稳定性团聚体粒径分布以及不同形态的铁铝氧化物含量,分析各形态铁铝氧化物含量对土壤团聚体稳定性的影响。[结果](1)4种林分类型土壤团聚体水稳性大团聚体(0.25mm)含量均在90%以上,水稳定性大团聚体含量和平均质量直径(MWD)均表现为:杉木林针阔混交林阔叶混交林竹林。(2)不同形态铁铝氧化物含量大小整体上表现为:游离态氧化铁Fe_d游离态氧化铝Ald无定形氧化铁Fe_o无定形氧化铝Alo络合态氧化铁Fe_p络合态氧化铝Al_p,各形态的氧化铁含量随土层加深均增加。(3)增强回归树BRT分析结果显示,对土壤团聚体MWD影响最大的是Al_p,贡献率为43.6%;其次是Ald(23.5%)和Fe_d(19.5%);Fe_o(6.9%),Alo(4%)及Fe_p(2.4%)的影响程度较小。[结论]Al_p,Ald和Fe_d能促进土壤团聚体稳定,络合态氧化铝Al_p对土壤团聚体稳定性的促进作用大于游离态铁铝氧化物Ald和Fe_d。