Spatial variability of cadmium,pH, organic matter in soil and its dependence on sampling scales

Distribution of cadmium, pH _KCl , and organic carbon content in the soil over a 29-ha field was evaluated. Cadmium concentrations were found mostly within the interval 0.17–1.27 ppm, with increasing trend towards one edge of the field. Cadmium concentrations were correlated with pH and organic carbon content. A one-hectare section of the original area was selected to analyze spatial variability of cadmium, pH and organic carbon content using geostatistical techniques. Cadmium concentrations were found to be spatially dependent and anisotropic, whereas pH levels did not reveal space dependence. Similar spatial behaviour of cadmium and organic carbon was observed. Linear correlation analysis at the one-hectare section revealed strong correlation between organic carbon and Cd, whereas no coincidence between Cd and pH was found. Extensive application of a cadmium-contaminated sludge in the past is suggested as a possible cause of this phenomenon.     

Solubility,sorption and desorption of native and added cadmium in relation to properties of soils in New Zealand

Solution cadmium (Cd) concentrations and sorption and desorption of native and added Cd were studied in a range of New Zealand soils. The concentration of Cd in solution and the concentrations and patterns of native soil Cd desorbed and added Cd sorbed and desorbed varied greatly between the 29 soils studied. Correlation analysis revealed that pH was the most dominant soil variable affecting solution Cd concentration and sorption and desorption of native and added Cd in these soils. However, organic matter, cation exchange capacity (CEC) and total soil Cd were also found to be important. Multiple regression analysis showed that the log concentration of Cd in solution was strongly related to soil pH, organic matter and total Cd, which in combination explained 76% of the variation between soils. When data from the present study were combined into a single multiple regression with soil data from a previously published study, the equation generated could explain 81% of the variation in log Cd solution concentration. This reinforces the importance of pH, organic matter and total Cd in controlling solution Cd concentrations. Simple linear regression analysis could at best explain 53% of the total variation in Cd sorption or desorption for the soils studied. Multiple regression analysis showed that native Cd desorption was related to pH, organic matter and total Cd, which in combination explained 85% of the variation between soils. For sorption of Cd (from 2 μg Cd g^–1 soil added), pH and organic matter in combination explained 75% of the variation between soils. However, for added Cd desorption (%), pH and CEC explained 77%. It is clear that the combined effects of a range of soil properties control the concentration of Cd in solution, and of sorption and desorption of Cd in soils. The fraction of potentially desorbable added Cd in soils could also be predicted from a soil’s K_d value. This could have value for assessing both the mobility of Cd in soil and its likely availability to plants.     

油枯对镉污染土壤的钝化研究

为了研究油枯对镉(Cd)污染土壤的钝化效果,以油枯为外源添加物(质量比:1%、2%、3%、4%、5%),模拟田间条件在塑料桶中进行为期45 d的培养,对镉污染土壤中Cd形态分布特征、DTPA提取态Cd(DTPA-Cd)含量、pH、有机质含量进行分析。结果表明,添加油枯可显著降低镉污染土壤中可交换态镉(Ex-Cd)的比例,提高碳酸盐结合态镉(Cb-Cd)、铁锰氧化物结合态镉(Fe-Mnb-Cd)以及有机质及硫化物晶格态镉(OMb-Cd)的比例,而残渣晶格结合态镉(RLb-Cd)变化不明显。添加油枯显著降低镉污染土壤中DTPA-Cd含量,降幅最高可达49%。镉污染土壤p H值维持在6.0左右,1%~4%添加处理中土壤pH波动幅度较大;而5%添加处理的土壤pH波动幅度小。添加油枯均能显著提高镉污染土壤中有机质含量。由此可见,油枯对镉污染土壤有较好的钝化效果,这为重金属污染土壤的修复和农业废弃物的循环利用提供了参考。     

土壤主要理化性质对湘粤污染农田镉稳定效果的影响

利用盆栽试验研究了稳定剂(石灰、海泡石联合施用)对湖南、广东两省区不同性质土壤上生长的小青菜(Brassica chinensis L.)生物量、重金属吸收以及土壤pH和重金属提取态含量的影响,探讨了影响镉(Cd)稳定修复效果的土壤性质参数。结果表明:施加稳定剂对增加酸性土壤上小青菜生物量效果显著,土壤pH、有机质(OM)、全量Cd和黏粒是影响小青菜生物量变化的主要因素;土壤pH、阳离子交换量(CEC)、OM、黏粒是影响小青菜Cd含量变化的主要因素;土壤pH、CEC、全量Cd和黏粒是影响土壤提取态Cd含量变化的主要因素。     

控释尿素减施对双季稻田土壤剖面养分分布特征的影响

为探讨双季稻田控释尿素施用对养分在土壤剖面的垂直分布与迁移的影响,通过长期田间定位试验,研究比较普通尿素(U)和控释尿素(CRU)减施稻田剖面的养分累积和分布。结果表明:随着土层深度的增加,土壤全氮、NO_3~-—N、有机质、全磷、速效磷和全钾含量呈下降趋势,NH_4~+—N含量先下降后升高,速效钾含量呈上升趋势,土壤pH升高且趋于稳定。施肥会降低0—20cm土层pH和速效钾含量。与U处理相比,0—20cm土层CRU处理全氮含量提高7.72%~19.45%,且随着施N量的增加呈上升趋势;40—60cm土层CRU处理NH_4~+—N含量降低6.99%~19.23%。施用CRU可以有效降低土层NH_4~+—N向下淋溶,提高0—40cm土层全氮和NO_3~-—N含量,避免土壤N素流失。施用CRU对不同深度土层有机质、速效磷、全磷、速效钾、全钾和pH的影响不显著,但减量过大会导致有机质降低。CRU减量10%~20%处理显著提高双季稻成熟期N、P、K的吸收量。相关分析表明,不同用量控释尿素处理早、晚稻成熟期N、P、K吸收量与籽粒产量均呈显著正相关。总之,CRU处理有效地控制N素向下淋溶,减少因N肥施用带来的潜在面源污染,而CRU减施可更好地维持和提高土壤的养分水平和肥力,促进养分累积,实现生态与经济效益的双赢。     

Cadmium sorption by two acid soils as affected by clearing and cultivation

Abstract

The objective of this study was to determine the effect of clearing and cultivation on the sorption of cadmium (Cd) by two acid soils from Zimbabwe with differing cultivation stories. In their original state, not cleared‐not cultivated (virgin soils), the two soils exhibited noticeable and similar capacities to sorb Cd. The Mazowe soil contains the highest level of organic matter (40 g kg^‐1) and a effective cation exchange capacity (ECEC) of 144 mmol_c kg^‐1. Yet, Bulawayo soil (23.5 g kg^‐1 organic matter and ECEC of 146 mmol_c kg^‐1) has higher pH and Mn and Fe oxide content and these characteristics seemed to counteract the effect of lower organic matter. After 50 years of cultivation, The Mazowe soil has lost 60% of its organic matter and ECEC, and consequently the ability of its soil matrix to bind Cd has proportionally decreased. In Bulawayo (cleared in 1983 and first ploughed in 1984), on the contrary, the organic matter and ECEC of the cultivated soil remains over 95% of the values on its virgin counterpart. In this soil, the retaining ability for Cd has not still been affected. In the two soils Cd sorption was highly pH‐dependent. The extent of sorption was minimal under acidic conditions and increased sharply as the pH was raised. The immediate reversibility of the sorption process proved to be very low. When sorption and desorption data were compared it was clear that soil characteristics like high organic matter and oxide content which showed to enhanced Cd sorption, contributed at the same time to slow down the backward reaction.     

北京典型耕作土壤养分的近红外光谱分析

为研究土壤养分含量分布信息,以从北京郊区一块试验田采集的72个土壤样品为试验材料,应用傅里叶变换近红外光谱技术分析了土样的全氮、全钾、有机质养分含量和pH值。采用偏最小二乘法(PLS)对光谱数据与土壤养分实测值进行回归分析,建立预测模型,以模型决定系数(R2)、校正标准差(RMSECV)、预测标准差(RMSEP)和相对分析误差(RPD)作为模型精度的评价指标。结果表明,利用该模型与光谱数据对土壤全氮、全钾、有机质养分含量和pH值进行预测,结果与实测数据具有较好的一致性,最高决定系数R2达到0.9544。偏最小二乘回归方法建立的养分预测模型能准确地对北京地区褐土土质全氮、有机质、全钾和pH值4种养分进行预测。     

土壤镉吸附的研究进展

综述了土壤镉吸附的机理和土壤pH、有机质含量、粘粒矿物类型及含量、土壤溶液中竞争性阳离子、共存阴离子、土壤温度等土壤性质对土壤镉吸附的影响；总结了土壤镉的吸附量随土壤pH增加、温度升高及有机质、铁锰氧化物和粘土矿物含量增加而增加的机理；竞争性阳离子的存在抑制镉的吸附，土壤溶液中共存阴离子对镉吸附的影响取决于阴离子种类和土壤类型。     

pH regulation of carbon and nitrogen dynamics in two agricultural soils

Soil pH is often hypothesized to be a major factor regulating organic matter turnover and inorganic nitrogen production in agricultural soils. The aim of this study was to critically test the relationship between soil pH and rates of C and N cycling, and dissolved organic nitrogen (DON), in two long-term field experiments in which pH had been manipulated (Rothamsted silty clay loam, pH 3.5-6.8; Woburn sandy loam, pH 3.4-6.3). While alteration of pH for 37 years significantly affected crop production, it had no significant effect on total soil C and N or indigenous mineral N levels. This implies that at steady state, increased organic matter inputs to the soil are balanced by increased outputs of CO₂. This is supported by the positive correlation between both plant productivity and intrinsic microbial respiration with soil pH. In addition, soil microbial biomass C and N, and nitrification were also significantly positively correlated with soil pH. Measurements of respiration following addition of urea and amino acids showed a significant decline in CO₂ evolution with increasing soil acidity, whilst glucose mineralization showed no response to pH. In conclusion, it appears that changes in soil pH significantly affect soil microbial activity and the rate of soil C and N cycling. The evidence suggests that this response is partially indirect, being primarily linked to pH induced changes in net primary production and the availability of substrates. In addition, enhanced soil acidity may also act directly on the functioning of the microbial community itself.     

Effect of dissolved organic matter on the precipitation and mobility of the lead compound chloropyromorphite in solution

Chloropyromorphite, CPM, Pb₅(PO₄)₃Cl, is one of the most insoluble lead minerals. Inducing the formation of CPM by application of phosphate to soil has been suggested for immobilizing Pb at contaminated sites. We have examined the effect of organic matter on the completeness and the rate of CPM precipitation and on the particle size and the mobility of CPM crystals. We did experiments at pH 3–7 and with varying content of dissolved organic C, 0–72 mg C l^?1, mixing Pb(NO₃)₂ (0.5 mmol l^?1) and phosphate (2 mmol l^?1) solutions. The organic matter was extracted from samples of a forest floor. The precipitates were identified by X‐ray diffraction, and their size and shape were analysed by scanning electron microscopy and by photon correlation spectroscopy. The presence of organic matter in the solutions did not affect the mass of CPM that precipitated within 30 minutes at pH 5, 6 and 7. At pH 3 and 4, however, organic matter strongly inhibited the precipitation. The particles were markedly smaller in solutions containing organic matter than without at all pHs and passed through water‐saturated columns filled with calcareous sand, whereas the precipitates from the carbon‐free solutions did not. We suggest that the organic matter blocked the surfaces of crystal seeds and impaired crystal growth. At high pH, organic matter may additionally decrease the crystal size of the individual crystals by increasing the number of crystal seeds. We conclude that organic matter in the solution might limit the potential of phosphate to immobilize Pb in soil because it favours the formation of mobile colloids.     

SOIL NUTRIENT CHANGES WITH FERTILIZER TYPE IN CASSAVA-BASED CROPPING SYSTEM

ABSTRACT

The changes in soil nutrient status following the application of different fertilizer types were studied in field experiments involving maize-melon intercrop relayed into a cassava-soybean intercrop between 1995 and 1997. The soil at the experimental site was a Kanhaplic Haplustalf, which was under continuous cultivation with arable crops for seven years and fallow for four years. The effects of organic and inorganic fertilizers were investigated singly and in combination. The type of fertilizer had no significant effect on the soil pH, although, cropping significantly lowered the pH from 6.0 to 5.7. Cropping also significantly reduced the soil organic matter and total nitrogen (N). The soil organic matter (OM) and total N were most depleted with organic fertilizer application. Complementary application of organic and inorganic fertilizers limited the degree of depletion from 31.0 to 12.1 g kg^?1 of OM and 1.8 to 0.6 g kg^?1 total N. Soil available P was increased (60%) by inorganic fertilizer while the organic fertilizer increased it by 145% and the combined fertilizer by 186%. Exchangeable calcium (Ca) was depleted by about 12% with organic fertilizer application, 15% by inorganic fertilizer and about 19% with complementary application of organic and inorganic fertilizers. Exchangeable sodium (Na) was reduced from 0.43 to about 0.38 cmol kg^?1 while magnesium (Mg) was increased from 0.5 to about 0.6 cmol kg^?1.     

A field study on factors influencing Cd levels in soils and in grain of oats and winter wheat

The influence of selected factors on Cd levels in soils and in grain of oats and winter wheat was investigated. Soil and grain were sampled at sites randomly distributed over Sweden. Organic soils generally had higher Cd contents and lower pH levels than mineral soils, and plants growing in organic soils tended to have higher Cd contents than plants growing in mineral soils. In mineral soils the amount of soil Cd extractable in 2M HNO₃ was positively correlated with the pH and the contents of organic matter and clay. The studied variable best correlated with the Cd content of oat grain grown on mineral soils was the pH (negative correlation). Soil contents of organic matter, clay, HNO₃-extractable Cd and Zn were also found to be significantly related to the Cd content in a stepwise regression analysis. In winter wheat grain, Cd content was best correlated with the HNO₃-extractable Cd (positive correlation). Additional significant factors were pH, grain yield and contents of organic matter, clay and HNO₃-extractable Zn. In winter wheat the presence of Zn reduced Cd uptake, and vice versa; no such mutually antagonistic relationship was apparent in oats. In oats, but not in wheat, it was possible to predict most of the differences in grain Cd content, caused by the factors described above, based on the variation in CaCl₂-extractable soil Cd. Analysis of samples from field trials indicated that there were differences in Cd content between varieties of both crops. Variation in factors described generally explained most of the differences in soil- and grain Cd levels between regions.     

镉在胡敏酸上的吸附动力学和热力学研究

采用镉离子选择电极研究了镉在胡敏酸上的吸附特征。实验结果表明 ,胡敏酸对镉的等温吸附规律与介质pH有关。当pH为 3 0 0和 3 50时符合Freundlich方程 ,当pH在 4 0 0～ 6 50之间更好地符合Langmuir方程 ;在pH为 3 0 0～ 6 50之间 ,吸附量与pH成显著正相关。温度升高吸附量降低 ,吸附热与反应介质的pH有关 ,pH升高 ,吸附反应放热增加 ;胡敏酸对镉的吸附作用力随介质pH改变发生较大变化 ,当pH为6 50时主要为配位基交换作用。胡敏酸对镉的吸附含有部分不释放氢的静电吸附 ,其吸附反应动力学用Elovich方程拟合效果较好     

The Influence of pH and Organic Matter from Sugarcane By-products on Soil Cadmium Fractionation

ABSTRACT

Crop wastes or by-products can have the potential to be used as effective amendments to improve agricultural soil quality and/or crop yields subject to appropriate screening and testing. Sugarcane (Saccharum officinarum L.) waste by-products from an ethanol production plant, including boiler ash, filter cake, and vinasse, were applied as soil amendments at 5%, 10%, 20%, and 40% (w/w) to study the relationship between pH and organic matter (OM) on cadmium (Cd) bioavailability and adsorption via organic matter using the Cd sequential extraction procedure. Soil pH was significantly affected by aging of the treatment with boiler ash, filter cake, and vinasse. At the end of the experiment, the Cd concentrations with all treatments were mainly released in the first two extraction steps of the sequential procedure, i.e., most mobile and easily mobilized fractions. Pearson correlation analyses revealed a negative relationship between pH and bioavailable Cd and between OM and oxidizable Cd. The pH reduction induced by the amendments was a major factor affecting soil Cd bioavailability. The effect of OM on Cd fractionation could not be clearly observed and interpreted in this study.     

不同质地土壤对镉的吸附特性及影响因子研究

通过Cd²⁺吸附解吸试验,探究了初始Cd²⁺浓度、p H、有机质、土壤质地和枯草芽孢杆菌-生物质炭复合体对土壤吸附Cd²⁺影响。结果表明:土壤对Cd²⁺的吸附能力随着溶液浓度、p H的升高而增加,土壤有机质可显著提高土壤对Cd²⁺的固定能力,壤土对Cd²⁺的吸附能力显著高于砂质壤土。土壤施加枯草芽孢杆菌-生物质炭复合体后,土壤对于Cd²⁺的吸附能力显著提高,并且施加枯草芽孢杆菌–生物质炭复合体为20 ml/kg时对Cd²⁺的吸附量提高11.7%;Freundlich模型(R²=0.997)可以很好地拟合Cd²⁺吸附过程。枯草芽孢杆菌–生物质炭复合体的施加降低了土壤表面Cd²⁺的解吸能力,进一步证明复合体能加强土壤对Cd²⁺的固定稳定化,具有作为钝化剂修复土壤重金属污染、降低食品污染风险的潜力。     

浙西石灰岩地区土壤和稻米镉含量研究

为理解石灰岩地区农田土壤重金属积累特点及污染风险,以浙西石灰岩地区为例,随机选择了153块重金属污染农田,点对点采集了土壤和水稻样品,分析了土壤和糙米中镉的含量及土壤性状,探讨了石灰岩地区污染农田土壤与稻米镉积累特点及其与土壤性状的关系。结果表明,土壤全镉随粘粒含量的增加而增加,随土壤pH的下降而下降;土壤有效镉占全镉的比例与土壤pH呈负相关,糙米中镉含量与土壤有效镉、水溶性镉呈显著正相关;糙米中镉含量与土壤pH、有机质含量及粘粒含量均呈现显著负相关,土壤pH是影响石灰岩地区农田糙米镉积累最为重要的因素。《土壤环境质量－农用地土壤污染风险管控标准（试行）》（GB 15618—2018）的污染风险筛选值并不适用于石灰岩地区高pH的土壤。当6.5 < pH ≤ 7.5时,土壤重金属镉含量与农产品中重金属镉超标结果并不一致,其风险筛选值（0.60 mg kg?1）偏低,实际的风险筛选值可能在0.80 mg kg?1以上。土壤水溶性镉较土壤全镉和有效镉能更好地评估石灰岩地区农作物重金属镉的污染风险。     

Methane emission and entrapment in flooded rice soils as affected by soil properties

Laboratory incubation experiments were conducted to study the effects of soil chemical and physical properties on CH₄ emission and entrapment in 16 selected soils with a pH range of 4.7–8.1, organic matter content of 0.72–2.38%, and soil texture from silt to clay. There was no significant correlation with CH₄ emission for most of the important soil properties, including soil aerobic pH (measured before anaerobic incubation), total Kjeldahl N, cation exchange capacity, especially soil organic matter, and soil water-soluble C, which were considered to be critical controlling factors of CH₄ emission. A lower CH₄ emission was observed in some soils with a higher organic matter content. Differences in soil Fe and Mn contents and their chemical forms contributed to the this observation. A significant correlation between the CH₄ emission and the soil organic C content was observed only after stratifying soils into subgroups according to the level of CH₄ emission in soils not amended with organic matter. The results also showed that the soil redox potential (Eh), anaerobic pH, anerobic pH, and biologically reducible Fe and Mn affected CH₄ emission significantly. Urea fertilization promoted CH₄ emission in some soils and inhibited it in others. This result appeared to be related to the original soil pH. CH₄ entrapment was positively correlated with soil clay content, indicating the importance of soil physical characteristics in reducing CH₄ emissions to the atmosphere.     

ACCUMULATION OF CADMIUM AND ZINC FROM DIFFUSE IMMISSION ON ACID SANDY SOILS,AS A FUNCTION OF SOIL COMPOSITION

Sandy soils, in the border area of Belgium and the Netherlands (the Kempen region), are heavily contaminated by atmospheric deposition of cadmium and zinc from nearby smelters. Groundwater contamination by leaching from these low retention soils is subject of study. There are reports of high cadmium and zinc concentrations in groundwater in the area, but in most cases the direct sources are unknown. In an attempt to predict present or future risk of groundwater contamination by soil leaching, metal binding processes (retardation) were studied that are specific for these soil types under the existing acidifying conditions. From four fields nine contaminated profiles were sampled and analyzed for cadmium and zinc. Average concentrations of 131 μg g^-1 zinc and 1.6 μg g^-1 cadmium with maximum values of 2989 μg g^-1 respectively 16.3 μg g^-1 were found. In addition pH and contents of organic matter, aluminium, iron, and manganese were determined. The relative importance of these soil parameters for metal retardation is derived from the profiles. The data show that organic matter is the most important soil component for binding cadmium and zinc. Adsorption of cadmium and zinc on aluminium, iron and manganese (hydr) oxides appears to be of minor importance at low pH (<5.5).     

Influence of water solubility of granular zinc fertilizers on plant uptake and growth

Abstract

Zinc (Zn) fertilizer application has increased during the past three decades. This increase has created the need for more information regarding the availability and agronomic effectiveness of Zn containing fertilizers because differences of opinions exist relating the relationships between Zn water solubility and plant availability. Plant availability of eight commercialized Zn fertilizer materials having different water solubilities was measured under greenhouse conditions. Corn (Zea mays L.) plants were grown for 40 days in a soil (loamy, mixed, mesic arenic Ustollic Haplargid) amended with lime to two pH's: 6.3 and 7.4. To evaluate the effect of pH, some Zn fertilizers were used at both soil pH levels while all Zn fertilizers were used in the pH 7.4 soil. The experimental design was a factorial combination of pH, Zn fertilizers, and Zn rates of 0,2.1,4.2,8.4 mg Zn kg^?1 soil. Dry matter production and Zn uptake increased significantly when the soil pH decreased from 7.4 to 6.3. The highest dry matter production was obtained with ZnSO₄ (ZnSO₄ H₂O, 99.9% total water soluble Zn), Zn20 (Zn oxysulfate, 98.3% total water soluble Zn), and Zn27 (Zn oxysulfate, 66.4% total water soluble Zn). While ZnFe (Zn iron ferrite, 0.3% total water soluble Zn), ZnK (Zn oxide, KO61, 1% total water soluble Zn), and ZnOS (Zn oxysulfate, 0.7% total water soluble Zn) were less effective followed by Zn40 (Zn oxysulfate, 26.5% total water soluble Zn) and ZnOxS (Zn oxysulfate, 11% total water soluble Zn). The same trend was observed for Zn concentration and uptake. Regression correlations showed that the higher the water solubility, the more effective the Zn fertilizer in increasing dry matter production. Assuming that 5 to 10 kg Zn ha^?1 are the rates commonly recommended, about 50% water soluble Zn is required to adequately supply the crop's needs. Lower fertilizer rates were needed as Zn solubility increased. The cadmium (Cd) and lead (Pb) concentrations and uptakes in corn forage were not significant for any of the sources and rates.