Fe2+对水稻生长及土壤微生物活性的影响

通过盆栽试验,模拟冷浸田土壤亚铁毒害,研究了土壤-水稻-亚铁-微生物相互作用的体系中,外加Fe2+ 不同处理水平 (0、 100、 200、 400、 800和1600 mg/kg) 对水稻苗期和分蘖期相关生理指标、 土壤微生物活性及其生态特征的影响。结果表明, 在含一定亚铁本底（207.77 mg/kg）的正常稻田土壤中,外源性Fe2+的加入将逐步抑制水稻生长、 降低土壤微生物活性。外源Fe2+浓度达100 mg/kg后,水稻的株高、 干物质积累量显著降低; 水稻叶片生理指标叶绿素含量（SPAD值）、 脯氨酸含量、 抗氧化酶系统活性则显著增加,表明外源Fe2+浓度100 mg/kg 是本研究条件下外源Fe2+ 对水稻生长产生显著毒害影响的临界点; 同时随外源Fe2+浓度的增加, 土壤微生物活性指标土壤微生物量碳、 微生物三大基础菌系总量（细菌、 真菌、 放线菌）、 功能菌系总量（氨化细菌、 固氮菌、 纤维分解菌）、 铁还原菌总量总体是先快速下降,后逐渐平稳降低。 半效应浓度EC50分析表明,外源Fe2+浓度100 mg/kg 为多数土壤微生物活性指标（微生物基础菌系总量、 功能菌系总量、 铁还原菌）EC50变化的临界值; 体系中土壤微生物活性指标和水稻生长指标的变化存在显著的相关性, 表明供试土壤亚铁对水稻生长的影响是亚铁对土壤-植物-土壤微生物系统同步影响的结果。综上结果可知,外源Fe2+浓度100 mg/kg为导致供试土壤中水稻生长及土壤微生物活性受到显著负效应的临界值,进而推知,本研究所用土壤对水稻生长和微生物活性的亚铁毒胁迫临界浓度约为300 mg/kg（含本底）, Fe2+含量超出该浓度时,需采取合理的农艺措施控制其负效应。     

Survival of rhizobia in soil is sensitive to elevated zinc in the absence of the host plant

The survival of free-living rhizobia in soil is sensitive to elevated heavy metals in soil and can explain adverse effects of metals on symbiotic nitrogen fixation in soils. A survival experiment was set-up to derive critical cadmium (Cd) and zinc (Zn) concentrations in a range of field-contaminated soils in the absence of their host plant (Trifolium repens L.). Soils applied with metal salts or sewage sludge >10 years ago were sampled and were inoculated with Rhizobium leguminosarum bv. trifolii (10⁸ cells g⁻¹ soil) and incubated outdoors for up to 6 months. The most probable number (MPN) decreased 1-2 orders of magnitude in uncontaminated soils during the incubation. There was no significant effect of total metal concentrations on rhizobia survival in soils contaminated with Cd salts or with high Ni/Cd sewage sludge with highest Cd concentrations between 18 and 118 mg Cd kg⁻¹. In contrast, survival was strongly affected in soils contaminated by sewage sludge, where Zn was the principal metal contaminant. Neither total Cd nor soil solution Cd was large enough to attribute these effects to Cd when compared with the soil series, where Cd salts had been applied. The MPN decreased at least one order of magnitude above total Zn concentrations of 233 mg Zn kg⁻¹ (soil pH 5.6) and 876 mg Zn kg⁻¹ (soil pH 6.3). The EC50s of log MPN were 204 and 604 mg Zn kg⁻¹, respectively, and were lower than those for the symbiotic nitrogen fixation measured in the pot trial on the same soils (respectively 602 and 737 mg Zn kg⁻¹). This study corroborates the evidence that symbiotic nitrogen fixation is affected by Zn in the field when Zn decreases the free-living population of rhizobia to below a critical threshold.     

Silicon alleviates the toxicity of cadmium and zinc for maize (Zea mays L.) grown on a contaminated soil

Although silicon (Si) is not an essential element, it presents a close relationship with the alleviation of heavy‐metal toxicity to plants. This work was carried out to evaluate the effects of Si application to soil on the amelioration of metal stress to maize grown on a contaminated soil amended with Si (0, 50, 100, 150, and 200 mg kg^–1) as calcium silicate (CaSiO₃). Additionally, the cadmium (Cd) and zinc (Zn) bioavailability as well as their distribution into soil fractions was also studied. The results showed that adding Si to a Cd‐ and Zn‐contaminated soil effectively diminished the metal stress and resulted in biomass increase in comparison to metal‐contaminated soil not treated with Si. This relied on Cd and Zn immobilization in soil rather than on the increase of soil pH driven by calcium silicate application. Silicon altered the Cd and Zn distribution in soil fractions, decreasing the most bioavailable pools and increasing the allocation of metals into more stable fractions such as organic matter and crystalline iron oxides.     

Effects of Soil Amended with Cadmium and Lead on Growth,Yield, and Metal Accumulation and Distribution in Parsley

A greenhouse experiment was designed to determine the cadmium (Cd) and lead (Pb) distribution and accumulation in parsley plants grown on soil amended with Cd and Pb. The soil was amended with 0, 5, 10 20, 40, 60, 80, and 100 mg Cd kg^?1 in the form of cadmium nitrate [Cd(NO₃)₂] and 0, 5, 10, 50 and 100 mg Pb kg^?1 in the form of lead nitrate [Pb(NO₃)₂]. The main soil properties; concentrations of the diethylenetriaminepentaacetic acid (DTPA)–extractable metals lead (Pb), Cd, copper (Cu), iron (Fe), zinc (Zn), and manganese (Mn) in soil; plant growth; and total contents of metals in shoots and roots were measured. The DTPA-extractable Cd was increased significantly by the addition of Cd. Despite the fact that Pb was not applied, its availability was significantly greater in treatments 40–100 mg Cd kg^?1 compared with the control. Fresh biomass was increased significantly in treatments of 5 and 10 mg Cd kg^?1 as compared to the control. Further addition of Cd reduced fresh weight but not significantly, although Cd concentration in shoots reached 26.5 mg kg^?1. Although Pb was not applied with Cd, its concentration in parsley increased significantly in treatments with 60, 80, and 100 mg Cd g^?1 compared with the others. Available soil Pb was increased significantly with Pb levels; nevertheless, the increase was small compared to the additions of Pb to soil. There were no significant differences in shoot and root fresh weights between treatments, although metal contents reached 20.0 mg Pb kg^?1 and 16.4 mg Pb kg^?1 respectively. Lead accumulation was enhanced by Pb treatments, but the positive effect on its uptake was not relative to the increase of Pb rates. Cadmium was not applied, and yet considerable uptake of Cd by control plants was evident. The interactive effects of Pb and Cd on their availability in soil and plants and their relation to other metals are also discussed.     

Immobilization of heavy metals in soils using inorganic amendments in a greenhouse study

The effect of red mud (10 g kg^–1), a by‐product of the alumina industry, zeolite (20 g kg^–1), a naturally‐occurring hydrous aluminosilicate, and lime (3 g kg^–1) on metal lability in soil and uptake by fescue (Festuca rubra L.) (FEST) and amaranthus (Amaranthus hybridus L.) (AMA) was investigated in four different soils from Austria. The soil collection locations were Untertiefenbach (UNT), Weyersdorf (WEY), Reisenberg (REI), and Arnoldstein (ARN). The latter was collected in the vicinity of a former Pb‐Zn smelter and was highly polluted with Pb (12300 mg kg^–1), Zn (2713 mg kg^–1), and Cd (19.7 mg kg^–1) by long‐term deposition. The other soils were spiked with Zn (700 mg kg^–1), Cu (250 mg kg^–1), Ni (100 mg kg^–1), V (100 mg kg^–1), and Cd (7 mg kg^–1) salts in 1987. The two plant species were cultivated for 15 months. Ammonium nitrate (1 M) extraction was used in a soil : solution ratio of 1:2.5 to assess the influence of the amendments on the labile metal pools. The reduction of metal extractability due to red mud was 70 % (Cd), 89 % (Zn), and 74 % (Ni) in the sandy soil (WEY). Plant uptake in this treatment was reduced by 38 to 87 % (Cd), 50 to 81 % (Zn), and 66 to 87 % (Ni) when compared to the control. Sequential extraction revealed relative enrichments of Fe‐oxide‐associated metal fractions at the expense of exchangeable metal fractions. Red mud was the only amendment that decreased lability in soil and plant uptake of Zn, Cd, and Ni consistently. Possible drawbacks of red mud application (e.g., As and Cr concentration) remain to be evaluated.     

Respiration and priming effects after fructose and alanine additions in two copper- and zinc-contaminated Australian soils

The objective of the present study was to determine whether substrate-induced priming effects in soils are sensitive to increasing levels of Cu and Zn. Soils were collected from ten plots of two Australian field experiments (Spalding and Avon) where increasing amounts of Cu or Zn had been added 2?years prior to sampling, reaching maximum values of 5,880?mg?kg^?1 for Cu and 7,400?mg?kg^?1 for Zn. In a 21-day incubation experiment, the effect of uniformly ¹⁴C-labeled fructose and alanine on the mineralization of the soil organic carbon (SOC) was investigated. With increasing heavy metal content, the initial peak of soil respiration after substrate addition was retarded, indicating that the microorganisms utilizing these substrates were inhibited in soils highly contaminated with heavy metals. Both substrates strongly changed the mineralization of the soil organic matter (SOM), i.e., priming effects were induced. In the soil samples with high Cu concentrations from Spalding, fructose induced a stronger additional mineralization of the SOC than in the lower contaminated samples. In the samples with the highest Zn contamination level, negative priming effects, i.e., a reduced mineralization of SOM, were observed. In contrast, heavy metal effects in the Avon soil (pH?7.6) were less pronounced since substrate mineralization and priming effects were not directly related to the increasing heavy metal content. Apart from direct toxic heavy metal effects, the tested microbial activity parameters were also indirectly affected through the toxic heavy metal effects on plant growth. At the highest heavy metal contaminations, no fresh biomass inputs occurred during the past 2?years so that microorganisms in these soils were highly substrate-limited. As a consequence, complex interactions between different levels of heavy metal contamination, the microbial activity, and the input of SOC via plant biomass have to be considered.     

Microbial Biomass and Tolerance of Microbial Community on an Aged Heavy Metal Polluted Floodplain in Japan

The objective of the present study was to increase understanding of the effects of heavy metal pollution and soil properties on microorganisms in relation to the biomass and microbial functional community. Soil samples were collected from aged polluted and reference sites on a floodplain. The soil Cu, Zn and Pb total concentrations were much higher at the polluted sites (average 231.6–309.9 mg kg^?1, 195.7–233.0 mg kg^?1, and 72.4–86.0 mg kg^?1, respectively) than at the reference site (average 33.3–44.0 mg kg^?1, 76.7–98.0 mg kg^?1, and 30.8–41.6 mg kg^?1, respectively), while the available heavy metal concentrations in CaCl₂ extraction were similar in all sites. Small seasonal variations in the size of microbial biomass were observed. Ambient soil properties (e.g. total C, N, pH, moisture content, and CEC) affected the soil microbial biomass more than the heavy metal pollution. However, the aged pollution tended to impact on the composition of the microbial community. PICT (pollution-induced community tolerance) test using BIOLOG Ecoplates showed enhanced tolerance of the microbial community to Cu stress in the polluted site. In non polluted but low nutrient, low pH and low moisture soil, the microbial biomass was lower and the microbial community was more vulnerable to Cu stress. In spite of the low heavy metal availability due to ageing, the BIOLOG technique provided sensitive detection of microbial community level changes in PICT analysis.     

Yield response of crops amended with sewage sludge in the field is more affected by sludge properties than by final soil metal concentration

Adverse effects on crop yield or quality have been reported in sewage‐sludge treated soils at soil total metal concentrations below those of the current EU directives. A field trial was set up in Belgium (2002–2004) to assess crop response to the application of sewage sludge below these soil thresholds but with sludge metal concentrations either above (high‐metal) or below (low‐metal) sludge metal limits. Two lime‐stabilized and two raw, dewatered sludges were applied annually at rates of 10, 25 and 50 t dry matter (dm) ha^?1 for 3 years with four rates of N‐fertilizer as a reference. Final soil metal concentrations increased to maximums of 1.6 mg Cd kg^?1 and 225 mg Zn kg^?1 through sludge applications. Maize yield was marginally affected by treatments in year 1, whereas wheat and barley grain yields in subsequent years increased up to threefold with increasing sludge or fertilizer rates and were mainly explained by grain‐N. However, the grain yield of winter wheat in year 2 was reduced by about 14% in lime‐stabilized high‐metal sludge treatments compared with wheat receiving N‐fertilizer at equivalent grain‐N. Wheat grain and straw analysis showed no nutrient deficiencies but Zn concentrations in grain and straw were greater than in N‐fertilizer and lime‐stabilized, low‐metal sludge treatments, suggesting Zn toxicity. Sludge properties other than Cd concentration (e.g. electrical conductivity) affected crop Cd in the first year (maize), whereas significant correlations between Cd application and wheat grain Cd were found in the second year. Wheat grain Cd concentrations reached the international trade guideline of 0.1 mg Cd kg^?1 fresh weight in the plots amended with lime‐treated, high‐metal sludge even though soil Cd remained below EU limits. In the third year, barley grain Cd remained largely below EU limits. We discuss the possibility that sludge properties rather than soil total metal concentrations are related to effects on crops in the initial years after sludge applications. In none of the 3 years were any adverse effects on crops found for sludge meeting current EU regulations.     

Metal uptake in maize, willows and poplars on impoldered and freshwater tidal marshes in the Scheldt estuary

Foliar Cd and Zn concentrations in Salix, Populus and Zea mays grown on freshwater tidal marshes were assessed. Soil metal concentrations were elevated, averaging 9.7 mg Cd kg^?1 dry soil, 1100 mg Zn kg^?1 dry soil and 152 mg Cr kg^?1 dry soil. Cd (1.1–13.7 mg kg^?1) and Zn (192–1140 mg kg^?1) concentrations in willows and poplars were markedly higher than in maize on impoldered tidal marshes (0.8–4.8 mg Cd kg^?1 and 155–255 mg Zn kg^?1). Foliar samples of maize were collected on 90 plots on alluvial and sediment‐derived soils with variable degree of soil pollution. For soil Cd concentrations exceeding 7 mg Cd kg^?1 dry soil, there was a 50% probability that maize leaf concentrations exceeded public health standards for animal fodder. It was shown that analysis of foliar samples of maize taken in August can be used to predict foliar metal concentrations at harvest. These findings can therefore contribute to anticipating potential hazards arising from maize cultivation on soils with elevated metal contents.     

Soil Phosphorus Management Based on the Agronomic Critical Value of Olsen P

Fertilizer phosphorus (P) is generally added to agricultural soils to meet the needs of crop production. In this study, the crop yield and soil Olsen P were measured every year (5–18 years) at 16 winter wheat (Triticum aestivum L.) –maize (Zea mays L.) crop rotation sites in cinnamon soil (Luvisols in FAO system). The mean agronomic critical value of Olsen P for maize was 14.2 mg kg^?1 and for winter wheat was 14.4 mg kg^?1 when using the Liner-plateau and Mitscherlich models. The change in soil Olsen P was positively linearly correlated with the P budget (P < 0.01), and an increase of 4.70 mg kg^?1 in soil Olsen P for each 100 kg ha^?1 of P budget in the 0–20 cm soil layer. A model of P fertilizer recommendation rate that integrated values of the change in soil Olsen P in response to P budget and the agronomic critical value of Olsen P was used, in order to adjust current levels of soil Olsen P to the agronomic critical value at the experimental sites over the next 5 years, P fertilizer application rate should be in the range of 0–87.5 kg P ha^?1.     

Retention of Cd, Cu, Pb and Zn by Wood Ash, Lime and Fume Dust

Heavy metals are of interest due to their deleterious impacts on both human and ecosystem health. This study investigated the effectiveness of wood ash in immobilizing the heavy metals Pb, Cd, Cu and Zn from aqueous solutions. The effects of initial metal concentrations, solution pH, ash dose and reaction time on metal sorption, as well as the metal sorption mechanisms were studied. To investigate the effect of initial metal concentrations, solutions containing Cd, Zn (25, 50, 75, 100 or 125 mg L^?1), Cu (25, 50, 75, 100, 125, 150 or 175 mg L^?1) or Pb (250, 500, 750, 1000, 1250, or 1500 mg L^?1) were reacted with 10 g L^?1 ash for two hours. For the effect of pH, solutions containing 100 mg L^?1 of Cd, Cu or Zn or 1500 mg L^?1 of Pb were reacted with 15 g L^?1 ash over a pH range of 4 to 7. The wood ash was effective in immobilizing the four metals with a sorption range of 41–100 %. The amounts of metals retained by the ash followed the order of Pb > Cu > Cd > Zn. As expected, absolute metal retention increased with increasing initial metal concentrations, solution pH and ash dose. Metal retention by the ash exhibited a two-phase step: an initial rapid uptake of the metal followed by a period of relatively slow removal of metal from solution. Metal retention by the ash could be described by the Langmuir and Freundlich isotherms, with the latter providing a better fit for the data. Dissolution of calcite /gypsum minerals and precipitation of metal carbonate/sulfate like minerals were probably responsible for metal immobilization by the ash in addition to adsorption.     

Initial results from long-term field studies at three sites on the effects of heavy metal-amended liquid sludges on soil microbial activity

In a long‐term study of the effects on soil fertility and microbial activity of heavy metals contained in sewage sludges, metal‐amended liquid sludges each with elevated Zn, Cu or Cd concentrations were applied over a 3‐year period (1995–1997) to three sites in England. The experiments were sited adjacent to experimental plots receiving metal‐rich sludge cakes enabling comparisons to be made between the effects of heavy metal additions in metal‐amended liquid sludges and sludge cakes. The liquid sludge additions were regarded as ‘worst case’ treatments in terms of likely metal availability, akin to a long‐term situation following sewage sludge additions where organic matter levels had declined and stabilised. The aim was to establish individual Zn (50–425 mg kg^?1), Cu (15–195 mg kg^?1) and Cd (0.3–4.0 mg kg^?1) metal dose–response treatments at each site, but with significantly smaller levels of organic matter addition than the corresponding sludge cake experiments. There were no differences (P > 0.05) in soil respiration rates, biomass carbon concentrations or most probable numbers of clover Rhizobium between the treatments at any of the sites at the end of the liquid sludge application programme. Soil heavy metal extractability differed between the metal‐amended liquid sludge and metal‐rich sludge cake treatments; Zn and Cd extractabilities were higher from the liquid sludge additions, whereas Cu extractability was higher from the sludge cake application. These differences in metal extractability in the treated soil samples reflected the contrasting NH₄NO₃ extractable metal contents of the metal‐amended liquid sludges and sludge cakes that were originally applied.     

Response of Lettuce and Rhizosphere Biota to Successive Additions of Zinc and Cadmium to a Tropical Entisol

Response of lettuce and rhizosphere biota to successive addition of zinc (Zn) and cadmium (Cd) was assessed in a pot experiment using limed and unlimed tropical Entisol. Cadmium (2.5 mg kg^?1 soil) and Zn (50 mg kg^?1 soil) were spiked to soil 1 month after germination, and successive applications were superimposed as 5 and 10 times the first dose. Plants were analyzed for metal uptake and mycorrhizal colonization 1 week after each metal application. Rhizosphere soils were assessed for extractable Zn and Cd as well as populations of bacteria, fungi, and metal-tolerant fungi. The greatest metal doses resulted in 84–88 mg Zn and 8–10 mg Cd kg^?1 soil and 5–7.5 mg Cd and 70–72 mg Zn kg^?1 dry matter. Metal-tolerant fungi population increased from 9–13% to 26–63%, but mycorrhizal colonization and bacterial population were inhibited by 88% and 96%, respectively. Liming had relieved metal stress on rhizosphere biota but did not affect metal uptake.     

Cadmium and zinc accumulation in willow and poplar species grown on polluted soils

Woody plant species that produce high biomass have been proposed for use in phytoremediation technology. We investigated the accumulation of cadmium (Cd) and zinc (Zn) in Salix babylonica, S. caprea, S. dasyclados, S. matsudana × alba, S. purpurea, S. smithiana, Populus tremula, and P. nigra clones grown in a pot experiment on a Calcaric and a Eutric Cambisol (pH 7.2 and 6.4) of different levels of contamination (total metal concentrations in mg kg^–1 in soil A: 32.7 Cd, 1760 Zn; soil B: 4.34 Cd, 220 Zn). Generally, the tested clones tolerated large metal concentrations in soils and had larger Cd and Zn concentrations in leaves compared to the roots. The largest Cd concentrations in leaves were found in two clones of S. smithiana (440 mg kg^–1 on soil A; 70 mg kg^–1 on soil B). One of the S. smithiana clones had also the largest Zn concentrations (870 mg kg^–1) on soil B but accumulated slightly less Zn than a S. matsudana × alba clone (2430 mg kg^–1) on soil A. The Cd concentrations in leaves of both S. smithiana clones on soil A are the largest ever reported for soil‐grown willows. The bioconcentration factors of the best performing clone reached 15.9 for Cd and 3.93 for Zn on the less contaminated soil B. Also based on the metal contents in leaves, this clone was identified as the most promising for phytoextraction. The metal concentrations in leaves observed in the pot experiment do not reflect those found in a previous hydroponic study and the leaf‐to‐root ratios are clearly underestimated in hydroponic conditions. This demonstrates the need for testing candidates for phytoextraction crops on soils rather than in hydroponics. Our data also show that the phytoextraction potential should be tested on different soils to avoid misleading conclusions.     

基于序贯高斯条件模拟的土壤重金属含量预测与不确定性评价——以宜兴市土壤Hg为例

土壤重金属含量的定量预测和预测结果的不确定性评价对生态风险评估具有现实意义。将1 155个表层土壤Hg样本分成两个无交集的数据集,309个样本用于模拟,另外864个样本用于验证,运用序贯高斯条件模拟方法对宜兴市土壤Hg的空间分布进行估值和模拟,并通过与传统地统计方法中的简单克里格估值进行对照,同时利用高斯序贯指示模拟探索单点和多点联合的不确定性。结果表明:基于同一个半方差模型,100次序贯高斯条件模拟方法得到的E-type型与简单克里格估值在空间分布上基本一致,两种方法的精度基本相同;随机抽取了第1、25、50、75、100次序贯高斯条件模拟的单次实现,将模拟结果和插值结果与846个点进行验证,5个单次实现的平均预测误差和均方根预测误差略高;以0.15 mg kg~(-1)作为临界阈值的单点超阈值概率虽然较高,但其置信度不足以划定污染区域,在划定污染区域时应采用多点联合概率评估其可靠性。     

Changes in copper content and distribution in young,old and abandoned vineyard acid soils due to land use changes

We studied total Cu content and its distribution in 33 surface soil samples cultivated with vines for variable lengths of time in the Monterrei designation of origin (DO), located in Galicia (NW Spain). The study was focused on the influence of land use changes on soil degradation by effect of Cu accumulation and availability. Total copper concentration in soils ranged from 25 to 272 mg kg⁻¹. The time during which each soil was cultivated with vines was found to affect both the total concentration of copper and its distribution. The average concentration of copper in young vineyards was 64 mg kg⁻¹, whereas those in old and abandoned vineyards were 100 and 132 mg kg⁻¹, respectively. Copper bound to organic matter and to amorphous inorganic colloids were greater in old and abandoned vineyards, where they accounted for 51 and 52 per cent, respectively, of total copper, than in young vineyards (39 per cent). Copper bound to crystalline Al and Fe colloids accounted for 21, 22 and 12 per cent of total Cu in old, abandoned and young vineyards respectively. The prevalence of Cu bound to the organic fraction reduces the adverse environmental effects of this metal on soil organisms and plants. However, some management practices such as organic matter addition or liming should be implemented in order to delay or avoid soil degradation in young vineyards. For abandoned vineyards, the influence of new land uses on potential Cu mobilisation necessitates careful examination. Copyright © 2007 John Wiley & Sons, Ltd.     

Evaluation of certain Ni soil tests for an initial estimation of Ni sufficiency critical levels

Although Ni is officially recognized as an essential micronutrient for all higher plants, the majority of the published research on soil availability of Ni focuses on its hazardous role as a heavy metal. The objective of the study was to evaluate certain Ni soil tests in uncontaminated soils for an initial estimation of its sufficiency critical levels. Nickel was extracted from 30 cultivated soils employing the following extraction methods: DTPA, AB‐DTPA, AAAc‐EDTA, Mehlich‐3, 0.1 M HCl, and 0.1 M HNO₃. Ryegrass (Lolium perenne L.) was grown in pots containing the soils, harvested five times, certain plant parameters were determined, and the Cate–Nelson procedures were used for Ni critical levels determination. Among the six methods, HCl was the least reliable extractant for the evaluation of soil available Ni, whereas the most significant (p ≤ 5%) relationships between Ni concentration or Ni uptake by ryegrass and Ni soil tests were consistently obtained for AAAc‐EDTA or Mehlich‐3 extractable Ni. In many cases, > 80% of the variability of Ni concentration or uptake by ryegrass was explained by these two soil tests without the inclusion of other soil properties that affect Ni bioavailability. Sufficiency critical levels of Ni in soil were ≈ 2 mg kg^–1 for both methods. Consequently, as an initial approach, concentrations of AAAc‐EDTA or Mehlich‐3 extractable Ni < 2 mg kg^–1 are probably a good guide to indicate soils that will respond to Ni fertilization.     

Effects of associations between humic acids and iron or aluminium on the flocculation and aggregation of kaolin and quartz

The aggregative effect of organic matter on soil particles is conditioned by its composition and concentration and the degree to which it is associated with metal ions and oxides in the soil. We treated suspensions of kaolin or quartz substrates at pH 5 with metal (Fe or Al; c. 3 to 23 mg g^?1 of substrate) or humic acid (HA; 7 to 53 mg g^?1 of substrate) or both. In the absence of added Fe or Al, the proportion of HA retained by the substrate decreased from 98.5 to 50.8% for kaolinitic samples, and from 35.8 to 23.4 for quartz-based samples, as the HA dose increased. In the presence of Fe or Al, the proportion of HA removed from solution increased and was always >91%. Untreated kaolin flocculated between pH 2.0 and 4.5. This flocculation interval narrowed as the dose of HA increased, widened as the dose of HA-A1 increased, but was barely affected by HA-Fe. Similarly, the aggregative effect of HA-Fe associations on kaolin was smaller than that of HA-A1 associations, which induced formation of aggregates >100 μm that were essentially absent in the untreated substrate. There was a similar but less marked difference between the aggregative effects of HA-Fe and HA-A1 on quartz.     

Potential hazards of lime application in a damaged pine forest ecosystem in Berlin,Germany

Ninety percent of the pines (P. Sylvestris) in the forests of Berlin (West) are classified as damaged. Needle and leaf analyses do not indicate nutrient deficiencies. In site of high S-inputs (55 kg ha^?1 yr^?1 with throughfall) total acid inputs are moderate (2.4 kmol ha^?1 yr^?1) due to their neutralization by carbonatic dusts. Heavy metal depositions have led to accumulations in the forest floor (e.g. Pb 150 mg kg^?1, Cd 0.5 mg kg^?1). The dominating soil type, a cambic arenosol (Ustipsamment) is strongly acidified (pH 3.2 – 4.0) and poor in available nutrients. On an experimental plot, the application of dolomitic lime (6.1 tons ha^?1) and fertilizer (145 kg ha^?1 K₂SO₄) led to a significant increase m pH and base saturation in the top 10 cm of the mineral soil after 2 yr. The data on element fluxes give evidence for increased mineralization rates, enhanced heavy metal accumulation in the forest floor and increased soil solution concentrations of potentially hazardous substances (Al, Cd, NO₃). The lime application is discussed in terms of site specific effects on ecosystem stability and groundwater quality.     

重金属和有机污染物在修饰土中的吸附

Sorption characteristics of both an organic pollutant （phenol） and a heavy metal （cadmium ion） on the clay layer of a Lou soil （Eum-orthic Anthrosol in Chinese Soil Taxonomy） along with the sorption mechanism were investigated using three soil treatments： modification with a cationic surfactant cetyltrimethylammonium bromide added at an amount equivalent to 50% and 100% of the soil CEC （50? and 100?）, modification with an amphoteric surface-modifying agent dodecyldimethylbetaine （commercially known as BS-12） added at an amount equivalent to 50% and 100% of the soil CEC （50% BS and 100%BS）, and an unmodified control （CK）. Results showed that the BS soil treatments increased sorption of both the heavy metal Cd^2＋ and the organic pollutant phenol. The equilibrium sorption amount of Cd^2＋ decreased in the order： 50%BS 〉 100%BS 〉 CK 〉 50? 〉 100?, with the BS soil treatments being about 1.3 to 1.8 times higher and the CB soil treatments about 23% to 41% lower than CK. Both the single-site and two-site Langmuir models could be applied to describe the sorption of Cd^2＋ in each soil treatment. The equilibrium sorption amount of phenol on the soil samples decreased in the order： 100? 〉 50? 〉 100%BS 〉 50%BS 〉 CK, with the CB soil treatments being 41.0 to 79.6 times higher and the BS soil treatments 4.0 to 8.3 times higher than CK. The Freundlich equation could also be used to describe the sorption characteristics of phenol. In the BS soil treatments, both an organophobic long carbon chain and hydrophilic charged groups resulted in a relatively strong sorption ability for both heavy metals and organic pollutants. In addition, the sorption ratio K, the ratio of phenol sorption amount of the modified soil to that of CK, increased initially and decreased later with the amount of phenol added, and the critical sorption ratio Kc, the peak value of the sorption ratio curve plotted against the added phenol concentration, was a good index for evaluating the sorption ability of phenol in the soil.