Shrinkage of clay soils: A statistical correlation with other soil properties

The hypothesis that the shrinkage of soils is greater when expansible minerals are dominant was tested with 63 soils containing between 40 and 64% clay. Shrinkage between pF 2 and 4 (0.1 and 10 bar) correlated significantly with the expansible mineral content (measured by ethylene glycol retention) for remoulded but not for dried and rewetted specimens. Shrinkage between pF 4 and 6 (10 and 10³ bar) was strongly correlated with the expansible mineral content for both kinds of specimens. The physical significance of the results is discussed, and it is concluded that interlamellar shrinkage is not the principal component of bulk shrinkage.     

Contamination of soils and groundwater with new organic micropollutants: A review

The input of organic micro- and nanopollutants to the environment has grown in recent years. This vast class of substances is referred to as emerging micropollutants, and includes organic chemicals of industrial, agricultural, and municipal provenance. There are three main sources of emerging pollutants coming to the environment, i.e., (1) upon soil fertilization with sewage and sewage sludge; (2) soil irrigation with reclaimed wastewater and (3) due to filtration from municipal landfills of solid wastes. These pollutants contaminate soil, affect its inhabitants; they are also consumed by plants and penetrate to the groundwater. The pharmaceuticals most strongly affect the biota (microorganisms, earthworms, etc.). The response of microorganisms in the contaminated soil is controlled not only by the composition and the number of emerging pollutants but also by the geochemical environment.     

Fate of lignins in soils: A review

Lignins are amongst the most studied macromolecules in natural environments. During the last decades, lignins were considered as important components for the carbon cycle in soils, and particularly for the carbon storage. Thus, they are an important variable in many soil-plant models such as CENTURY and RothC, and appeared determinant for the estimation of the soil organic matter (SOM) pool-size and its stabilization. Recent studies challenged this point of view. The aim of this paper was to synthesise the current knowledge and recent progress about quantity, composition and turnover of lignins in soils and to identify variables determining lignin residence time. In soils, lignins evolve under the influence of various variables and processes such as their degradation or mineralization, as well as their incorporation into SOM. Lignin-derived products obtained after CuO oxidation can be used as environmental biomarkers, and also vary with the degree of degradation of the molecule. The lignin degradation is related to the nature of vegetation and land-use, but also to the climate and soil characteristics. Lignin content of SOM decreases with decreasing size of the granulometric fractions, whereas its level of degradation increases concomitantly. Many studies and our results suggest the accumulation and potential stabilization of a part of lignins in soils, by interaction with the clay minerals, although the mechanisms remain unclear. Lignin turnover in soils could be faster than that of the total SOM. Different kinetic pools of lignins were suggested, which sizes seem to be variable for different soil types. The mechanisms behind different degradation kinetics as well as their potential stabilization behaviour still need to be elucidated.     

一种新型处理农村生活垃圾装置的研制及工艺试验

在农村生活垃圾产生量和污染程度日益增加,而填埋场地选址困难的情况下,为了探索有机生活垃圾的出路,本文研究了一种新型一体化处理生活垃圾的装置及工艺,以广州市番禺区猛涌村生活垃圾为研究对象,进行了2个月的中试试验。研制的堆肥装置分4个小仓,每个小仓容纳垃圾1.56 m3,总容积6.24m3,抽风机功率为1.1kw•h-1,抽风时间为每隔2h一次,每天10次,每次30分钟,总时间为6h,能耗低。通过12天高温发酵,12天后熟化,12天最终熟化的堆肥方式,温度能达到60℃至少5天以上,出仓时减容率约为40%,整个处理过程无二次污染,结果表明该装置及工艺可以用来处理农村生活垃圾,环保效应好,充分做到垃圾减量化、无害化和资源化。     

Iron hydroxides in soils: A review of publications

Iron hydroxides are subdivided into thermodynamically unstable (ferrihydrite, feroxyhyte, and lepidocrocite) and stable (goethite) minerals. Hydroxides are formed either from Fe³⁺ (as ferrihydrite) or Fe²⁺ (as feroxyhyte and lepidocrocite). The high amount of feroxyhyte in ferromanganic concretions is proved, which points to the leading role of variable redox conditions in the synthesis of hydroxides. The structure of iron hydroxides is stabilized by inorganic elements, i.e., ferrihydrite, by silicon; feroxyhyte, by manganese; lepidocrocite, by phosphorus; and goethite, by aluminum. Ferrihydrite and feroxyhyte are formed with the participation of biota, whereas the abiotic formation of lepidocrocite and goethite is possible. The iron hydroxidogenesis is more pronounced in podzolic soils than in chernozems, and it is more pronounced in iron-manganic nodules than in the fine earth. Upon the dissolution of iron hydroxides, iron isotopes are fractioned with light-weight ⁵⁴Fe atoms being dissolved more readily. Unstable hydroxides are transformed into stable (hydr)oxides, i.e., feroxyhyte is spontaneously converted to goethite, and ferrihydrite, to hematite or goethite.     

Methylmercury production in flooded soils: A laboratory study

The effect of soil flooding on methylmercury (MeHg) production was studied by placing humus and peat with water in 40 liter vessels. Total mercury (Tot-Hg), MeHg, nutrients, total organic carbon (TOC) and color were measured in water. Potential mercury methylation and demethylation rates in water and in flooded soils (humus and peat) were measured using radiochemical methods under aerated and non-aerated conditions during a period of 117 days. In general, the potential methylation in humus and peat were one order of magnitude higher than in the water phase. During the experiment, methylation increased in humus and in peat but decreased in water. Demethylation decreased in all compartments. Anoxis increased methylation in soils but not in the water phase. On the other hand, demethylation was clearly higher in anoxic conditions. Tot-Hg increased more rapidly than MeHg in the water of the vessels, and a more rapid MeHg increase was observed in peat vessels than in humus vessels. Highest concentrations of MeHg (5.42 ng/L peat, 7.98 ng/L humus) were measured in non-aerated vessels. Water color correlated negatively with methylation in water but positively with MeHg concentrations, indicating that humic substances are the main MeHg carriers but are not active melhylating agents. Methylmercury fluxes to water (3.6–44 ng/m^2*d) were of the same order of magnitude as those measured in field experiments in Canada and in a beaver lake in Finland but were notably higher than those fluxes from unflooded catchmets. The results indicate that increased net methylation in flooded humus and peat soils, especially in anoxic conditions, is the main reason for increased MeHg concentrations in reservoirs.     

Chemical aspects of uranium behavior in soils: A review

Uranium has varying degrees of oxidation (+4 and +6) and is responsive to changes in the redox potential of the environment. It is deposited at the reduction barrier with the participation of biota and at the sorption barrier under oxidative conditions. Iron (hydr)oxides are the strongest sorbents of uranium. Uranium, being an element of medium biological absorption, can accumulate (relative to thorium) in the humus horizons of some soils. The high content of uranium in uncontaminated soils is most frequently inherited from the parent rocks in the regions of positive U anomalies: in the soils developed on oil shales and in the marginal zone of bogs at the reduction barrier. The development of nuclear and coal-fired power engineering resulted in the environmental contamination with uranium. The immobilization of anthropogenic uranium at artificial geochemical barriers is based on two preconditions: the stimulation of on-site metal-reducing bacteria or the introduction of strong mineral reducers, e.g., Fe at low degrees of oxidation.     

长期定位施肥对土壤效应的研究进展

近年来,长期定位施肥研究因其经历气候、年份的时间长,气候类型多,土壤功能变化幅度大以及获得的研究结论相对准确等特点,越来越受到研究人员的重视,国内外在长期定位施肥对土壤效应的影响研究取得了丰硕的成果。本文对国内外的长期定位施肥对土壤物理、养分、微生物以及酶类等方面的影响进行了比较客观详尽的阐述,并在此基础上提出了未来本领域的研究重点,以期对开展相关的研究提供借鉴。     

生物炭在农业土壤中应用的回顾与展望

Soil degradation, characterized by declines in nutrient status and simultaneous accumulation of pesticide residues, is a major problem affecting agricultural ecosystems. Previous studies indicate that biochar application to soil has promise as a practical method to alleviate these pressures: increasing crop yield and enhancing pesticide degradation. Here, we review the roles of biochar in both chemical and biological promotion of pesticide degradation and the potential benefits of biochar relating to the efficiency of fertilizer use, availability of nutrients, and nutrient exchange. Biochar typically has a high surface area featuring many functional groups, a high cation exchange capacity, and high stability. Major factors that impact on the nutrient retention characteristics of biochar (e.g., feedstock, pyrolysis temperature, and application rate) are also discussed herein. Nonetheless, more studies of the long-term impacts on soil properties from biochar addition are still required before it can be possible to accurately quantify the sustainability of this approach to sequester carbon and restore soil function.     

Molecular mechanisms of plant adaptation to acid soils: A review

Acid soils are widespread and limit global plant production. Aluminum(Al)/manganese(Mn) toxicity and phosphorus(P) deficiency are the major limiting factors affecting plant growth and productivity on acid soils. Plants, however, have evolved various strategies to adapt to these stresses. These strategies include using both external and internal mechanisms to adapt to Al toxicity, regulating Mn uptake, translocation, and distribution to avoid Mn toxicity, and orchestrating a set of P transport me...     

龙山县富硒土壤资源调查初报

通过对该县寒武系、奥陶系、志留系、二叠系地层上发育的土壤的取样化验分析, 发现以上地层中土壤都富硒(Se),且同一地层中相同母岩及母岩上发育的土壤含Se量相近,生长在这些土壤上的植物都是富Se植物。     

Denitrification in the rooting zone of cropped soils with regard to methodology and climate: A review

Summary Denitrification N losses can be determined by three methods. The first is by estimating the non-recovery of ¹⁵ N-labelled compounds (¹⁵N-balance method). Using this method, denitrification losses are deduced from the balance of an N budged (¹⁵N-labeled fertilizer), having accounted for transformations in soil, plant uptake, and leaching losses. The evolution of gaseous N from native soil N is not taken into account by this procedure. Studies on arable land with annual crops in the temperate zone have shown that of the fertilizer N applied, about 20–500% (10–70 kg N^* ha^–1) is not recovered at the end of the growth period. The second method of determining denitrification N losses is by in situ field measurement of ¹⁵ N ₂ and ¹⁵ N ₂ O production. Under this procedure, ¹⁵N-enriched N is applied to a plot and the denitrification N losses are determined by covering the soil. The method allows a quantitative estimate of the relative contributions to the emitted gas by both the original enriched source and the native soil N. N-evolution rates measured on arable land under a temperate climate are approximately the same order of magnitude as the N losses estimated by the non-recovery of ¹⁵ N method. The third measuring procedure is based on the acetylene inhibition phenomenon. This principle uses the inhibition of bacterial N₂O reduction to N₂ in the presence of acetylene (C₂H₂). The methoddetermines the denitrification of all NO₃ ^–-N irrespective of its source. Measurements on classical crop production systems show maximum N losses in the temperate climate of about 20–30 kg N^* ha^–1 during the growth period of annual crops. A similar level of denitrification is estimated for grassland sites under the same climate. In the subtropics (mediterranean climate with hot summers and mild winters), from both intensively cultivated arable land and grassland sites, N losses may exceed 200 kg^* ha^–1 year^–1. Without the use of irrigation the denitrification flux is negligible in spite of the high temperatures in this climate.     

Extracting soil microarthropods with olive oil: A novel mechanical extraction method for mesofauna from sandy soils

Many soil ecologists still encounter practical difficulties when extracting microarthropods from the soil. Methods using a humidity gradient, established by the use of a heat source, for collecting soil animals appeared not sufficiently efficient in case of sandy soils. For such type of soils, flotation techniques proved more suitable. The use of toxic or aggressive flotation fluids like kerosene, dibromo ethane, carbon tetrachloride and heptane, however, makes these methods less favourable. To circumvent this problem, a novel technique has been developed based on the flotation principle but using olive oil. The method uses a pumping system that injects olive oil at the base of a Perspex column in which the soil sample is suspended in water using a propeller. In this way, intensive contact between oil droplets and the organisms is established, increasing extraction efficiency. After stopping the propeller, animals can easily be collected from the oil floating to the water surface. Adding coloured mites to soil samples was used to determine extraction efficiency of the method. Average (±SD) recoveries of 82.7 ± 7.4% (n = 34) and 89.7 ± 10.0% (n = 10), respectively were obtained when extracting storage mites and predatory mites from a sandy soil.     

利用粘粒矿物修复重金属污染农业土壤研究进展

Heavy metal contamination of agricultural soils poses risks and hazards to humans.The remediation of heavy metal-polluted soils has become a hot topic in environmental science and engineering.In this review,the application of clay minerals for the remediation of heavy metal-polluted agricultural soils is summarized,in terms of their remediation effects and mechanisms,influencing factors,and future focus.Typical clay minerals,natural sepiolite,palygorskite,and bentonite,have been widely utilized for the in-situ immobilization of heavy metals in soils,especially Cd-polluted paddy soils and wastewater-irrigated farmland soils.Clay minerals are able to increase soil pH,decrease the chemical-extractable fractions and bioavailability of heavy metals in soils,and reduce the heavy metal contents in edible parts of plants.The immobilization effects have been confirmed in field-scale demonstrations and pot trials.Clay minerals can improve the environmental quality of soils and alleviate the hazards of heavy metals to plants.As main factors affecting the immobilization effects,the pH and water condition of soils have drawn academic attention.The remediation mechanisms mainly include liming,precipitation,and sorption effects.However,the molecular mechanisms of microscopic immobilization are unclear.Future studies should focus on the long-term stability and improvement of clay minerals in order to obtain a better remediation effect.     

中国亚热带土壤的1.4nm过渡矿物: 综述

This paper is a review of some advances in the studies on 1.4-nm intergrade mineral of soils in subtropical China. 1)1.4-nm intergrade mineral occurs ubiquitously in soils of subtropical China. The 1.4-nm mineral in red soil and yellow soil is mainly 1.4-nm intergrade mineral, and in acidic yellow-brown soil (pH < 5.5) is vermiculite alone or 1.4-nm intergrade mineral together with vermiculite. The distribution and the content of 1.4-nm intergrade mineral in the mountain soils are more widespread and higher than those of the corresponding soils in horizontal zone. 2) The interlayer material of 1.4-nm intergrade mineral in these soils appears to be hydroxy-A1 polymers instead of hydroxy-Fe, proto-imogolite or kaolin-like material. There is a significant positive correlation between A1 amount extracted from the soil with sodium citrate after DCB extraction and pH value of the citrate solution after the extraction. The citrate can also extract a certain amount of silicon from the soil, but the silicon may not come from interlayer of 1.4-nm intergrade mineral. 3) It was seldom studied that either vermiculite or smectite did the natural 1.4-nm intergrade mineral come from in soil, or it was commonly thought to come from vermiculite. A recent report has revealed that it can come from smectite. There are some different behaviors between the 1.4-nm intergrade mineral derived from vermiculite and that from smectite. For example, they exert different influences on the formation of gibbsite. The 1.4-nm intergrade mineral derived from smectite may promote the formation of gibbsite in the yellow soil. 4) The type of 1.4-nm minerals in soils. i.e., vermiculite or 1.4-nm intergrade mineral, may be significant to soil properties, such as soil acidity, exchangeable Al, electric charge amount and specific surface area. Therefore, the management for the soil in which 1.4-nm mineral is mainly 1.4-nm intergrade mineral or vermiculite should be dealt with differently.     

沿海酸性硫酸盐土中气态N损失的短期研究

NO x and N 2 O emissions from coastal acid sulfate soils (CASS) cultivated for sugarcane production were investigated on the coastal lowlands of northern New South Wales,Australia.Two series of short-term measurements were made using chambers and micrometeorological techniques.Series 1 occurred during the wet season,the water-filled pore space (WFPS) was between 60%-80% and the site flooded during the measurements.Measurements were made directly after the harvest of soybean crop,which fixed an estimated 100 kg N ha-1,and the emission amounted to 3.2 kg NO x-N ha-1 (12 d) and 1.8 kg N 2 O-N ha-1 (5 d).Series 2 was made towards the end of the dry season when the WFPS was less than 60%.In Series 2,after an application of 50 kg N ha 1,emissions were markedly less,amounting to 0.9 kg N ha-1 over 10 d.During both series when the soil was moist,emissions of NO x were larger than those of N 2 O.The emission of NO x appeared to be haphazard,with little time dependence,but there was a clear diurnal cycle for N 2 O,emphasising the need for continuous measurement procedures for both gases.These results suggest that agricultural production on CASS could be important sources of greenhouse gases and nitrogen practices will need to be optimised to reduce the offsite effects of atmospheric warming,acidification or nitrification.Many questions still remain unanswered such as the emissions during the soybean bean filling stage and crop residue decomposition,the longer-term losses following the fertiliser application and emissions from CASS under different land uses.     

Crop residue contributions to phosphorus pools in agricultural soils: A review

The phosphorus (P) content of crop residues and its availability to a subsequent crop can range from agronomically insignificant, to quantities in excess of crop P requirement. However, the contribution of crop residues to the P nutrition of subsequent crops has not been widely recognised, and simple predictive tools are lacking. By reviewing the published literature in which quantitative measurements of P transformations from plant residues applied to soil have been reported, we have evaluated the contribution of crop residue-derived P to the P nutrition of subsequent crops, assessed the key factors involved and summarised the knowledge as an empirical model. The contribution of crop residues to P availability is likely to be significant only under conditions where large amounts of crop residues of relatively high P concentration are applied to soil. Crop residues with low P concentration, such as cereal stubble (eg. due to re-translocation of a large proportion of stubble P into grain), will not make an agronomically significant contribution to soil P availability, but may reduce P availability due to assimilation in the microbial biomass. However, a productive green manure crop may release sufficient P to meet the requirements of a subsequent cash crop. The release of P from crop residues is significantly reduced in systems where the P-status of crops and soils is low, which reinforces the reliance on external P inputs for sustained crop productivity. The large variability in the potential contributions of plant residues to the P nutrition of subsequent crops suggests that there is a strong need to integrate model predictions of organically-cycled P with fertiliser management strategies.     

Acidification of soils and radioactive hot particles behavior: A macrokinetic approach

The accident at the Chernobyl nuclear power plant led to an ejection into the atmosphere of the dispersed nuclear fuel together with reactor containment materials. Subsequent fallout has created radioactive pollution over large areas in Europe. Highly active (“hot”) solid-phase particles of the fallout are the carriers of a great number of longlived radionuclides. Particles are subjected to alteration in the environment and release radionuclides in biologically accessible forms into soil- and groundwaters and further in animal and human food chains. A macrokinetic model approach on the hot particles alteration was developed. The effect of soil solution acidification on the kinetics of the alteration of hot particles of different matrix (nuclear fuel, graphite, materials of metallic construction) was examined. Acidification will increase the rate of radionuclide release from particles which kinetics of alteration is controlled by the rate of matrix dissolution.     

Modern approaches to remediation of heavy metal polluted soils: A review

The main principles and approaches to remediation of in situ polluted soils aimed at the removal or control of heavy metals (washing, stabilization, phytoremediation, and natural restoration) are analyzed. The prospects of gentle methods of stabilization oriented at the reduction of the mobility and biological availability of heavy metals due to the processes of adsorption, ionic exchange, and precipitation are emphasized. The use of sorbents and the traditional application of liming and phosphates to fix metal pollutants in soils is considered. The necessary conditions for successful soil remediation are the assessment of its economic efficiency, the analysis of the ecological risks, and confirming the achievement of the planned purposes related to the content of available metals in the soils.