Effect of surface contamination on results of plant analysis

Abstract

Chemical analysis of plants is often done without paying attention to the ubiquitous natural presence of exogenous material on the plant surface. The analytical result will then be higher than the endogenous plant concentration. It is shown that this error can be related to three parameters: (i) the surface loading L, (ii) the enrichment factor (EF) of the exogenous material with respect to the soil, and (iii) the plant‐to‐soil concentration ratio (CR). These factors are considered for 19 essential and trace elements and the results indicate that the error can range from insignificant to disastrous. Experimental data are mostly for needles of spruce trees growing in a relatively clean surrounding, but the proposed relations can be extended to estimate the effect for other plant species and surroundings.     

Changes in the microbial community of an arable soil caused by long-term metal contamination

The effects of past applications of farmyard manure (FYM, applied from 1942 to 1967), metal‐contaminated sewage sludge (applied from 1942 to 1961) and mineral fertilizer (NPK, applied from 1942 until now) on the microbial biomass and community structure in a sandy loam, arable soil from the Woburn Market Garden Experiment, UK, were investigated in 1998. Concentrations of Cu, Ni and Zn in soils which previously received sewage sludge were less than current European Union (EU) limits, but the soil Cd concentration was more than twice the permitted limit. Organic‐C concentration in the FYM‐treated soil and contaminated soils was about twice that of NPK‐treated soil. The initial microbial biomass‐C and estimates of total bacterial numbers by acridine orange direct count were significantly (P < 0.05) greater in the FYM‐treated soil compared with the NPK‐treated and the most contaminated soils. Total phospholipid fatty acid (PLFA) concentration (another measure of biomass) was significantly greater in the FYM‐treated soil compared with either the low or high metal‐contaminated soils, both of which contained similar PLFA concentrations. In the metal‐contaminated soils, in contrast, fluorescent Pseudomonas counts, as a percentage of total plate counts, were at least 1.5 times greater than in the uncontaminated soils. The concentrations of these microbial parameters were significantly (P < 0.05) less in the NPK soil than in all the other treatments. Biomass‐C as a percentage of organic‐C was also significantly (P < 0.05) greater in the uncontaminated soils compared with the metal‐contaminated soils. Biomass specific respiration rates in the metal‐contaminated soils were c. 1.5 times those in the FYM‐treated soil. In the metal‐contaminated soils, the concentration of mono‐unsaturated and hydroxy‐fatty acids (derived from phospholipids), and lipopolysaccharide hydroxy‐fatty acids (all indicative of Gram‐negative bacteria) were significantly (P < 0.05) greater than branched fatty acids (indicative of Gram‐positive bacteria). Furthermore, Gram‐negative counts were 62–68% greater than Gram‐positive counts in the metal‐contaminated soils. Branched fatty acid concentration was significantly (P < 0.05) greater in the FYM‐treated soil than in the metal‐contaminated soils. Gram‐positive counts were also 63% greater than Gram‐negative counts in the FYM‐treated soil. We found that effects of the relatively small heavy metal concentration caused measurable decreases in soil microbial biomass‐C concentrations, acridine orange direct counts and Gram‐positive counts. There were also increases in biomass specific respiration rates, and the microbial community had changed substantially, nearly 40 years after the metal inputs ceased. We conclude that, at the very least, the current EU permitted limits for heavy metals in agricultural soils should not be relaxed.     

Areal identification of groundwater nitrate contamination sources in periurban areas

Background, Aims and Scope  The purpose of this study is to verify a method for groundwater contamination risk assessment in urban and periurban areas using Geographic Information Systems (GIS). The method is based on agricultural hazard evaluation. In urban and periurban areas, the problem of dealing with NO₃ concentrations mainly entails identifying nitrate sources from the excessive use of fertilizers, or leaks from the sewage network and old septic systems. Residential areas coexisting with farming, and high and increasing nitrate concentrations, were identified in a densely inhabited area (>2 million inhabitants in about 1,000 km²) with an alluvial aquifer, located in southern Italy. Methods  First of all, comparison between the Contamination Vulnerability Map and the distribution of NO₃ concentrations highlights anomalous areas with low or moderate vulnerability in spite of the diffuse nitrate contamination of the aquifer. Assuming the agricultural origin of the nitrates, the hazard is calculated using the ANHI (Agricultural Nitrate Hazard Index), a parametric index which assesses the potential hazard of nitrate contamination originating from agriculture on a regional scale (Padovani and Trevisan 2002). The ANHI integrates two categories of parameters: the hazard factors (HF), which represent all farming activities that cause, or might cause, an impact on soil quality in terms of nitrate (use of fertilizers, application of livestock and poultry manure, food industry wastewater and urban sludge), and the control factors (CF) which adapt the hazard factors to the characteristics of the site (geographical location, climatic conditions and agronomic practices). Organization, processing and mapping are performed using a Geographical Information System (GIS: ILWIS 3.3 and ARCGIS 9.1). Results  The ANHI Map is obtained by multiplying the hazard factors (HF) and the control factors (CF), and dividing the resulting values into 6 classes. Finally, the Potential risk Map (R) is obtained by coupling the potential hazard of nitrate pollution (ANHI) and the aquifer Contamination Vulnerability Map. Discussion  By using spatial statistics, the Potential Agricultural Nitrate Contamination Risk Map and the Nitrate content of the aquifer correlation can be correlated. Where areas with low correlation in the Land Use Map are in the ‘urban areas and artificial land’ class, the source of the groundwater nitrate is not necessarily related to intensive farming and livestock. Conclusions  The Potential Agricultural Nitrate Contamination Risk Map in urban and periurban environments indicates the relationship between the high nitrate values and land use, giving useful information about the source of nitrate in groundwater. Recommendations and Perspectives  Based on this study, we formulate a hypothesis on the source of groundwater nitrate which should be verified on several case studies using nitrogen isotope techniques.     

中国北方典型地区农用地膜污染现状调查及其防治对策

通过对我国北方典型地区的调查,初步探索了该地区土壤农膜残留量和残膜特征.研究表明,河北省典型地区温室大棚、蔬菜田和作物田的农膜土壤残留量平均分别为5.629、7.369和2.822 kg·hm-2,黑龙江省典型地区温室大棚、蔬菜田和作物田残留量平均分别为4.169、3.682和2.430 kg·hm-2,各采样点之间存在着较大差异,但普遍较高,均明显高于未使用农膜的对照土壤.两地区之间除作物田的土壤农膜残留量没有明显差异外,河北地区其他两类土壤中的农膜残留量水平明显高于黑龙江地区,这种差异与各地区在农事活动及农膜使用上的差异具有一定的相关性.上述两地区土壤中残留农膜尺寸基本一致,主要集中在10～15 cm之间.该文针对我国目前农膜使用情况及其污染现状,提出了相应的防治对策.     

中国北方典型地区农用地膜污染现状调查及其防治对策

通过对我国北方典型地区的调查，初步探索了该地区土壤农膜残留量和残膜特征。研究表明，河北省典型地区温室大棚、蔬菜田和作物田的农膜土壤残留量平均分别为5.629、7.369和2.822 kg·hm^-2，黑龙江省典型地区温室大棚、蔬菜田和作物田残留量平均分别为4.169、3.682和2.430 kg·hm^-2，各采样点之间存在着较大差异，但普遍较高，均明显高于未使用农膜的对照土壤。两地区之间除作物田的土壤农膜残留量没有明显差异外，河北地区其他两类土壤中的农膜残留量水平明显高于黑龙江地区，这种差异与各地区在农事活动及农膜使用上的差异具有一定的相关性。上述两地区土壤中残留农膜尺寸基本一致，主要集中在10～15 cm之间。该文针对我国目前农膜使用情况及其污染现状，提出了相应的防治对策。     

Quantification of anthropogenic lead in Slovak forest and arable soils along a deposition gradient with stable lead isotope ratios

Isotope ratios of Pb may provide the opportunity to determine the contribution of Pb from a point source to Pb concentrations in soil. Our objective was to quantify the contribution of anthropogenic Pb to total Pb and chemical Pb fractions in contaminated soil profiles with the help of ²⁰⁶Pb/²⁰⁷Pb isotope ratios. We sampled 5 forest and 5 arable Cambisols along a transect from a Cu smelter and determined Pb concentrations and ²⁰⁶Pb/²⁰⁷Pb isotope ratios in total digests of all horizons and in 7 chemical fractions of the A horizons. In the organic layer under forest, Pb concentrations decreased from 2155 mg kg^—1 at 1.1 km distance from the smelter to 402 mg kg^—1 at 8 km distance; in the Ap horizons, it decreased from 126 to 72 mg kg^—1. In the total digests, ²⁰⁶Pb/²⁰⁷Pb isotope ratios could be explained by simple mixing of smelter‐ and background‐Pb as indicated by the correlation between the inverse of the Pb concentration and the ²⁰⁶Pb/²⁰⁷Pb ratio (r = 0.93). The mean proportion of smelter‐Pb in soil horizons decreased with depth from 87% (Oi) to 21% (C) under forest and from 64% (A) to 30% (B) in the arable soils. The smelter‐Pb proportions in the B horizons ranged from 6 to 66% and were independent of the distance from the smelter indicating variable leaching rates. The ²⁰⁶Pb/²⁰⁷Pb ratios in the chemical fractions could not be explained by a simple mixing model. Thus, the ²⁰⁶Pb/²⁰⁷Pb ratios may be used to determine the contribution of anthropogenic Pb in total digests but not in chemical Pb fractions.     

云南山区宜耕未利用地开发适宜性评价与潜力分区

为更好地引导云南山区宜耕未利用地的开发,该文以云南省典型的山区县―弥渡县为例,将GIS（geographical information system,GIS）空间分析技术、层次分析法（analytical hierarchy process,AHP）及特尔菲法（Delphi）相结合,分别构建宜耕未利用地开发适宜性评价模型、新增耕地指数及补充耕地潜力模型、宜耕未利用地开发潜力分区评价模型,对云南山区宜耕未利用地开发适宜性与潜力分区进行了分析。结果表明,研究区宜耕未利用地开发适宜性分为4个等级：最适宜、中等适宜、勉强适宜、不适宜,面积分别为71.21、1177.39、1681.00和62.00 hm2,分别占研究区总面积的2.38%、39.36%、56.19%、2.07%。研究区宜耕未利用地实际开发潜力为1248.60 hm2,预计新增耕地面积977.45 hm2。潜力分区结果表明,研究区可划分为5个潜力区和1个非潜力区。其中,Ⅰ级潜力区实际开发潜力164.97 hm2,可新增耕地144.21 hm2;Ⅱ级潜力区实际开发潜力53.38 hm2,可新增耕地46.66 hm2;Ⅲ级潜力区实际开发潜力210.64 hm2,可新增耕地164.01 hm2;Ⅳ级潜力区实际开发潜力773.93 hm2,可新增耕地590.11 hm2;Ⅴ级潜力区实际开发潜力45.68 hm2,可新增耕地32.46 hm2。研究结果的应用表明,该种方法得出的适宜性评价结果、新增耕地测算结果及潜力分区结果与当地实际较为吻合。     

黄河三角洲农业用地动态变化模拟与情景分析

为明确农业用地变化的动态特征和影响要素,预测不同情景下的农业用地的时空变化格局。利用遥感和地理信息系统技术对黄河三角洲地区4期TM和ETM+影像进行解译判读,获取区域内1992－2005年间农业用地动态演化特征,并构建元胞自动机模型对2001年和2005年的农业用地格局进行模拟。2001年和2005年农业用地模拟的总体精度分别为82.90%和84.48%,Kappa系数分别为0.658和0.689。模拟结果表明元胞自动机模型能够较好地模拟研究区域内农业用地动态变化,为农业用地的演变模拟提供了一种适用的工具。利用元胞自动机模型对4种情景下（面积减少5%、增加5%、10%和15%）的农业用地演变进行了预测。情景分析表明刁口故道附近的农业用地并不稳定,容易发生变化,是需要重点关注的区域。     

下辽河平原典型地域耕地系统弹性时空分异特征

科学准确地刻画耕地系统弹性时空分异格局是制定耕地保护差别化管理制度的基本前提。为此,该研究以下辽河平原典型地域沈阳市为研究区,基于社会生态系统弹性思维的抵抗力-适应力-转型力视角,重构耕地系统弹性的科学内涵,探讨2009—2018年研究区耕地系统弹性时空分异特征及影响因素。结果表明:1)耕地系统弹性是由耕地系统的抵抗力、适应力和转型力共同作用的结果,分别发挥维持现状、治理弹性和优化弹性的作用;2)2013年为研究区耕地生产力发生突变的时间节点,突变后期研究区整体和各区县的耕地系统弹性均显著减弱,耕地系统适应力减弱是耕地系统弹性减弱的主要因素,其次为转型力和抵抗力;3)突变前后研究区耕地系统弹性整体均呈现出中部高,西北部低的空间分布格局,高高型集聚的耕地向西部和北部迁移,低低型集聚的耕地集中于南部;4)耕地系统弹性变化同时受人类活动和自然禀赋综合影响,农业建设活动和自然条件分别是研究区中南部和西北部的耕地系统弹性空间分异的主要原因。研究表明阐明耕地系统抵抗力、适应力和转型力之间的作用关系可为刻画耕地系统弹性的时空分异格局提供有效途径,据此构建差别化的耕地保护制度体系,为实现下辽河平原农业...     

基于改进灰色聚类模型的矿区耕地损毁程度评价

为更加客观准确地反映矿区耕地的损毁程度, 更好地服务于耕地保护与土地复垦, 针对经典灰色聚类法单纯用阈值法确定权重, 不能较好地反映指标的损毁程度对聚类对象影响的局限性, 本文设定了有效土层厚度为主导限制性指标, 并将相对限制性指数融入到灰色聚类法中, 构建了GCM_DR(Grey Clustering Method_Dominant Restrictive Indicator & Relatively Restrictive Index)矿区耕地损毁程度评价模型, 并选用我国某高潜水位矿区塌陷损毁耕地进行了评价模型应用的验证。结果表明: 研究区2个塌陷盆地共计8个评价单元的损毁等级分别为Ⅱ、Ⅲ、Ⅳ、Ⅴ、Ⅰ、Ⅱ、Ⅲ、Ⅲ, 该趋势与其他方法基本一致, 结合实地调研情况, 表现了较高的可靠性; 主导限制性指标的设定使得该模型既考虑到了综合因素又兼顾主导因素, 一定程度上减小了评价任务的工作量, 提高评价工作的效率; 与经典灰色聚类模型相比, 改进后的模型强调指标的相对限制性, 损毁程度大的指标权重较大, 聚类系数向损毁级别高的方向倾斜, 表现了较好的灵敏性; 在确定权重时改进后的模型强调聚类指标的相对损毁程度, 一定程度上减小了分级跨度不同导致的权重分配的不合理性。因此, GCM_DR模型可应用于矿区耕地损毁程度评价工作中, 在了解耕地损毁现状、编制土地复垦方案、确定赔偿责任范围等方面有较好的应用价值。     

Transformation and contamination of soils in iron ore mining areas (a review)

Current concepts of soil transformation and contamination in iron ore mining areas have been reviewed. Changes of soils and ecosystems in the mining areas are among the largest-scale impacts of economic activity on the nature. Regularities in the radial differentiation, spatial distribution, and accumulation of heavy metals in soils of different natural zones are analyzed. The effects of mining technogenesis and gas–dust emissions from enterprises on soil microbial communities and fauna are considered. In zones of longterm atmotechnogenic impact of mining and processing plants, the stable state of ecosystems is lost and/or a new technoecosystem different from the natural one, with own microbial cenosis, is formed, where communities of soil organisms are in the stress state. In the ore mining regions, embriozems are formed, which pass through specific stages of technogenically-determined development, as well as technosols, chemozems, and technogenic surface formations with variable material compositions and properties. Technogenic soils and soil-like bodies form a soil cover differing from the initial one, whose complexity and contrast are not related to the natural factors of differentiation.     

Humus composition of soils under forest, coffee and arable cultivation in hilly areas of south Sumatra, Indonesia

To understand the effect of land use changes on the composition of humus in tropical soils, samples from land under primary forest, secondary forest, coffee plantation, and arable crops were investigated at three sites in south Sumatra, Indonesia. Total carbon and total nitrogen contents were 1.7 to 4.3 times and 1.1 to 2.8 times greater in the topsoil under primary forest than under the other types of land use. Following change from primary forest to other uses, the proportion of humic acids in the organic matter of the topsoils decreased while that of the fulvic acid fraction increased. Within the range of land uses, differences in the yields of humic acids and fulvic acid fractions were, respectively, larger and smaller than those in total carbon content. The humic acids were classified into the low and middle classes in the degree of humification. Absorption due to the green fraction of humic acids, Pg, was detected in the UV‐visible spectra of almost all the humic acids. No relation was observed between the degree of humification of humic acids or the strength of Pg absorption in their spectra and land use change. The fulvic acid fractions were fractionated on insoluble polyvinylpyrrolidone (PVP) into the adsorbed fractions consisting of humic substances and the non‐adsorbed fractions consisting of non‐humic substances. A positive correlation between the amount of the fulvic acid fraction and the percentage of the PVP‐adsorbed fraction within it indicated that the variation in the amount of the fulvic acid fraction was attributable to acid‐soluble humic substances. The ionization difference spectra of solutions between pH 12 and pH 7 suggested that the chemical structures of the PVP‐adsorbed fulvic acids have been altered by land use change.     

Quantification of infiltration processes in urban areas by accounting for spatial parameter variability

Background, Aims, and Scope  As a consequence of human living and activity, water infiltration to the urban subsurface occurs from a variety of different sources, like precipitation, irrigation, leaking pipes and sewers, septic tanks and rainwater infiltration ponds. This infiltration is strongly related with quality issues of the infiltrated water and further impact on groundwater quality. In order to set up an integrated urban water balance it becomes essential to estimate the infiltration processes, i.e. water flow and solute transport, from these different infiltration sources and to take into account the large spatial variability of sediment properties, the geometric settings of these sources and the groundwater table. For that purpose, the development of simple, physically-based quantification approaches is required in order to establish an efficiently working prediction and risk analysis tool within the framework of an integrated urban water management system. The scope of the presented work was to demonstrate the applicability of the developed approaches at urban scale. Methods  Since a detailed, three-dimensional, numerical quantification of the infiltration processes within the entire urban area is not possible, the individual sources were considered as independent within the EU AISUWRS project. Different models were developed for balancing infiltration from areal and point sources with respect to the related flow pattern. The analytical model UL_FLOW, based on one-dimensional, steady state analytical solutions, allows the estimation of conservative tracer residence times in layered sediments under varying infiltration rates. The numerical model WSTM, based on a three-dimensional random walk approach, calculates water and solute transport from pipe leaks. Additionally, the sources were classified in accordance to the spatial distribution of the parameters determining the infiltration processes. Results  UL_FLOW was applied to data sets from the city of Rastatt within a case study of the AISUWRS project. Each neighbourhood of water balance computation by the Urban Volume and Quality Model (UVQ) was defined as an areal infiltration source with unique parameter values for sediment depth, profile and properties, as well as infiltration rate time series. Groundwater recharge and residence time series were computed for each neighbourhood. Relevant statistical parameters obtained by time series analyses from those time series could be mapped by GIS. Point infiltration, particularly from sewers, was classified due to the sediment parameters and the distance to the groundwater table at each source location in order to reduce computational efforts. WSTM computations provided time series of groundwater recharge and tracer breakthrough for some specific cases. Discussion  The analytical model UL_FLOW provides fast and efficient computation of groundwater recharge and residence times accounting for storage effects within the unsaturated zone of urban areas. The reliability of this model has been shown by cross validation with HYDRUS1D. Because of the high computational effort, WSTM could provide only short-term simulations for some specific parameter sets for which residence time estimates could be derived. Conclusions  UL_FLOW provides an analytical modelling tool for balancing one-dimensional areal infiltration and estimating residence times under varying conditions including spatial parameter variability. These balances could be used for assessing the impact of those infiltration sources on groundwater quality. The tracer breakthrough from point infiltration sources computed by WSTM could also be used for such kinds of assessment. The larger spatial parameter variability associated with these sources could be handled by classification in GIS environments. Recommendations and Perspectives  Similar to the areal sources, a simple balance approach for point sources based on analytical solutions needs to be developed for estimating residence times in order to avoid large computational efforts. Such a model would complete the balancing of all kinds of infiltration sources in urban areas efficiently. Since the approaches are based on the balance of the physical processes, they have a large predictive capability and could be included into an integrated urban water balance and management system. The mapping of the statistical values of the residence times provides a tool to compare parts of the urban areas and to visualize differences between urban water management scenarios.     

Heavy metal contamination near major highways,industrial and urban areas in belgian grassland

An investigation was made of the Zn, Cu, Mn, and Pb contents in samples of soil and grass collected along highways and in fields adjoining industrial zones in Belgium. Soil contamination by Zn and Pb was quite pronounced along highways and in some cases contamination by Mn was also observed. Contamination by these heavy metals decreased rapidly with increasing distance from the highway. High values of metal accumulation in plants located near highways were observed. The accumulation of Pb was particularly pronounced. Contamination by Cu, Zn, Pb and possibly Mn in soils of some urban gardens was also recorded.     

阴山北麓干旱半干旱区地表土壤风蚀测试与分析

为定量评价阴山北麓干旱半干旱区不同地表土壤的抗风蚀效果，采用野外风洞原位测试方法进行试验研究。结果表明：风速一定时，退化草地、传统耕作农田的风蚀模数明显高于相应的无退化草地和保护性耕作农田；无退化草地和保护性耕作农田的风蚀模数曲线随风速变化平缓且不存在转变临界点。风速为18m／s时，无退化草地、保护性耕作农田的抗风蚀效率分别可达85．1％和90．8％，对8级大风具有较好的抗风蚀效果。     

Spatial variability of groundwater solute concentrations at the water table under arable land and coniferous forest. Part 2: Field data for arable land and statistical analysis

The spatial variability of groundwater solute concentrations at the water table beneath a fine to medium sandy soil (Gleyic Podzol) under arable land was investigated. Samples were taken in March (within a period of high seepage) within the first decimeter below the groundwater table at horizontal intervals of 0.5 m along a 30 m transect perpendicular to the direction of plowing. At the time of sampling the field was fallow, the preceding crop was maize. Nitrate, sulfate, potassium, and calcium concentrations, as well as electrical conductivity were determined and analyzed by geostatistical and spectral analysis methods. Semivariance analysis shows spatial dependence between measurements (except for potassium) within a range of about 6 m. Spectral and cospectral analysis show a pattern of periodic variations with a period of 12 m for nitrate, sulfate, calcium, and electrical conductivity. This pattern is related to the manner in which the mineral fertilizer is spread (width of a single application = 12 m). The periodic variation of sulfate is 180° out-of-phase and has a phase shift of 0.4 m with respect to nitrate, calcium, and electrical conductivity, which is probably due to separate application. The concentration of potassium shows a spatial trend, presumably due to a trend in the amount of potassium fertilizer applicated from one side of the field to the other.     

激光微地貌扫描仪测定侵蚀过程中地表糙度

为研究激光微地貌扫描仪用于测定南方红壤地区地表微地貌的演变特征和规律的可行性,该研究应用亚毫米级高精度激光扫描和计算机数字图像处理相结合的方法,在野外原位研究了鄂南3个典型红壤(泥质页岩发育红壤、第四纪红黏土发育红壤1和第四纪红黏土发育红壤2)模拟降雨条件下坡面侵蚀过程中的地表糙度变化过程,初步探讨了降雨和径流对红壤坡面微地貌形态演变作用。结果表明:1)随着降雨进行,雨滴打击和径流搬运的联合作用导致地表糙度降低,间歇式降雨后,供试土壤泥质页岩发育红壤、第四纪红黏土发育红壤1和第四纪红黏土发育红壤2的地表糙度分别降低了18.2%、18.4%和11.8%;2)地表糙度变化主要发生在降雨初期,第1场降雨前后,泥质页岩发育红壤、第四纪红黏土发育红壤1和第四纪红黏土发育红壤2的地表糙度降低幅度分别为16.1%、19.7%和9.6%,均达到显著水平。采用亚毫米级高精度激光扫描和计算机数字图像处理相结合的方法,能很好地定量化研究坡面水蚀过程中地表糙度的演变特征和规律。研究为南方红壤区坡面水蚀过程中地表微地貌的研究提供一定的参考,对土壤侵蚀过程模拟与预测模型的研究具有一定的参考价值。     

农村居民点土地整理及其对耕地的影响

为明晰农村居民点土地整理的目的与效果及其对耕地数量的影响,根据目前农村居民点土地整理的研究进展,从土地整理潜力、土地整理模式及土地整理政策建议三方面对该领域研究成果进行梳理,分析了目前农村居民点土地整理研究中存在的问题,阐明了农村居民点土地整理对于保障中国粮食安全的重要意义,提出了理论与实际相结合为主导的农村居民点土地整理及进一步明确大力开展农村居民点土地整理以便增加耕地数量的建议。     

Microbial community phenotypic profiles change markedly with depth within the first centimetre of the arable soil surface

The nature of the first few millimetres of a soil horizon strongly affects water infiltration rates, generation of run-off, and soil detachment. Whilst much is known about the physics and erosion of soil surfaces at this scale, little is known about their microbiology, particularly in temperate arable systems. This investigation aimed to discover whether any early colonisation stages of microbiotic crusts exist within the soil surface of temperate arable systems. The phenotypic structure of the microbial community was measured by means of phospholipid fatty acid analysis (PLFA) in soils sampled from the surface of arable fields that had been either cultivated 4 weeks previously or left undisturbed for 4-6 months. Within the top circa 1 mm of the soil that had been undisturbed for 6 months or more, distinct microbial communities were found to be present, which were statistically significantly different from the communities found in subsequent depths to circa 10 mm, where differences between communities were less pronounced. The PLFA responsible for the majority of the variation seen between depths was 16:0, the proportion of which was shown to decrease with depth. This was not the case in the recently cultivated soils, where communities were more homogeneous with respect to depth.