Effect of sampling size on the determination of accurate pesticide residue levels in Japanese agricultural commodities

The uncertainty in pesticide residue levels (UPRL) associated with sampling size was estimated using individual acetamiprid and cypermethrin residue data from preharvested apple, broccoli, cabbage, grape, and sweet pepper samples. The relative standard deviation from the mean of each sampling size (n = 2(x), where x = 1-6) of randomly selected samples was defined as the UPRL for each sampling size. The estimated UPRLs, which were calculated on the basis of the regulatory sampling size recommended by the OECD Guidelines on Crop Field Trials (weights from 1 to 5 kg, and commodity unit numbers from 12 to 24), ranged from 2.1% for cypermethrin in sweet peppers to 14.6% for cypermethrin in cabbage samples. The percentages of commodity exceeding the maximum residue limits (MRLs) specified by the Japanese Food Sanitation Law may be predicted from the equation derived from this study, which was based on samples of various size ranges with mean residue levels below the MRL. The estimated UPRLs have confirmed that sufficient sampling weight and numbers are required for analysis and/or re-examination of subsamples to provide accurate values of pesticide residue levels for the enforcement of MRLs. The equation derived from the present study would aid the estimation of more accurate residue levels even from small sampling sizes.     

Use of centrifugal photosedimentation to measure the particle size distribution of clays

A procedure is developed which allows centrifugal photosedimentation to be used for analysing samples, such as clays, containing a broad range of particle sizes. The implicit assumptions that have to be made are discussed and the calculation of the particle size distribution from photosedimentation data is described. In particular, it is important to be certain that any light scattering theory, used to correct for the variation in light scattering with particle size, accurately represents the light scattering behaviour of clays. Appropriate theories of light scattering that can be used to correct photo sedimentation data for the variation in light scattering with particle size are identified. For kaolinite, over the size range 100 nm?1 μm, the anomalous diffraction theory for oblate ellipsoids was found to be a suitable theory for correcting photosedimentation data.     

Investigation of the Effect of Mesh Size on the Effectiveness of Hotplate Aqua Regia Extractions

Aqua regia extractions with subsequent inductively coupled plasma determinations are a very common method of elemental analysis of soils and sediments. Before extraction, the material must be dried and sieved. Small variations in this early step can have a significant impact on the later outcomes, especially for unassisted (for example, without ultrasonic or microwave) extraction procedures. Therefore the impact of mesh size on the sieving process was investigated. A mesh size of 2.0 mm or greater yielded unacceptably high variations between the subsamples and a very poor recovery rate when compared to a 0.063-mm sieve. A mesh size of 0.3 mm resulted in the best outcomes, losing nearly no material in the fine sediment samples and about a tenth in the coarse samples. The precision was high for the 0.3-mm samples as well, only negligibly surpassed by the 0.1-mm samples for some materials.     

不同地貌起伏状况下网格尺寸与DEM精度关系研究

不考虑DEM采样点上高程误差,以不同地貌类型区为试验地,运用统计分析方法,对不同地貌起伏的样地随机抽取采样点,比较当DEM网格尺寸变化时,对DEM高程值计算的误差以及对剖面曲率计算结果的误差,分析不同地貌起伏状况下DEM网格尺寸变化与DEM精度之间定量定性的关系,得出表示地形复杂程度的平均剖面曲率和网格尺寸是影响DEM精度的两个重要因素。通过一系列表达式推导得出网格尺寸变化与DEM精度之间定量关系。由此模型,用户可以根据不同地貌和DEM的精度要求选择适宜的网格尺寸范围,进一步为生产实践中应用提供理论依据。     

察尔汗盐湖沙漠沙丘沉积物粒度特征分析

在对柴达木盆地沙漠地区两次野外实地调查的基础上,选取察尔汗盐湖沙漠盛行风向沿线的线形沙丘和新月形沙丘沉积物样品进行了粒度特征分析。结果表明,研究区沙区沙粒度组成以细沙和中沙占优,粉沙和黏土含量明显,粒度变化遵循沿盛行风向粒径变细的规律;粒度参数特征表现出沉积物平均粒径较国内其他沙漠偏粗,分选较差,呈正偏-近对称形分布,线形沙丘成熟度比新月形沙丘偏高;沉积物累计概率曲线特征指示研究区沙区沙的沉积环境以跃移搬运为主,存在明显的悬移搬运和微弱的滚动搬运。     

Simplified method for quantifying the hydraulic properties of shrinking soils

In general, soils and their pore size systems are assumed to be rigid during the loss of water on drying. In reality, it is not the case for most soils, especially for soils with high quantities of clay or organic matter. As a result of shrinking, there are changes in the bulk density, the porosity, the pore size distribution, and the hydraulic properties of these soils. Currently, only a few methods enable the shrinkage behavior of soil samples to be determined while simultaneously quantifying the corresponding soil hydraulic properties. Either the methods need proprietary software for data processing, the equipment used is expensive or the calculation of the hydraulic properties is executed by inverse modelling. The aim of this study was to develop an alternative, simplified method for the simultaneous and automatic determination of the soil hydraulic properties, taking shrinkage into account. The HYPROP® evaporative device was combined with a circumference meter. A preliminary investigation found that the diameter of the cylindrical samples used for the HYPROP decreased linearly during evaporation from the bottom to the top. To sum up, recording the perimeter change in the middle position of the sample during drying‐out, together with the corresponding tension and water content, was sufficient to determine the hydraulic functions taking shrinkage into account. Measurements are presented for 6 samples which are different in texture and geological origin. The maximum shrinkage (19.5% by vol. between saturation and 5,000 hPa) was measured in the peat samples. The minimum shrinkage was quantified at 0.68% by vol. for the silty loam samples from Chile. The advantages of the method presented are: (1) the water retention curve and the hydraulic conductivity function can be determined simultaneously in the range between saturation and close to the wilting point, at a high resolution and taking into consideration shrinkage; (2) the method and device are simple and robust to use; (3) little time is required for measurement, between 3 and at most 10 d; (4) the functions are described over the whole tension range, using more than 100 user‐defined data points; (5) the evaluation of the volumetric soil water content measurement in shrinking soils is improved; and (6) common data models can be fitted to the hydraulic data as well as to the shrinkage data.     

采样点数量对长三角典型地区土壤肥力指标空间变异解析的影响

通过对江苏省如皋市888个采样点的不重复随机抽样,探讨了采样点数量对土壤肥力指标空间变异解析的影响。从半方差函数估计的可靠性角度考虑,在长江冲积物形成的土壤上,针对县级农业管理和生态环境规划的土壤肥力指标调查采样,采集250个样点较为合适。另外,仅使用交互验证和独立验证评价半方差函数估计的可靠性及确定采样点数量是不完善的,而平均克里格方差理论上随采样点数量的增加而单调递减,可以作为不同采样点数量条件下,综合评价半方差函数估计可靠性及确定采样点数量的补充指标。     

An investigation of the effects of breakwaters on beach sediment characteristics

The south-east reach of Castiglione della Pescaia beach, Italy, has been studied to demonstrate the effect of the breakwaters on sediment characteristics as regards as the cuspate shape of the shoreline.Several samples have been collected to investigate the longshore distribution of sediment parameters such as mean size, sorting and skewness. In addition, comparison with data from natural cuspate beaches has been made. It shows an opposite sediment size distribution while sorting and skewness are almost the same for cusps and bays. That is a consequence of different hydrodynamic processes evenly resulting in a similar shoreline morphology.The grain size analysis has also allowed to state that the sediment of the protected beach is substantially of the same quality of that where natural conditions prevail and that the influence of breakwaters can be neglected in terms of skewness sign.Statistical tests, using mean size, confirmed the main longshore direction of sediment transport, calculated theoretically.Core samples have been taken in order to examine the subsurface sediment characteristics in the breakwater protection area.The core sediments show a predominant positive skewness while the grab and the berm samples are more frequently negatively skewed.The analysis of core stratigraphy taken in different periods shows a sea-bed scour of at least 1 m in the aggradational protected area during ordinary sea-storms.     

Grain-size analysis by laser diffractometry: comparison with the sieve-pipette method

Results of a traditional sedimentation technique for grain-size analysis (the sieve-pipette method) were compared with those of a laser diffraction grain-size analyser, the Coulter LS-100. Milled quartz samples and silty soil samples were used to investigate the effect of particle shape. The reproducibility of the Coulter LS-100 was better than that of the sieve-pipette method, except for the sand fraction. The agreement between the two methods is strongest for the milled quartz samples. The Coulter LS-100 underestimated the clay content of the silty soil samples and generally overestimated the clay content of the milled quartz samples. This indicates the importance of particle morphology. The milled quartz grains are very angular and somewhat elongated whereas the clay minerals in the clay fraction of the silty soil samples usually have a platy shape. Reduced major axis relationships are calculated which may be used to convert Coulter LS-100 results to those of the sieve-pipette method. Correlation is strongest for percentiles size data. The Coulter LS-100 underestimates the clay, but correctly estimates the sand fraction. This results in a weak relationship for the total silt fraction as measured by the two techniques. Therefore, an alternative method is proposed for estimating this fraction. A comparison of our data with published data and relationships suggests that the calibration relationships are quite robust as long as the clay mineralogy of the samples is similar.     

An investigation of the effects of breakwaters on beach sediment characteristics

The south-east reach of Castiglione della Pescaia beach, Italy, has been studied to demonstrate the effect of the breakwaters on sediment characteristics as regards as the cuspate shape of the shoreline.Several samples have been collected to investigate the longshore distribution of sediment parameters such as mean size, sorting and skewness. In addition, comparison with data from natural cuspate beaches has been made. It shows an opposite sediment size distribution while sorting and skewness are almost the same for cusps and bays. That is a consequence of different hydrodynamic processes evenly resulting in a similar shoreline morphology.The grain size analysis has also allowed to state that the sediment of the protected beach is substantially of the same quality of that where natural conditions prevail and that the influence of breakwaters can be neglected in terms of skewness sign.Statistical tests, using mean size, confirmed the main longshore direction of sediment transport, calculated theoretically.Core samples have been taken in order to examine the subsurface sediment characteristics in the breakwater protection area.The core sediments show a predominant positive skewness while the grab and the berm samples are more frequently negatively skewed.The analysis of core stratigraphy taken in different periods shows a sea-bed scour of at least 1 m in the aggradational protected area during ordinary sea-storms.     

渭河河床沉积物颗粒组成对渗透系数的影响

正确认识河流沉积物颗粒组成与渗透系数之间的关系,对于准确测算河床渗透系数具有重要的意义。以渭河关中段为研究对象,采用水头下降竖管渗透实验法对渭河关中段4个河段的43个点位做渗透系数的原位测定,获取各点位的垂向渗透系数(Kv)值。对测定点的沉积物样品进行了粒度分析,并进一步分析了Kv与沉积物颗粒组成之间的相关关系。结果表明,垂向渗透系数与其沉积物的含砂量以及砂土与黏土含量比值均呈指数正相关,与黏土率呈指数负相关。研究获得的垂向渗透系数与沉积物颗粒组成的拟合方程为通过颗粒分析计算垂向渗透系数提供了依据。     

A Single Parameter for Within‐Sample Uniformity of Seed Size in Grain,with an Emphasis on Pulses

The standard methodology for assessing seed size distribution of pulses is to sieve seeds into size classes, weighing each class and calculating a weighted mean of the sieve sizes (seed size index). A single unit measure of uniformity of size within a sample via sieving is not available, despite being an important trait in terms of appearance, ease of milling, and consistency in processing. This study investigated several different models for estimating the size variability within seed samples by using a variety of desi and kabuli chickpea, faba bean, lupin, lentil, and mungbean samples. Fitting a normal distribution to the frequency distribution and using the estimated variance parameter as a measure for seed size variability was found to be the most suitable method for attaining seed size and a single value of uniformity. Mean seed size (SS _norm ) and within‐sample size variability (SV _norm ) were unrelated variables, thus allowing selection of more uniform samples of any desired size in breeding programs. Sieve selection is discussed and needs to be appropriate for the samples under investigation. Examples of using the R software to calculate these measures and the R functions needed are available as supplementary files to facilitate the use of this proposed method. This method will be useful to pulse breeders and researchers and in the development of image analysis methods characterizing seed sizes of pulse samples and other grains.     

Measurement of the size distribution of water-filled pores at different matric potentials by stray field nuclear magnetic resonance

The water retention characteristic provides the traditional data set for the derivation of a soil's pore‐size distribution. However, the technique employed to achieve this requires that assumptions be made about the way pores interconnect. We explore an alternative approach based on stray field nuclear magnetic resonance (STRAFI‐NMR) to probe the water‐filled pores of both saturated and unsaturated soils, which does not require information relating to pore connectivity. We report the relative size distributions of water‐occupied pores in saturated and unsaturated samples of two sets of glass beads of known particle size, two sands, and three soils (a silty loam, a sandy loam and a loamy sand), using measurements of the NMR T₁ proton relaxation time of water. The T₁ values are linearly related to pore size and consequently measured T₁ distributions provide a measure of the pore‐size distribution. For both the sands and the glass beads at saturation the T₁ distributions are unimodal, and the samples with small particle sizes show a shift to small T₁ values indicating smaller voids relative to the samples with larger particles. Different matric potentials were used to reveal how the water‐occupied pore‐size distribution changes during drainage. These changes are inconsistent with, and demonstrate the inadequacies of, the commonly employed parallel‐capillary tube model of a soil pore space. We find that not all pores of the same size drain at the same matric potential. Further, we observe that the T₁ distribution is shifted to smaller values beyond the distribution at saturation. This shift is explained by a change in the weighted average of the relaxation rates as the proportion of water in the centre of water‐filled pores decreases. This is evidence for the presence of pendular structures resulting from incomplete drainage of pores. For the soils the results are similar except that at saturation the T₁ distributions are bimodal or asymmetrical, indicative of inter‐aggregate and intra‐aggregate pore spaces. We conclude that the NMR method provides a characterization of the water‐filled pore space which complements that derived from the water retention characteristic and which can provide insight into the way pore connectivity impacts on drainage.     

Influence of corn size distribution on the diastatic power of malted barley and its impact on other malt quality parameters

Detailed studies were carried out on the influence of corn size distribution on the values obtained for diastatic power (DP) of commercially malted barley. Malted barley was screened using a screening box, and the DP activities of the different corns retained on the different compartments of the screening box were determined. The malt samples retained on the 2.8 mm screen had the highest DP activity, whereas the small corns (相似文献   

A comparative study of three methods of water removal prior to resin impregnation of two soils

The water in replicate samples from sub-surface horizons of a clayey and a fine-silty soil was removed either by oven-drying, freeze-drying or by acetone-replacement prior to resin impregnation. Pore space photograms (pores >60 μm diam.) from thin sections were analysed on a Quantimet 720 image analysing computer following each drying technique. During oven- and freeze-drying the clayey soil contracted considerably and subsequently satisfactory impregnation of these samples was either difficult or impossible. This macro-shrinkage caused a decrease in number and lengths of most planar pores and a decrease in size and number of all intra-aggregate pores. The loss in pore space and continuity obviously affected resin impregnation. The clayey samples in which water was replaced by acetone, and all samples of the silty soil, however pretreated, showed no measurable macro-shrinkage and all impregnated well. Oven-drying the silty soil appears to increase the porosity, causing an increase in size of all pores. A mechanism for this apparent enlargement is proposed. It is evident that acetone-replacement of the soil water prior to resin impregnation is the best of the three methods used here and should be seriously considered when image analysis is to be carried out on resin-impregnated blocks from soils of similar or related textures.     

Origin of extractable titanium and vanadium in the a horizons of scottish podzols

The A horizons of Scottish podzols often contain unusually high amounts of EDTA-extractable Ti and V. Five such soils developed on different parent materials were studied, total and EDTA-extractable Ti, V and Fe being determined in the samples and their particle size fractions. The fine sand accounts for 50–80% of the total and extractable amounts of all three elements in the total soil although, in general, both the total and extractable Ti and V concentrations increase with decreasing particle size. Thus the clays contain up to 420 ppm Ti and 27 ppm V extractable with EDTA. The main Ti minerals in the samples are anatase, rutile and ilmenite. Observations by scanning electron microscopy of the surfaces of the minerals show clear evidence of chemical, and possibly physical weathering, processes that may lead to the accumulation of Ti in fine fractions, but not to downward translocation. Vanadium is probably associated with iron oxides and ferromagnesian minerals, from which it is released by weathering and subsequently adsorbed by the clay fraction. Electron paramagnetic resonance spectra confirm that most of the V extracted from the samples and their clay fractions is in the vanadyl, (VO)²⁺, form.     

Microbial biogeography at the soil pore scale

Microbial communities exist and are active in a complex 3-D physical framework which can cause a variety of micro-environments to develop that are more or less suitable for microbial growth, activity and survival. If there is a significant microbial biogeography at the pore scale in soil, then the relationship between microbial diversity and ecosystem function is likely to be affected by micro-environmental variations at the pore scale. In this laboratory study we show that there is a significant pore-scale microbial biogeography by labelling microbial communities in different pore size classes of undisturbed soil cores with ¹³C-labelled fructose (a soluble, labile substrate). This was achieved by adding the substrate solution to the samples at different matric potentials (−100 kPa, −3.15 kPa and −1 kPa; placing the substrate in pores with maximum diameter of 0.97, 9.7 and 97 μm, respectively) and incubating the samples for two weeks. The mineralisation of soil organic carbon and fructose was measured as CO₂ and ¹³C-CO₂, respectively, in the jar headspace throughout the incubation. At the end of incubation we analysed the total microbial community structure using PLFA. The structure of microbial communities in different pore size classes was measured by PLFA stable isotope probing. Total PLFA profiles suggested that there was little effect of the incubation conditions on microbial community structure. However, labelled PLFA profiles showed that microbial community structure differed significantly among pore size classes, the differences being due primarily to variations in the abundance of mono-unsaturated lipids (Gram-biomarkers) and of the fungal biomarker (C18:2(9,12)). This is the first evidence for a significant microbial biogeography at the pore scale in undisturbed soil cores.     

三峡库区紫色土坡地土壤颗粒流失特征

选取20°长期耕作紫色土坡面径流小区进行模拟降雨试验,分析坡面土壤的颗粒组成及其变异,比较侵蚀泥沙颗粒组成的过程变化及其与坡面土壤颗粒组成的差异。结果表明,紫色土具有较宽变幅的颗粒组成,0.002～0.25mm的颗粒含量最高,坡面土壤存在较大的异质性;降雨初期侵蚀泥沙中<0.05mm的单粒和微团聚体含量都在65%以上,富集率分别为1.30,1.44,整个泥沙中的富集率分别为1.12,1.10,是侵蚀泥沙的主体,这其中又主要是0.002～0.05mm的粉粒和微团聚体;泥沙中<0.01mm的物理性粘粒及>0.25mm的水稳性团聚体富集率分别为1.10,1.16;随着降雨时间延长,单个泥沙样的颗粒组成逐渐接近雨前表土。     

渭河咸阳段近代洪水沉积物粒度分形特征研究

对渭河咸阳段高漫滩沉积物的粒度分形进行了研究。首先确定沉积物粒度分布具有分形特征的无标度区,然后计算出分维数。在无标度区范围内相关系数R2均大于0.95,沉积物粒度平均分维值为2.12,说明沉积物粒度分布具有很好的分形特征。将分维值作为一种新的沉积物粒度分析参数,与其传统粒度参数如平均粒径、标准偏差(σ)、偏度(SK)、峰度(KG)进行比较,利用SPSS软件分析Pearson相关系数,得出粒度分维值与其平均粒径的相关系数为0.807,与其标准偏差的相关系数为0.707,与其峰度的相关系数为0.675,与其偏度的相关系数为0.112。分析结果表明,沉积物粒度分维值与其平均粒径、标准偏差、峰度呈现明显的正相关关系,与其偏度呈现出并不明显的正相关关系。     

土壤透气性及粘土颗粒比表面积与粘土颗粒粒度分布分形维数关系

采用数字显微系统测定了部分华南地区土壤中粘土颗粒粒径分布分形维数值,提出了土壤中粘土颗粒群粒度分布分形维数的几何法计算模型,并就这种分形维数与土壤比表面积和土壤透气性等性质的相互关系作了初步探讨。结果表明,采用数字显微系统测定的粘土颗粒粒径分布分形维数值介于2.2708到2.9483之间,与常规方法测定结果吻合;含砂较多的土壤样品,BET比表面积和Blaine透气时间随粒度分布分形维数值增大而减小;含粘粒较多的土壤样品,BET比表面积和Blaine透气时间同随粒度分布分形维数值增大而增大。