A FLOTATION METHOD FOR THE RAPID MEASUREMENT OF THE WET BULK DENSITY OF SOIL CLODS

A flotation method for the rapid measurement of the wet bulk density of soil clods is described in which the clods are sprayed with a waterproof coating of a resin and then immersed sequentially in liquids of different specific gravity. It is compared with the wax coating method for a selection of soil textures and moisture contents and shown to be ten times as rapid when used to measure wet bulk density with an accuracy of ± 0.05 g cm^-8. The flotation method was used to show that, for three contrasting soils, clod wet bulk density is independent of clod size.     

Comparison of clod and core methods for determination of soil bulk density

Abstract

An interagency forest monitoring program has been initiated on a systematic network of forested plots often accessible only by foot traffic along a compass line. Extensive site classification and physiochemistry data are being collected for vegetation and soil indicators of forest health. In order to select a suitable technique for obtaining an estimate of mineral soil bulk density, conventional clod and core methods were compared across a wide range of forest soils within the Coastal Plain of southeastern Virginia. Replicate soil clods and cores were collected from two to four horizons within each of six pedons representing different soil series. Following analysis, the sample data were used to evaluate main and interaction effects due to differences in the method, series, horizon, and texture effects. Differences between the clod and core data were highly significant on average (P < 0.001) as were all of the main effects. Both methods exhibited high precision (average CV < 5%) within the individual horizons sampled. The two data sets were highly correlated (r = 0.98), and the regression equation used to predict clod bulk density with data from the core method is: Clod BD = (1.011 x Core BD) + 0.068; standard errors of ±0.042 and ±0.048 for the slope and intercept, respectively. From an operational standpoint, the core method appears to have many advantages over the clod method for sampling in remote locations.     

Simple Modification of the Clod Method for Determining Bulk Density of Very Gravelly Soils

Abstract

The accuracy of the clod method in determining fine‐earth bulk density in very gravelly soils can be affected by the difficulty of fine‐earth separation from both coarse fragments and the coating substance. A modification of the paraffin‐coated clod method is presented that accurately determines fine‐earth bulk density of very gravelly soils. The modification involves washing the paraffin‐coated clod in boiling water to separate paraffin from gravel and hardened soil aggregates. Samples were analyzed with an existing gravel correction method, herein referred to as the hand removal method (HRM), and the proposed modification, which is named the gravel washing method (GWM). Bulk density means for HRM and GWM were 1.29 and 1.41 g cm^?3, respectively. This trend of higher bulk densities for GWM was consistent across pedons sampled in the study and was attributed to its ability to completely remove wax from gravels and hardened soil aggregates, effectively separating the fine‐earth fraction.     

Use of class pedotransfer functions based on texture and bulk density of clods to generate water retention curves

Abstract. Water retention properties of 219 horizons were measured in Cambisols, Luvisols and Fluvisols, mainly from the Paris basin. We derived class pedotransfer functions (class PTFs) based on texture alone and in a second stage class PTFs based on classes combining texture and clod bulk density. The performance of these two types of PTFs were discussed at −330 and −15000 hPa water potential on an independent set of 221 horizons. Results showed that PTFs based on sets grouped by texture and clod bulk density provide estimates with an accuracy that is (i) greater than with class PTFs based on texture alone, and (ii) similar to the estimation accuracy recorded with continuous PTFs. As a consequence, the lack of interest in class PTFs should be reconsidered to bridge the gap between the available basic soil data and hydraulic properties which are generally missing, particularly when pertinent soil characteristics can be derived from the data available in soil databases. The two types of class PTFs providing gravimetric water contents at seven water potentials ranging from −10 to −15 000 hPa were converted to volumetric water content using the soil bulk density. Finally, the parameters of van Genuchten's water retention curve model were computed for every class PTF.     

Estimating soil stress distribution by using depth‐dependent soil bulk‐density data

Depth‐dependent soil bulk density (BDS) is usually affected by soil‐specific factors like texture, structure, clay mineralogy, soil organic‐matter content, soil moisture content, and composition of soil solution and is also affected by external factors like overburden‐stress history or hydrological fluxes. Generally, the depth‐dependent BDS cannot be predicted or extrapolated precisely from a limited number of sampling depths. In the present paper, an easy method is proposed to estimate the state of soil mechanical stress by analyzing the packing characteristics of the profile using soil bulk‐density data. Results for homogeneous loess profiles exposed to the site‐specific climatic conditions show that the depth‐dependent relation of void ratio vs. weight of overburden soil can be described systematically so that deviations from the noncompacted reference state can be detected. We observed that precompaction increased from forest soils (reference) to agricultural soils with decreasing depth.     

THE OCCURRENCE AND PREDICTION OF CLODS IN POTATO RIDGES IN RELATION TO SOIL PHYSICAL PROPERTIES

Clod crushing resistance, bulk density, moisture content, and size distribution, together with fifteen bulk soil physical properties, were determined at thirty sites. Regression analyses indicated that the plasticity index of the soil is the principal property affecting both the clod crushing resistance and the yield of clods. Other less closely related properties are not always consistent in their effect between clod size ranges. A‘clod factor’ was derived from the product of the clod crushing resistance and the weight of clods in the ridge for each soil. The clod factor is linearly correlated with plasticity index (r= 0·587, P= 0·002) and a clod factor > 1000 was found for soils with a plasticity index greater than about 5. Harvest observations suggest that where the clod factor exceeded 1000, the efficiency of a mechanical potato harvester was reduced.     

Comparison of Soil Sampling Devices for Soil Bulk Density Determination for Carbon Sequestration Monitoring

Soil bulk density is often used to adjust soil carbon (C) values for changes in soil density because of management differences in C-sequestration studies. Often hand-sampling devices used for soil fertility monitoring may be used for sampling soil to a depth of up to 30 cm. Four sampling devices of differing characteristics that can be used with hand-sampling equipment across full tillage, reduced tillage, and no-tillage to determine soil bulk density were evaluated. There were no significant differences in soil bulk density values between three cylindrical devices, which measured from 19 to 31 mm in diameter. However, a 21 mm × 76 mm rectangular device gave significantly lower bulk density values than the cylindrical devices. Calculation of soil organic carbon (SOC) mass per unit area showed similar results for the cylindrical devices with the rectangular device giving a significantly lower value than the cylindrical devices. Using a cylindrical device on a hand probe in a consistent manner will give satisfactory results when sampling surface soils.     

Depth variations in hydraulic conductivity within a single lift of compacted clay

Compacted clay liners are commonly used as components of the lower portion of composite double liner systems for hazardous waste containment. Because the overlying leachate collection and removal systems and the FMLs are not perfect leachate still comes into contact with the lower liner and thus makes it critical that the clay liner component be constructed to achieve the lowest possible hydraulic conductivity. This research was conducted to evaluate the effects of clod size on the hydraulic conductivity of compacted soils and the uniformity of conductivity with depth within a lift of compacted soil. Two subsoils, one from the Beaumont series (smectitic) and one from the Kosse series (kaolinitic), were evaluated in the laboratory and then compacted in large fixed wall permeameters using maximum clod sizes of <2.5, <5.0, and <7.5 cm to a compacted lift thickness of 23 cm. Measurements were made of the hydraulic conductivity of the entire lift, the lower two thirds of the lift, and the lower one third of the lift. The results show that the conductivity of the lower one third of the lift can be as great as 8.7 times that measured for the entire lift and indicates that liners need to be constructed using thin lifts to achieve more uniform low conductivity throughout the liner. The data also indicated that under the carefully controlled conditions of this study and with the clod sizes used, the clod size did not have a significant effect on the hydraulic conductivity of the soils tested. Soil bulk density was poorly correlated with hydraulic conductivity and indicates that measuring the bulk density of a compacted soil is an inadequate method for assuring low hydraulic conductivity. Measurements of the time to the first appearance of leachate indicated that 8 to 17 d are required for water to penetrate a 23 cm thick compacted liner with an average conductivity of 1 × 10^?7 cm s^?1.     

不同取样方式下土壤质地空间插值的精度分析

为研究土壤质地的合理取样方式,进而研究其空间变异情况,为田间施肥及灌溉提供依据,本试验利用地统计学方法和GIS技术,在重庆市彭水县重庆烟草试验站,利用289个表层土样,研究了16 m间距的栅格取样法(对照,253个土样,扣除36个验证样点)、34 m间距的栅格取样法(115个土样)和随机取样法(115个土样)3种取样方式下土壤质地的空间插值精度。3种土壤颗粒指标中粉粒占68.43%,砂粒含量最少,占12.68%,黏粒含量略高于砂粒。砂粒和黏粒具有中等强度的变异性,粉粒具弱变异性,且数据符合正态分布。地统计分析显示,在分析该区域土壤质地时,采用栅格取样方法应适当增大取样间距,而采用随机取样方法可适当缩小取样间距。交叉检验显示,土壤质地成分在3种取样方式下的插值精度均以对照最大,栅格取样次之,随机取样最小。综合考虑插值误差、样品采集和分析成本及时效性等因素,本研究建议在该区域进行土壤质地空间变异规律分析为生产服务时应采用随机取样。     

Three‐dimensional scanning for measurement of bulk density in gravelly soils

The measurement of bulk density in gravelly soils (>15% soil particles >2 mm) is more time‐consuming than for other soils. The excavation method, usually employed for measurement of bulk density in gravelly soils, includes excavating a void and calculating volume of the void from the weight and density of the material (e.g. sand and plaster cast) used to fill the void. A 3‐dimensional (3D) scanning system was developed to measure the volume of the void created when using the excavation method. The 3D scanning system combined a time‐of‐flight camera (Kinect ™), the KinectFusion algorithm, MeshLab and a portable computer to produce a 3D model of the void or plaster cast. Experiments were completed at three field sites where soil gravel (>2 mm) content ranged from 35 to 71% to assess the performance of the system. The void volume measured using the 3D scanning system was highly correlated with measurements using the plaster cast method (r  = 0.99). The cumulative time taken to measure soil bulk density using 3D scanning was significantly (P  <  0.001) less than for the sand replacement at 0–10, 10–20, 20–30 and 30–40 cm depth. The faster measurement of subsurface bulk density is a significant advantage of the 3D scanning system; the time taken to measure bulk density to 40 cm in 10 cm increments using the 3D scanning system was about one‐third of the sand method.     

The effect of texture on strength of southeastern coastal plain soils

The effect of texture on soil strength was analyzed for 17 soils, mainly from the Southeastern Coastal Plains. All samples were tested with a 5-mm, flat-tipped probe after equilibration at 100 kPa of soil-water tension. Both mechanical compression and water consolidation (compaction by wetting and drying) were used to compact the soils. Probe resistance of water-consolidated samples was significantly affected by texture. In fact, bulk density or probe resistance of soils compacted by methods of constant compactive force or constant methodology correlated well with texture for Coastal Plain soils.

A secondary effect of texture involved a significant, positive correlation of silt with probe resistance for sandy soils low in organic matter. Bulk densities at root-restricting conditions (2 MPa) compared well with bulk density values obtained by water consolidation and the Random Packing Model of Gupta and Larson, all of which were significantly correlated to texture.     

坡面径流小区集流桶含沙量测量方法对比

准确测量坡面径流小区集流桶含沙量是定量精准监测坡面土壤侵蚀的关键,野外径流小区观测方法测量精度、影响因素及其适用性的研究是实际应用的基础。该研究以第四纪红土为研究对象,采用室内模拟试验,对比不同含沙量（1.05、5.07、10.49、50.72、101.45、439.10 kg/m3）、不同水深（30、60、90 cm）下4种集流桶含沙量测量方法的精度,并对测量结果进行修正。结果表明：1）在60 cm水深、不同含沙量下,4种测定方法中,以机械+全剖面法测量误差总体最低;2）水深和含沙量是影响坡面径流小区集流桶取样测量误差的重要因素。总体而言,含沙量越高,测量误差越大;不同含沙量下,水深对测定误差影响程度不一,当含沙量小于50.72 kg/m3时,水深对机械+全剖面法测量精度无显著影响;3）4种方法的测量值与真实值均呈极显著正线性相关,含沙量测量值经过方程修正后相对误差明显降低。4）在含沙量小于5.07 kg/m3时,人工搅拌法可以应用于野外径流小区观测;当含沙量大于等于101.45 kg/m3后,全剖面法可以直接用于野外径流小区观测;机械法、机械+全剖面法在野外径流小区观测中可以直接使用。研究结果为集流桶含沙量取样测量方法在红壤区应用提供依据。     

Core sampling technique for bulk density and porosity determination on a clay loam soil

Seasonal fluctuations in bulk density and porosity determined from soil cores have been observed to be independent of soil and cropping treatments on the clay and clay loam soils of southwestern Ontario. An experiment was conducted to determine if the fluctuations may be a result of inconsistencies in core sampling technique. Three core sampling techniques were compared on five dates on each of four long-term cropping treatments which provided a range in soil water contents and structure. The core sampling techniques compared were: (1) a typical hand-held, hammer driven, double cylinder core sampler with the recommended procedure; (2) a typical hand-held, hammer driven, double cylinder core sampler with an excess number of blows; (3) pressing the double cylinder core sampler into the soil hydraulically. Variations in core sampling technique significantly affected the observed values of bulk density, total porosity, and air-filled porosity at field soil water contents ranging from 12.6 to 23.8% by weight. However, hammering, compared with hydraulically pressing, the core sampler into the soil, appears to cause more distortion within the soil core which increases variability. The effect of sampling date, and its inherent effect on soil moisture, was generally greater than the effect of the core sampling techniques. Therefore, providing a consistent technique is used, observed seasonal fluctuations in bulk density, total porosity, and air-filled porosity on Brookston clay loam soil are apparently not the result of variations in the core sampling technique.     

深圳城市绿地土壤肥力质量评价及管理对策

城市绿地是城市生态系统的重要组成部分,被称为城市的"肺"。城市绿地土壤通过其支持的植物、微生物和自身的功能,美化和净化城市环境,对城市的可持续发展具有重要意义。采集深圳市中心城区主要公园绿地、道路绿化带、住宅区绿地和单位附属绿地0～20cm,20～40cm土壤,研究了土壤质地、容重、孔隙度、阳离子交换量、pH、有机质、氮、磷、钾等物理化学性质。结果表明,深圳城市绿地土壤以砂壤和轻壤土为主,20～40cm土壤中松砂和紧砂土占有一定比例,土壤砾石含量高,重砾质土壤占91%以上;表层土壤(0～20cm)容重大,孔隙度小,阳离子交换量低;土壤pH较自然土壤明显增高,以中性和微酸性为主。土壤有机质处于较低的水平;全氮、碱解氮和全磷处于很低水平,有效磷处于中等水平;土壤全钾、速效钾处于中等或以上水平。0～20cm土壤中有机质、全氮、碱解氮显著高于20～40cm土壤。根据深圳城市绿地土壤质量状况,提出了加强深圳城市绿地土壤科学管理的措施和建议。     

Application of a visual soil examination and evaluation technique at site and farm level

Visual soil examination and evaluation (VSEE) techniques are semi‐quantitative methods that provide rapid and cost‐effective information on soil quality. These are mostly applied at site or field level, but there is an increased need for soil quality indicators at farm level to allow integration with other sustainability indicators. The objectives of this study were to develop and apply a protocol for application of a VSEE technique at site level, to assess the VSEE observations against standardized laboratory analyses and to aggregate VSEE observations to farm level using an appropriate sampling design. The study was conducted at ten dairy farms in a reclaimed polder in the Netherlands with clay and organic soils. A stratified random sampling design was used to account for spatial variability in land use and soil series. VSEE was carried out using the Visual Soil Assessment approach. Results show that 81% of sites were assessed as good and the remainder as moderate to poor. For the clay soils, field observations of soil structure were significantly correlated with pH, bulk density, soil organic matter (SOM) and mean weight diameter of aggregates, whereas for organic soils, soil structure significantly correlated with pH, bulk density, organic C and SOM. The range in overall scores calculated at farm level was smaller than at site level, and most farms were assessed as good.     

Estimating water retention curves of forest soils from soil texture and bulk density

Forest soils differ significantly from the arable land in their distribution of the soil bulk density and humus content, but the water retention parameters are primarily derived from the data of agricultural soils. Thus, there is a need to relate physical parameters of forest soils with their water retention characteristics and compare them with those of agricultural soils. Using 1850 water retention curves from forest soils, we related the following soil physical parameters to soil texture, bulk density, and C content: air capacity (AC), available water capacity (AWC), and the permanent wilting point (PWP). The ACs of forest soils were significantly higher than those of agricultural soils which were related to the low bulk densities of the forest soils, whereas differences in AWCs were small. Therefore, for a proper evaluation of the water retention curves (WRCs) and the parameters derived from them, further subdivisions of the lowest (< 1.45 g cm^‐3) of the three bulk density classes was undertaken to the wide range of low soil densities in forest soils (giving a total of 5 bulk density classes). In Germany, 31 soil texture classes are used for the estimation of soil physical parameters. Such a detailed classification is not required because of insignificant differences in WRCs for a large number of these classes. Based on cluster analysis of AC, AWC, and PWP parameters, 10 texture collectives were obtained. Using 5 classes of bulk densities, we further calculated the ACs, AWCs, and the PWPs for these 10 classes. Furthermore, “van Genuchten parameters” (θ r, θ s, α, and n) were derived which described the average WRC for each designated class. In a second approach using multiple regression analysis, regression functions for AC, AWC, and PWP and for the van Genuchten parameter were calculated.     

Determination of bulk density of soil clod by saturation

A method for the bulk density determination on soil clod is described. Clods are oven-dried, weighed and equilibrated over water saturated sand columns. Total volume of the clod is computed from the volume of its components - solid, and air. Air volume is calculated from the increase in weight of the dry clod on saturation.     

A method for predicting soil susceptibility to the compaction of surface layers as a function of water content and bulk density

Identifying the vulnerability of soils to compaction damage is becoming an increasingly important issue when planning and performing farming operations. Soil compaction models are efficient tools for predicting soil compaction due to agricultural field traffic. Most of these models require knowledge of the stress/strain relationship and of mechanical parameters and their variations as a function of different physical properties. Since soil compaction depends on the soil's water content, bulk density and texture, good understanding of the relations between them is essential to define suitable farming strategies according to climatic changes. In this work we propose a new pedotransfer function for 10 representative French soils collected from cultivated fields, a vineyard and forests. We investigate the relationship between soil mechanical properties, easily measurable soil properties, water content and bulk density. Confined compression tests were performed on remoulded soils of a large range of textures at different initial bulk densities and water contents. The use of remolded samples allowed us to examine a wide range of initial conditions with low measurement variability. Good linear regression was obtained between soil precompression stress, the compression index, initial water content, initial bulk density and soil texture. The higher the clay content, the higher the soil's capacity to bear greater stresses at higher initial water contents without severe compaction. Initial water content plays an important role in clayey and loamy soils. In contrast, for sandy soils, mechanical parameters were less dependent on initial water content but more related to initial bulk density. These pedotransfer functions are expected to hold for the soils of tilled surface layers, but further measurements on intact samples are needed to test their validity.     

基于图像处理和SVR的土壤容重与土壤孔隙度预测

土壤容重和土壤孔隙度是衡量土壤结构的重要参数。传统的土壤容重、土壤孔隙度获取方法费时费力,且大多数预测模型的输入变量获取难度较高。该研究利用土壤粗糙度、土壤阻力与土壤容重的相关关系,以土壤表面图像的颜色参数和纹理参数表征土壤粗糙度,同使用车载式土壤阻力测量系统获得的土壤阻力一起,从信息融合的角度构建了支持向量机回归（Support Vector Regression,SVR）土壤容重预测模型和SVR土壤孔隙度预测模型。图像处理使用HSV颜色空间进行阈值分割,得到HSV颜色参数,纹理参数使用灰度共生矩阵的能量、熵、对比度和逆方差。使用主成分分析对颜色参数和纹理参数进行主成分提取。将SVR模型的预测结果同环刀法测得的标准值进行相关性分析,决定系数R2达到了0.867。土壤孔隙度SVR预测模型决定系数R2达到了0.743。在相同的运行环境下,将SVR模型与决策树回归模型结果做了对比,决策树回归对土壤容重和土壤孔隙度的预测精度R2分别为0.734和0.690,验证得到SVR预测模型具有更好的预测精度。研究可为节省试验成本,以及快速、有效预测土壤容重和土壤孔隙度提供方法和参考。     

A review of visual soil evaluation techniques for soil structure

Soil structure forms a key component of soil quality, and its assessment by semi‐quantitative visual soil evaluation (VSE) techniques can help scientists, advisors and farmers make decisions regarding sampling and soil management. VSE techniques require inexpensive equipment and generate immediate results that correlate well with quantitative measurements of physical and biochemical properties, highlighting their potential utility. We reviewed published VSE techniques and found that soils of certain textures present problems and a lack of research into the influence of soil moisture content on VSE criteria. Generally, profile methods evaluate process interactions at specific locations within a field, exploring both intrinsic aspects and anthropogenic impacts. Spade methods focus on anthropogenic characteristics, providing rapid synopses of soil structure over wider areas. Despite a focus on structural form, some methods include criteria related to stability and resiliency. Further work is needed to improve existing methods regarding texture influences, on‐farm sampling procedures and more holistic assessments of soil structure.