体积置换法直接测量土壤质量含水率及土壤容重

土壤含水率直接测量是相关研究和应用的基础,在土壤力学、作物栽培、农田灌溉、生态环境等研究和实践中十分重要。该文提出了一种与传统烘干称质量法相当的体积置换法直接测量土壤质量含水率及土壤容重。该方法在假设一定土壤颗粒密度的前提下,用一定体积的标准取样环刀取得土样后,通过向待测量土体补充水分使土壤达到饱和,用一定体积的水置换土壤中的充气空隙,直到土样达到饱和状态;再通过测量得到的初始/原始土样质量、饱和后土壤的质量以及已知土壤颗粒密度和水密度,计算得到被置换的充气空隙的体积,进而由此计算得到土壤质量含水率和土壤容重。采用3种不同土壤,即陕西杨凌黏黄土、北京粉壤土和江西黏红土,分别预配制成7种不同初始土壤体积含水率,含水率约为:风干土(含水率2%～3%)、5%、10%、15%、25%、30%和饱和含水率,以及3种不同土壤容重:1.25、1.35和1.45g/cm3进行室内试验。用类似的土样,采用传统方法烘干土样8、12、24、48h后,测量确定土壤的质量含水率,通过延长烘干时间测得数据表明,传统方法烘干8h所测得的质量含水率仍有1%～3.2%的含水率误差。最终试验结果表明体积置换方法测得的土壤含水率比传统烘干土样8h所测得的结果大2%～3%,比烘干土样48h所测得的结果大1%左右。体积置换方法测量操作过程简单,耗时较少,节约能源,测量结果具有较高精度。     

Influence of gravimetric water content and bulk density on the dielectric properties of soil

Moisture content and bulk density largely characterize physical and mechanical soil status and behaviour. A nondestructive determination of these soil properties is essential. Time domain reflectometry (TDR), although widely accepted for determination of volumetric water content, θ, has its limitations, and recently a frequency domain (FD) sensor has been developed and tested. An equation relating relative permittivity, ?′, to gravimetric water content, w, and bulk density, p, was established for three soil types (sand, sandy loam and clay). If ?′ and w are known, our model can be used to calculate bulk density and associated volumetric water content, θ, keeping in mind that θ= pw. Utilization is found in long-term monitoring of moisture fluctuations or short-term detection of traffic-induced soil compaction.     

基于介电特性与SPA-SVR算法的水稻含水率检测方法

为提高基于介电法水稻含水率的检测精度,以北粳3号水稻为研究对象,利用阻抗分析仪及自制同轴圆柱型电容器测量了不同含水率水稻在1 kHz～1 MHz频率下的相对介电常数ε′及介质损耗因数ε"。采用x-y共生距离法划分了72个样本校正集和48个样本预测集。利用无信息变量消除法及连续投影法选取介电参数(ε′、ε"及ε′和ε"两者结合)的特征变量,分别利用所提取的特征变量以及单频、全频下的介电参数来建立预测水稻含水率的多元线性回归及支持向量机回归模型,分析模型的预测性能,并对最佳模型的含水率预测结果进行温度补偿。结果表明:基于ε′与ε"两者结合并利用连续投影法提取特征变量建立的支持向量机回归模型预测效果最佳,其预测集决定系数为0.980,预测均方根误差为0.403%。最佳预测模型对不同品种水稻的含水率预测值与烘干法测得的含水率实测值的绝对误差集中分布在±0.5%内,该研究可为粮食含水率的检测提供参考。     

Development of on-line measurement system of bulk density based on on-line measured draught, depth and soil moisture content

On-line measurement of soil compaction is needed for site specific tillage management. The soil bulk density (ρ) indicating soil compaction was measured on-line by means of a developed compaction sensor system that comprised several sensors for on-line measurement of the draught (D) of a soil cutting tool (subsoiler), the soil cutting depth (d) and the soil moisture content (w). The subsoiler D was measured with a single shear beam load cell, whereas d was measured with a wheel gauge that consisted of a swinging arm metal wheel and a linear variable differential transducer (LVDT). The soil w was measured with a near infrared fibre-type spectrophotometer sensor. These on-line three measured parameters were used to calculate ρ, by utilising a hybrid numerical–statistical mathematical model developed in a previous study. Punctual kriging was performed using the variogram estimation and spatial prediction with error (VESPER) 1.6 software to develop the field maps of ρ, soil w, subsoiler d and D, based on 10 m × 10 m grid. To verify the on-line measured ρ map, this map was compared with the map measured by the conventional core sampling method.

The spherical semivariogram models, providing the best fit for all properties was used for kriging of different maps. Maps developed showed that no clear correlation could be detected between different parameters measured and subsoiler D. However, the D value was smaller at shallow penetration d, whereas large D coincided with large ρ values at few positions in the field. Maps of ρ measured with the core sampling and on-line methods were similar, with correlation coefficient (r) and the standard error values of 0.75 and 0.054 Mg m⁻³, respectively. On-line measured ρ exhibited larger errors at very dry zones. The normal distribution of the ρ error between the two different measurement methods showed that about 72% of the errors were less than 0.05 Mg m⁻³ in absolute values. However, the overall mean error of on-line measured ρ was of a small value of 2.3%, which ensures the method accuracy for on-line measurement of ρ. Measurement under very dry conditions should be minimised, because it can lead to a relatively large error, and hence, compacted zones at dry zones cannot be detected correctly.     

Grazing-induced spatial variability of soil bulk density and content of moisture, organic carbon and calcium carbonate in a semi-arid rangeland

The landscape of many semiarid rangelands is characterized by a two-phase, shrub–intershrub vegetation mosaic, each phase having different soil properties. However, this broad subdivision groups together types of intershrub surface cover that may also differ in their soil properties and play important roles in ecosystem functioning. In the northern Negev region of Israel, we examined the soil properties associated with flock trampling routes and rock fragment clusters, as well as those associated with the remainder of the intershrub area and shrub patches. Moisture content, organic carbon content, bulk density and calcium carbonate content of the soil were determined for the above four types of cover, inside and outside long-term grazing exclosures. Soil was sampled in the peak of the growing season and in the end of the dry season, on a north- and a south-facing hillside, and from two depths. The shrub patches exhibited the highest soil moisture and organic carbon contents, and the lowest bulk density and calcium carbonate contents. The trampling routes showed opposite trends. The rock fragment clusters and the remainder of the intershrub area did not generally differ and had intermediate values of these properties. Grazing did not have a significant effect on soil properties at the whole-plot scale, but there were highly significant interactions between grazing and type of cover. Compared with the former trampling routes in the exclosures, the active trampling routes outside them had higher bulk density and lower moisture and organic carbon contents. The intershrub area had higher moisture and organic carbon contents under grazing than in the exclosures. Grazing increased the spatial heterogeneity of the soil properties examined via the creation of a network of trampling routes on the hillsides. The routes themselves, which constituted over 20% of the landscape cover, had degraded soil properties but they led to the improvement of the properties of the remainder of the intershrub area via functionally important source–sink relationships. The study of the soil of regions in which such networks are apparent should be duly cognizant of this intershrub subdivision in addition to the widely recognized shrub–intershrub dichotomy.     

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.     

不同土壤含水率、体积质量及光谱反射率的关系模型

为了准确、快速地检测湿胀干缩型土壤含水率,该文提出了基于近红外光谱技术的土壤含水率分析方法。该文以湖北省黄棕壤、潮土、水稻土为研究对象,利用美国Ocean Optic公司的NIR256-2.5微型光纤光谱仪在暗室环境下对不同含水率下的土壤样本进行光谱反射率的测定和特征分析,并同时测量相应的土壤体积质量,研究土壤含水率、体积质量、光谱反射率之间的相关关系,通过采用2种土壤含水率表示方法与3种土壤光谱反射率表示方法反映土壤含水率与光谱反射率之间关系的对比试验分析,消除土壤其它性状对土壤反射率反演土壤含水率的影响,得到较适宜地进行土壤光谱反射率反演土壤含水率的匹配表示方法,构建三者之间关系的曲面模型和体积质量变化的土壤体积含水率与土壤光谱反射率的关系指数模型。研究结果表明,构建的3种土壤的曲面回归模型,决定系数均大于0.977,F值均达极显著水平,光谱反射率与体积质量的偏回归系数检验亦达显著或极显著水平。采用指数模型表述1 400、1 900 nm波长处的归一化减土光谱反射率与体积质量变化的土壤体积含水率的关系,其决定系数均在0.9以上,对模型进行验证,其预测误差在0.3左右,精度较高,所建模型拟合效果好。该研究可为用近红外光谱检测体积质量变化的土壤含水率提供科学资料。     

基于流变学法研究容重和含水率对土壤结构力学稳定性的影响

土壤结构力学稳定性不仅与土壤质量和肥力密切相关,而且还与农业器具设计和农业水土工程建设紧密联系。该研究以黄土高原广泛分布的塿土和黄绵土为研究对象,采用振幅扫描试验模拟振荡荷载过程,研究土壤容重和含水率对土壤结构力学稳定性的影响。结果表明：1）随土壤容重的增加,土粒间接触点增多,使得剪切强度参数：线性黏弹区的剪切应力和储能模量均增加,土壤结构强度增强;黄绵土屈服点的剪切应变和塿土的积分z随容重增加先增大后降低,表明土壤颗粒存在一个最稳定的排列组合方式。同时,剪切强度参数对土壤容重的响应更为敏感。2）随含水率的增加,土壤颗粒间黏聚力和摩擦力降低,剪切强度参数：线性黏弹区的剪切应力、屈服点的剪切应力、最大剪切应力均降低,土壤结构强度降低;当剪切应变在线性黏弹区时,塿土的弹性随含水率的增加而增加,而较大的剪切应变下的塿土的弹性和黄绵土总的弹性随含水率增加均降低。3）对比2种土壤,因塿土的黏粒、有机质、阳离子交换量、比表面积等较高,增加了土粒间的胶结强度,使得塿土的弹性和剪切强度较高,而黄绵土结构更具脆性。该研究结果表明基于流变仪中的振幅扫描测试所获取的流变学参数能够定量表征土壤细观结构力学稳定性,为进一步深入认识土壤微观力学特性提供了丰富的评价参数。     

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.     

初始含水量和容重对黑土压缩特性的影响

东北黑土区农业机械化水平高,农机作业压实导致的土壤结构和物理性状退化问题日益严重,压缩特性是定量分析土壤压实过程的有效手段,但目前黑土压缩特性随初始含水量和初始容重的变化规律尚不明确。为了解初始含水量和初始容重对黑土压缩特性的影响程度及其变化关系,该研究以重塑黑土为对象,设0.15、0.20、0.25、0.30、0.35、0.40 g/g共6个初始含水量水平,设1.00、1.10、1.20、1.30、1.45、1.60 g/cm³共6个初始容重水平,使用固结仪进行单轴压缩试验测定土壤压缩曲线,分析初始含水量和容重对压缩特性影响。结果表明,土壤初始含水量、容重及两者交互作用均极显著影响重塑黑土压缩特性(P<0.001),据此建立了预测压缩特性的土壤传递函数。黑土的预固结压力为10.42～1 106.17 kPa,与初始含水量显著线性正相关、与初始容重显著线性负相关(P<0.05);压缩指数为0.311～0.852,与初始含水量和容重呈二元多项式方程的关系,随初始容重的增大而降低,在中等含水量时最大;回弹指数为0.007～0.321,与初始含水量正相关,与...     

利用介电参数和变量筛选建立玉米籽粒含水率无损检测模型

为了实现玉米含水率的快速无损检测,该文利用精密阻抗分析仪和自制介电参数测量传感器通过激励电压在1 kHz～5.462 MHz频率范围内测量了热风干燥过程中不同含水率与不同温度下玉米籽粒的介电常数ε''和介电损耗ε"。通过对双介电参数频谱的分析,对含水率回归模型建模频段进行了初步选择,以1.072～5.462 MHz之间15个测量频点的双介电参数和温度值T共计31维变量作为支持向量回归机（support vector regression,SVR）模型的输入全变量,分别利用竞争性自适应重加权算法（competitive adaptive reweighted sampling,CARS）、迭代保留信息变量算法（iteratively retains informative variables,IRIV）和CARS-IRIV联合算法筛选特征变量,建立全变量、CARS、IRIV和CARS-IRIV筛选特征变量与玉米籽粒含水率的SVR模型。引入鲸鱼优化算法（whale optimization algorithm,WOA）优化SVR模型参数c（惩罚因子）和g（核函数参数）,结果表明CARS-IRIV筛选特征变量（ε''3.854MHz、ε"3.854MHz、ε''5.462MHz、ε"5.462MHz、T）建立的SVR模型经WOA优化后（CARS-IRIV-WOA-SVR）具有最优的预测精度,预测集决定系数、预测集均方根误差和剩余预测偏差分别为0.998 4,0.40%和24.55,且模型复杂度最低。该研究为基于双介电参数和支持向量回归机实现玉米含水率快速无损检测提供了新的研究思路和基础数据。     

过量施用氯离子的扩散: I. 土壤湿度、容重及温度的影响

Diffusion coefficients of chlorde ions in four soils of different exture with varying effective moisture content and varying bulk density from 1.1 to 1.6 g cm^3 under three different temperatures were determined by the diffusion-cell method using ^36Cl-labelled CaCl2 solution.The result showed that activation energy decreased with water content,which indicated that the threshold fro diffusion was lower at a higher soil moisture rate .Therefor,the diffusion coefficient(D) of chloride ions in soil increased consistently with soil moisture,Although a near linear increase in the diffusion coefficient with increasing soil moisture or bulk density in all the soils was observed,the increase rate in different soils was not the same.The D value increased with teperature,and with temperature increased by 10℃ in the range from 5℃to 45℃ the D valve increased by 10%-30%,averaging about 20%.     

基于介电特性与IRIV-GWO-SVR算法的番茄叶片含水率检测

为了探究利用介电特性检测作物水分状况的可行性,研究了一种基于介电特性的有效、快速、精确检测番茄叶片含水率的方法。以300片不同含水率的番茄叶片为研究对象,通过LCR测量仪测定叶片在0.05~200 k Hz下的相对介电常数ε′和介质损耗因数ε″,并采用干燥法测量叶片含水率。利用迭代保留信息变量法(iteratively retains informative variables,IRIV)对介电参数进行特征变量选取,并与连续投影算法(successive projections algorithm,SPA)进行比较,利用支持向量回归机(support vector regression,SVR)分别建立叶片全变量、2种特征变量与叶片含水率的关系模型。结果表明,基于迭代保留信息变量法选取特征变量的支持向量回归模型(IRIV-SVR)具有良好的预测能力,但预测精度仍需提高,故引入灰狼优化算法(grey wolf optimizer,GWO)优化模型的参数c(惩罚因子)和g(核函数参数)。最终,经GWO优化后的模型(IRIV-GWO-SVR)的预测集决定系数R2与均方根误差RMSE分别为0.963 8,0.020 7。因此,利用介电特性结合IRIV-GWO-SVR算法预测番茄叶片含水率是可行的,同时为其他叶片含水率检测提供了一种新的方法和思路。     

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.     

The effect of bulk density, water content and soil type on the diffusion of chloride in soil

The relative importance of soil bulk density, water content and potential on the self-diffusion and impedance factors of ³⁶C1 in a sandy loam and loamy clay were studied. The soil bulk densities used represented a range of conditions from freshly tilled seedbeds to compacted soils. The volumetric water contents and pF were the main factors controlling the soil impedance factors, with bulk density making a small but significant contribution.
Soil type affects the impedance factors through differences in anion exclusion volumes, the water contents of poorly connected pores that contribute little to the diffusion process, and tortuosity of the diffusion pathways.     

Simple and rapid spectrophotometric method for determination of adrenaline and isoprenaline

A simple, rapid, and specific method for determination of adrenaline bitartrate and isoprenaline sulfate was developed. The method is based on the oxidation reaction in aqueous solution of either adrenaline bitartrate or isoprenaline sulfate in the presence of silver oxide to give a red aminochrome measurable at 490 nm. The color is stable for 2 h. Beer's law is valid within a concentration range of 5-80 micrograms/mL for each drug. All variables were studied to optimize the reaction conditions. The method is specific for catecholamine drugs having a secondary amine in the side chain. Other catecholamines such as orciprenaline and noradrenaline do not interfere, and no interference was observed in the presence of common pharmaceutical adjuvants. Interference due to sodium metabisulfite and sodium chloride was circumvented. The validity of the method was tested by analyzing adrenaline injections and isoprenaline tablets. Good recoveries were obtained for these preparations. The results were comparable to those obtained by official procedures. The proposed method is also recommended as a stability indicating assay for oxidative degradation of both drugs.     

Improving the calibration of dielectric TDR soil moisture determination taking into account the solid soil

The influence of soi?s solid phase on the dielectric constant of the soil over a range of moisture contents has been studied. Samples of soil, soil-like, and also other porous materials were analysed using Time Domain Reflectometry (TDR) to determine the contribution of bulk density and porosity to the function that relates dielectric constant to water content. The study showed that bulk density, and thus also porosity, substantially affects the relation between dielectric constant and water content. Two equivalent, empirical, normalized conversion functions were found, one accounting for bulk density and the other for porosity. Each of them reduced the root mean square error of the dielectric TDR determinations of moisture to 0.03, regardless of the material?s bulk density and porosity.     

Evaluating baseline data for trace elements,pH, organic matter content,and bulk density in agricultural soils in Nigeria

Agricultural soil samples were collected about 1 km apart over 21 km from 32 tilled/cultivated plots of yam, rice, and cassava in urban, rural, and the derelict Enyibga lead-zinc mine (EM) in the Abakaliki area, Nigeria during the rainy season in September, 1992. In the derelict mine, mean elemental contents increased in the order Cd < Ni < Cu < Mn < Pb < Zn; while in the urban, rural, and all soils combined, the order increased as follows: Cd < Cu < Ni < Pb < Zn < Mn. The overall mean distribution of all soils shows Mn and Zn to approach and exceed toxic levels, respectively. In all soils, the total mean concentrations of Cu and Ni are well below toxic levels. The Abakaliki area is less likely to be subjected to Cd-contaminated soils. Pb was excessively high at EM and, moderately high at Mgbowo Street in the urban area, but very less so in the rural areas. The rural agricultural areas of Agbaja, Nkwaegu, and Amaegu, including the isolated Ezza Road as well as the peripheral Expressway had relatively lower levels of heavy metals, pH and organic matter content than the urban conglomeration of Mile 50, Mgbowo Street, and Azuiyiokwu including the derelict mining village of Enyigba and EM; except that Ezza Road had pH and organic matter as high as the densely populated urban cultivated areas. The relationship between bulk density and organic matter was highly dependent on pH.     

Improved method for the rapid determination of terpenoid aldehydes in cotton

A simple, rapid method for the extraction of cotton terpenoid aldehydes from green tissues and seed is described. Samples were treated by ultrasonification with acidified acetonitrile/water followed by centrifugation. The resulting extract was injected directly onto a C(18) HPLC column and no sample concentration or further cleanup steps were required. The level of gossypol, the most labile of the target analytes, decreased by only 2% after 12 h of storage at room temperature, thus enabling automated analysis of individual terpenoid aldehydes by HPLC. The method gives excellent reproducibility and enables large numbers of samples to be screened quickly and accurately.