Integrating geospatial and multi‐depth laboratory spectral data for mapping soil classes in a geologically complex area in southeastern Brazil

Soil mapping across large areas can be enhanced by integrating different methods and data sources. This study merges laboratory, field and remote sensing data to create digital maps of soil suborders based on the Brazilian Soil Classification System, with and without additional textural classification, in an area of 13 000 ha in the state of São Paulo, southeastern Brazil. Data from 289 visited soil profiles were used in multinomial logistic regression to predict soil suborders from geospatial data (geology, topography, emissivity and vegetation index) and visible–near infrared (400–2500 nm) reflectance of soil samples collected at three depths (0–20, 40–60 and 80–100 cm). The derived maps were validated with 47 external observations, and compared with two conventional soil maps at scales of 1:100 000 and 1:20 000. Soil suborders with and without textural classification were predicted correctly for 44 and 52% of the soil profiles, respectively. The derived suborder maps agreed with the 1:100 000 and 1:20 000 conventional maps in 20 and 23% (with textural classification) and 41 and 46% (without textural classification) of the area, respectively. Soils that were well defined along relief gradients (Latosols and Argisols) were predicted with up to 91% agreement, whereas soils in complex areas (Cambisols and Neosols) were poorly predicted. Adding textural classification to suborders considerably degraded classification accuracy; thus modelling at the suborder level alone is recommended. Stream density and laboratory soil reflectance improved all classification models, showing their potential to aid digital soil mapping in complex tropical environments.     

The use of land form-soil associations in irrigation soil surveys in northern Nigeria

The problems of soil mapping for irrigated agriculture on the savanna landscapes near Kano are discussed. Using data from a detailed soil survey, the possibility of establishing the major variations in soil properties relevant to irrigation by landform-soil association mapping is considered. In the landform classes identified, some soil textural and colour properties have within-class variances somewhat lower than their between-class variances, and moderate interclass correlations. The magnitude of the between-class differences in these properties is great enough to indicate whether the soils can be irrigated successfully and to help determine the irrigation method. Other soil properties including infiltration rate and topsoil available water capacity also differ significantly between landform classes, but their within-class variabdity is still relatively high, indicating the need for further investigations. The variability of most soil chemical properties across the area is not successfully accounted for by landform-soil association mapping. The results suggest that landform-soil association mapping can be a useful means of establishing imgability a feasibility survey level.     

Determination of soil texture: Comparison of the sedimentation method and the laser‐diffraction analysis

Laser‐diffraction analysis (LDA) is a rapid automated method achieving highly resolved frequency distributions of particle sizes. Recently, LDA has come into use in environmental sciences. However, in the size range of silt and clay deviations from the particle‐size analysis with the standard pipette method, which is regarded as the reference method for soil‐texture classification, have been reported. Therefore, this study concentrates (1) on the verification of systematic relations between both methods using a series of soils of Lower Saxony (Germany) and (2) on the general applicability of the laser‐diffraction method to soil‐texture classification as well as (3) texture‐based estimates of air capacity, available field capacity, and permanent wilting point. The comparison of LDA with the pipette method demonstrated highly significant linear correlations in each of the particle‐size fractions from clay to coarse silt. The slope of regressions ranged from 0.4 with fine silt to 3.1 with clay. If the clay content derived from LDA was applied to texture classification, the resulting textural classes differed from the standard textural classes, except for purely sandy samples with a clay content of <5%. However, the linear‐regression model enabled an approach of the LDA‐based clay content to values produced with the standard pipette method. Using this transformation, a texture classification became practicable in many cases, but, despite of a high significance level between LDA and pipette method, still led to wrong textural classes in several cases. A comparison with regression models from other regions in Europe showed both similarities and discrepancies, even for similar substrates. Hence, the laser‐diffraction analysis cannot be used for the texture classification of soil samples without verification by the standard pipette method.     

基于近红外光谱和正交信号-偏最小二乘法对土壤的分类

不同质地的土壤,由于蓄水能力和土壤颗粒大小的不同使得其光谱特性不同,这为采用近红外光谱技术对土壤质地进行判别分析提供了依据。该研究利用正交信号校正(OSC)方法可以获得与浓度有关的谱图信息这一优势,将其与偏最小二乘方法(PLS)结合,采用近红外光谱技术对不同质地的土壤:砂土、壤土、黏土进行判别分析。结果表明:建模样本的相关系数可达0.965,采用该模型对其余45个样本分别进行了预测,三种土壤预测样本的判别正确率分别为:93.3%,86.6%和86.6%。说明OSC方法可以提取谱图中的微弱的质地信息,实现土壤质地的快速鉴别分析。     

应用Markov链理论定量描述区域冲积土壤质地层次的垂向变化特征

冲积土壤剖面质地层次的垂向变化是一个十分复杂的问题,长期以来都是定性描述而无法定量化,但土壤剖面的质地层次组合特点对土壤水分转化和溶质运移等具有重要影响,对其定量地描述和研究是进一步准确定量区域农田水转化和溶质运移的基础。马尔可夫链理论是用来描述随时间（空间）变化的一个离散状态序列的状态转移特性的,本文就其引入来研究冲积土壤剖面质地层次的垂向变化规律。研究结果表明,区域冲积土壤剖面质地层次的垂向变     

A classification scheme for earthworm populations (Lumbricidae) in cultivated agricultural soils in Brandenburg,Germany

Earthworm activity is observed at long‐term monitoring sites as an indicator of soil function to assess changes resulting from environmental and management conditions. In order to assess changes, characteristic values of earthworm populations under different site conditions have to be known. Therefore, a classification scheme for site‐specific earthworm populations was developed for soil in agricultural use, taking interactions between earthworm populations and soil properties into account. Characteristics of sites grouped by means of a cluster analysis after principal‐component analysis served as a basis for the derivation of the classification scheme. Soil variables found to characterize site differences with respect to earthworm populations were the texture of the topsoil, the texture of the subsoil, and the soil organic‐matter (SOM) content. The textural classes of the topsoil were divided into five groups comprising sandy soils (Ss), silty sand soils (Su), slightly loamy sand soils (Sl2), medium to strongly loamy sand soils (Sl3/Sl4), and loam and clay soils. Soil organic matter was divided into grades of equal size in a range from <1%, 1%–2% up to >6%. The variables “earthworm abundance” and “earthworm species” were selected to represent earthworm populations and were divided into six groups ranging from very low to extremely high. Defined groups of earthworm populations showed a clear structure in relation to soil textural groups and the content of SOM. From this distribution, a classification scheme was derived as basis for prognostic values of site‐specific earthworm populations, thus enabling the interpretation of changes over time. For some soil textural groups, selected variables appeared to enable the derivations of expected earthworm densities and species composition outside the range of the given database, but for some soil textural groups, broader databases will be needed to specify these derivations.     

Presumptive effect of aggregates on textural classification

Although the term soil texture has often connoted the primary particle-size distribution, the textural class names seem to have the established concept of soil structure and do not yet lose their original meanings. It is expected, therefore, that the textural classification becomes more significant if the secondary particles, aggregates, are taken into account.

From a review of reports on this topic, the following assumption is made; a constant proportion of the primary clay fraction forms part of the aggregates of sand size where the value of the proportion is -0.3. Comparing the usual textural classification with the proposed one, most of the areas in which one fraction predominates are almost similar, except for loam in the usual classification, because the loams are the soils in which no one fraction dominates. Generatly speaking, the physical properties of the loams are various owing mainly to aggregate formation, and thus the loams are .simulative to the productive sandy soils under suitable conditions. Moreover, Heavy Clay in the usual textural classification is clayey, even if aggregates are taken Into account, and its voids are all surrounded by clay particles excepting the pores in the aggregates.     

THE INFLUENCE OF TEXTURE ON THE MOISTURE CHARACTERISTICS OF SOILS

The available-water capacity (AWC) of soil profiles in the field may be estimated by (a) measuring the thickness of each soil horizon; (b) assessing its texture; and (c) summing the products of the thickness of each horizon and the mean values of AWC for the relevant textural classes. (This mean value of AWC was calculated from the average particle-size composition and from a relationship between particle size composition and AWC.) Estimates of AWC using this method were compared with measured values for each of 39 soils. When a 21 textural-class system was used to describe the soils, the mean error (the error of the estimated AWC value relative to the measured value) was ±10 per cent and with a 12 class system the mean error was ±17 per cent.     

广西主要土壤的磁化率剖面初探

本文初步探讨了广西主要的富铝化土壤、岩成土壤以及水稻土的磁化率剖面特征。各土壤间磁化率剖面差别非常明显，建议将其作为土壤分类的参考。     

Physical properties and moisture retention characteristics of some nigerian soils

Measurements were made of physical characteristics of 119 samples from 23 profiles derived from two parent materials in Nigeria. The laboratory analyses included texture, plasticity and shrinkage characteristics, and a range of soil moisture constants including saturation point and moisture retention at various suctions. Simple and multiple correlation coefficients and regression analyses were conducted to investigate the possibilities of obtaining estimates of soil moisture retention from the textural analysis. Clay and sand contents are correlated with various soil moisture constants. The textural analysis may therefore be used to estimate moisture holding capacity at different suctions for these and similar soils with a predominantly uniform clay mineralogy, dominated by kaolinite and sesquioxides. Moisture retention curves indicate that the “field capacity” for most of these soils is better estimated at 60 or 100 cm of water suction rather than at 0.3 bar. A plot of the pF curves indicated only slight differences between moisture retention at 2 or 3 bar suction and at 15 bar suction.     

区域农田土壤质地剖面的随机模拟模型

冲积土壤剖面的质地层次分层是该类土壤的重要特性,对农田水分转化和溶质运移具有重要影响。本文论据已取得的研究结果,采用Ｍａｒｋｏｖ链理论提出了区域冲积土壤质地层次的随机模拟模型－ＭＣ模型和ＭＣ－ＬＮ模型,采用蒙特卡罗方法模拟了研究区的土壤质地剖面,并与实测结果进行了对比。     

对全国第二次土壤普查中土类、亚类划分及其调查制图的辨析

按照中国发生分类对新采集的68个北京市山区的土壤剖面进行了分类命名,并与剖面点所在土壤普查图上的分类名称进行比较,结果是只有18个剖面的分类名称一致。造成分类名称不一致的原因:1发生分类以区域典型土壤剖面分类命名,而区域内很多土壤不同于典型土壤剖面;2发生分类往往以现代生物气候带为主要分类标准命名区域土壤,而不是根据土壤性质;3分类不一致的最大原因可能是制图精度不够。研究认为,土壤分类必须依据土壤性质本身,而不是土壤形成因素;采取野外单土壤性质调查制图,室内叠加单土壤性质图形成多属性图斑,根据分类系统对它们进行综合分类,以提高分类制图精度。     

Evaluation of Different Predictor Models for Detailed Soil Particle-Size Distribution

An accurate mathematical representation of soil particle-size distribution (PSD) is required to estimate soil hydraulic properties or to compare texture measurements using different classification systems. However, many databases do not contain full PSD data, but instead contain only the clay, silt, and sand mass fractions. The objective of this study was to evaluate the abilities of four PSD models (the Skaggs model, the Fooladmand model, the modified Gray model GM (1,1), and the Fredlund model) to predict detailed PSD using limited soil textural data and to determine the effects of soil texture on the performance of the individual PSD model. The mean absolute error (MAE) and root mean square error (RMSE) were used to measure the goodness-of-fit of the models, and the Akaike''s information criterion (AIC) was used to compare the quality of model fits. The performance of all PSD models except the GM (1,1) improved with increasing clay content in soils. This result showed that the GM (1,1) was less dependent on soil texture. The Fredlund model was the best for describing the PSDs of all soil textures except in the sand textural class. However, the GM (1,1) showed better performance as the sand content increased. These results indicated that the Fredlund model showed the best performance and the least values of all evaluation criteria, and can be used using limited soil textural data for detailed PSD.     

VARIATIONS IN THE USEFULNESS OF RAPID SOIL MAPPING IN THE NIGERIAN SAVANNA

The rapid soil mapping required in developing countries can only be done by relating soils to land form and geology. A usefulness classification of mapping units is suggested. The most useful contain the least soil variation. Units with regular soil variation within them are more useful than those with random variation. In the Nigerian Savanna the most useful units are on hill remnants and homogeneous sediments, particularly coarse siliceous sandstones and fixed dunes. The least useful are on dissected areas, heterogeneous sediments, igneous and metamorphic rocks. The least fertile soils often dominate the most useful units. Rapid soil mapping should be useful in the north and the lower Niger and Benue valleys.     

A digital computer program for particle size analysis and textural classification of soils

Abstract

A digital computer program was written for the determination of particle size distribution and textural classification of soil samples. The textural classification is based on the South African texture‐triangle.     

Geogenesis, pedogenesis, and multiple causality in the formation of texture-contrast soils

Coarse-over-fine vertical texture contrasts (VTC) are common in soils and weathering profiles in a variety of environmental settings, including many where inheritance or surficial processes alone cannot account for them. A multiple causality model is presented here which shows that texture contrasts can form in response to a combination of ubiquitous phenomena. There are six key elements: downward translocation by water, erosional winnowing, soil mixing by bioturbation, the tendency for surface clay additions to be mobilized while subsurface clays are more likely to remain in place, and biological facilitation of moisture flux. No element alone is sufficient to create a VTC, but not all are necessary in any given regolith. The model is illustrated by application to case studies in the Ouachita Mountains, Arkansas; ridgetops in eastern Kentucky; the lower coastal plain of North Carolina; and the upper coastal plain of east Texas. The implications for interpretation of soils, paleosols, and weathering profiles is that the presence of a textural contrast, by itself, does not connote any particular set of geogenic or pedogenic processs or controls. Texture contrasts may be geogenic, pedogenic, or both. Given the widespread occurrence of the mechanisms of the multiple causality model, vertical texture contrasts are inevitable.     

河南省多级地貌特征及与土壤多样性的关系

从土壤多样性向地多样性发展符合土壤地理学的研究趋势,选择河南省作为研究区,将地貌这一主要的地学要素加入到土壤多样性的研究中,并用改进的仙农熵公式对多级地貌空间分布多样性及其与土壤多样性的相关性进行探讨。首先,对河南省1︰175万地貌类型图进行矢量化得到地貌类型等级系统;然后,对地貌和土壤的构成组分多样性和2种不同分类体系的分支率进行计算并分析其特征;最后,在3 km×3 km网格尺度下分析地貌和土壤多样性间的相关性。研究表明:河南省共有3个一级地貌,12个二级地貌和37个三级地貌;随着土壤和地貌分类的等级细化,其分类个数和构成组分多样性值均呈上升趋势,即土壤和地貌所有分类单元在数量构成上的均匀程度越来越高;两种分类系统中,土壤分类较地貌分类有更详细的分类体系,且分支率有较大范围的变化;河南省一级地貌、二级地貌和三级地貌的空间分布多样性值和面积值均最大的类型分别是流水地貌、冲积平原和泛滥平坦地,是不同级别的优势地貌类型;一级地貌类型与土类、亚类和土属多样性间存在紧密的相关关系,且以流水地貌与土壤多样性间的相关性最强。     

Soil texture and nitrogen mineralization potential across a riparian toposequence in a semi-arid savanna

Soil texture is an important influence on nutrient cycling in upland soils, with documented relationships between mineral particle size distribution and organic matter retention, nitrogen (N) mineralization, microbial biomass and other soil properties. However, little is known of the role of mineral particle size in riparian soils, where fluvial sorting creates strong spatial contrasts in the size distribution of sediments in sedimentary landforms. We studied total organic carbon (TOC) and total N (TN) storage and net N mineralization relative to soil texture and landform in soils of a riparian toposequence along the Phugwane River in Kruger National Park, South Africa. TOC, TN and potential N mineralization related strongly to particle size distribution in all soils along the toposequence. TOC and TN were positively correlated with silt and clay concentration (r² =0.78). In long-term laboratory incubations, N mineralization was greatest in fine-textured, N-rich soils, although the proportions of soil N mineralized were inversely related to fine particle concentrations (r²=0.61). There were differences in TOC, TN and potential N mineralization among landform types, but none of these soil properties were statistically significant after accounting for the effect of particle size. These results demonstrate the influence of particle size in mediating N retention and mineralization in these soils. Predictable differences in soil texture across alluvial landforms contribute to corresponding contrasts in soil conditions, and may play an important role in structuring riparian soil and plant communities.     

国内外土壤质地自动分类程序介绍

土壤质地是反映土壤物理特性的一个综合指标,土壤质地命名的自动化将有效提高土壤质地分类工作的效率。本文结合土壤质地自动分类程序研究的现状与特点,着重阐述并讨论了目前较为成熟的TAL、TRANGLE和STAC自动分类计算机程序的设计、功能、使用和实例及其异同与优缺点。土壤质地命名的应用试验表明:TAL和TRANGLE程序在批处理数据量、分类制、图形显示、统计功能等方面存在局限,STAC程序则相对较为完善、方便、实用。