R. Protz

Chemistry and micromorphology of aggregation in earthworm casts

The mechanisms by which earthworms produce and stabilize soil aggregates are not well understood yet this information is necessary before management practices that promote the beneficial aspects of their activity can be devised. Therefore, selective chemical pretreatments and micromorphological observations were used to investigate the nature of aggregate formation and stabilization in worm casts. Passage of soil through worms disrupted pre-existing microaggregates due to breakage of some bonds of the water and cation bridge type; however, incorporated organic debris fragments became plasma encrusted and served as nuclei for new aggregates. In excreted pellets, aging and drying facilitated close approach and bonding of plant and microbial polysaccharides and other organic compounds associated with the organic fragments to clay, thereby stabilizing the new microaggregates. In the soil material investigated, these bonds consisted predominantly of clay-polyvalent cation-organic matter (C-P-OM) linkages involving calcium when the worms were provided alfalfa- or corn-leaf diets.

The representative elementary area (REA) in studies of quantitative soil micromorphology

Abstract A fundamental question to be answered for studies in quantitative micromorphology at varying scales is: What is the minimum area on a soil thin section or block that is required to represent the pedofeature of interest based on its distribution in soil space? This paper investigates the necessity of establishing a representative elementary area (REA) in the study of pedofeatures for quantitative analysis of pedofeatures. It also proposes a means by which an absolute REA may be determined. This was achieved by suggesting that the REA for voids on 3.5×4.7 cm soil thin sections is attained at the area where the measurements made on a parameter in three successive areas of measurements do not change ±10% relative to the next greater area of measurement. Using this method, the REA for void pedofeatures in the size range of 50 to 2000 μm on 3.5×4.7 cm thin sections from silt loam agricultural soils of southern Ontario was investigated. The REA was achieved for total void area between 50 and 500 μm in diameter in 99% (97 of 98) of the thin sections, whereas for total perimeter 97% (95 of 98) of the sections achieved the REA. The average REA between 50 and 500 μm in diameter for total void area and perimeter was 5.09 and 5.00 cm 2 , respectively. The average REA between 500 and 2000 μm for total void area and perimeter was 6.73 and 4.95 cm 2 , respectively. It is suggested that the REA determination should be performed in every quantitative soil micromorphological study in order that the parameter of interest is an adequate representation of that feature in soil space.

Relationships amongst organic matter content, heavy metal concentrations, earthworm activity, and soil microfabric on a sewage sludge disposal site

Abstract From 1973 to 1980, sewage sludge precipitated by three chemical treatment processes (aluminum sulphate, ferric chloride and calcium hydroxide) was applied to replicated plots on a silt loam soil at four different rates. The sludge was contaminated by heavy metals associated with industrial activity in the metropolitan areas from where it was collected. The grass on the plots has been mown regularly from 1973 onwards. Soil and earthworm populations were subjected to analysis in 1989 and 1990. Soil pits were dug and sampled to a depth of 50 cm in four plots receiving the highest rates of the three different types of sewage treatment processes (and a control plot treated through the same period with ammonium nitrate) to determine heavy metal contents and soil organic matter distributions with depth. The earthworm fauna of the plots was almost entirely represented by populations of Lumbricus terrestris L. that were analyzed for abundance and biomass following collection using the formalin expulsion method. Earthworm biomass was higher in sludge treatments than in control plots. Cadmium concentrations in earthworm tissues were correlated with soil Cd concentrations Only worms from Al-sludge treatments had elevated tissue concentrations of Cd. Cadmium distributions in sludgetreated soils were correlated with organic matter distributions in the soil profile (for individual profiles). Intact blocks of soil were removed from soil pits for chemical analysis of the soil microfabric by PIXE (proton induced X-ray emission) and electron micro-probe (EMP). Concentrations of several trace metals on the inner walls of the earthworm channels correlated with those added to the soil via the sludge. Water flow through earthworm burrows lined with fecal material, which had higher metal concentrations than the adjacent soil matrix, could move soluble forms of the elements, thus accelerating leaching of metals into the aquifer from surface-applied sludge.

An application of spectral image analysis to soil micromorphology, 1. methods of analysis

Abstract Digital images of polished soil sections were produced using an Eikonix Scanner (4096 detectors in a linear array). Separate images were collected in each of the red, green and blue wavelengths of visible (incandescent source) light and in the blue wavelength for ultraviolet (UV) illumination. These spectral data sets were registered, displayed and analyzed as colour composite images with an EASI/PACE spectral image analysis system. Visual identification and delineation of pedological features were based on their morphologies and colours. This task was aided by the image enhancement capabilities of the system. Features classified included skeletal grains, void space, mottles, organic material, manganese concretions, carbonates and depletion zones. An interpretive colour code for image display of these classified soil features was proposed and implemented. The percentages of the total image area occupied by each of these pedological features were derived from the final image classification.

Image analysis of soils ― present and future

Abstract With the present state of technology it is possible to impregnate and prepare thin sections from dry or wet soil samples. Thus we can measure the size, shape and distribution patterns of voids and pedological features at different moisture contents. Automated section polishing equipment makes it feasible to produce successive planes at varying intervals (e.g., as narrow as 10 μm) in impregnated blocks. Recent advances in computer software, hardware and imaging technology make it feasible to store the information from successive soil planes for integrated analysis. These advances can be readily adapted for use with SEM-EDXRA and STEM-EDXRA equipment. Thus it is now possible to physically locate and chemically analyse many soil components in three-dimensional soil space. These advances will help soil scientists develop quantitative models of complex soil processes within real soil space. In the future, we foresee improvements in image analysis equipment that will allow the use of spectral data in order to distinguish features in soil samples. In addition, we foresee the need to integrate all levels of imagery, from global to submicroscopic, allowing for the extrapolation of data from the microscope to landscapes and vice versa.

A new method for the identification of sediment stratification in soils of the Blue Springs Basin, Ontario

Abstract Eight soil profiles were sampled from the upland and lowland components of four glacial-fluvial landforms in the Blue Springs drainage basin, Guelph, Ontario. Sediment stratification in these soils was established at depths where statistically significant changes in the values of the ratios of % total sand/% total silt that are calculated on clay-free and carbonate-free basis take place. Limits of significance for differences between populations of stratified sediments were established from the standard error of determination of the ratios of % total sand/% total silt at the 0.01 probability level. A texturally uniform sediment is characterized by a regression line in which the depth ( X ) is the independent variable and the value of the ratio of % total sand/% total silt ( Y ) corresponding to the depth is the dependent variable.

Calcium-Dominated Organans in Humic Podzols from the Hudson and James Bay Lowlands of Ontario (CANADA)

Abstract The SEM-EDXRA analysis of cutans within five Humic Podzolic soils derived from calcareous sands and gravels revealed the presence of Ca-dominated organans. It is postulated that organic matter saturated by H and Al is translocated through the Ae-horizon and precipitated within the Bh horizon in the presence of calcareous material. Weathering of the calcareous material within the Bh horizon results in the partial replacement of the H and Al in the organans by Ca.

An application of spectral image analysis to soil micromorphology, 2. Comparison of two soil profiles

Abstract Pedological features in undisturbed samples from similar depths in two Brookston clay loam soil (Orthic Humic Gleysol or Typic Haplaquoll) profiles were compared: one in the never-cultivated state (NC) and the other under long-term (30 years), continuous-corn (Zea mays L.) (CC). Colour digital images of polished section samples from the NC Ah2, Bg and Ckg and the CC Ap, Bkg and Ckg horizons were produced with an Eikonix scanner and analyzed with an EASI/PACE spectral image analysis system. The spectral intensity values of delineated features were grouped into classes to produce maps of their spatial distribution. Image areal percentages for the features were measured. Void space feature results were compared with previous point-counting and single-channel image analyses. Quantitative and visual results for features indicated that the soil compaction associated with the CC cropping practice gave the Ap horizon properties that more closely resembled those of the deeper B and C horizons than those of the NC Ah2 horizon. These properties included: (1) a reduced macroporosity ( 50%); (2) organic material dispersed throughout the peds (light-coloured) and concentrated only along the macropores (dark-coloured); and (3) weakly developed gleysolic characteristics (faint mottles) in the interior regions of the peds (27% of sample area).

Extractable organic fractions of podzolic and associated soils in the Hudson Bay-James Bay Lowlands☆

Abstract Black B horizons are a striking morphological feature of some of the young Podzolic and Podzolic-like soils derived from calcareous, gravelly storm ridges in the Hudson Bay-James Bay Lowlands. Organic matter extracted by 0.1 M sodium hydroxide-0.1 M sodium pyrophosphate was analyzed in an attempt to determine the fractions responsible for the dark-colored B horizons. No significant differences were found in percentage of extractable C, pyrophosphate extractable Fe and Al or Ch/Cf and Ca/Cf ratios of the dark (commonly black) and lighter-colored (commonly reddish brown) B horizons. The dark B subhorizons occurred within or immediately above calcareous material and the lighter colored B horizons occurred usually in acid material overlying calcareous material. Like B horizons of Podzolic soils in other areas of Canada, those of the Hudson Bay-James Bay area have the following properties: extractable C ⩾50% of organic C, the ratio of C in humic to C in fulvic acid (Ch/Cf)

The relationships of the clay mineral suites to the parent rocks of eight soil profiles in Sarawak, Malaysia

Abstract The clay mineralogy of eight selected soil profiles developed on acid igneous, pyroclastic and sedimentary rocks was investigated. The effects on the clay mineralogy of the parent-rock mineralogy and physical conditions within each soil profile were evaluated. The results indicate that the mineralogies of the parent rocks control the type of clay minerals formed in Sarawak. In the soils derived from pyroclastic and coarse-grained acid igneous rocks without muscovite, the clay-mineral suites consist almost exclusively of kaolinite and gibbsite with small amounts of goethite. In contrast, in the soils developed from fine-grained acid igneous and sedimentary rocks with muscovite, the clays contain relatively large amounts of interstratified mica-vermiculite and chlorite-vermiculite in addition to gibbsite and/or kaolinite. The presence of gibbsite in these soils depends on the presence of plagioclase feldspar in the parent rock.