A.J. Koppi

Rare earth element trends and cerium-uranium-manganese associations in weathered rock from Koongarra, Northern Territory, Australia

At Koongarra, Australia, three drill cores form the Cahill Schist Formation containing U-ore, and regolith above it containing secondary U-ore, were studied to ascertain the distribution of rare earth elements (REEs) and U. The unaltered schist has a REE trend similar to the Post Archaean Australian Shale (PAAS), which is, therefore, used as a normalising standard. Unweathered rock from the zone of primary U mineralisation contained strong enrichment of the heavy REEs, and this pattern is retained during most of the weathering. Strongly bleached and very weathered shallow samples from this zone do not show enrichment of HREEs. In general, however, weathering appears to have little effect on the pattern of REEs in the bulk rock at this site. Zones rich in Mn oxy-hydroxides, occurring as coatings on fissure surfaces, contain large concentrations of Ce and U, with a clear Ce anomaly (Ce/Ce* = 3.8). The Ce and U apparently occur together as microcrystalline oxides within (1-2 {mu}m diameter) globules on mineral surfaces in the Mn-rich zones. 46 refs., 10 figs., 2 tabs.

Modifications to a method of rapid assessment of soil macropore structure by image analysis

Abstract The use of image analysis in pore structural studies is reviewed with the general conclusion that methods tend to be slow. A method of rapid assessment of soil pore structure is discussed, and three modifications to the original technique are presented. These are: (1) development of a technique for obtaining and video-digitising a single vertical structural monolith to 0.7 m; (2) use of resins containing different coloured dyes in the field and laboratory, allowing assessment of a larger number of parameters to discriminate between total and surface-connected pore space; (3) adaptation of the technique to measure roots in situ. These modifications are illustrated for comparison of natural and cultivated soil profiles, compaction trials from eastern Australia, and from laboratory experiments. Future modifications and enhancements including colour digitisation, computed axial tomographic (CAT) scanning and the use of random-process models are discussed. It is concluded that image processing and measurement techniques coupled with suitable laboratory and field methods and simple, yet sensible, models of the soil geometry provide powerful new techniques for visualising and measuring soil structure. These new techniques should be used to complement more conventional methods, however.

The use of a simple field air permeameter as a rapid indicator of functional soil pore space

Abstract Currently there is a lack of quantitative data on the functional classification of soil structure, particularly in routine soil surveys, because field physical measurements of flow characteristics are slow and require expertise. A simple air permeameter was developed which allows rapid, in situ measurements to be made of the intrinsic permeability of the soil to air ( k a ). Measurements of k a are highly dependent on the structure of the soil, in particular the size and continuity of macropores, and therefore can be used as an estimate of functional pore space (pore space contributing to the transmission of air and water) in the soil. Values of k a ranged from 5.6 μm 2 for a compacted alluvial soil under pasture to 276.8 μm 2 for a red-brown earth under native grass, cultivated one year before the time of measurement. Development of a functional pore space scoring table for use in the field has shown that k a 0.5 can be estimated from morphological descriptions of the soil. However, field descriptions are qualitative, subjective and difficult to apply consistently. The air permeameter can discriminate between the structural differences in soil under different management practices. The air permeameter should appeal to pedologists who wish to have a quantitative aid in the interpretation of soil structure.

The effect of cultivation on the properties of a Rhodoxeralf from the wheat/sheep belt of New South Wales

Abstract Adjacent cultivated and never-cultivated areas of land were compared for a variety of chemical and physical properties to determine the effect of traditional cultivation practices on an Australian Rhodoxeralf. Those properties which changed most as a result of clearing and cultivation were pH, electrical conductivity, organic carbon, nitrogen and profile macroporosity. These changes are due to various processes including soil mixing, fertilizing, crop-growing and an altered water balance. The heterogeneity of the sites was also investigated in order to ascertain the effect of cultivation on the natural variability of the soil. The cultivated soil was found to be much less diverse than the adjoining virgin soil. Whether this is of ultimate benefit to crops is open to conjecture.

In-situ soil organic matter studies using scanning electron microscopy and low temperature ashing

Abstract The in-situ distribution and morphology of organic materials located on, or near, structural surfaces within some soils is examined on a submicroscopic scale by comparing scanning electron microscope images of the same areas of soil samples before and after low temperature ashing. Electron-translucent organic matter coatings up to 1 2 μm thick, and thinner, electron-opaque organic matter coatings were found on structural surfaces within these soils. Oribatid faecal pellets in one of the soils were found to contain aluminosilicate clay minerals. Fine-clay sized spheres of biogenic opaline silica were found to be contained within the epidermis of a decaying root. These studies show that the combined use of low temperature ashing and scanning electron microscopy will be a valuable technique for in-situ investigations of submicroscopic organic matter within soils.

The effect of tillage and gypsum application on the macropore structure of an Australian Vertisol used for irrigated cotton

Abstract Structural degradation of Vertisols (cracking grey clay soil) as a result of growing cotton under furrow irrigation has resulted in declining cotton yields. This degradation may be ameliorated with suitable management. A field experiment at Warren, N.S.W., Australia was set up to assess the long-term effects of repeated deep ripping plus gypsum, as compared with the more traditional shallow cultivation, on the physical condition and cotton lint yield of a sodic Vertisol. The soil was sampled 7 years after the experiment began for an assessment of soil macropore structure. Soil samples from successive depth intervals down the profile were impregnated with resin and the macropore structure described visually and quantitatively using image analysis. Other physical and chemical attributes such as shear strength, bulk density, pore space relations, pH, exchangeable sodium percentage, electrical conductivity, total cations, calcium to magnesium ratio and organic matter, were also measured from the same soil profiles. Results from both image analysis and conventional soil measurements indicated there was a structurally degraded zone from 25 to 60 cm in the shallow cultivated treatment. This was in contrast to a more porous and weaker soil in the deep ripped plus gypsum treatment that produced slightly larger cotton yields. The image-analysis data were a valuable supplement to the more conventional methods of quantifying soil structure.

Micromorphology of authigenic celestobarite in a duripan from central Australia

Abstract The micromorphology and elemental composition of celestobarite crystals in a duripan from central Australia are examined. These crystals are flabellate (fan-shaped), have a Ba/Sr ratio of 11.1, and are up to 50 μm in size. The location of the celestobarite crystals within silicified roots and in close association with calcite and clay coatings indicates that these celestobarite crystals are authigenic and were formed under aridic environments.

Cotton root growth in a compacted Vertisol (Grey Vertosol). II. Correlation with image analysis parameters

A differential staining procedure was developed to study the degree of association between soil structural form parameters, derived using the SOLICON image analysis system, and the root growth of cotton plants. Under the climatic conditions that prevailed during the experimental period, severe impedance of taproots was associated with a clod width in the range 28 mm to ≥30 mm and a macroporosity value in the range 0.00–0.04 m3/m3. The new root assessment procedure detected soil structural features, for example, well-aerated zones adjacent to near-surface roots in degraded soil not shown by other methods and allowed direct measurement of the proportion of a root’s surface in contact with the soil atmosphere. However, the assessment method should be complemented by direct measurement of the morphology of nearby cotton taproots that have been pulled from the soil. Features that can be assessed include root flatness, the number of lateral roots, root obliquity, and the degree of tapering. In this experiment the lack of flattening in roots pulled from the compacted soil suggested that poor aeration was a bigger problem for the cotton plants than mechanical impedance. Root deformation was not associated with a large decline in lint yield at this site because the crop was irrigated frequently and did not suffer any nutritional stress, and the relatively steep field slope permitted rapid surface drainage.

Comparison of four methods for liberating various aggregate fractions in Vertosols to study their morphology

Topsoil samples from 3 Vertosols located at Narrabri, Warren, and Dalby were treated with 4 aggregate liberation methods to determine their suitability for analysis by scanning electron microscopy (SEM). In addition to the ability of each method to liberate aggregates for assessment, the potential for consequent morphological deformation was also considered. It was found that the aggregate slaking in water and modified wet sieving methods were suitable for liberating aggregates >100 μm in diameter, whereas the ultrasonic agitation method readily liberated aggregates 250, 100–250, 20–100, 2–20, and <2 μm in diameter.

Soil structural quality: a case study of soil macropore attributes after seedbed preparation with different wheel traffic systems

We report an image analysis study of soil macropore attributes in the top 100 mm of a winter barley (Hordeum vulgaris L.) seedbed in Scotland that had been prepared by chisel-ploughing and secondary tillage of a clay loam soil using either zero, reduced ground pressure, or conventional wheel-traffic systems. Five intact blocks of soil were collected from one plot of each traffic system. After impregnation of vertical faces with a mixture of resin and fluorescent dye, binary images of soil pore space were produced and pore attributes were analysed. The volume of macropores in the soil of a zero traffic system (Z) was greater by a factor of two than that in soil after conventional (C) or reduced ground pressure (R) traffic. The average size of pores in Z was 0.83 mm, compared with 0.59 mm in C and R; the average distance between pores was 16 mm in Z, and 33 mm and 25 mm in C and R, respectively. Although the macropore attributes in the latter two systems were generally similar when averaged over the entire 100 mm depth, differences between these systems were evident in the attribute values in both smoothed profiles and partitioned 20-mm thick zones. The results suggested that for the clay loam soil, at that location, soil structural quality was superior in a zero traffic system to that achieved with either conventional or reduced ground pressure traffic. Although the severity of structural degradation from using conventional traffic was moderated by use of reduced ground pressure equipment, the areal extent of soil damage may be greater with the latter system. Here, image analysis of soil pores gave an insight into the structural state of the soil that would be difficult to achieve by other techniques, though a more complete characterisation would require prior knowledge of the pattern of applied wheel traffic.