A.G. Jongmans

Rock-eating fungi

Weatherable minerals under many European coniferous forests contain a network of numerous tubular pores, formed by organic acids exuded by fungi. We believe that symbiotic mycorrhizal hyphae translocate dissolved minerals from the isolated micropores directly to their host plants, bypassing competition for nutrient uptake by other organisms. The discovery of this pathway challenges current ideas about nutrient uptake from the bulk soil solution and criteria for critical loads of acidic deposition on forests.

Advances in understanding the podzolization process resulting from a multidisciplinary study of three coniferous forest soils in the Nordic Countries

Advances in understanding the podzolisation process resulting from a multidisciplinary study at three coniferous forest soils in the Nordic countries

Soil structure and characteristics of organic matter in two orchards differing in earthworm activity

By consuming plant remains and soil, earthworms incorporate organic matter (OM) into the soil and form biogenic soil structures, which can affect OM dynamics. We carried out a (micro)morphological study of soil structure development and OM distribution in two orchards (45 year) in a Dutch calcareous marine loam: RI − without, and KR + with high earthworm activity, the result of different levels of heavy metal contamination from fungicides. In both soils, sedimentary–stratification was absent to 60 cm depth and equal amounts of biogenic calcite spheroids were counted, suggesting similar earthworm activity in the past. In RI − the current vol.% of worm-worked groundmass in thin sections was 6% in the Ah and 7% in the Bw horizon compared with 51% in the Ah and 16% in the Bw horizon of KR + . Disappearance of earthworms with time in RI − gave rise to a compacted physicogenic soil structure with angular and prismatic aggregates and the absence of earthworm biopores. Due to restricted fragmentation and incorporation of OM fragments in casts, a litter layer formed at the soil surface. OM coatings were present in fissures and root pores of the Ah horizon, indicating the absence of mixing of organic and mineral soil materials. OM fragments were relatively coarse (>50m) and heterogeneously distributed through the Ah groundmass. Stronger decalcification in RI − than in KR + could be ascribed to higher production of organic acids in the litter layer of RI − and the absence of soil homogenisation by earthworms. In KR + earthworm activity was high, which has resulted in a biogenic structure with granular and subangular blocky aggregates and many worm casts and biopores. Particulate OM was relatively fine ( <50m) and encapsulated with clayey material in casts and micro-aggregates. The organic C content was not significantly ( P< 0.05) higher in the Ah horizon of KR + , than in the Ah horizon of RI − (15.7 and 13.7 g kg −1 , respectively). The lower C mineralization rates in KR + below 6 cm depth, however, might be an indication of higher microbial substrate-use efficiency or physical protection of OM against decomposition. The latter explanation would accord with the observed encapsulation of OM in micro-aggregates, and with studies on other management systems that favour biogenic aggregate formation. The quality of the soil macro- and microstructures, degree of soil compaction and decalcification and soil OM dynamics were strongly determined by the occurrence of earthworms in soils.

Chemical, mineralogical and morphological characterization of three podzols developed on glacial deposits in northern Europe.

The chemistry, mineralogy and micromorphology of three soil profiles formed on genetically different Quaternary deposits have been studied in relation to the podzolization process. The soil materials showed quite uniform geochemical composition both within and between the study sites independent of great geographical distance and there is accumulation of sesquioxides in the Bs horizons at all three sites. Mineralogical distributions derived from calculated normative compositions, X-ray diffraction analysis and thin section point counting show similar depth-related trends. The clay fractions at all three sites are dominated by a vermiculitic phase which contains variable degrees of polymeric hydroxy-Al in the interlayer space in most B horizons.

The role of earthworms in the formation of sandy surface soils in a tropical forest in Ivory Coast.

Abstract Soils with relatively sandy topsoils over clayey subsoils are widespread, but their genesis is not always clear. We tested the hypothesis that earthworms stimulate the formation of the sandy surface soils by producing clay-rich worm casts that are susceptible to erosion, in an undisturbed forested watershed in southwestern Ivory Coast. Soils of the watershed were strongly weathered and acidic. Their contents of ironstone gravel and of clay, organic matter and plant nutrients decrease in a downslope direction. Production of worm casts increased in the same direction from 0.1 to 0.2 kg m −2 yr − near the top of the watershed to between 2.3 and 9.6 kg M −2 yr − near the valley bottom, with an areal average of 3.2 kg m −2 yr − . Casts were invariably richer in clay and silt, organic matter and N, P, Ca and Mg than nearby bulk surface soil. Casts were easily disintegrated by rain splash and overland flow and cast material contributed to the 0.12 kg m −2 yr − of highly organic suspended sediment removed by surface water drainage. Selective erosion of worm casts was probably more important than eluviation of clay in removing clay from the surface soils. Increasing production and disintegration of casts with decreasing elevation probably played a major role in lowering contents of clay and nutrients in the surface soils in the lower parts of the area.

Soil formation in a Quaternary terrace sequence of the Allier, Limagne, France. Macro- and micromorphology, particle size distribution, chemistry

Abstract Soil formation in a terrace chronosequence of nine gravelly Quaternary terraces was studied, based on macro- and micromorphological, mineralogical, chemical, and physical characteristics. Based on textural characteristics, the C horizon of the youngest soil appears to be representative for the parent material of lower B and C horizons in the youngest soils, and of all horizons in older soils. The parent materials contain a volcanic and a granitic component. With increasing age of soils, the following stages of soil formation were observed: Holocene soils on lowest terraces show evidence for mixing of sedimentary layers by biological activity, resulting in texturally homogeneous A and B horizons. In the absence of periglacial processes, soil formation in Holocene and in Late Pleistocene terraces took place under continuously well-drained conditions. Late Pleistocene soils on higher terraces show effects of clay illuviation, with prominent weathering features in A horizons. Middle and Early Pleistocene soils on the highest terraces were influenced by periglacial conditions and display effects of various cycles of soil forming processes alternated with periglacial processes, increasing in complexity with age. Weathering of all minerals except quartz, neoformation of clay, and clay illuviation has resulted in distinct differentiation between sandy A and E horizons and a clayey B horizon. Periglacial processes during the Quaternary, weathering, clay formation and clay illuviation have caused a considerable compaction and decreased water permeability. This has resulted in imperfect drainage, now reflected by abundant, locally cemented, iron and manganese oxide segregations in the surface horizon, typical for surface water gley with evidence of ferrolysis. Ferrolysis, the increased weathering of clay under influence of alternating oxidation-reduction in the seasonally waterlogged surface soil, may have further contributed to the marked textural change between A and E versus B horizons. Easily weatherable minerals, observed in strongly leached surface layers of older end-members of the terrace sequence might be attributed to aeolian volcanic inputs. The Holocene and Late Pleistocene soils are intensively used as arable land, as a result of the continuously well-drained conditions. On account of the poor drainage, the Middle and Early Pleistocene soils are used mainly for grassland and forest.

Allophane, imogolite, and gibbsite in coatings in a Costa Rican Andisol

Abstract Neoformation of allophane, imogolite, and gibbsite has been studied extensively in soils in humid climates, but little is known about their micro distribution patterns. such information may provide insight about the conditions at the micro-site scale, responsible for their formation and disappearance. Our study describes amorphous and crystalline coatings in a Melanudand on a 18,000 yr old andesitic lava in Costa Rica. Fine-textured, white to yellow coatings could be observed in the B, C, and R horizon in the field. In thin sections the coatings are translucent and isotropic in plane polarized light (PPL), indicating that they consist of amorphous material. In the B horizon, under crossed polarized light, isotropic coatings show a gradual transition towards crystalline outer margins and spots, while in PPL such transition cannot be observed, suggesting a genetic relationship. Submicroscopical analyses reveal that the amorphous coatings in the R and C horizon consist of allophanic material with a molar Al/Si ratio of 0.9, those in the B horizon consist of allophanic material and imogolite with a molar Al/Si ratio of 1.4. The amorphous coatings resulted from precipitation of Al and Si liberated upon weathering of primary minerals in an initial stage of lava weathering. The crystalline coating parts in the B horizon consist of gibbsite and represent the ultimate stage of mineral neoformation. The different coating composition in the soil horizons is the result of different leaching conditions at a macro and micro scale. Care should be taken to compare results obtained at different sampling scales with different analytical methods.

Genesis of two Planosols in the Massif Central, France

Abstract Two Planosols developed on gravelly Quaternary sediments of the river Allier in the Limagne rift valley. Massif Central, France were studied. Parent material contained in addition to a granitic component large amounts of volcanic particles. Morphological, chemical, mineralogical and physical properties of both profiles were investigated to indicate some of the changes which have taken place during pedogenesis. Both profiles were characterized by pronounced textural contrasts between sandy A and E horizons and clayey B horizons. Soil formation rather than a transient depositional environment is thought to be responsible for this marked textural change. Clear dissolution features of all mineral grains, except quartz, and increasing amounts of volcanic fragments with depth suggested weathering. Increasing ratios of mobile basic cations to TiO 2 with increasing depth corroborated this observation. The presence of non-laminated isotropic and anisotropic limpid clay coatings were also evidence of in-situ mineral weathering. In both profiles kaolinite predominated as clay mineral, and increased towards the surface. Micromorphological observations of microlaminated dusty and impure clay coatings in B horizons of both profiles were clear signs of clay illuviation. Bulk densities were high in lower E horizons and upper B horizons. Field observations and micromorphological data showed clear signs of periglacial features. The combination of pedogenic and periglacial processes has apparently lead to a considerable compaction. Abundant cemented iron and manganese features, predominantly occurring in E horizons suggested surface water gleying. Micromorphological observations of illuviation coatings in B horizons and of fine material in A and E horizons demonstrated grainy aspects suggesting ferrolysis.

Mineral micro- and nano-variability revealed by combined micromorphology and in situ submicroscopy

Abstract A combination of micromorphology and different in situ sub microscopical techniques, performed on thin sections of soil, saprolite, and rock samples, was used to assess possible relationships between micro- and nano-variability and macro- and micro-environmental conditions of mineral transformation during weathering. Four examples, presented in this study illustrate variability in morphology, chemistry and mineralogy of secondary minerals present in pseudomorphs after primary silicate minerals in volcanic soils present in the humid tropics. The study was based on micromorphological characterization of secondary (clay) minerals, with complementary submicroscopical analysis such as scanning electron microscopy with energy dispersive X-ray analysis (SEM–EDXRA), performed on uncovered thin sections, step scan X-ray diffraction (SSXRD) and transmission electron diffraction (TEM–EDS) carried out either on disturbed powder samples or undisturbed microsamples, obtained by micro-drilling in thin sections. These techniques highlight a very complex mineralogy in pseudomorphs after primary minerals, including secondary minerals that generally are assessed to be formed under contrasting physicochemical conditions (gibbsite and 2:1 phyllosilicates in a pseudomorph after plagioclase; halloysite, kaolinite, smectite and aluminum and iron oxi-hydroxides in pseudomorphs after pyroxenes). The study by TEM of undisturbed microfabrics of secondary minerals in a clay pseudomorph after pyroxene revealed typical distribution patterns, with mineralogical compositions varying over some microns. The combination of techniques gave an improved insight on the complexity and variability of the nature composition and distribution of secondary minerals formed during weathering. It indicates the influence of sequential weathering processes on mineral micro- and nano-variability.

Micromorphology and submicroscopy of isotropic and anisotropic Al/Si coatings in a Quaternary Allier terrace, (France)

Abstract Jongmans, A.G, Oort, van F., Buurman, P. and Jaunet, A.M. 1994. Micromorphology and submicroscopy of isotropic and anisotropic Al/Si coatings in a Quaternary Allier terrace, (France). In: A.J. Ringrose-Voase and G.S. Humphreys (Editors), Soil Micromorphology: Studies in Management and Genesis. Proc. IX Int. Working Meeting on Soil Micromorphology, Townsville, Australia, July 1992. Developments in Soil Science 22, Elsevier, Amsterdam, pp. 285–291.