Time for non-illuvial Bt horizons?

The Bt horizon is the diagnostic horizon of the Luvisolic Order in Canada. According to the Canadian System of Soil Classification (CSSC), the Bt must be formed from clay illuviation through the processes of lessivage (i.e., physical transport of clay). In a study of a Luvisol catena in the central Saskatchewan, we demonstrate that Ae/Bm horizons overlying IIBt horizons are formed in a sandy mantle overlying till (i.e., a lithological discontinuity) and that the sandy mantle contributed negligible amounts of illuvial clay despite the presence of clay skins on ped surfaces in the IIBt horizon. We extended the results of this study to the regional scale by examining sand fractions in 63 pedons of Luvisol-dominated soil associations from soil surveys in the Northern Forest Reserves (between latitudes 53^oN and 55^oN). Of the 63 pedons, 13 had lithological discontinuities identified in their profile description and a further 27 had discontinuities identified through shifts in the sand fractions between horizons. For the profiles with discontinuities, inherited particle size differences are a more likely cause of coarse-over-fine textural contrasts than lessivage. A regional analysis of the distribution of Luvisol-dominated associations showed distinct zonations that account, in part, for the differences in the occurrence of lithological discontinuities. Based on these results, we suggest that the criteria for Bt horizons in the CSSC should be broadened to include non-illuvial coarse-over-fine texture-contrast horizons and that the criteria for the Luvisolic order also be broadened to include these non-illuvial Bt horizons.

Radiocarbon and Stable Carbon Isotopes of Labile and Inert Organic Carbon in the Critical Zone Observatory in Illinois, USA

ABSTRACTWe applied the high temperature pyrolysis-combustion technique to partition the total soil organic carbon (SOC) into labile and inert carbon pools for accelerator mass spectrometry radiocarbon (AMS 14C) dating and stable carbon isotope (δ13C), SOC, and carbonate carbon (CC) content analyses to examine SOC variability at a Critical Zone Observatory site in Illinois, USA. The AMS 14C dates of labile and inert carbon in the top 1.55 m overlap except in the Bt horizon. Below 1.55 m the labile carbon is younger by 8000–14,800 years. The SOC content decreases from 3.61% to 0.12% and CC content increases from 0% to 19.16% at this depth. Results indicate that SOC production exceeds its loss in the weathering zone causing a continuous turnover of both SOC pools. A small amount of modern SOC infiltrates into deeper sediment below 1.55 m, making the labile carbon pool much younger. Their difference of AMS 14C contents, ΔF14C, reveals 3−5% more modern carbon in the labile SOC pools except in the Bt horizon, further quantifying that <3−5% modern carbon with potential pollutants is translocated into the unweathered sediments. The δ13C reveals the sources for SOC cycling dynamics in both carbon pools at this site.

Morphological Analysis of Quartz Grains of Two Horizons in a Ultisol, Paraná – Brazil (Análise morfológica de grãos de quartzo de dois horizontes de Argissolos, Paraná – Brasil)

This research aimed to compare the surface morphology of quartz grains of the E and Bt horizons of an Ultisol of the Aratu stream basin, in the city of Floraí, Paraná. The Ultisol is derived from sandstones of the Caiuá Formation and it is subjected to mesothermal humid subtropical climate. The materials from the E horizon showed abundant porosity compared to the Bt horizon ones, due to the filling of pores by coating of clay and iron oxides. On the surface of the quartz grains of the E horizon, several features were identified such as ";craters";, pyramidal microfeatures, gulfs of dissolution, elongated cavities, and silica reprecipitation, resulting from the chemical change, and fragmented grains resulting from a phenomenon called ";plasma infusion."; In the Bt horizon, nearly all the detrital grains were surrounded by clay and iron oxide. The detrital grains of the Bt horizon were better preserved, showing little corrosion features and rare fragmented grains, compared to the E horizon. These analyzes showed that the water flow accounts for the superficial alteration of detrital quartz grains when they are under the influence of humid subtropical climate. R E S U M OA pesquisa teve como objetivo comparar a morfologia superficial de grãos de quartzo dos horizontes E e Bt de um Argissolo da bacia do córrego Aratu, no município de Floraí, PR. O Argissolo é derivado de arenitos da Formação Caiuá e submetido a clima subtropical úmido mesotérmico. Os materiais do horizonte E apresentam porosidade abundante quando comparados com os do horizonte Bt, em razão do preenchimento dos poros por revestimentos de argila e óxidos de ferro. Foram identificadas na superfície dos grãos de quartzo do horizonte E várias feições tipo “crateras”, microfeições piramidais, golfos de dissolução, cavidades alongadas, reprecipitação de sílica, oriundas da alteração química, e grãos fragmentados devido ao fenômeno denominado “plasma infusion”. No horizonte Bt, praticamente todos os grãos detritais estão envolvidos por argila e óxidos de ferro. Os grãos detritais do horizonte Bt estão mais preservados, exibindo poucas feições de corrosão e raros grãos fragmentados, se comparados com os do horizonte E. Essas análises demonstraram que o fluxo hídrico é o responsável pela alteração superficial dos grãos detritais de quartzo quando sob a influência de clima subtropical úmido. Palavras-chave: Argissolo, morfologia de grãos de quartzo, alteração geoquímica, fluxo hídrico

Wpływ Wapnowania i Nawożenia Mineralnego na Zawartość Rozpuszczalnych Form Pierwiastków Śladowych W Glebie Płowej / The Influence of Liming and Mineral Fertilization on the Content of Trace Elements Soluble Forms in Haplic Luvisols Formed from Loess

The research was carried out on a permanent fertilization field in the area of the Rzeszow Foothills Region, with Haplic Luvisols formed from loess. The following plants were cultivated in a 4-year cropping system: pasture sunflower, winter wheat, potatoes and spring barley. Various mineral fertilizers NPK + Mg constans and various mineral fertilization NPK + Mg Ca constans were applied in the experiment. Liming was applied in the form of CaO (at the dose of 2.86 t Ca × ha.1). The experiment included 14 fertilizer objects, in 4 replications according to the method of random sub-blocks. Analysis of variance (ANOVA) was applied in statistic processing for a double classification: liming (A) and mineral fertilization (B) . independently of liming. As a result of the testing, it was found that liming raised the content of Cr in Ap and Bt horizons. Mineral fertilization raised the content of Co and Cr in Ap and Bt horizons and Cd and Pb in Bt horizon. The combined effect of liming and mineral fertilization decreased the content of Ni and Co in Ap horizon and Cd in Bt horizon and raised the content of Cr in Ap and Bt horizons and Pb in Bt horizon.

Luvisolic soils of Canada: Genesis, distribution, and classification

Lavkulich, L. M. and Arocena, J. M. 2011. Luvisols of Canada: Genesis, distribution, and classification. Can. J. Soil Sci. 91: 781–806. Luvisols link the soil continuum on the Quaternary landscapes. These soils are developed from parent materials rich in Ca and Mg in a relatively humid climate. An acidic eluvial horizon overlying a phyllosilicate-enriched illuvial Bt horizon is the common horizon sequence in Luvisolic soils. Lessivage or the translocation of clays with minimal chemical alteration is the characteristic soil-forming process and results to the diagnostic Bt horizon with well-developed, oriented clay skins or cutans. These soils commonly form intergrades with Chernozems, Podzols and Vertisols. With time, the eluvial horizons experience increased chemical weathering and further release of sequioxides to form Brunisolic and Podzolic sequences within the eluvial Ae in biseqeual soils. Lessivage significantly influences several ecosystem functions of soils. The high amounts of phyllosilicates in the Bt horizon serve as one of the most active sorption sites in soils for metals and organic materials including soil carbon. Sorption of cations takes place through cation exchange reactions and determines the availability of cations to plant roots as well as in the “colloid facilitated transport” of strongly sorbing metals and organic pollutants. Clays in Bt can be restrictive to water and air movement as well as to root growth and distribution. Agricultural and forestry practices such as tillage can compact the structure of Luvisols and may decrease soil productivity.

The Upper Pleistocene loess/palaeosol sequence from Schatthausen in North Baden-Württemberg

The loess/palaeosol sequence from the section at Schatthausen in North Baden-Württemberg gives evidence for a younger Bt horizon superimposing the last interglacial palaeosol. This result requires a more careful investigation of polygenetic superimposing palaeosols to avoid misinterpretation of the chronostratigraphic positions. The humic horizon and the underlying Bt horizon were most likely formed during two soil forming periods, as evidenced by means of palaeopedology, phytoliths and luminescence dating. The lowermost Bt horizon (Bt1) was most likely formed during the Eemian interglacial, marine isotope substage (MIS) 5e. The sediment of the uppermost Bt horizon (Bt2) was deposited about 71.5±7.4 ka ago and subsequently superimposed by soil formation most likely during early MIS 3. The Ah horizon covering the Bt gave infrared optically stimulated luminescence (IRSL) age estimates between 52.5±5.5 ka and 45.4±4.7 ka confirming soil formation during MIS 3. Periods of increased dust accumulation rates can be distinguished for the loess/palaeosol sequence by IRSL age estimates. These are from the youngest to the oldest: The Late Glacial loess (MIS 2) with a weighted mean age of 15.2±0.6 ka (N=7), the Middle Pleniglacial sediments (MIS 3) with a weighted mean age of 48.9±2.5 ka (n=4) and the Lower Pleniglacial/Early Glacial sediments (MIS 4/MIS 5) with a deposition age of 71.5±7.4 ka and older loess deposits. The IRSL age estimates are in excellent agreement with the geological estimates and correlate well with the dust peaks of Greenland Icecore record (GRIP). The loess record from Schatthausen complements the loess/palaeosol sequence from the nearby Nußloch section with the late glacial loess and its intercalcated Cryic Gleysols.

Quantification of soil volumes in the Eg & Bt-horizon of an Albeluvisol using image analysis

In this study, we provide a strategy to quantify the effects on soil evolution of driving forces such as human activities or global change. This strategy was developed for situations in which soil evolution resulted in the formation of a complex juxtaposition of soil volumes with distinct properties including soil colours. It is based on image analysis. Our approach proceeds in two steps: (1) to find the minimum sample size over which the soil anisotropy can be neglected and (2) to define a Representative Elementary Volume (REV) of that sample. This approach was developed on the Eg & Bt horizon of a drained Albeluvisol in which three decimetric soil monoliths were sampled at 60, 110 and 210 cm from a drain. The monoliths were sliced into 1.5-cm horizontal layers. Each slice was photographed and studied by image analysis. At the monolith scale, there was neither lateral nor vertical anisotropy. The sampled monoliths were larger than the REV allowing quantification of the different soil volumes constituting this particular horizon. We quantified significant evolutions of the abundance of the different soil volumes characterized by their colour as a function of the distance to the drain. Such a quantification of the effects on soil evolution of human activities or global change equally applies for Podzols, Calcisols or Gleysols for which pedogenesis also resulted in contrasted soil colour evolutions. Key words: Soil change, pedogenesis quantification, artificial drainage, image analysis, Albeluvisol, representative elementary volume

Micromorphological evidence of pedogenetic pathway of a Podzolic Gray Luvisol (Falmouth series) in Nova Scotia

A catena of Podzolic Gray Luvisols (Falmouth series) – Gleyed Gray Luvisols (Queens series) – Orthic Gleysols (Kingsville series) is commonly found on fine loamy, weakly calcareous parent materials in Nova Scotia, with Podzolic Gray Luvisols occupying the best drained landscape positions. The hypothesis that podzolic B horizons of Podzolic Gray Luvisols were developed on degraded Bt horizons was investigated by micromorphological characterization of one Podzolic Gray Luvisol pedon. Although not visible in field examinations, argillans were common in thin sections of the Bf and Bm horizons. These argillans were not associated with the walls of voids or the surface of grains. Argillans of the Bt horizons, however, were associated with features such as cracks, vughs, and channels. The upper Bt horizon (i.e., Bt1gj) showed signs of degradation. The pale brown matrix color was more like the Bm horizon above than the dark brown Bt2gj horizon below. The strongly acidic nature of the Bt1gj horizon may have triggered degradation. It is concluded that the Bf and Bm horizons were developed on degraded Bt horizons through the translocation of amorphous Fe and Al and organic matter. Key words: Pedogenesis, micromorphology, Luvisols, bisequal soils