Ap Horizon Research Articles

Estimation of cation exchange capacity and cation saturation of Luvisols developed from loess

The cation exchange capacity and saturation of the sorptive complex with base cations are very important indicators for quality assessment of soils, because they define soil fertility and resistance to chemical degradation. The objective of the following study was to estimate the cation exchange capacity and saturation with exchangeable cations of Luvisols developed from loess, under agricultural use. The study comprised 12 pedons under winter wheat culture, classified into various complexes of soil suitability. Exchangeable cations of alkaline character were assayed with the Pallmann method in 1 mol NH4Cl dm-3 extract with pH 8.2. The content of cations Ca2+, K+ and Na+ was determined with a flame photometer, while that of Mg2+ was measured with the AAS method. In the Ap horizons of the analyzed soils, the quantitative sequence of base cations was most frequently Ca2+>Mg2+>K+>Na+. The total exchange bases (TEB) was favourable in most of the soils (3.8-16.9 cmol(+) kg-1), and the total acidity (TA) was varied (0.53.7 cmol(+) kg-1) but generally low. The cation exchange capacity (CEC) in the Ap, Et, EB, Bt and BC horizons of the soils was assessed as medium or high (5.2-17.9 cmol(+) kg-1). Only the C horizon, containing calcium carbonate, was characterised by very high CEC (76.2 cmol(+) kg-1). The base saturation (BS) was highly favourable in most of the soils (62.9-99.4%) and increased deeper into the pedon. The soils were characterised by generally favourable shares of particular cations: the percentage of Ca2+ was 51.5-95.1%, most often higher than the optimum, while the shares of Mg2+ and K+ were slightly below the optimum. The calculated quantitative ratios between the cations showed very strong variation of values among particular pedons. The content of Mg2+ cations and the values of TEB and CEC in the Ap horizons of soils from the very good wheat complex were lower than in the Ap horizons of soils from the good wheat complex and the deficient wheat complex, whereas the levels of Ca2+, K+, Na+ and H+ as well as BS displayed only minor differences.

Micromorphological analysis on the influence of the soil mineral composition on short-term aggregation in semi-arid Mediterranean soils .

Aggregation in soils is the result of the interaction of the soil organic components and soil minerals. The reactivity of the mineral phase is acknowledged to interfere with aggregates formation and stabilization, but its influence on aggregation in semi-arid Mediterranean soils remains mostly unknown. In this study, we used micromorphological analysis of aggregates formed in a 28-d incubation in two agricultural soils differing only in the composition of the mineral phase in the upper Ap horizon (a carbonate-depleted Palexeralf with 21.5% clay, and a contiguous carbonate-rich Typic Calcixerept with 20.9% clay before decarbonation which was reduced to 10.4% upon decarbonation). The two soils belong to the same agricultural field and have had similar management for decades. Soil samples were completely disaggregated into their fractions < 250 μm, and incubated with fresh organic matter to stimulate re-aggregation. Macroaggregates (> 2 mm) formed during the incubation were separated at days 3, 7, 14, 21 and 28 and used to prepare thin sections. Macroaggregates were more abundant at day 3, and then decreased in number in the two soils, which indicates a dependency between organic matter decomposition and stable macroaggregates formation. They contained a greater proportion of smaller aggregates in the decarbonated soil. Micromorphological analysis revealed significant differences in the fabric and physical characteristics of these macroaggregates, in which bonds among primary particles were observed to be led by clays in the Palexeralf while the coarse fraction appeared embedded in a micromass with crystallitic b-fabric corresponding to carbonates in the Calcixerept. This resulted in a more compact fabric and less porosity in macroaggregates in the Calcixerept. Image analysis of thin sections was used to quantify and characterize the pore system of macroaggregates. Porosity (pores > 20 μm) was more than double (36.9% for 15.6%) within macroaggregates in the decarbonated soil, with more elongated pores. Although in both soils most pores were 20 to 150-μm in equivalent diameter, some porosity > 150 μm was observed only in macroaggregates from the decarbonated soil. These observations allow hypothesizing that the mechanisms responsible for aggregates stabilization and/or formation are different in the two soils, and that they result in different physical characteristics of soil aggregates. The implications of such differences on air and water flow rates within aggregates, and thus on the soil microbial activity and organic matter decomposition, as well as on soil erodibility, need to be studied and accounted for when evaluating the effect of soil management and other practices on soil quality in semi-arid Mediterranean agrosystems.

Profile Distribution of Carbon Fractions Under Long‐term Rice‐wheat and Maize‐wheat Production in Alfisols and Inceptisols of Northwest India

AbstractThe knowledge of profile distribution of soil organic carbon (SOC) in long‐term agricultural systems could help to store atmospheric carbon in the soil. We investigated profile distribution of easily oxidisable Walkley–Black SOC pool (SOCWB) under long‐term rice‐wheat (R‐W) and maize‐wheat (M‐W) cropping systems under soils of different pedogenesis. The soil samples were collected from the characteristic genetic horizons and analysed for carbon fractions. The SOCWB was the highest in soils under R‐W systems in both Alfisols and Inceptisols. The SOCWB stock in the deeper profile horizons under R‐W system was significantly (p < 0·05) higher than that under M‐W system especially in Typic Hapludalfs. Long‐term R‐W system could store on average 3·55 Mg ha−1 more SOCWB than M‐W system in the Ap horizon. The SOCWB stock in the Ap horizon of all pedons was significantly (p < 0·05) higher in Alfisols than that in Inceptisols. About 60–90% of the total profile SOCWB stock was contributed by B‐horizon because of its greater extent. Considering the whole profile, clay was negatively correlated with SOC fractions; however, the SOC fractions were closely related to each other. This study reveals that the distribution of SOCWB is different in long‐term R‐W and M‐W systems not only in surface but also in the deeper horizons and the magnitude of the variation is influenced by the specific pedogenic processes. This indicates the significance of profile SOCWB stock instead of topsoil SOCWB stock in quantifying carbon retention potential of the long‐term management practices. Copyright © 2014 John Wiley & Sons, Ltd.

GEMAS: Spatial distribution of the pH of European agricultural and grazing land soil

During 2008 the GEochemical Mapping of Agricultural Soils (GEMAS) project collected 2108 agricultural (ploughed soil, Ap horizon, 0–20cm) and 2023 grazing land soil samples (Gr, 0–10cm) evenly spread over 33 European countries and covering an area of 5.6million km2. The pH of all samples was determined by one single laboratory applying a 0.01M CaCl2 extraction, and following a strict quality-control procedure. The resulting pH-value distributions for European Ap and Gr soil are both bimodal. Broad acidic modes, with pH between 4 and 6, and sharp alkaline modes, with pH between 7 and 8 due to the Ca2+ buffer system, are clearly separated. The European median pH is 5.8 for the GEMAS Ap soil samples and 5.5 for the GEMAS Gr soil samples. According to the pH distribution maps, Europe is separated into two main zones: northern Europe with generally lower pH values (Ap: 5.2, Gr: 4.8), dominated by acidic soils occurring in Fennoscandia, and southern Europe with higher pH values (Ap: 6.3, Gr: 5.9), dominated by carbonate rich soils. The separation line coincides with the southern border of the sediments of the last glaciation. The dominant factors controlling pH at the European scale are thus geology (crystalline bedrock) in combination with climate (temperature and precipitation). The GEMAS pH maps mainly reflect the natural site conditions on the European scale, whilst anthropogenic impact is hardly detectable. The GEMAS results provide a unique set of homogenous and spatially representative soil pH data for the continent. The data set defines a dependable continental-scale background, and offers the possibility to calibrate studies on more detailed scales.

Selected amino acids uptake by microorganisms in soil of differently managed mountain meadows

This work was aimed at determination of the effect of 13 years abandonment of previously long-term mown mountain meadows on uptake of L-glutamic acid (14CO2H[14CH2]2[NH2]14CO2H) and L-alanine (14CH314CH[NH2]14CO2H) by microbial community of Ap horizon (3–13 cm). The study plots has been located near to the experimental stand “Bílý Kříž“ which is located in the Moravian-Silesian Beskids Mountains (N 49°30’17”, E 18°32’28”), on a slope with an elevation of 825–860 m a. s. l. and southeast orientation, and soil classified as an Oxyaquic Hapludalf. The study was performed to test method for measurement of 14C-labelled amino acids uptake by soil microbial community and to increase knowledge on particular processes of N-transformation in soil of these ecosystems. The results obtained in this work showed that 13 years abandonment of mountain meadow did not significantly (P > 0.05) influence rate of glutamic acid or alanine uptake by soil microbial community. Further research including determination of amino acids use by soil microbial biomass with expression of their partitioning between production of new microbial biomass and energy metabolism is necessary.

Development of a clay-rich interval above a limestone substrate in the Condroz region of southern Belgium

A profile comprising a limestone substrate overlain by a clay-rich interval, which represents a common sequence, was studied with the objective of determining the relationship between substrate and cover. The profile was characterized by various types of mineralogical and chemical analyses, and by a micromorphological study. The mineralogical and chemical data demonstrate that the cover is unrelated to the parent rock, including all horizons below the loess-derived Ap horizon. Thin section observations show that the basal C3 horizon is largely composed of illuvial clay, deposited around claystone fragments, resulting in a fabric that, together with profile position, relates the interval to so-called beta horizons. In higher parts, up to a level recognized as a lithological discontinuity based on mineralogical composition, the profile largely consists of fragments of clay coatings and disintegrated claystone fragments, with an overall upward increase in degree of pedoturbation. The source of the clay is assumed to be Cenozoic deposits that are known to occur in the region. The main conclusion of this study is that clay intervals overlying limestone can have a complex mode of development, to be studied by a combination of methods, and with implications for the valorization of existing soil maps.

Phosphorus fractions in bulk subsoil and its biopore systems

SummaryImproving phosphorus (P) accessibility in subsoils could be a key factor for sustainable crop management. This study aims to explain the quantity of different P fractions in subsoil and its biopore systems, and to test the hypothesis that crops with either fibrous (fescue) or tap‐root systems (lucerne and chicory) leave behind a characteristic P pattern in bulk subsoil, biopore linings and the rhizosphere. The crops were cultivated for up to 3 years in a randomized field experiment on a Haplic Luvisol developed from loess. Aqua regia‐extractable P (referred to as total P) and calcium acetate lactate‐extractable P (PCAL) were assessed at 0–30 (Ap horizon), 30–45 (E/B horizon), 45–75 and 75–105 cm subsoil depths. In addition, sequential P fractionation was performed on different soil compartments between 45 and 75 cm depths. The results showed that total P stocks below the Ap horizon (30–105 cm) amounted to 5.6 t ha−1, which was twice as large as in the Ap, although the Ap contained larger portions of PCAL. Both PCAL and sequential P extractions showed that biopore linings and the rhizosphere at the 45–75 cm depth were enriched, rather than depleted, in P. The content of inorganic P (81–90% of total P) increased in the following order: bulk soil = biopores <2 mm ≤ rhizosphere ≤ biopores >2 mm. Biopores >2 mm and rhizosphere soil were clearly enriched in resin‐ and NaHCO3‐extractable Pi and Po fractions. However, we failed to attribute these P distribution patterns to different crops, suggesting that major properties of biopore P originated from relict biopores, rather than being influenced by recent root systems. The stocks of the sum of these P fractions in the bulk subsoil (182 kg ha−1 at 45–75 cm depth) far exceeded those in the biopores (3.7 kg ha−1 in biopores >2 mm and 0.2 kg ha−1 in biopores <2 mm). Hence, these biopores may form attractive locations for root growth into the subsoil but are unlikely to sustain overall plant nutrition.

Late Pleistocene ‐ Holocene palaeosols in the north of Sonora, Mexico: chronostratigraphy, pedogenesis and implications for environmental history

SummaryRed palaeosols of the late Pleistocene‐early Holocene, both buried and non‐buried, were studied recently in Sonora (NW Mexico) to reconstruct their pedogenesis as well as the palaeoenvironmental conditions. The alluvial palaeosol‐sedimentary sequence of the La Playa archaeological site is a key locality for the buried San Rafael palaeosol, which exhibits a 2Ah‐2Bw‐2BCk‐3Bgk profile and was defined as a Chromic Cambisol. Radiocarbon dates from pedogenic carbonates and charcoal set the soil formation interval between > 18 000 and 4300 calibrated years before present (cal. year BP). Micro‐morphological observations together with profile distribution of clay, carbonates, organic carbon, pedogenic iron oxides and rock magnetic properties indicated a strong eluvial‐illuvial redistribution of carbonates, moderate silicate weathering and gleying in the lower horizon. Although this soil was much more developed than the overlying syn‐sedimentary late Holocene Fluvisols, clay mineral composition and stable carbon isotope signatures of humus and carbonates were similar in both soils. We suggest that pedogenesis of the San Rafael palaeosol took place under a slightly more humid climate and relative geomorphic stability. This agrees with the regional palaeoclimate reconstruction, which indicates a moister climate during the Late Wisconsin glaciation (MIS 2). An abrupt termination of the San Rafael pedogenesis marked by disturbance and aridization features in the Ap horizon of the palaeosol could be linked to a global drought around 4200 years cal. year BP. Surface Chromic Cambisols in northern Sonora show similar pedogenetic characteristics to the buried red palaeosols of La Playa. They appear to be a relict component of the present day soil mantle.

The double mosaic-regeneration of vegetation and soil after clearing, burning, and cultivation: lessons from the Forchtenberg experiment

A multidisciplinary experimental research programme has run since 1997 at an experimental test area on the Hohenlohe plain near Forchtenberg, southwest Germany, where a 3.5 ha area of a mixed Carpinus betulus, Fraxinusexcelsior, Acer pseudoplatanus and Fagus sylvatica forest is being used to research into questions on the early steps of cultural landscape development in Central Europe. The experiments which are being conducted here include forest clearance, burning and cultivation, as well as the recording of the succession stages of vegetation and soil. With respect to vegetation development, the first stage is that of ordinary regrowth, starting with colonisation by grasses and herbs followed by a shrub cover, its topping by pioneer trees or by their re-growth from stumps, leading to a new tree layer. The first stages of this forest regeneration are already visible in the third year after felling, with respect to vegetation as well as soil surface development. The alternative pathway of regeneration of the vegetation is represented as the “ruderal way”, which is characterised by a monotypic colonisation by high forbs such as Eupatorium, Epilobium or mostly Cirsium, which slows the development of a shrub cover. Topsoil and soil surface recovery goes parallel to that of vegetation. A first stage of pellicular soil surfaces is followed by grass felts and later on by leaf overlays which are often mixed with bare crumbly surfaces as signs of rapid turnover. Charcoal may either be displaced by earthworms or concentrated and weathered in situ by the soil microfauna of enchytraeids, mites and collembols. Charcoal also records the earlier cultivation by forming an Ap horizon. The development of ruderal vegetation within the forest environment should be considered when reconstructing the development of cultural landscapes.

Rare earth elements of a 1000-year paddy soil chronosequence: Implications for sediment provenances, parent material uniformity and pedological changes

A series of paddy soil profiles with approximately 50, 300, 700 and 1000years of paddy cultivation history and an uncultivated mud beach profile under nearly identical landscape and climate conditions were studied. The signatures of rare earth elements (REEs) were used to identify sediment provenances and parent material uniformity of the studied profiles and to assess long-term paddy management effects on REE mobilization and fractionation. The distribution patterns of samples on a δEuN–ΣREEs plot indicate that the parent materials of paddy soils and the uncultivated soil mainly originate from Yangtze River sediments. The REE chondrite-normalized curve could be used to adequately evaluate parent material uniformity, thus allowing further studies of soil REE changes along a time sequence of paddy cultivation. To understand anthro-pedogenic effects on REE mobilization and fractionation, the REE concentrations of paddy soils were normalized to those of the uncultivated soil. Paddy management resulted in accumulation of all REEs within the upper 100cm, possibly due to anthropogenic inputs such as irrigation water and phosphate fertilizers. In particular, a distinct positive Ce anomaly was observed. This was likely due to periodic reduction and oxidation processes caused by artificial submergence and drainage. These REE signatures are especially marked in the anthrostagnic epipedon (Ap), as compared with the hydragric horizon (Bg). The positive Ce anomaly increased gradually with increasing paddy cultivation age. This demonstrates the utility of Ce anomaly as a trace of the frequency and intensity of redox conditions. The relative enrichment of all REEs and gradual accumulation with paddy cultivation time in the Ap horizons imply low mobility of REEs in the investigated paddy soils. In conclusion, our study demonstrates the effectiveness of various REE proxies as tracers of sediment provenances and parent material uniformity in present paddy soils. It also reveals the effects of long-term paddy management on REE enrichment and positive Ce anomalies.

The changes of enzymatic activity of soil under eastern galega (Galega orientalis Lam.) after NPKCa fertilization

Changes in the enzymatic activity of soil variably fertilized with NPKCa were investigated in a field experiment carried out in 2005–2010. The study was conducted with a legume plant, i.e. eastern galega (Galega orientalis Lam.). The experiment was completely randomized and carried out in three replications with the following mineral fertilization: control, N, P, K, NPK, NP, NK, PK, NPKCa, PKCa, Ca, NKCa, and NPCa. Mineral fertilization was applied in kg/ha: (N-20, P-50, K-160, Ca-150). The soil samples collected from the Ap horizon (0–30 cm) of the rhizosphere in spring after the 1<sup>st</sup>, 2<sup>nd</sup> and 3<sup>rd</sup> swathing had a pH<sub>KCl</sub> in range from 6.55 to 6.93. The activity of acid phosphatase and alkaline phosphatase was at a low level. The highest activity of urease was recorded in the soil fertilized with NPK, whereas the highest activity of dehydrogenases was in the soil fertilized with PKCa.

Adsorption, degradation and mobility of carbendazim in profiles of Polish mineral soils

Herein, we report the results of a study aimed at estimating the potential of carbendazim for translocation into groundwater and its retention in 27 profiles of the most common Polish arable soils, including Arenosols (AR) formed from sand, Luvisols (LV) formed from loamy sand or loam and Luvisols or Cambisols (LV&CM) formed from loess or loess-like formations. The adsorption of carbendazim was characterized by very high variability because the distribution coefficients were in the range of 0.86–16.71mLg−1 for AR, 1.92–184.41mLg−1 for LV and 0.65–57.11mLg−1 for the LV&CM profiles. The effectiveness of desorption from the soil using 0.01M CaCl2 was in the range of 35.7–87.0%, 9.5–76.7% and 22.5–75.5% for the AR, LV and LV&CM profiles, respectively. The obtained half-lives for the selected soil profiles, which were recalculated at 10kPa and 20°C, were in the range of 13.3–39.7d in the Ap horizon and increased to 368d down the soil profile. A comparison of the horizons from the same depth indicated that the degradation rate was the highest in soils with the highest microbial activity and pH. The simulations using FOCUS PELMO indicated that carbendazim was retained in the Ap horizon, and its concentration in groundwater at a depth of 1m was not expected to exceed the European Union contamination limit. The nonlinear regression modeling studies of the pH-dependent adsorption of this fungicide have shown that it is well described in typical arable soils assuming that the protonated form of carbendazim adsorbs on clay and the neutral form adsorbs onto organic matter. In sandy soils with a low pH and low content of organic matter, the adsorption of carbendazim cations onto the sand should also be incorporated into the model.

Determination of soil properties with visible to near- and mid-infrared spectroscopy: Effects of spectral variable selection

Spectral variable selection is an important step in spectroscopic data analysis, as it tends to parsimonious data representation and can result in multivariate models with greater predictive ability. In this study, we used VIS-NIR (visible to near-infrared) diffuse reflectance and DRIFT (diffuse reflectance infrared Fourier transform in the mid-infrared range, MIR) spectroscopy to determine a series of chemical and biological soil properties. Multivariate calibrations were performed with partial least squares regression (PLSR) using the full absorbance spectra (VIS-NIR: 400–2500nm with 5-nm intervals; MIR: 4000–800cm−1 with 4-cm−1 intervals) and with a combination of PLSR and CARS (competitive adaptive reweighted sampling) to integrate only the most informative key variables. The CARS procedure has as yet not been applied in the field of soil spectroscopy. As set heterogeneity is crucial for an optimal calibration, we tested these approaches to a sample set of 60 agricultural samples covering a broad range of different parent materials, soil textures, organic matter contents and soil pH values. Soil samples were taken from the Ap horizon (0–10cm depth), air-dried and pulverised before the lab spectroscopic measurements were performed. In a cross-validation approach, the CARS–PLSR method was markedly more accurate than full spectrum-PLSR for all investigated soil variables and both spectral regions. With MIR data and CARS–PLSR, excellent results (indicated by a residual prediction deviation (RPD) greater than 3.0) were obtained for organic carbon (OC), nitrogen (N), microbial biomass-C (Cmic) and pH values; for hot water extractable C (Chwe), RPD was 2.60. The accuracies obtained with VIS-NIR data were considerably lower than those with the MIR spectra; best results were retrieved for pH and Cmic (approximately quantitative as indicated by RPD values between 2.0 and 2.5). The information content of the MIR data was substantially different from the VIS-NIR information, as indicated by 2D correlation analysis. We found an overall blurred 2D correlation pattern between both spectral regions with moderate to low correlation coefficients, which suggested that the heterogeneity of the studied soil sample population had led to a very complex blurring of overtones and combination bands in the NIR region.Statistical CARS selections were physically reasonable. MIR key wavenumbers for the studied C fractions were inter alia identified at the bands at 2920cm−1 and 2850cm−1 (both aliphatic CH-groups) and the region between 1740 and 1600cm−1 (CO-groups) and represent hydrophobic and hydrophilic compounds of soil organic matter. Important VIS-NIR wavelengths for assessing C fractions and N were located nearby the prominent water absorption band at 1915nm and the hydroxyl band at 2200nm.The simplicity of the approach, parsimony of the multivariate models, accuracy levels in the cross-validation and physically reasonable selections indicated a successful operation of the CARS procedure. It should be further examined with a larger number of samples using separate calibration and validation sets.

Metabolic fate of the 14C-labeled herbicide clodinafop-propargyl in soil

The metabolic fate of 14C-phenyl-labeled herbicide clodinafop-propargyl (CfP) was studied for 28 days in lab assays using a soil from Germany (Ap horizon, silt loam, and cambisol). Mineralization amounted to 12.40% of applied 14C after 28 days showing a distinct lag phase until day 7 of incubation. Portions of radioactivity extractable by means of 0.01 M CaCl2 solution (bioavailable fraction) decreased rapidly and were 4.41% after 28 days. Even immediately after application, only 57.31% were extracted with the aqueous solvent. Subsequent extraction using accelerated solvent extraction (ASE; acetonitrile/water 4:1, v/v) released 39.91% of applied 14C with day 0 and 26.16% with day 28 of incubation from the samples. Non-extractable portions of radioactivity thus, increased with time amounting to 11.99% (day 0) and 65.00% (day 28). A remarkable increase was observed between 14 and 28 days correlating with the distinct increase of mineralization. No correlation was found throughout incubation with general microbial activity as determined by DMSO reduction. Analysis of the CaCl2 and ASE extracts by radio-TLC, radio-HPLC and GC/MS revealed that CfP was rapidly cleaved to free acid clodinafop (Cf), which was further (bio-) transformed; DT50 values (based on radio-TLC detection of the parent compound) were far below 1 day (CfP) and about 7 days (Cf). TLC analysis pointed to 2-(4-hydroxyphenoxy)-propionic acid as further metabolite. Due to fractionation of non-extractable residues, most of the 14C was associated with fulvic and humic acids, portions in humin fractions and non-humics were moderate and low, respectively. Using a special strategy, which included pre-incubation of the soil with CfP and then mineralization of 14C-CfP as criterion, a microorganism was isolated from the soil examined. The microorganism grew using CfP as sole carbon source with concomitant evolution of 14CO2. The bacterium was characterized by growth on commonly used carbon sources and by 16S rDNA sequence analysis. The sequence exhibited high similarity with that of Rhodococcus wratislaviensis (99.56%; DSM 44107, NCIMB 13082).

Changes in soil total C and N contents at three chronosequences after conversion from plantation pine forest to dairy pasture on a New Zealand Pumice soil

The large amounts of carbon (C) and nitrogen (N) sequestered as organic matter in soils have implications for global and national C and N balances and greenhouse gas emissions. Changes in soil management can affect the amount of C and N stored in soil. We investigated the change in land use from radiata pine plantation to ryegrass–white clover dairy pasture on the total C and N content of Taupo Pumice Soil. Samples were taken at three study sites (Atiamuri, Tokoroa and Wairakei) in North Island, New Zealand. Soils were cored to 60 cm depth and subsampled by soil horizon, and bulk density cores were taken from soil pits. A chronosequence of sites was obtained after conversion from pines to pasture. Long-term pastures (40–80 years) and mature pine plantations were included for further comparison. Regression analyses were completed after logarithmic transformation of the time data. The data were highly variable, but significant (P < 0.05) increases in total C and N were found at the Atiamuri and Wairakei sites. However, there was no significant change in the total C content of the profile at the Tokoroa site. Increases in total C and N were greatest in the Ap horizon and were most rapid 1–5 years after conversion. Overall rates of increase in the first 10 years after conversion were 0.167 kg C m–2 year–1 for total C and 0.032 kg N m–2 year–1 for total N, dropping to 0.027 kg C and 0.005 kg N m–2 year–1 for the 10–50-year period. The change in land use from plantation forest to dairy pasture has resulted in a moderate increase or no change in soil storage of C. Compared with total C, increases in total N storage were proportionately greater in all three examples of this Taupo Pumice Soil.

Application of High Carbon:Nitrogen Material Enhanced the Formation of the Soil A Horizon and Nitrogen Fixation in a Tropical Agricultural Field

It is known that cropping causes soil carbon loss, which is a critical issue, especially in tropical agriculture. Nitrogen input generally increases net primary production but does not increase soil carbon content because nitrogen input enhances soil organic carbon mineralization by microorganisms. A farmer conducted a trial in which he applied material with a high carbon:nitrogen (C:N) ratio without additional nitrogen fertilizer, and achieved a higher productivity than that of conventional farms. Based on his results, we conducted a survey to evaluate the effects of high C:N ratio organic material on the productivity, soil profile, microbial activity, and carbon and nitrogen balance of soil. Results demonstrate that high C:N ratio organic material enhanced the formation of the soil A horizon and increased soil carbon and nitrogen content. Approximately, 15 - 20 t·ha-1·crop-1 of fresh waste mushroom bed was applied to 15 crops over 4.5 years, and the total input of carbon and nitrogen were 5014 and 129 g·m-2, respectively. The soil nitrate nitrogen concentration was the same as that of the neighboring forest soil, which was lower than the standard limit for conventional agriculture; however, the average productivity of crops was approximately four times that of the national average. The soil Ap horizon increased in thickness by 7 cm, and aggregates reached a thickness of 29 cm in 4.5 years. The output/input ratios of total soil nitrogen and carbon were approximately 2.68 - 6.00 and 1.30 - 2.35, respectively, indicating that this method will maintain the carbon and nitrogen balance of the system. The observed soil microbial activity was one order of magnitude higher than that of a fallow field. The results indicate that this agricultural method remediates soil degradation, and improves food production.

Hydrophysical properties of Humic Latosols from Brazil

A b s t r a c t. The hydrophysical properties of the prevalent Humic Latosols (organic matter rich and charcoal stained soils) were related to structural sustainability under loading. Intact cores collected at the Ap, AB, Bw horizons were used for hydrophysical characterization. Precompression stresses at 10 suctions were obtained to estimate the load bearing capacities. We observed the dominance of kaolinite with some occurrences of gibbsite and hydroxy-interlayered vermiculite in the clay mineralogy. The high organic matter content in the Ap horizon favours crumb structure with the structural unit presenting high porosity and water retention. The structure of the AB and Bw horizons was, however, granular with structural units having low porosity. Possible influence of earlier incidences of fire enhanced the organic mat ter and carbon content in the soil reducing down the profile from 42.5 g kg -1 at the Ap to 16.4 g kg

Composition and structure of microaggregates in soils of the Behr hillocks, southern Astrakhan district

Study of the composition, structure and morphology of microaggregates less than 1 mm in size in soils of one of the Behr hillocks revealed a high share of the clay-salt segregations (microaggregates and cutans). It was established that the segregation type depends on the mud content in soil, while the packing of particles, as well as the size and morphology of microaggregates, depend on the content and properties of salts. The clay component in the microaggregates is mainly represented by smectite. Carbonate (calcitic, dolomitic, and ferruginous) clay-salt microaggregates were found in all horizons of the studied soils, except for horizon Ap on the subhillock plain in the former rice paddy. Gypsum clay-salt microaggregates were identified in the salic horizon Bs of soils. The microaggregates in solonchaks were formed with the contribution of Na-Mg-Ca chlorides and sulfates. The formation of clay-salt aggregates promoted high microstructuring of soils and stability of the Behr hillocks under arid climatic conditions.

Chernozem properties of Black Soils in the Baltic region of Germany as revealed by mass-spectrometric fingerprinting of organic matter

Black Soils with dark-coloured, mollic horizons occur in the Baltic region of Germany and their classification as Chernozems was previously discussed. Mollic topsoil horizons are diagnostic for steppe soils. We therefore hypothesized that the molecular characterization of soil organic matter (SOM) by pyrolysis-field ionization-mass spectrometry (Py-FIMS) is suitable to identify similarities between the Black Soils and Chernozems as well as soils from other major soil groups with mollic horizons or otherwise high SOM content. Data were collected from a set of 341 topsoil samples and analysed based on 139 Py-FI mass spectra and thermograms. The OC content in Black Soils reached high values matching those of Haplic Chernozems from Germany and typical steppe climate ecosystems. Arable soil use converted Ah horizons to lighter-coloured Ap horizons that nonetheless had a similar or higher OC content than underlying Ah horizons. Arable soil use led to less stable SOM as indicated by a higher percentage of volatilized organic matter (VM) upon pyrolysis. Furthermore, VM was especially high (21–52%) for redoximorphic soils, whereas it ranged between 5.1 and 15% in the Black Soils, Chernozems and other steppe soils such as Phaeozems or Kastanozems. Assignment of marker signals from Py-FI mass spectra to the compound classes revealed that Black Soils, all Chernozems and other steppe soils had more phenols and N-containing compounds but less sterols and suberin than most of the other soil groups investigated. The percentage of volatilized organic matter (VM) – with low values hinting at SOM stabilization in soil – ranged from 5 to 52%. It was especially high for redoximorphic (21%) and organic soils (52%), whereas it ranged between 5.1 and 15% in the Black Soils, Chernozems and other steppe soils. Principal component analysis unravelled the SOM composition patterns of different soils and showed that the Black Soils clustered together with typical Chernozems, while soils of other units differed. This indicates that sources and especially humification pathways of SOM were different in these soils compared to Black Soils and Chernozems. Notably, this was the case for Colluvic soils (=Colluvic Regosols), redoximorphic soils (e.g. Gleysols, Stagnosols), Luvisols and Phaeozems, although colluviation, influence of ground- or stagnant water, and clay migration were found in several Black Soils as well. Our findings do not support a strong, direct influence of colluviation and perched water on the SOM composition in the mollic horizons of Black Soils. The data also show that the Chernozem-specific SOM formation and clay migration, as in Luvisols and Phaeozems, are temporally discrete processes. The results underline that Chernozem formation in Central Europe is a relic process and is not only due to steppe ecosystem conditions. Rather, it depends on parent substrate properties, especially clay and carbonate content, secondary carbonate input and anthropogenic soil use. These factors preserved or even regraded the relic Chernozems since the Atlantic stage.

The microbial communities and potential greenhouse gas production in boreal acid sulphate, non-acid sulphate, and reedy sulphidic soils

Acid sulphate (AS) soils along the Baltic coasts contain significant amounts of organic carbon and nitrogen in their subsoils. The abundance, composition, and activity of microbial communities throughout the AS soil profile were analysed. The data from a drained AS soil were compared with those from a drained non-AS soil and a pristine wetland soil from the same region. Moreover, the potential production of methane, carbon dioxide, and nitrous oxide from the soils was determined under laboratory conditions. Direct microscopic counting, glucose-induced respiration (GIR), whole cell hybridisation, and extended phospholipid fatty acid (PLFA) analysis confirmed the presence of abundant microbial communities in the topsoil and also in the deepest Cg2 horizon of the AS soil. The patterns of microbial counts, biomass and activity in the profile of the AS soil and partly also in the non-AS soil therefore differed from the general tendency of gradual decreases in soil profiles. High respiration in the deepest Cg2 horizon of the AS soil (5.66μgCg−1h−1, as compared to 2.71μgCg−1h−1 in a top Ap horizon) is unusual but reasonable given the large amount of organic carbon in this horizon. Nitrous oxide production peaked in the BCgc horizon of the AS and in the BC horizon of the non-AS soil, but the peak value was ten-fold higher in the AS soil than in the non-AS soil (82.3 vs. 8.6ngNg−1d−1). The data suggest that boreal AS soils on the Baltic coast contain high microbial abundance and activity. This, together with the abundant carbon and total and mineral nitrogen in the deep layers of AS soils, may result in substantial gas production. Consequently, high GHG emissions could occur, for example, when the generally high water table is lowered because of arable farming.