Ap Horizon Research Articles

Potentially Toxic Effects of Phosphogypsum on Palexerults in Western Spain

We studied effects of phosphogypsum (PG) rates ranging from 1.4 to 84.2 Mg ha−1 applied to the Ap horizon of a plinthic Palexerult on the ionic composition of the soil solution, as well as their impact on biomass production in wheat [Triticum aestivum (L.), cv. Jabato]. Similar soil samples were treated with highly pure gypsum (G) or the industrial byproduct red gypsum (RG) at rates equivalent to PG applications of 4.2 and 33.7 Mg ha−1 for comparison with the action of PG. All treatments increased the Ca, Mg, K, Na, and SO4 concentrations to the same extent; however, RG at high rates (30.6 Mg ha−1) raised the Na and Mg concentrations more markedly than did the other two amendments. Phosphogypsum provided the greatest increases in F, Al, and Si, the last two as a result of the corrosive effects of F on soil silicates; the increases were all proportional to the applied PG rate, and as a result, the higher PG rates increased the activities of all Al ionic species relative to G, RG, and the control. Application of G and RG at rates equivalent to PG applications of 4.2 and 33.7 Mg ha−1 increased biomass production compared with the control. Phosphogypsum increased biomass production at lower rates (0–16.8 Mg.ha−1), but biomass was virtually zero at rates above 67.3 Mg ha−1 The highest PG rates increased plant Al and F contents, the last reaching toxic levels for cattle.

Study of Immobilized Microbial Composition on the Reclamation Process of Heavy Metal Polluted Soils

ABSTRACTHeavy metal pollutions are in certain cases phytotoxic. Bioremediation can sometimes be realized with the using of microorganisms for “removing” of problematic pollutions from soil and underground water by helping the phytoremediation processes. The purpose ot the study is to determine the influence of biotransformed lignites' derivatives (HA) alone and as an agent for immobilization of micro fungi upon some bioremediation processes in heavy metal polluted soils. The pot vegetative test is realized with Ap horizons of polluted soils from the regions of Lead-Zink Procesing Plant Plovdiv (Alluvial-Meadow, Eutric Fluvisol, FAO) HA are a matrix for immobilization of T.viride and T. harzianum (105CFU/ml solution), at a background treatment with Fe-zeolite. Test plants—garlic and grass mixture. A strong influence of the studied meliorating agents—bioproducts - upon bioremediation processes in polluted soil is observed. A good effect of immobilized micro flora on bioremediation processes is determined. The total content of the accumulated heavy metals from the test culture demonstrates the possibility of using HA as an immobilizing factor for T.viride and T. harzianum during rehabilitation of the productivity of heavy metal polluted soils.

Effect of different agricultural management systems on chemical fertility in cultivated tepetates of the Mexican transvolcanic belt

Volcanic soils in their natural state often require some amelioration to accommodate their use for agriculture. Tepetates are defined as hardened volcanic tuffs derived from geo-pedological processes; they have been partially altered by weathering. Tepetates occupy extensive areas of Mexico's Central Highlands and some of them have been adapted for agricultural use after the mechanical breaking up of this hard material. In their native condition tepetates contain only traces of C, N and available P. So, after their incorporation into agriculture production, the addition of fertilisers becomes necessary to improve soil fertility. In the present work changes in certain chemical and physico-chemical soil properties of cultivated tepetates were studied in the short-term (2002–2005) and medium-term (1986–2005) scales. Experimental plots situated in Tlalpan (State of Tlaxcala) were subjected to the following agricultural management systems: Traditional (Tt), Improved (Ti) and Organic (To). In the short term (4 years), the To management system, in which organic residues and manures were added, led to a decrease in the acidification tendency after cultivation, a recovery of initial exchangeable K + levels, and an increase in soil organic C (SOC), total nitrogen (Nt) and available P (Pa) contents in the Ap horizon. The Ti management, in which crop residues and more chemical fertilisers were added, was especially efficient in increasing the concentration of available P. After 20 years of traditional cultivation, the tepetates showed a decrease in soil pH and exchangeable Mg 2+ and K + values, leading to a decline of the base saturation. These results point to the fragility and low buffer capacity of these systems. In contrast, a tendency of SOC, Nt and Pa accumulation was observed after 20 years of cultivation, influenced by the agricultural management system applied. Tepetates adapted for agricultural use evolved into more fertile substrates over the years of cultivation.

Formation of a cultivated spodosol in east-central Finland

The processes involved in Spodosol (Podzol) formation are still being debated. The pedogenic processes in a Spodosol, 10,700 years-old, at Sotkamo that has been cultivated for about 50 years were studied by characterizing the morphology and analyzing the major chemical properties, texture and mineralogy. Before cultivation, organic acids produced by decomposition of organic matter from pine litter in O and A horizons had weathered primary minerals in A and E horizons releasing Al and Fe. Percolating waters moved the organo-metallic complexes from A and E horizons to Bhsm and Bs horizons where the complexes coated and bridged sand grains eventually forming cemented ortstein. Because of the high biotite content of the parent material, the index of accumulation of Fe and Al in the Bhsm horizon (Al + 0.5 Fe = 4.1%) was the highest reported in Spodosols of Finland. The data support the theory of downward movement of Al and Fe as organo-metallic complexes with formation of some ferrihydrite but little or no formation of imogolite type materials. Little, if any, podzolization has likely occurred since the initiation of cultivation because, after agricultural liming and consequent increase of pH in the Ap horizon, organic compounds are likely to chelate Ca and Mg rather than Al and Fe.;

Impact of varying soil structure on transport processes in different diagnostic horizons of three soil types

When soil structure varies in different soil types and the horizons of these soil types, it has a significant impact on water flow and contaminant transport in soils. This paper focuses on the effect of soil structure variations on the transport of pesticides in the soil above the water table. Transport of a pesticide (chlorotoluron) initially applied on soil columns taken from various horizons of three different soil types (Haplic Luvisol, Greyic Phaeozem and Haplic Cambisol) was studied using two scenarios of ponding infiltration. The highest infiltration rate and pesticide mobility were observed for the Bt 1 horizon of Haplic Luvisol that exhibited a well-developed prismatic structure. The lowest infiltration rate was measured for the Bw horizon of Haplic Cambisol, which had a poorly developed soil structure and a low fraction of large capillary pores and gravitational pores. Water infiltration rates were reduced during the experiments by a soil structure breakdown, swelling of clay and/or air entrapped in soil samples. The largest soil structure breakdown and infiltration decrease was observed for the Ap horizon of Haplic Luvisol due to the low aggregate stability of the initially well-aggregated soil. Single-porosity and dual-permeability (with matrix and macropore domains) flow models in HYDRUS-1D were used to estimate soil hydraulic parameters via numerical inversion using data from the first infiltration experiment. A fraction of the macropore domain in the dual-permeability model was estimated using the micro-morphological images. Final soil hydraulic parameters determined using the single-porosity and dual-permeability models were subsequently used to optimize solute transport parameters. To improve numerical inversion results, the two-site sorption model was also applied. Although structural changes observed during the experiment affected water flow and solute transport, the dual-permeability model together with the two-site sorption model proved to be able to approximate experimental data.

Infiltração da água no solo no sistema pedológico Campus do Arenito, cidade gaúcha, noroeste do estado do Paraná

Considerando a importância do conhecimento do comportamento hídrico das coberturas pedológicas para os estudos de prevenção e contenção dos processos erosivos, o presente trabalho foi realizado em uma vertente com sistema pedológico "Latossolo Vermelho eutrófico/Argissolo Vermelho eutrófico", oriundo do arenito Caiuá, localizado na fazenda experimental da Universidade Estadual de Maringá, município de Cidade Gaúcha, noroeste do Estado do Paraná. Após abordagem morfológica detalhada do sistema pedológico, realizaram-se ensaios de infiltrometria nos principais horizontes diagnósticos e suas respectivas transições em seis perfis de solos dispostos ao longo da vertente. A dinâmica hídrica da cobertura latossólica encontra-se marcada por um comportamento distinto entre a superfície e a subsuperfície. Os horizontes superficiais Ap, AB e, ou, BA exibem ao longo do tempo uma alternância de condições de umidade, ora mais úmidos, ora mais secos, devido à distribuição e intensidade das chuvas. Em profundidade, no horizonte Bw, as condições hídricas dependem da movimentação da água vertical e lateral, não respondendo, portanto, diretamente às variações atmosféricas como na superfície. Na cobertura argissólica, o bloqueio da drenagem vertical ocorre no topo do Bt, gerando acima (horizonte AE) uma zona mais constantemente úmida. De modo geral, os horizontes superficiais dos Argissolos não apresentam as alternâncias de umedecimento e secamento verificadas nos Latossolos; permanecem sempre mais úmidos do que aqueles, em razão dos fluxos hídricos laterais de montante.

Impacts of long‐term waste‐water irrigation on the development of sandy Luvisols: consequences for metal pollutant distributions

SummaryStudies relating macro‐ and microscopic aspects of impacts of long‐term contaminative practices on soils are scarce. We performed such an approach by assessing the fate of metal pollutants in an area close to Paris, where sandy Luvisols were irrigated for 100 years with urban waste water. As a result, these soils display strong accumulation of organic matter, dissolved salts and metal pollutants in surface horizons, but also migration of metals to depth. We examined soil development and metal distribution patterns in two irrigated soils, in comparison with a non‐irrigated reference soil. Soil macromorphological characteristics were studied in the field. Soil micromorphology and micro‐scale metal distributions were both studied in situ in thin sections, the latter by synchrotron X‐ray mapping. Microscopic study focussed on characteristic parts of the Ap and Bt horizons, mainly involved in metal retention. For Ap horizons, both large and diffuse metal concentrations were revealed, mainly associated with organic matter and dissolved components added by irrigation water. For Bt horizons, zinc accumulation was detected on clay‐iron coatings. Our results suggest that with time, a double metal‐filtering capacity has developed in these sandy Luvisols: in the Ap horizon, an anthropogenic filter resulted from input of metal pollutants together with highly reactive organic matter, carbonates and phosphates, thus favouring metal immobilization and limiting migration to depth. In the Bt horizon, the evidence is of a second, natural filter. However, this filtering capacity is endangered by clay destruction due to ferrolysis, as revealed by micromorphology. Ferrolysis, here initiated by intensive irrigation practices, leads to a reduction of the natural filtering potential and an increasing risk of metal transfer towards the groundwater.

Environmental Behaviour of Metolachlor and Diuron in a Tropical Soil in the Central Region of Brazil

The environmental behaviour of metolachlor and diuron was studied in the Central-western region of Brazil, by means of a field study where six experimental plots were installed. The soil was classified as a Latosol, and the soil horizons were characterized. Sorption of metolachlor and diuron was evaluated in laboratory batch experiments. Metolachlor and diuron were applied to the experimental plots on uncultivated soil in October 2003. From this date to March 2004, the following processes were studied: leaching, runoff and dissipation in top soil. Koc of metolachlor varied from 179 to 264 mL g−1 in the soil horizons. Koc of diuron in the Ap horizon was 917 mL g−1, decreasing significantly in the deeper horizons. Field dissipation half-lives of metolachlor and diuron were 18 and 15 days, respectively. In percolated water, metolachlor was detected in concentrations ranging from 0.02 to 2.84 μg L−1. In runoff water and sediment, metolachlor was detected in decreasing concentrations throughout the period of study. Losses of 0.02% and 0.54% of the applied amount by leaching and runoff, respectively, were observed confirming the high mobility of this herbicide in the environment. In percolated water, diuron was detected with low frequency but in relatively high concentrations (up to 6.29 μg L−1). In runoff water and soil, diuron was detected in decreasing concentrations until 70 days after application, totalizing 13.9% during the whole sampling period. These results show the importance of practices to reduce runoff avoiding surface water contamination by these pesticides, particularly diuron.

The Aristarchus Plateau on the Moon: Mineralogical and structural study from integrated Clementine UV–Vis–NIR spectral data

Combining UVVIS and NIR Clementine spectral data, we characterize the mineralogy of the different volcanic and crustal materials occurring on the Aristarchus Plateau and its close vicinity, in order to investigate their stratigraphic relationships and understand the nature of the crust in this region of the Moon. From an iterative linear mixture modeling, we provide a comprehensive description of the distribution and amount of surface mixture of the units, and document the stratigraphic relationships in the region of study. The determination of clear relationships and origin of the different units forming the structure of the Plateau is not obvious as the surface materials (to a depth less than 1 km) represent complex materials from the Imbrium impact event. In the Aristarchus region, we show that the Imbrium ejecta has a norite and anorthosite rich composition, with the presence of a clinopyroxene component in the uppermost layer (AER and NE units in the text). Alternatively, AER may form a rather thick horizon emplaced on an NE-rich unit, or AER and NE form a single thick horizon showing a gradational compositional change from AER to NE, from the south to the north of the Plateau. Due to its size, the Aristarchus crater must have penetrated through the Imbrium ejecta and exposed underlying layers formed by pre-Imbrian ejecta and/or the original crust. The regional crustal unit (AP for “Aristarchus peak” in the text), i.e., the deepest horizon exposed by the Aristarchus crater likely originates from a pluri kilometer depth, and is represented by feldspar-rich materials with clinopyroxene and olivine as mafic components. Other deep crustal units, at a stratigraphic level close to the deepest horizon AP, or intermediate between AP and the uppermost horizon AER, and locally distributed in the Aristarchus crater and its vicinity (Aristarchus A crater, and the scarp forming the southern edge of the Plateau), are represented by pyroxene-bearing anorthosite (SC unit) and olivine-rich (OL unit) composition. Although in low abundance, olivine-rich materials are found to be widespread in this region of the Moon. Volcanic pyroclastic deposits (DMD) are widely exposed on the Plateau, with high abundances and a fairly homogeneous composition. We suggest their emplacement could have possibly lasted up to the Eratosthenian, thus leading to a more important pyroclastic activity in time than previously thought, and a rather voluminous and stable reservoir for their source. Based on their UVVIS and NIR spectral characteristics, SW-type materials characterizing the mare basalts west of the Plateau are not detected as a major component across the Plateau. However, SW-type material is significantly present in the complex ejecta of the Aristarchus crater, probably due to the particular morphology of the target, straddling the edge of the Plateau which rises about 2 km above Oceanus Procellarum. The present study based on the integrated visible–near infrared Clementine dataset paves the way for high spatial resolution surveys based on recent photometric observations (e.g., AMIE/Smart-1) and/or upcoming detailed spectroscopic observations [LISM/Kaguya–Selene; M3 (Moon Mineralogy Mapper)/Chandraayan-1].

Field‐Scale Variation in Microbial Activity and Soil Properties in Relation to Mineralization and Sorption of Pesticides in a Sandy Soil

Pesticides applied to agricultural soils are subject to environmental concerns because leaching to groundwater reservoirs and aquatic habitats may occur. Knowledge of field variation of pesticide-related parameters is required to evaluate the vulnerability of pesticide leaching. The mineralization and sorption of the pesticides glyphosate and metribuzin and the pesticide degradation product triazinamin in a field were measured and compared with the field-scale variation of geochemical and microbiological parameters. We focused on the soil parameters clay and organic carbon (C) content and on soil respiratory and enzymatic processes and microbial biomass. These parameters were measured in soil samples taken at two depths (Ap and Bs horizon) in 51 sampling points from a 4-ha agricultural fine sandy soil field. The results indicated that the spatial variation of the soil parameters, and in particular the content of organic C, had a major influence on the variability of the microbial parameters and on sorption and pesticide mineralization in the soil. For glyphosate, with a co-metabolic pathway for degradation, the mineralization was increased in soils with high microbial activity. The spatial variability, expressed as the CV, was about five times higher in the Bs horizon than in the Ap horizon, and the local-scale variation within 100 m(2) areas were two to three times lower than the field-scale variation within the entire field of about 4 ha.

Spatial Variation in 2‐Methyl‐4‐chlorophenoxyacetic Acid Mineralization and Sorption in a Sandy Soil at Field Level

The phenoxyacetic acid herbicide MCPA (2-methyl-4-chlorophenoxyacetic acid) is frequently detected in groundwater beneath Danish agricultural fields. We investigated spatial variation in microbial MCPA mineralization potential in a flat agricultural field of fine sandy soil (USDA classification: Humic Dystrudept) located on the Yoldia plains of Northern Jutland, Denmark. Samples for determination of MCPA mineralization and sorption were collected from the Ap and Bs horizons at 51 sampling sites located in a 200 x 220 m grid. Spatial variation in sorption was low in both horizons (distribution coefficient, 0.36-4.16 L kg(-1)). Sorption correlated strongly with soil organic carbon content in both horizons (CV, 93 and 83%, respectively) and negatively with soil pH. [Ring-(14)C]-MCPA mineralized readily in the Ap horizon, with 49 to 62% of the (14)C-MCPA being converted to (14)CO(2) during the 67-d incubation period. With the subsoil, mineralization of (14)C-MCPA varied considerably between samples (0.5-72.8%). At neither depth was there correlation between (14)C-MCPA mineralization and sorption, soil pH, organic carbon content, clay content, number of colony-forming units (CFU), pseudomonad CFU, or any of the four microbial activity parameters measured. The presence of microbial genes encoding for the TfdA enzyme was quantified using real-time polymerase chain reaction. No correlation was found between MCPA mineralization potential and the natural background number of tfdA genes present in the soil samples. The degradation kinetics suggests that the high (14)C-MCPA mineralization rate detected in soil samples was linked to growth of the MCPA-degrading soil microbial community.

Agronomic Implications of the Application of Lime plus Gypsum By‐products to a Hyperdistric Acrisol from Western Spain

: A laboratory experiment involving the use of leaching columns reproducing the topmost portion of a Hyperdystric Acrisol (FAO 1998) or plinthic Palexerult (Soil Survey Staff 2003) treated in its Ap horizon with sugar foam wastes and phosphogypsum was conducted. The amendments increased the contents in exchangeable calcium (Ca) of the Ap horizon and, to a lesser extent, also that of the AB horizon. However, the contents in exchangeable magnesium (Mg) and sodium (Na) decreased as much in Ap as they did in AB; by contrast, the potassium (K) content exhibited a less marked decrease. The potassium chloride (KCl)–extractable aluminium (Al) of the Ap horizon was dramatically decreased much more than that of the AB horizon by the amendments. In the soil solution from Ap, the amendments raised the pH and decreased the Al concentration; in that from AB, however, they caused an initial pH decrease, a tendency that reversed as the gypsum was leached and eventually led to the pH exceeding that in the soil solution from control. The first few water extractions exhibited increased Mg concentration. This trend was reversed in the second leaching cycle, where the concentrations of Mg in the amended columns were lower than those in the controls. In the soil solution, the variation of the Ca and sulphate (SO4 2–) concentrations was influenced by the salt‐sorption effect. The total Al content in soil solution from AB increased during the first leaching cycle and then decreased during the second. The amendments decreased the activities of Al3+, AlOH+2, and Al(OH)2 + in the Ap horizon and increased those of Al3+, AlSO4 +, Al(SO4)2 −, and AlF+2 in the first leaching cycle in the AB horizon. The productivity of the Ap horizon after the treatments was assessed using a wheat crop (T. aestivum, var. ‘Jabato’) in a greenhouse.

Effects of polyacrylamide and organic matter on microbes associated to soil aggregation of Norfolk loamy sand

Polyacrylamide (PAM) has been reported to increase aggregation and improve soil physical properties in loamy sand soils, but nothing is known about the effects of PAM on microbes involved in aggregate formation. We studied the effects of PAM (0, 30 and 120 mg kg −1) and organic matter (wheat [ Triticum aestivum] and pecan [ Carya illinoinensis]) incubated in a Norfolk soil (a blend of 90% E horizon and 10% Ap horizon) for 96 days at 10% water content on microorganisms that have the ability to aggregate soil. We used an in vitro soil sedimentation assay to test the aggregative ability of the predominant, heterotrophic bacteria from the culturable portion of microaggregates (0.25–0.05 mm), fatty acid methyl ester (FAME) profiling to identify the isolates, and DNA sequencing to find their position in a phylogeny with known taxa. Among all the identified bacterial species, 19 were soil aggregators. There was a PAM effect across all residue types indicating that the highest proportion of soil aggregating isolates was at 120 mg kg −1 PAM. This suggests that soil conditions created by the addition of 120 mg kg −1 PAM favored the growth of bacteria functioning as soil aggregators. There was evidence of interaction between PAM and residue type. Differences were found in the PAM effect but only when no residue was added. The amount of soil aggregating basidiomycete fungi from the different aggregate size fractions was also determined using an enzyme-linked immunosorbent assay (ELISA). There was a higher amount of soil aggregating basidiomycete fungi in macroaggregates (2.00–1.00 and 1.00–0.50 mm classes) generated from PAM and/or wheat residue amended soil compared to the control soil, but no difference was found in treatments with pecan residue added. This suggests that PAM and PAM with wheat can be utilized as a source of nutrient for the basidiomycetes, but pecan appeared to inhibit their growth. This study is the first to provide evidence that adding PAM to soil favored the growth and survival of specific fungi and bacterial species functioning as soil aggregators in vitro.

Dynamics of Microbial Community in Japanese Andisol of Apple Orchard Production Systems

In this study, two fields of temperate Andisols from high‐input and low‐input (zero‐input) management practices of an apple orchard were selected to assess microbial community dynamics based on environmental variables. Soils from an Ap horizon were sampled in five consecutive months from May to September and assessed for phospholipid fatty acids as a biomarker of soil microbial community, soil hardness, bulk density, porosity, pH, electrical conductivity (EC), organic carbon (C), available nitrogen (N) and phosphorus (P), and exchangeable cations as soil environmental variables. For all sample dates, total phospholipid fatty acids (PLFAs), total bacterial PLFAs, fungal PLFA, mycorrhizal PLFA, PLFA for actinomycetes, and earthworm were higher in low‐input management than high‐input management. Total PLFAs showed a high degree of seasonality, having August maxima and May minima. Significant effect on the relationships among soil environmental variables and microbiological attributes were observed. Soil management practices also showed a remarkable effect on the relationships among microbiological traits, indicating that some mechanism regulated soil microbial dynamics under two soil management practices. Comparatively higher correlations among the microbiological attributes were observed in low‐input management than high‐input management. Irrespective of soil management practices, bacterial and fungal lipid biomarkers were negatively correlated, suggesting that these subsets of fatty acids are contrasting components of the microbial biomass. Bulk density has negative influence on all soil microbial communities except fungi. On the other hand, linoleic acid and organic C were positively correlated, referring to the distribution of soil organic C implying an upper layer of soils. Microbial community composition and structure were greatly affected by sampling date and to a lesser extent by long‐term management practice. In this study, both ecosystems were characterized by a very diverse microbial community.

Soil and crop responses to long-term potato production at a benchmark site in northwestern New Brunswick

Concerns about deteriorating soil quality led to Agriculture and Agri-Food Canada establishing a network of 23 soil quality monitoring benchmark sites with the objective of providing a baseline data set for assessing change in soil quality and biological productivity of representative Canadian farming systems. A site (22-NB) was established in 1990 in northwestern New Brunswick to monitor changes in Podzolic and Brunisolic soils developed on coarse loamy till on a rolling landscape under intensive potato (Solanum tuberosum L.) production [potato-potato-barley (Hordeum vulgare L.) rotation] that was cultivated along the contour with variable grade diversions and a grassed waterway. Soil samples were collected in 1990 and again in 2000. Field saturated hydraulic conductivity (Kfs) at 10–20, 26–36 and 50–60 cm, earthworm counts and crop yield measurements were conducted annually. 137Cs data were collected in 1990 to estimate soil displacement at the site. Runoff and soil loss between May 01 and Nov. 30 were measured annually. The soil conservation system at site 22-NB has resulted in annual runoff and soil loss of only 9 mm and 311 kg ha-1, respectively. Measured values of 137Cs averaged 2114 Bq m-2 (70% of baseline). Changes in the Ap horizon properties between 1990 and 2000 included significant (P < 0.05) increases in available P (+ 86.7 mg kg-1) and K (+ 13.4 mg kg-1) and significant reductions in available Mg (−45.8 mg kg-1) and SOC (−0.51 g kg-1). The Kfs of 10- to 20-cm, 26- to 36-cm and 50- to 60-cm depths were 1.3, 1.0 and 1.0 cm h-1, respectively. Very few earthworms were present (0.05 worms m-2). The upper terrace was consistently the highest yielding in both potato and barley, while the lowest terrace was consistently the lowest yielding in both crops. Crop yields may have been affected by micro-climate and other soil differences as a result of site position.While the system of contour tillage with variable grade diversions and grassed waterway conserved both soil and water, the potato-potato-grain rotation did not maintain SOC levels or sustain earthworm populations. Associated heavy rates of fertilization also lead to increased levels of soil K and P. Key words: Soil quality, soil organic carbon, hydraulic conductivity, earthworms, runoff, water erosion

Dynamics of the dispersity of model soddy-podzolic soils in a long-term lysimetric experiment

Changes in the particle-size composition and specific surface area were considered for soddy-podzolic soils in large lysimeters of the Soil Research Station of Moscow State University, which simulated anthropogenically modified soils with different sequences of genetic horizons in a long-term (1961–2002) experiment. Changes were detected in the degree of dispersion of the soil horizons occurring under conditions inadequate for their genesis: a decrease in the clay content by 7% and in the external specific surface area from 28.9 to 7.4% in the illuvial horizon placed on the surface and the accumulation of colloidal mineral fractions in the Ap horizon buried at a depth of 80–100 cm. The degree of change depended on the occurrence depth of the buried horizons and increased with approaching the surface. The changes in the dispersity of the model soddypodzolic soils in the lysimetric experiment were primarily due to the translocation of the fine fractions with vertical water flows. The long-term experiment carried out under completely controlled conditions showed that, at the initial functioning stages of the soils with anthropogenically modified profiles, this process was well detectable and significant for the monitoring studies.

Thermal diffusivity and temperature regime of soils in large lysimeters of the experimental soil station of Moscow State University

The thermal diffusivity of the upper horizons of model soddy-podzolic soils in the lysimeters depends on their water contents and varies within 2.1-4.32 × 10 -7 m 2 /s in the Ap horizon, 1.59-3.99 × 10 -7 m 2 /s in the B1 horizon, 1.28-3.74 × 10 -7 m 2 /s in the plowed B2 horizon, and 1.12-4.10 × 10 -7 m 2 /s in the B2 horizon. The dependence of the thermal diffusivity on the soil water content is described by an inverted parabolic curve for the Ap horizon, an S-shaped curve for the B1 and B2 horizons, and by a curve of transitional type for the plowed B2 horizon. The temperature regimes of model soils with different morphologies of the profile do not differ much and are close to the soil temperature regime under natural conditions on the plots of the weather station of Moscow State University.

Agronomic Implications of Converter Basic Slag as a Magnesium Source on Acid Soils

The feasibility of using converter basic slag (CBS) as a source of Mg for gypsum‐amended acidic soils was studied in a Plinthic Palexerult from western Spain. An experimental farm was established and the Ap horizon of the soil was amended with limestone (L), phosphogypsum (PG), or red gypsum (RG) to alleviate Al toxicity. The PG and RG were supplied at 8.0 and 8.8 Mg ha−1, respectively. In addition, the gypsum‐amended plots received either CBS at 0.9 Mg ha−1 or limestone at 1.1 Mg ha−1 We studied the effects of the treatments on the exchange complex, soil solution, and the biomass production of ‘Jabato’ wheat (Triticum aestivum L.) under field and greenhouse conditions. The CBS proved highly effective in replenishing Mg lost from the soil through application of gypsum amendments. In the field experiment, only the RG + CBS treatment resulted in a statistically significant increase of biomass production relative to the control. In the greenhouse experiment, all treatments resulted in significantly increased production relative to the control, the largest (26 times) by RG + CBS. The PG + CBS and RG + CBS treatments resulted in significantly increased production relative to PG + L and RG + L, which testifies to the favorable effect of the Mg supplied by CBS. Also, the treatments including RG resulted in significantly increased production with respect to those including PG; the increased productivity is tentatively ascribed to a potential toxic effect of Al–F ion pairs, which were more abundant in the soil solution of PG‐treated soil.

The effect of afforestation with Scots pine (Pinus silvestris L.) of sandy post-arable soils on their selected properties. II. Reaction, carbon, nitrogen and phosphorus

Despite the extensive literature on the effect on soil properties of afforestation of former arable land, we still lack full understanding of whether the changes proceed in the same direction and at the same rate, and of how long is required to achieve a state of soil equilibrium typical of a natural forest ecosystem. Therefore, as part of a study comparing post-arable sandy soils (Dystric Arenosols) afforested with Scots pine (Pinus silvestris L.) with arable soils and soils of continuous coniferous forests, the range and direction of changes in pH, organic carbon (Corg), total nitrogen (Ntot), ammonium (N-NH4) and nitrates (N-NO3) in soil solution, total (Ptot) and available (Pav) phosphorus were determined. The studies were carried out in south-east Poland (51°30′-51°37′N, 22°20′-22°35′E). Ten paired sites of afforested soils (five with 14- to 17-year-old stands and five with 32- to 36-year-old stands) with adjacent cultivated fields, and five sites of continuous forest with present stands of ca. 130–150 years old were selected. Soil samples were taken from the whole thickness of master horizons and, in the case of the A horizon of the afforested soils, from three layers: 0–5 (A0–5), 5–10 (A5–10) and 10–20 cm (A10–20). The cultivated soils in the Ap horizon showed higher pH (by ca. 1.0 unit), lower Corg and C:N, similar Ntot, lower N-NH4, higher N-NO3, higher Ptot and Pav contents compared with the Ah horizon of continuous forest soils. The results indicated decreased soil pH in the former plough layer of the afforested soils, with the greatest decrease observed in the 0–5 cm layer. In these soils, the Corg content was considerably higher in the A0–5 layer, but lower in the two deeper layers and in the whole A horizon (0–20 cm) compared with the Ap horizon of the arable soils. The results indicate that the Corg content, after an initial phase of decline, again achieved a level characteristic of arable soils. The Ntot content in all layers of the A horizon of the afforested soils was lower than in the Ap horizon of the arable soils, and showed a reduction with stand age, especially in deeper layers. The C:N ratios in the mineral topsoil increased with stand age. N-NH4 content increased and N-NO3 decreased after afforestation. The Ptot and Pav contents in all layers and in the whole A horizon of the afforested soils, on stands of both ages, was lower than in the Ap of the cultivated soils. From the results, it could be concluded that, after more than 30 years of tree growth, the soils of the A horizon were still more similar to arable than to continuous forest soils with respect to Corg, Ptot and Pav. With respect to pH, N-NH4 and N-NO3, especially in the 0–5 cm layer, they were more similar to continuous forest soils than to cultivated soils, but with respect to Ntot and C:N ratio they were somewhere in between.

Stabilization mechanisms of organic matter in four temperate soils: Development and application of a conceptual model

AbstractBased on recent findings in the literature, we developed a process‐oriented conceptual model that integrates all three process groups of organic matter (OM) stabilization in soils namely (1) selective preservation of recalcitrant compounds, (2) spatial inaccessibility to decomposer organisms, and (3) interactions of OM with minerals and metal ions. The model concept relates the diverse stabilization mechanisms to active, intermediate, and passive pools. The formation of the passive pool is regarded as hierarchical structured co‐action of various processes that are active under specific pedogenetic conditions.To evaluate the model, we used data of pool sizes and turnover times of soil OM fractions from horizons of two acid forest and two agricultural soils. Selective preservation of recalcitrant compounds is relevant in the active pool and particularly in soil horizons with high C contents. Biogenic aggregation preserves OM in the intermediate pool and is limited to topsoil horizons. Spatial inaccessibility due to the occlusion of OM in clay microstructures and due to the formation of hydrophobic surfaces stabilizes OM in the passive pool. If present, charcoal contributes to the passive pool mainly in topsoil horizons. The importance of organo‐mineral interactions for OM stabilization in the passive pool is well‐known and increases with soil depth. Hydrophobicity is particularly relevant in acid soils and in soils with considerable inputs of charcoal. We conclude that the stabilization potentials of soils are site‐ and horizon‐specific. Furthermore, management affects key stabilization mechanisms. Tillage increases the importance of organo‐mineral interactions for OM stabilization, and in Ap horizons with high microbial activity and C turnover, organo‐mineral interactions can contribute to OM stabilization in the intermediate pool. The application of our model showed that we need a better understanding of processes causing spatial inaccessibility of OM to decomposers in the passive pool.