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1.
The organic matter (OM) in biopore walls and aggregate coatings may be important for sorption of reactive solutes and water as well as for solute mass exchange between the soil matrix and the preferential flow (PF) domains in structured soil. Structural surfaces are coated by illuvial clay‐organic material and by OM of different origin, e.g., earthworm casts and root residues. The objectives were to verify the effect of OM on wettability and infiltration of intact structural surfaces in clay‐illuvial horizons (Bt) of Luvisols and to investigate the relevance of the mm‐scale distribution of OM composition on the water and solute transfer. Intact aggregate surfaces and biopore walls were prepared from Bt horizons of Luvisols developed from Loess and glacial till. The mm‐scale spatial distribution of OM composition was scanned using diffuse reflectance infrared Fourier transform (DRIFT) spectroscopy. The ratio between alkyl and carboxyl functional groups in OM was used as potential wettability index (PWI) of the OM. The infiltration dynamics of water and ethanol droplets were determined measuring contact angles (CA) and water drop penetration times (WDPT). At intact surfaces of earthworm burrows and coated cracks of the Loess‐Bt, the potential wettability of the OM was significantly reduced compared to the uncoated matrix. These data corresponded to increased WDPT, indicating a mm‐scaled sub‐critical water repellency. The relation was highly linear for earthworm burrows and crack coatings from the Loess‐Bt with WDPT > 2.5 s. Other surfaces of the Loess‐Bt and most surfaces of the till‐derived Bt were not found to be repellent. At these surfaces, no relations between the potential wettability of the OM and the actual wettability of the surface were found. The results suggest that water absorption at intact surface structures, i.e., mass exchange between PF paths and soil matrix, can be locally affected by a mm‐scale OM distribution if OM is of increased content and is enriched in alkyl functional groups. For such surfaces, the relation between potential and actual wettability provides the possibility to evaluate the mm‐scale spatial distribution of wettability and sorption and mass exchange from DRIFT spectroscopic scanning.  相似文献   

2.
In the clay‐illuvial horizons (Bt) of Luvisols, surfaces of biopores and aggregates can be enriched in clay and organic matter (OM), relative to the bulk of the soil matrix. The OM composition of these coatings determines their bio‐physico‐chemical properties and is relevant for transport and transformation processes but is largely unknown at the molecular scale. The objective of this study was to improve the interpretation of spectra from Fourier transform infrared spectroscopy in diffuse reflectance mode (DRIFT) by using thermograms and released ion intensities obtained with pyrolysis‐field ionization mass spectrometry (Py‐FIMS) for a more detailed analysis of the mm‐scale spatial distribution of OM components at intact structural surfaces. Samples were separated from earthworm burrow walls, crack coatings, uncoated cracks, root channels, and pinhole fillings of the Bt‐horizons of Luvisols. The information from Py‐FI mass spectra enabled the assignment of OM functional groups also from spectral regions of overlapping DRIFT signal intensities to specific OM compound classes. In particular, bands from C=O and C=C bonds in the infrared range of wave numbers between 1,641 and 1,605 cm?1 were related to heterocyclic N‐compounds, benzonitrile, and naphthalene. The OM at earthworm burrow walls was composed of chemically labile aliphatic C‐rich and rather stable lignin and alkylaromatic compounds whereas the OM of thick crack coatings and pinholes was dominated by heterocyclic N and nitriles and high‐molecular compounds, likely originating from combustion residues. In combination with Py‐FIMS, DRIFT applications to intact samples seem promising for generating a more detailed mm‐scale spatial distribution of OM‐related sorption and wettability properties of crack and biopore surfaces that may serve as preferential flow paths in structured soils.  相似文献   

3.
The surfaces of macropores or aggregates can act as hot spots for biogeochemical processes and solute transport during preferential flow. For the characterization of organic matter (OM) at macropore surfaces non‐destructive methods have been applied such as diffuse reflectance infrared Fourier transform spectroscopy (DRIFT). However, effects of organic components on DRIFT signal intensities are often difficult to distinguish from those of mineral components. Here, DRIFT spectra from intact earthworm burrow walls and coated cracks were re‐evaluated to improve the interpretation of C–H and C=O bands. We compared DRIFT and transmission Fourier transform infrared (FTIR) spectra of entire samples that were from the same pedogenetic soil horizon (Bt) but different in mineral composition and texture (i.e., glacial till vs. loess). Spectra of incinerated samples were subtracted from the original spectra. Transmission FTIR and DRIFT spectra were almost identical for entire soil samples. However, the DRIFT spectra were affected by the bulk mode bands (i.e., wavenumbers 2000 to 1700 cm?1). These bands affected spectral resolution and reproducibility. The ratios between C–H and C=O band intensities as indicator for OM quality obtained with DRIFT were smaller than those obtained from transmission FTIR. The results demonstrated that DRIFT and transmission FTIR data required separate interpretations. DRIFT spectroscopy as a non‐destructive method for analyzing OM composition at intact surfaces in structured soils could be calibrated with information obtained with the more detailed transmission FTIR and complementary methods. Spectral subtraction procedure was found useful to reduce effects of mineral absorption bands. The improved DRIFT data may be related to other soil properties (e.g., cation exchange capacity) of hot spots in structured soils.  相似文献   

4.
In structured soils, water and reactive solutes can preferentially move through larger inter‐aggregate pores, cracks, and biopores. The surface roughness of such macropores is crucial for describing microbial habitats and the exchange of water and solutes between macropores and the soil matrix together with other properties. The objective of this study was to compare the roughness of intact structural surfaces from the Bt‐horizons of five Luvisols developed on loess and glacial till and to test the applicability of confocal laser scanning microscopy. Samples of 5 to 10 cm edge length with intact structural surfaces including cracks with and without clay‐organic coatings, earthworm burrow walls, and root channels were prepared manually. The surface roughness of these structures was determined with a confocal laser scanning microscope of the type Keyence VK‐X100K. The root‐mean‐squared roughness (Rq) the curvature (Rcu) and the ratio between surface area and base area (RA) were calculated from selected surface regions of interest of 0.342 mm2 with an elevation resolution of 0.02 µm. The roughness was smaller for coated as compared to uncoated cracks and earthworm burrows of the Bt‐horizons. This reduction of roughness by the illuviation of clayey material was similar for the structural surfaces of the coarser textured till‐Bt and the finer‐textured loess‐Bt. This similarity suggested a dominant effect of pedogenesis and a minor effect of the parent material on the roughness levels of structural surfaces in the Bt‐horizons. An expected “smoothing” effect of burrow wall surfaces by earthworm activity was not reflected in the roughness values compared to those of uncoated cracks at the chosen spatial scale. However, for root channel walls from one loess‐Bt, the roughness was reduced as compared to that of other structures. These results suggest that the surface roughness of the structural surface types should separately be considered when describing preferential flow and macropore‐matrix exchange or analysing root growth, microbial habitats, and colloidal transport in structured soils. The confocal laser scanning microscopy technique was found useful for characterizing the roughness of intact structural surfaces.  相似文献   

5.
In some soils, aggregate coatings and walls of biopores differ in the content of clay and organic carbon from that of the aggregate interiors or the soil matrix. The composition of the organic matter on aggregates and on the surfaces of biopores is largely unknown. We have compared the composition of organic matter between inner and outer parts of aggregates and between biopore walls and the soil matrix in a loamy arable soil and a sandy forest one. Hot‐water‐ and sodium‐pyrophosphate‐extractable organic matter was analysed by Fourier transform infrared (FT‐IR) spectroscopy. For the sandy forest soil, the FT‐IR spectra showed that organic matter from the walls of root channels contains fewer functional groups with absorption bands at 1740–1710 cm?1 and 1640–1600 cm?1 than that from burrow fillings. For the arable soil, the content of these functional groups in hot‐water‐soluble organic matter from the coatings is less than in that from the interiors in the topsoil, and the reverse is so in the subsoil, probably because water‐soluble organic matter containing these functional groups has moved from topsoil to subsoil. The results indicate that root channels in the forest soil have more reactive zones in an otherwise relatively inert sandy matrix, whereas aggregate coatings in the arable subsoil have a greater cation exchange capacity and a greater sorption potential for hydrophobic substances than the aggregate interiors.  相似文献   

6.
Improving 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.  相似文献   

7.
Short‐rotation forestry (SRF) on arable soils has high potentials for biomass production and leads to long‐term no‐tillage management. In the present study, the vertical distributions of soil chemical and microbial properties after 15 y of SRF with willows and poplar (Salix and Populus spp.) in 3‐ and 6‐year rotations on an arable soil were measured and compared to a pertinent tilled arable site. Two transects at different positions in the relief (upper and lower slope; transect 1 and 2) were investigated. Short‐rotation forestry caused significant changes in the vertical distribution of all investigated soil properties (organic and microbial C, total and microbial N, soil enzyme activities), however, the dimension and location (horizons) of significant effects varied. The rotation periods affected the vertical distribution of the soil properties within the SRF significantly. In transect 1, SRF had higher organic‐C concentrations in the subsoil (Bv horizon), whereas in transect 2, the organic‐C concentrations were increased predominantly in the topsoil (Ah horizon). Sufficient plant supply of P and K in combination with decreased concentrations of these elements in the subsoil under SRF pointed to an effective nutrient mobilization and transfer from the deeper soil horizons even in the long term. In transect 1, the microbial‐C concentrations were higher in the B and C horizons and in transect 2 in the A horizons under SRF than under arable use. The activities of β‐glucosidases and acid phosphatases in the soil were predominantly lower under SRF than under arable use in the topsoil and subsoil. We conclude, that long‐term SRF on arable sites can contribute to increased C sequestration and changes in the vertical distribution of soil microbial biomass and soil enzyme activities in the topsoil and also in the subsoil.  相似文献   

8.
In agricultural headlands, rooting and yield of crops may be limited because of soil‐structure changes as a consequence of multiple passes of turning machinery. We hypothesized that perennial forage crops can substantially alter soil structure in agricultural headlands. On one experimental field and two commercial farms on Haplic Luvisols from respectively loess and sandy loess in the Lower Rhine Bay (Germany), we investigated how 4 y of continuously grown grass/clover or alfalfa affected soil structure and the performance of subsequent spring wheat. Compared with a crop rotation with annual plowing to 30 cm soil depth, perennial forage crops led to increased soil C content (+1.3% to +22.8%) and N content (+4.2% to +15.1%), higher densities of medium and coarse biopores at a depth of 35 cm, more large water‐stable soil macroaggregates, higher biomass and abundance of anecic earthworms, and higher grain yield and grain protein content of spring wheat grown as the following crop. Root‐length density of spring wheat in the subsoil was not affected by the preceding perennial fodder crops in two of the three field trials. We concluded that besides increasing N input to the soil, perennial cropping of grass/clover or alfalfa has effects on soil structure that may substantially reduce yield losses in agricultural headlands.  相似文献   

9.
The potassium (K) content of soils developed from Pleistocene calcareous till, glacial sand and loess in NW Germany was investigated in order to characterize stores of K in feldspars (Kfeldspar) and mica/illite (Kmica/illite) as well as changes as a function of soil depth. From each horizon, up to seven sand, six silt and three clay fractions were separated. Kfeldspar and Kmica/illite were quantified by means of chemical composition and estimation by IR‐spectroscopy. On account of distinct differences in mineralogical composition between different particle size fractions, K‐content of the bulk soil < 2000 μm and the proportion of Kmica/illite and Kfeldspar are clearly related to grain size distribution of the sample. Generally, the K‐content of particle size fractions of a soil derived from calcareous till is significantly higher than that of a soil from glacial sands. Kmica/illite of clay and silt fractions increases with depth, reflecting greater mica/illite weathering at the soil surface, whereas Kfeldspar shows no noticeable change. Illite accumulates by lessivage in Bt horizons. On a whole‐soil basis, the Bt horizons of Luvisols derived from loess and calcareous till contain more Kmica/illite than either the A or the C horizons. By comparing the K‐content in the different particle size fractions with soil depth, the highest rate of change is found for soils derived from glacial sand. Gains in K in the silt fractions of soils from calcareous till and glacial sand result from weathering of feldspar sand grains. Additionally, decomposition of feldspar‐containing rock fragments of gravel size, and aeolian sedimentation, may also have contributed to these gains.  相似文献   

10.
Land use and mineral characteristics affect the ability of surface as well as subsurface soils to sequester organic carbon and their contribution to mitigation of the greenhouse effect. There is less information about the effects of land use and soil properties on the amount and composition of organic matter (OM) for subsurface soils as compared with surface soils. Here we aimed to analyse the long‐term (≥ 100 years) impact of arable and forest land use and soil mineral characteristics on subsurface soil organic carbon (SOC) contents, as well as on amount and composition of OM sequentially separated by Na pyrophosphate solution (OM(PY)) from subsurface soil samples. Seven soils with different mineral characteristics (Albic and Haplic Luvisol, Colluvic and Haplic Regosol, Haplic and Vertic Cambisol, Haplic Stagnosol) were selected from within Germany. Soil samples were taken from subsurface horizons of forest and adjacent arable sites continuously used for >100 years. The OM(PY) fractions were analysed for their OC content (OCPY) and characterized by Fourier transform infrared spectroscopy. Multiple regression analyses for the arable subsurface soils indicated significant positive relationships between the SOC contents and combined effects of the (i) exchangeable Ca (Caex) and oxalate‐soluble Fe (Feox) and (ii) the Caex and Alox contents. For these soils the increase in OC (OCPY multiplied by the relative C=O content of OM(PY)) and increasing contents of Caex indicated that OM(PY) mainly interacts with Ca2+. For the forest subsurface soils (pH < 5), the OCPY contents were related to the contents of Na‐pyrophosphate‐soluble Fe and Al. The long‐term arable and forest land use seems to result in different OM(PY)‐mineral interactions in subsurface soils. On the basis of this, we hypothesize that a long‐term land‐use change from arable to forest may lead to a shift from mainly OM(PY)‐Ca2+ to mainly OM(PY)‐Fe3+ and ‐Al3+ interactions if the pH of subsurface soils significantly decreases to <5.  相似文献   

11.
Formation of poorly crystallized weathering products in strongly to extremely acid forest soils Poorly crystallized weathering products, formed as a consequence of wide-spread extrem acidification and silicate weathering in forest soils, were examined using X-ray diffraction (XRD) and fluorescence (XRF), scanning electron microscopy (SEM, EDXRA) and chemical analyses. The investigations were carried out on five extremely acid forest soils (different Luvisols, a Gleyic Luvisol and a Luvic Podzol) derived from different parent materials (loess, sand loess, glacial sands/loam) in Northrhine Westfalia and Schleswig-Holstein. The results reveal an intense destruction of clay minerals and other silicates in the extremely acid topsoils leading to an accumulation of poorly crystallized to amorphous compounds. These weathering products occur predominantly as silicic coatings on the surface of soil aggregates or as small spherical precipitates on mineral surfaces. Besides Si they contain small amounts of Al and Fe.  相似文献   

12.
Surface and buried Andosols and buried Luvisols of the Nevado de Toluca Late Quaternary tephra-paleosol sequence (Central Mexico) were studied to show whether these soils present an evolutionary sequence and to determine the pedogenic mechanisms and environmental factors involved in the evolutionary process. Micromorphological observations and mineralogical composition of fine sand and clay fractions were used to detect type and succession of soil-forming process. Some of the buried Andosols, defined as “intergrade” Andosols, have a predominantly blocky structure, humus-depleted areas, redoximorphic features and thin clay coatings in Ah horizons. Clay fractions of buried Andosols contain halloysite besides amorphous components, whereas in modern Andosols, allophane is dominant. Luvisols have micro-areas with granular structure and abundant phytoliths in the groundmass of Bt horizons assumed to be the relict Andosol features. Luvisol clay fractions are dominated by halloysite and kaolinite. Primary minerals show micromorphological weathering features in all studied soils being stronger in Luvisols; however, even in Luvisols, sand fractions consist mostly of unstable volcanic silicates. We hypothesise that the studied profiles form an evolutionary sequence: Andosols–“intergrade” Andosols–Luvisols; the soil transformation is supposed to be linked to progressive crystallisation of 1:1 clay minerals. Comparing the Nevado de Toluca paleosol properties with the existing data on volcanic soil climo- and chronesequences and assessing the regional paleopedological and lacustrine records of Quaternary paleoclimates, we concluded that wet/dry climatic oscillations took place during the formation of the studied paleosols. Rapid crystallisation of 1:1 minerals occurred during dry phases, which speeded up the Andosol to Luvisol transformation and made it independent from the primary mineral weathering status. The Andosol to Luvisol transformation accelerated by climatic fluctuations is thought to be a common soil evolutionary pathway in the subtropical and tropical regions of recent volcanism, which suffered contrasting precipitation oscillations in the Quaternary.  相似文献   

13.
Both the ion accumulation on cation exchange resin and the transformation of test vermiculite in situ have been used to identify current processes in acid forest soils. We used such test materials to study weathering in a toposequence Dystric Luvisol–Spodo‐Dystric Cambisol on loess under deciduous forest in Belgium. The resin and a trioctahedral vermiculite were inserted for 2 years in the major horizons, down to a depth of 60 cm. The cation accumulation on the resin revealed that four main acid‐consuming systems are currently active in the toposequence. With decreasing acid neutralizing capacity, these systems are in the Luvisols: (i) the pool of exchangeable bases, (ii) the Al‐bearing minerals controlling the Al concentration in the liquid phase; and in the podzolized Cambisols: (iii) the less weatherable K‐bearing minerals, (iv) the Mg‐bearing phyllosilicates made free of Al interlayers in complexing conditions. The loss of cation exchange capacity in the test vermiculite is related to Al interlayering. However, this process masks a significant interlayer accumulation of magnesium, which is generated by the weathering of the test mineral itself. The largest interlayer accumulation of Mg occurs in the podzolized Cambisol, suggesting more intense weathering of the test vermiculite in this soil.  相似文献   

14.
The protective impact of aggregation on microbial degradation through separation has been described frequently, especially for biotically formed aggregates. However, to date little information exists on the effects of organic‐matter (OM) quantity and OM quality on physical protection, i.e., reduced degradability by microorganisms caused by physical factors. In the present paper, we hypothesize that soil wettability, which is significantly influenced by OM, may act as a key factor for OM stabilization as it controls the microbial accessibility for water, nutrients, and oxygen in three‐phase systems like soil. Based on this hypothesis, the first objective is to evaluate new findings on the organization of organo‐mineral complexes at the nanoscale as one of the processes creating water‐repellent coatings on mineral surfaces. The second objective is to quantify the degree of alteration of coated surfaces with regard to water repellence. We introduce a recently developed trial that combines FTIR spectra with contact‐angle data as the link between chemical composition of OM and the physical wetting behavior of soil particles. In addition to characterizing the wetting properties of OM coatings, we discuss the implications of water‐repellent surfaces for different physical protection mechanisms of OM. For typical minerals, the OM loading on mineral surfaces is patchy, whereas OM forms nanoscaled micro‐aggregates together with metal oxides and hydroxides and with layered clay minerals. Such small aggregates may efficiently stabilize OM against microbial decomposition. However, despite the patchy structure of OM coating, we observed a relation between the chemical composition of OM and wettability. A higher hydrophobicity of the OM appears to stabilize the organic C in soil, either caused by a specific reduced biodegradability of OM or indirectly caused by increased aggregate stability. In partly saturated nonaggregated soil, the specific distribution of the pore water appears to further affect the mineralization of OM as a function of wettability. We conclude that the wettability of OM, quantified by the contact angle, links the chemical structure of OM with a bundle of physical soil properties and that reduced wettability results in the stabilization of OM in soils.  相似文献   

15.
Characteristics and genesis of humus substances of typical forest and arable soils of Schleswig-Holstein The humus substances of Luvisols and Podzols (forest, conventional and ecological farming system) were investigated wet chemically with “Streu- und Humus-Stoffgruppenanalyse” just as macro- and micromorphologically. Low nutrient contents and reduced bioturbation retard the decomposition of litter in the forest soils. Humus accumulation and transfer of humic substances are larger in the Podzol than in the Luvisol. Under arable land use the amount of humus decreased more under conventional farming. Organic fertilization stimulates the bioturbation and decomposition of litter.  相似文献   

16.
Based 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.  相似文献   

17.
土壤侵蚀作用对黄土高原黏化层鉴定和淋溶土分类的影响   总被引：2，自引：1，他引：1  
张蕾  张凤荣  李超  靳东升 《土壤通报》2021,52(2):261-268
黏化层是淋溶土的首要诊断标准.一般情况下,黏化层是在长期相对稳定的湿润淋溶条件下形成的.但黏化过程很可能因为气候变化和土壤侵蚀作用而被打断.本文以山西土系调查16个淋溶土剖面为研究对象,通过对各剖面黏化层与上覆下伏层、各剖面间的基本特征及其理化性状分析,探索土壤侵蚀作用对黄土高原黏化层鉴定和淋溶土分类的影响.结果 表明...  相似文献   

18.
Abstract

A tillage system, ‘slit‐till’, has been developed that modifies plowpans and permits root penetration and proliferation into subsoil horizons. Slit‐till also provides a means of placing nutrients into subsoil zones where roots are concentrated. Greenhouse studies determined the effects of calcium nitrate, calcium phosphate, ammonium phosphate, ammonium nitrate, and dolomitic limestone on grain sorghum [Sorghum bicolor (L.) Moench] shoot and root development in a compacted layer of acid subsoil (pH 4.3), subject to a slit‐till treatment, and on chemical properties of soil adjacent to the injection site. Cylinders were prepared by layering A and B horizons of a Marvyn loamy sand (fine‐loamy, siliceous, thermic, Typic Hapludult) to form 56 cm of subsoil and 10 cm of topsoil in polyvinylchloride (PVC) tubing (20 × 66 cm). A 6‐cm‐thick hardpan (bulk density 1760 Mg.m‐3) was created at the top of the subsoil layer. The amendments, 500 μg/g of dolomitic limestone and 15 μg/g each of the other amendments, were injected into a 10 × 10 × 0.4 cm slit. Sorghum shoots and roots were harvested 49 days after plant emergence. Plant height was increased 15% by calcium nitrate, calcium phosphate, ammonium phosphate, and dolomitic limestone, but decreased 15% by ammonium nitrate. Twenty‐nine percent of the roots for the check occurred in the subsoil, but this increased to 49% with ammonium phosphate. Soil pH was increased and exchangeable aluminum was decreased by the dolomitic limestone up to 12 mm from point of injection.  相似文献   

19.
Soil organic matter (OM) stabilization by the mineral phase can take place through sorption and aggregation. In this study we examined both of these processes, (i) organic carbon (OC) sorption onto clay‐sized particles and (ii) OC occlusion in silt‐size aggregates, with the objective of evaluating their relative importance in OM storage and stabilization in soil. We studied two loamy soil profiles (Haplic Luvisol and Plinthic Cambisol) currently under agricultural use down to a depth of 2 m. Our approach was based on two parallel fractionation methods using different dispersion intensities; these methods isolated a free clay fraction (non‐occluded) and a clay fraction occluded within water‐stable silt‐size aggregates. The two clay fractions were analysed for their C content and 14C activity. The proportion of sorbed OC was estimated as OC loss after hydrofluoric acid (HF) demineralization. Our results showed an important contribution to SOM stabilization by occlusion of OC into silt‐size aggregates with depth through both soil profiles. In the Haplic Luvisol, OC associated with clay and located in silt‐size aggregates accounted for 34–64% of the total soil OC, whereas in the Plinthic Cambisol this occluded material represented 34–40% of total OC. In the Haplic Luvisol, more OC was located in silt‐size aggregates than was sorbed onto clay‐size minerals, suggesting that silt‐size aggregation plays a dominant role in OC storage in this soil. In the Plinthic Cambisol, the abundance of sorbed OC increased with depth and contributed more to the stored C than that associated with silt‐size aggregates. Radiocarbon dating of both clay fractions (either occluded within silt‐size aggregates or not) suggests, in the case of the Plinthic Cambisol, a preferential stabilization of OC within silt‐size aggregates.  相似文献   

20.
Pedogenetic differentiation of soil properties in aggregates Besides the pedogenetic differentiation of soils in horizons a differentiation within horizons across aggregates seems possible. The objective of this study is to check if there is a differentiation of soil properties across aggregates. From a Braunerde, a Podzol-Braunerde, and 2 Podsols from Bavaria and Slovakia aggregates of 10–30 mm in diameter were selected manually from both topsoil and subsoil horizons and mechanically fractionated into a core and a surface fraction. In the aggregate fractions Corg, Alo, and Fed were determined. Corg is generally depleted in the surface fractions of the A-horizons compared to the core fractions. This may be due to favoured microbial degradation of organic matter compared to the aggregate core and preferential leaching of organic C. In the subsoil horizons of the Braunerde Corg is lower in the aggregate surface fraction, in the Podzol, however, it is higher. In Podzols preferential C-input and sorption to aggregate surfaces seems to dominate. Lower Alo? and Fed?concentrations in the aggregate surface fractions of all A-horizons may be explained by preferential acidification of aggregate surfaces as the aggregate surfaces mainly buffer the proton input into structured mineral soils. In the B-horizons only in Braunerde Alo and Fed are lower in the aggregate surface fractions than in the core fractions. The Podzol B-horizons show preferential illuvial enrichment of sesquioxides at aggregate surfaces. Thus, pedogenesis results in the differentiation of soil properties not only between horizons but also within horizons on the level of aggregates. The resulting different chemical properties of aggregate surface and core fractions may affect the sorption capacity of structured soils.  相似文献   

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