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1.
Saturated hydraulic conductivity (Ks) is one of the soil properties used most often to predict soil behavior and suitability for a variety of uses. Because of the difficulty in Ks measurement and its variability with depth and across the landscape, Ks is commonly predicted from other more easily evaluated properties including texture, clay mineralogy, bulk density, pedogenic structure and cementation. Of these, texture and pedogenic structure are most commonly used to estimate Ks, but the reliability of these estimates has not been evaluated for common soils in the Southern Piedmont of Georgia. Thus, the objectives of this study were to evaluate Ks for major horizons in soils and landscapes in the Georgia Piedmont and to relate Ks to morphological properties of these horizons. Ten sites across the region were selected, and 21 pedons arranged in three transects were described from auger holes and pits. For each pedon, Ks was measured in upper Bt horizons, at 140 cm below the surface (Bt, BC, or C horizon), and at a depth intermediate between the shallow and deep measurements (Bt, BC, or C horizon) with a constant head permeameter. The Ks of individual horizons ranged from 1 × 10− 8 to 2 × 10− 5 m s− 1. At six of 10 sites evaluated, clayey upper Bt horizons had higher Ks than deeper horizons with less clay. This difference was attributed to weaker structure in the deeper BC horizons. Structural differences did not explain all variation in Ks with depth, however. Other soil and landscape properties including parent material composition, colluvium on lower slope positions, C horizon cementation, and depth of soil development also affected Ks of horizons in these soils and should be used to better estimate Ks.  相似文献   

2.
Considerable amounts of soil organic matter (SOM) are stabilized in paddy soils, and thus a large proportion of the terrestrial carbon is conserved in wetland rice soils. Nonetheless, the mechanisms for stabilization of organic carbon (OC) in paddy soils are largely unknown. Based on a chronosequence derived from marine sediments, the objectives of this study are to investigate the accumulation of OC and the concurrent loss of inorganic carbon (IC) and to identify the role of the soil fractions for the stabilization of OC with increasing duration of paddy soil management. A chronosequence of six age groups of paddy soil formation was chosen in the Zhejiang Province (PR China), ranging from 50 to 2000 years (yrs) of paddy management. Soil samples obtained from horizontal sampling of three soil profiles within each age group were analyzed for bulk density (BD), OC as well as IC concentrations, OC stocks of bulk soil and the OC contributions to the bulk soil of the particle size fractions. Paddy soils are characterized by relatively low bulk densities in the puddled topsoil horizons (1.0 and 1.2 g cm− 3) and high values in the plow pan (1.6 g cm− 3). Our results demonstrate a substantial loss of carbonates during soil formation, as the upper 20 cm were free of carbonates in 100-year-old paddy soils, but carbonate removal from the entire soil profile required almost 700 yrs of rice cultivation. We observed an increase of topsoil OC stocks from 2.5 to 4.4 kg m− 2 during 50 to 2000 yrs of paddy management. The OC accumulation in the bulk soil was dominated by the silt- and clay-sized fractions. The silt fraction showed a high accretion of OC and seems to be an important long-term OC sink during soil evolution. Fine clay in the puddled topsoil horizon was already saturated and the highest storage capacity for OC was calculated for coarse clay. With longer paddy management, the fractions < 20 μm showed an increasing actual OC saturation level, but did not reach the calculated potential storage capacity.  相似文献   

3.
Many biotic and abiotic factors influence recovery of soil communities following prolonged disturbance. We investigated the role of soil texture in the recovery of soil microbial community structure and changes in microbial stress, as indexed by phospholipid fatty acid (PLFA) profiles, using two chronosequences of grasslands restored from 0 to 19 years on silty clay loam and loamy fine sand soils in Nebraska, USA. All restorations were formerly cultivated fields seeded to native warm-season grasses through the USDA’s Conservation Reserve Program. Increases in many PLFA concentrations occurred across the silty clay loam chronosequence including total PLFA biomass, richness, fungi, arbuscular mycorrhizal fungi, Gram-positive bacteria, Gram-negative bacteria, and actinomycetes. Ratios of saturated:monounsaturated and iso:anteiso PLFAs decreased across the silty clay loam chronosequence indicating reduction in nutrient stress of the microbial community as grassland established. Multivariate analysis of entire PLFA profiles across the silty clay loam chronosequence showed recovery of microbial community structure on the trajectory toward native prairie. Conversely, no microbial groups exhibited a directional change across the loamy fine sand chronosequence. Changes in soil structure were also only observed across the silty clay loam chronosequence. Aggregate mean weighted diameter (MWD) exhibited an exponential rise to maximum resulting from an exponential rise to maximum in the proportion of large macroaggregates (>2000 μm) and exponential decay in microaggregates (<250 μm and >53 μm) and the silt and clay fraction (<53 μm). Across both chronosequences, MWD was highly correlated with total PLFA biomass and the biomass of many microbial groups. Strong correlations between many PLFA groups and the MWD of aggregates underscore the interdependence between the recovery of soil microbial communities and soil structure that may explain more variation than time for some soils (i.e., loamy fine sand). This study demonstrates that soil microbial responses to grassland restoration are modulated by soil texture with implications for estimating the true capacity of restoration efforts to rehabilitate ecosystem functions.  相似文献   

4.
The magnetic properties and magnetic mineralogy of a weathering sequence of soils developed on basalt parent material from eastern China, were studied by rock magnetism, X-ray diffraction and soil chemical analyses to establish the connection between mineral magnetic properties and pedogenic development in a subtropical region. The magnetic susceptibility of soils formed on basalt varied greatly and did not increase with the degree of pedogenic development. The frequency-dependent susceptibility (χfd) values of soils ranged from 1.0 to 11.1% and increased with the pedogenic development. Highly significant linear relationship was found between the frequency-dependent susceptibility and the Fed content (R2 = 0.683) and Fed/Fet ratio (R2 = 0.780) in soils, indicating that pedogenic SP ferrimagnetic grains were associated with enrichment of the secondary iron oxide minerals in the weathering process of soil. Rock magnetism analysis showed that the major magnetic carriers in the weakly weathered soil profiles are magnetite and/or maghemite, and the highly developed soil profiles are generally enriched in magnetite/maghemite grains of pedogenic origin and the magnetically hard haematite, indicating that the magnetic component was transformed from a ferrimagnetic phase (magnetite) to antiferromagnetic phase (hematite) during pedogenic development. Results indicated that some of the magnetic parameters of soils, in this case χfd, can be useful for pedogenic comparisons and age correlations in the weathering sequence of soil. It is thus suggested that multiparameter rock magnetic investigations represent a more powerful approach for pedogenesis.  相似文献   

5.
鼎湖山土壤有机质深度分布的剖面演化机制   总被引：20，自引：5，他引：20       下载免费PDF全文
根据鼎湖山森林植被带(SL)、灌丛—草甸过渡带土壤剖面(GC)有机质含量,有机质Δ14C、δ13C值,土壤粘粒含量及孢粉分析结果,研究华南亚热带山地土壤有机质深度分布特征的成因机制。结果表明土壤有机质的深度分布特征与土壤剖面的发育过程密切相关,随深度增大,有机质的来源数量不断减少,而成土时间增加,分解作用导致的有机质含量降低幅度增大,有机质含量不断减少。土壤有机质14C表观年龄随深度增加,土壤有机质δ13C值与有机质含量的深度变化具有明显对应关系,这些都是土壤剖面发育过程中有机质不同更新周期组分呈规律性分解的结果。粘粒的深度分布反映土壤剖面淋滤淀积的特点,表明土壤剖面经受了长期成土风化。土壤剖面的上述特征均为剖面发育过程中不断沉积、不断成土的结果,表明土壤剖面成土演化对于有机质深度分布具有显著制约。  相似文献   

6.
Rates of N mineralization were measured in 27 forest soils encompassing a wide range of forest types and management treatments in south-east Australia. Undisturbed soil columns were incubated at 20°C for 68 days at near field-capacity water content, and N mineralization was measured in 5-cm depth increments to 30 cm. The soils represented three primary profile forms: gradational, uniform and duplex. They were sampled beneath mature native Eucalyptus sp. forest and from plantations of Pinus radiata of varying age (<1 to 37 years). Several sites had been fertilized, irrigated, or intercropped with lupins. The soils ranged greatly in total soil N concentrations, C:N ratios, total P, and sand, silt, and clay contents. Net N mineralization for individual soil profiles (0–30 cm depth) varied from 2.0 to 66.6 kg ha-1 over 68 days, with soils from individual depths mineralizing from <0 (immobilization) to 19.3 kg ha-1 per 5 cm soil depth. Only 0.1–3.1% of the total N present at 0–30 cm in depth was mineralized during the incubation, and both the amount and the percentage of total N mineralized decreased with increasing soil depth. N fertilization, addition of slash residues, or intercropping with lupins in the years prior to sampling increased N mineralization. Several years of irrigation of a sandy soil reduced levels of total N and C, and lowered rates of N mineralization. Considuring all soil depths, the simple linear correlations between soil parameters (C, N, P, C:N, C:P, N:P, coarse sand, fine sand, silt, clay) and N mineralization rates were generally low (r<0.53), but these improved for total N (r=0.82) and organic C (r=0.79) when the soils were grouped into primary profile forms. Prediction of field N-mineralization rates was complicated by the poor correlations between soil properties and N mineralization, and temporal changes in the pools of labile organic-N substrates in the field.  相似文献   

7.
The island of Milos (Greece), part of the South Aegean volcanic arc with a typical Mediterranean climate, is covered with volcanic deposits of different ages. The objective of this study was to investigate the physicochemical and mineralogical properties of the soils developing on these volcanic deposits and their classification. Samples were taken from seven locations of soil on different parent material and of different ages. There were substantial differences in their particle size distribution, with sand ranging from 19% to 92%, silt from 3.5% to 50%, and clay from 5% to 46%. Organic matter content was low (< 2.0%). The soil pH ranged from 5.6 to 8.0. In two of the profiles, CaCO3 equivalents of 1.4% to 24.6% were found and a calcic horizon identified. The cation exchange capacity (CEC) and specific surface area (SSA) varied between profiles ranging from 3 cmol(+) kg− 1 to 47 cmol(+) kg− 1 and 30 m2 g− 1 to 380 m2 g− 1, respectively. The soils exhibited high base saturation. The amounts of Al, Fe and Si extracted with ammonium oxalate (Αlo, Feo and Sio) were particularly low (< 0.1%, < 0.17%, and < 0.1%, respectively) which demonstrates the absence of amorphous clay-silicate minerals (allophane). Fe extracted with dithionite citrate bicarbonate — DCB (Fed) was greater than Feo sharing the dominance of crystalline Fe oxides. Al and Si extracted with hot 0.5 M NaOH (Al2Ο3NaOH and SiΟ2NaOH) and with Τiron-C6H4Na2O8S2, (Al2Ο3Τ and SiΟ2Τ). SiΟ2NaOH and SiΟ2Τ were particularly high (mean values 3.4% and 4.5%, respectively), showing that amorphous silica was present. The clay fraction of the soil was dominated by the presence of 2:1 (vermiculite and smectite) and 1:1 (kaolinite) clay-silicates. Alo+ 1/2Feo was low (< 0.18%), while the P-retention in most soils was less than 15%. These soils do not exhibit andic properties and hence cannot be classified as Andisols. The silica saturation index (ISS) may be used for these soils to describe a pedogenetic environment rich in Si which favours the formation of pedogenic amorphous silica. The climate is the major determinant of the evolution of these soils.  相似文献   

8.
The aim of this study was to investigate the effects of increased N deposition on new and old pools of soil organic matter (SOM). We made use of a 4-yr experiment, where spruce and beech growing on an acidic loam and a calcareous sand were exposed to increased N deposition (7 vs. 70 kg N ha−1 yr−1) and to elevated atmospheric CO2. The added CO2 was depleted in 13C, which enabled us to distinguish between old and new C in SOM-pools fractionated into particle sizes. Elevated N deposition for 4 yr increased significantly the contents of total SOM in 0-10 cm depth of the acidic loam (+9%), but not in the calcareous sand. Down to 25 cm soil depth, C storage in the acidic loam was between 100 and 300 g C m−2 larger under high than under low N additions. However, this increase was small as compared with the SOM losses of 600-700 g C g C 0.25 m−1 m−2 from the calcareous sand resulting from the disturbance of soils during setting up of the experiment. The amounts of new, less than 4 yr old SOM in the sand fractions of both soils were greater under high N deposition, showing that C inputs from trees into soils increased. Root biomass in the acidic loam was larger under N additions (+25%). Contents of old, more than 4 yr old C in the clay and silt fractions of both soils were significantly greater under high than under low N deposition. Since clay- and silt-bound SOM consists of humified compounds, this indicates that N additions retarded mineralization of old and humified SOM. The retardation of C mineralization in the clay and silt fraction accounted for 60-80 g C m−2 4 yr−1, which corresponds to about 40% of the old SOM mineralized in these fraction. As a consequence, preservation of old and humified SOM under elevated N deposition might be a process that could lead to an increased soil C storage in the long-term.  相似文献   

9.
In previous studies, Al extracted by acid ammonium acetate (Ala) or Na-pyrophosphate (Alp), rather than silt or clay content and climate conditions, was the most important factor that controls organic matter (OM) levels in volcanic soils. Here, the hypothesis was tested that Ala is a comparable method (as much as CuCl2) to quantify the proportion of Al bound to OM in allophanic soils. As far as we know, there are no previous antecedents in which selective dissolution method has been compared with this extractant. Secondly, we examine the effects of (a) Al, (b) silt plus clay content (particles size 0-53 µm) and (c) clay mineralogy on the control of organic carbon (OC) level in Chilean volcanic soils. This was achieved by sampling 16 soils series (11 Andisols, one Alfisol and four Ultisols, USDA classification) including 48 soil pedons up to 0.4 m depth. Soils were analyzed for Ala, Alp, oxalate (Alo, Sio and Feo), cold NaOH (Aln) and un-buffered salts, CuCl2 (AlCu), LaCl3 (AlLa) and KCl (Alk). We also measured the Al-humus as soluble C fraction after pyrophosphate extraction and the C associated to the silt plus clay fraction after sonication and gravity decantation. The statistical package (S)MATR was used to examine bivariate linear regressions among soil properties by computing the standardized major axis (SMA). Our results indicate that Ala had a good correspondence with Alp (R2 = 0.76) in the top soil with Ala/Alp ratio of 0.19 and both extractans presented significant and positively relationship with soil OC (R2 > 0.62). Acid ammonium acetate was as effective as AlCu to determine the Al-OM in allophanic soils. It is cheaper than AlCu and Alp and 0.5 h shaking is required compared to 2 h of AlCu and 16 h of Alp. The efficiency of the extraction was: Aln ≥ Alo > Alp > AlCu ≥ Ala > AlLa > Alk. We also found that allophane content (estimated by Al/Si ratio) was strongly correlated (R2 = 0.82) with the OC in the fine silt plus clay and that Al-humus together with C in the finest particles explained (R2 > 0.60) the largest proportion of variation of soil OC across studied soils.  相似文献   

10.
One of the significant features of loess-derived soils in Kansas is the occurrence of clay-rich subsurface horizons above a layer enriched with pedogenic carbonates. In order to examine the extent of clay increase and pedogenic carbonate enrichment in a precipitation gradient, ten soil profiles from three different precipitation regions were studied using micromorphological and mineralogical techniques. The precipitation gradient was divided into three groups: 400–550 mm, 550–750 mm, and 750–1100 mm regions. The objectives were to (1) understand the cause of clay orientation in clay-rich horizons (2) investigate the reasons for the clay increase, and (3) observe the interaction of clay and pedogenic carbonate accumulation features along a precipitation gradient in Kansas. Although clay films were identified in the field for soils in the 400–550 mm regions, illuvial clay films were not observed in thin section analysis. The clay accumulations mostly occurred as grain coatings. The rest of the clay accumulations observed were very thin, striated, and mostly associated with voids. The argillic horizons had a granostriated b-fabric, which indicates stress orientation of micromass caused by high shrink–swell activity. Thick and continuous illuvial coatings were observed in the buried horizons of paleosols. In the other two regions where precipitation exceeds 550 mm, illuvial clay coatings with strong orientation were observed along with thin and striated stress-oriented clay. Both types of clay orientations exceeded 1% of the cross-sectional area for the thin section. Although illuvial clay features and pedogenic carbonates were observed in all soils at approximately the same depth, complete obliteration of clay coatings was not observed in these horizons. In-situ weathering of biotite was one of the reasons for the clay increase in all soil profiles. In all soils studied, the clay increase and cause of clay orientation cannot be attributed to a single genetic process or event. Both illuviation and shrink–swell activity were involved in the orientation of clay. Although orientation of clay and pedogenic carbonates were observed in all soils at approximately the same depth, the decomposition of clay coatings was not observed in these horizons.  相似文献   

11.
Woody plant invasion of grasslands is prevalent worldwide. In the Rio Grande Plains of Texas, subtropical thorn woodlands dominated by C3 trees/shrubs have been replacing C4 grasslands over the past 150 yr, resulting in increased soil organic carbon (SOC) storage and concomitant increases in soil total nitrogen (STN). To elucidate mechanisms of change in SOC and STN, we separated soil organic matter into specific size/density fractions and determined the concentration of C and N in these fractions. Soils were collected from remnant grasslands (Time 0) and woody plant stands (ages 10-130 yr). Rates of whole-soil C and N accrual in the upper 15 cm of the soil profile averaged 10-30 g C m−2 yr−1 and 1-3 g N m−2 yr−1, respectively, over the past 130 yr of woodland development. These rates of accumulation have increased soil C and N stocks in older wooded areas by 100-500% relative to remnant grasslands. Probable causes of these increased pool sizes include higher rates of organic matter production in wooded areas, greater inherent biochemical resistance of woody litter to decomposition, and protection of organic matter by stabilization within soil macro- and microaggregates. The mass proportions of the free light fraction (<1.0 g cm−3) and macroaggregate fraction (>250 μm) increased linearly with time following woody plant invasion of grassland. Conversely, the mass proportions of free microaggregate (53-250 μm) and free silt+clay (<53 μm) fractions decreased linearly with time after woody invasion, likely reflecting stabilization of these fractions within macroaggregate structures. Carbon and N concentrations increased in all soil fractions with time following woody invasion. Approximately half of the C and N accumulated in free particulate organic matter (POM) fractions, while the remainder accrued in stable macro- and microaggregate structures. Soil C/N ratios indicated that the organic C associated with POM and macroaggregates was of more recent origin (less decomposed) than C associated with the microaggregate and silt+clay fractions. Because grassland-to-woodland conversion has been geographically extensive in grassland ecosystems worldwide during the past century, changes in soil C and N storage and dynamics documented here could have significance for global cycles of those elements.  相似文献   

12.
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   

13.
Soil movement by tillage redistributes soil within the profile and throughout the landscape, resulting in soil removal from convex slope positions and soil accumulation in concave slope positions. Previous investigations of the spatial variability in surface soil properties and crop yield in a glacial till landscape in west central Minnesota indicated that wheat (Triticum aestivum) yields were decreased in upper hillslope positions affected by high soil erosion loss. In the present study, soil cores were collected and characterized to indicate the effects of long-term intensive tillage on soil properties as a function of depth and tillage erosion. This study provides quantitative measures of the chemical and physical properties of soil profiles in a landscape subject to prolonged tillage erosion, and compares the properties of soil profiles in areas of differing rates of tillage erosion and an uncultivated hillslope. These comparisons emphasize the influence of soil translocation within the landscape by tillage on soil profile characteristics. Soil profiles in areas subject to soil loss by tillage erosion >20 Mg ha−1 year−1 were characterized by truncated profiles, a shallow depth to the C horizon (mean upper boundary 75 cm from the soil surface), a calcic subsoil and a tilled layer containing 19 g kg−1 of inorganic carbon. In contrast, profiles in areas of soil accumulation by tillage >10 Mg ha−1 year−1 exhibited thick sola with low inorganic carbon content (mean 3 g kg−1) and a large depth to the C horizon (usually >1.5 m below the soil surface). When compared to areas of soil accumulation, organic carbon, total nitrogen and Olsen-extractable phosphorus contents measured lower, whereas inorganic carbon content, pH and soil strength measured higher throughout the profile in eroded landscape positions because of the reduced soil organic matter content and the influence of calcic subsoil material. The mean surface soil organic carbon and total nitrogen contents in cultivated areas (regardless of erosion status) were less than half that measured in an uncultivated area, indicating that intensive tillage and cropping has significantly depleted the surface soil organic matter in this landscape. Prolonged intensive tillage and cropping at this site has effectively removed at least 20 cm of soil from the upper hillslope positions.  相似文献   

14.
The origin of carbonate accumulations in termite mounds is a controversial issue. This study is an attempt to elucidate the processes of carbonate precipitation in Macrotermes mounds built on Ferralsols in Upper Katanga, D.R. Congo, whereby a differentiation between pedogenic and inherited carbonates is considered. Carbonate features were investigated for a 9 m deep termite-mound profile, and for an 18 m wide cross-section through a termite mound and the adjacent soil, using field and laboratory techniques. Field evidence for a pedogenic origin includes morphological type (soft powdery materials, nodules, and coatings on ped surfaces) and distribution patterns of the carbonates. Thin-section studies reveal that the carbonates occur predominantly as impregnative orthic nodules and less commonly as coatings, both clearly pedogenic; calcareous pellets are interpreted as locally reworked pedogenic carbonates. X-ray diffraction (XRD), scanning electron microscopy/energy dispersive X-ray spectrometry (SEM-EDS) and stable isotope (δ13C) analyses show that all isolated carbonate features consist of high-Mg calcite (4.9-12.3 mol% MgCO3) with δ13C signatures ranging from − 13.2‰ to − 11.5‰. Weddellite (CaC2O4. 2H2O) is identified in a thin-section and by XRD analysis, and appears to be locally transformed into calcite. The stable isotope composition of carbon suggests that calcite precipitated in equilibrium with soil CO2 generated during decomposition of soil organic matter, and locally most likely during oxidation of oxalate. This study proves that carbonates which accumulated in Macrotermes mounds are pedogenic precipitates, whose deposition is partly related to microbial decay of organic matter, subsequently redistributed to some extent by abiotic dissolution-reprecipitation and termite activity.  相似文献   

15.
Soil catenas integrate and amplify gravity transfer and differentiation processes of eluviation and illuviation in soil profiles. We quantified differences in these redistribution processes along granitic catenas across an arid to sub-humid climate gradient in Kruger National Park, South Africa. We measured soil properties in nine catenas sampled from three areas receiving annual rainfall of 470 mm (arid zone), 550 mm (semi-arid zone) and 730 mm (sub-humid zone). As rainfall increased, kaolinite replaced smectite as the dominant clay mineral in all landscape positions across the catenas. Toeslopes showed the strongest evidence of this transition with an excess of smectite in the arid catenas but complete prevalence of kaolinite in toeslopes of sub-humid catenas. The concentration and distribution of clay along the catenas were dependent on landscape position as well — soil profiles at and near the crests were clay depleted (as low as 1%) while those at the toeslopes had much more clay (up to 60%). Clay redistribution along catenas was sensitive to climate with the least amount of redistribution occurring in the dry sites and the most occurring in the wet sites. As a consequence, the sub-humid catenas had clay accumulation only in a small part of the toeslopes while the bulk of their length was represented by highly leached soils. In contrast, arid zone catenas showed little clay redistribution and semi-arid sites displayed the greatest within-catena clay redistribution and preservation. Clay movement and storage conditioned other soil properties such as CEC, base cation distribution, base saturation and pH.  相似文献   

16.
Earthworms are known to be important regulators of soil structure and soil organic matter (SOM) dynamics, however, quantifying their influence on carbon (C) and nitrogen (N) stabilization in agroecosystems remains a pertinent task. We manipulated population densities of the earthworm Aporrectodea rosea in three maize-tomato cropping systems [conventional (i.e., mineral fertilizer), organic (i.e., composted manure and legume cover crop), and an intermediate low-input system (i.e., alternating years of legume cover crop and mineral fertilizer)] to examine their influence on C and N incorporation into soil aggregates. Two treatments, no-earthworm versus the addition of five A. rosea adults, were established in paired microcosms using electro-shocking. A 13C and 15N labeled cover crop was incorporated into the soil of the organic and low-input systems, while 15N mineral fertilizer was applied in the conventional system. Soil samples were collected during the growing season and wet-sieved to obtain three aggregate size classes: macroaggregates (>250 μm), microaggregates (53-250 μm) and silt and clay fraction (<53 μm). Macroaggregates were further separated into coarse particulate organic matter (cPOM), microaggregates and the silt and clay fraction. Total C, 13C, total N and 15N were measured for all fractions and the bulk soil. Significant earthworm influences were restricted to the low-input and conventional systems on the final sampling date. In the low-input system, earthworms increased the incorporation of new C into microaggregates within macroaggregates by 35% (2.8 g m−2 increase; P=0.03), compared to the no-earthworm treatment. Within this same cropping system, earthworms increased new N in the cPOM and the silt and clay fractions within macroaggregates, by 49% (0.21 g m−2; P<0.01) and 38% (0.19 g m−2; P=0.02), respectively. In the conventional system, earthworms appeared to decrease the incorporation of new N into free microaggregates and macroaggregates by 49% (1.38 g m−2; P=0.04) and 41% (0.51 g m−2; P=0.057), respectively. These results indicate that earthworms can play an important role in C and N dynamics and that agroecosystem management greatly influences the magnitude and direction of their effect.  相似文献   

17.
A calcrete profile developed on the top of a calcareous consolidated dune located in a coastal area of NE Tunisia (semi-arid climate) was studied with the aim to investigate the behavior of the chemical elements (rare earth elements—REE—and other trace and major elements) during the processes associated with calcrete formation, particularly dissolution and precipitation of carbonates in the vadose zone. The profile shows a vertical sequence, with clear zonations from the surface downwards: a reddish soil at the land surface, a nodular horizon, a laminar-structured level, and the consolidated old dune. Chemical and mineralogical analyses of samples from all levels were performed by neutron activation analysis and X-ray diffraction (bulk samples and < 2 μm fraction). Detailed studies of iron speciation and iron minerals were done by Mössbauer spectroscopy. Microfauna, mineralogical and chemical variations in the Slimene weathering profile point to a long term aerial exposure of the old dune in a semi-arid carbonated environment leading to the development of a pedogenic calcrete profile. The mineralogical variations with depth indicate carbonate dissolution at the surface and downward leaching of calcium. Secondary carbonates overgrow primary ones and precipitate as coating or concretions below. Minerals found in the upper levels correspond to original materials of the old dune and also weathering phases and atmospheric inputs. Phyllosilicates decrease while calcite and K-feldspars increase with depth. Kaolinite was the only clay mineral found in the old dune. Illite and chlorite were also found in all samples with calcrete. Authigenic smectite formation occurs above the laminar-structured calcrete due to restricted drainage conditions. The most significant chemical variations associated with the calcrete formation are (i) enrichment of Co, U, Br, and REE in calcrete; (ii) depletion of middle REE in the upper levels, particularly Eu, and enrichment of middle REE and heavy REE in calcrete; and (iii) Hf, Zr, Cr, Th, Cs, Ta, Ga, Rb, and K appear to be retained in the upper levels, where calcite has been dissolved. Here iron is more reduced. Fe3+ occurs in iron oxides (goethite and hematite), and clay minerals. The ratio goethite/hematite appears to increase down the profile; and Fe2+ is mainly present in clay minerals.  相似文献   

18.
Native Indians (Macuxi, Ingarikó and Uapishana) in the Raposa–Serra do Sol Indian Reserve have been cultivating forest soils since the early XIX century, especially those derived from dolerite sills, scattered within the quartzitic dominated landscape. Representative soils developed from mafic rocks under Indian shifting cultivation in northeastern Roraima, were submitted to physical, chemical and mineralogical analyses to characterize their pedogenetic characteristics and infer on their status under native Indian shifting cultivation. The soil profiles were classified as: Orthic Ebanic Chernosol (USDA Mollisol), vertic Orthic Ebanic Chernosol (USDA Mollisol), Eutrophic Haplic Cambisol (USDA mollic Inceptisol) and Eutrophic Red Nitosol (USDA Red Alfisol), which occupy, respectively, lower slopes and less dissected terrains (Mollisols) and steeper slopes (Alfisols). The first two are eutrophic, and not typical of the Amazon region. Their mineralogies range from kaolinite/goethite rich upland, deeply weathered Nitosol, to 2:1 clay rich downslope Chernosols. The latter has primary minerals in the silt fraction and high CEC resulting in high fertility. The Nitosols reveal a process of severe topsoil loss, due to widespread sheet erosion from deforestation and shifting cultivation. Chemical analyses showed varied soil fertility, ranging from high levels in the Chernosols to a low level in the non-cultivated Nitosol. Phosphorus levels are limited in all soils, despite the high fertility. The Chernosols located in lowland, flat areas close to the valley floor are more suitable environments for the slash-and-burn native farming system. In the Chernosols and Cambisols, the clay activity below the value limit for this class indicates a current natural process of increasing leaching. The more weathered and eroded Nitosol showed low Fe-oxalate and Si-oxalate levels. Micronutrients such as total zinc and copper, decreased with depth and weathering. The Nitosols showed the highest phosphate adsorption levels (1.574 mg g− 1 of soil) which can be attributed to its clayey texture. Chernosols showed overall lower P adsorption values, increasing with depth. All soils under native Indian cultivation display signs of physical and chemical degradation due to shortened fallow under intense land use pressure in the Raposa–Serra do Sol Reserve.  相似文献   

19.
Interrill and rill erodibility in the northern Andean Highlands   总被引：2，自引：0，他引：2  
There is a lack of quantitative information describing the physical processes causing soil erosion in the Andean Highlands, especially those related to interrill and rill erodibility factors. To assess how susceptible are soils to erosion in this region, field measurements of interrill (Ki) and rill (Kr) erodibility factors were evaluated. These values were compared against two equations used by the Water Erosion Prediction Project (WEPP), and also compared against the Universal Soil Loss Equation (USLE) erodibility factor. Ki observed in situ ranged from 1.9 to 56 × 105 kg s m− 4 whereas Kr ranged from 0.3 to 14 × 10− 3 s m− 1. Sand, clay, silt, very fine sand and organic matter fractions were determined in order to apply WEPP and USLE procedures. Most of the evaluated soils had low erodibility values. However, the estimated USLE K values were in the low range of erodibility values. Stepwise multiple regression analyses were applied to ascertain the influence of the independent soil parameters on the Ki and Kr values. After this, we yield two empirical equations to estimate Ki and Kr under this Andean Highlands conditions. Ki was estimated using as predictors silt and very fine sand, while Kr used as predictors clay, very fine sand and organic matter content. Relationship among Ki, Kr and K are described for the Highland Andean soils.  相似文献   

20.
丹江中游典型小流域土壤颗粒及分形特征   总被引：2，自引：0，他引：2  
在丹江鹦鹉沟小流域,利用网格状取样和典型样地取样相结合的方法,进行土样采集,共计采样点268个,研究土壤颗粒组成和分形特征,以及与土壤全氮之间的相互关系。结果表明：土壤粉黏粒质量分数随土壤深度的增加而增大,不同土层下土壤粉黏粒质量分数平均值均表现为农地〉林地〉草地。经ANOVA分析,不同土地利用在10—40cm土层的粉黏粒质量分数存在显著差异（P〈0．05）。不同植被类型间土壤颗粒分形维数亦存在显著差异（P〈0．05）,10～20cm土层的土壤颗粒分形维数更能代表不同土地利用的差异。土壤颗粒分形维数与坡度呈显著负相关（P〈0．05）,与坡向和海拔无显著相关性。土壤全氮质量分数在0～20cm土层与中粗砂粒质量分数呈极显著正相关（P〈0．01）,土壤颗粒分形维数和土壤全氮质量分数在20～60cm土层均与土壤粉黏粒质量分数呈极显著正相关（P〈0．01）。鹦鹉沟流域0～10cm土层的土壤粉黏粒储量为13．28万t,不同土地利用下0～10cm土层每m2土壤粉黏粒储量表现为农地〉林地〉草地,分别为74．71kg／m2、71．54kg／m2和70．23kg／m2。  相似文献   

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