Bh Horizons Research Articles

Pedogenesis by upbuilding in an extreme leaching and weathering environment, and slow loess accretion, south Westland, New Zealand

Soil formation is usually envisaged as acting from the surface downwards. In many environments, however, the accumulation of sediment and soil formation are contemporaneous. It is only where the rate of one process far exceeds the rate of the other that assumptions of topdown pedogenesis are appropriate. The aspect of upbuilding pedogenesis that distinguishes it from topdown pedogenesis is that each increment of soil below the A horizon has experienced processes characteristic of all horizons above it. This study examines the influence of upbuilding soil formation in a high rainfall environment of rapid soil formation and slow loess accretion—an environment where upbuilding could have a noticeable influence on soil properties. Soils formed by topdown soil formation (topdown soils) are compared with soils formed in loess that accumulated from early Last Glaciation to the Holocene (upbuilding soils). Soils are compared in two environments: Alaquods on poorly-drained terraces and Placorthods or Dystrochrepts on well-drained moraine crests. We have assumed that properties of the upbuilding soils inherited during the current topdown phase of pedogenesis beginning in the Holocene are analogous to those in the topdown soils. In this manner soil properties evolved during upbuilding are distinguished. In well-drained upbuilding soils on moraines, subsoil organic carbon has mineralised so that profile trends are very similar to corresponding topdown soils. Upbuilding has enhanced weathering in subsoils which is reflected in lower pH, lower total P and lower primary inorganic P than in topdown soil counterparts. Total P concentrations in upbuilding soils are much lower than unweathered loess and constant throughout the subsoil, and there is almost no P in primary forms. In contrast, total P in C horizons of topdown soils reaches concentrations typical of the parent material and more than 30% of this is in a primary inorganic form. The differences are attributed to each subsoil increment of upbuilding soils having been part of acid A and E horizons. Oxalate extractable Fe and Al data indicate that podzolisation was active during upbuilding. Poorly-drained upbuilding soils on terraces have higher subsoil organic carbon (inherited from former A or O horizons) than comparable topdown soils. Buried A and O horizons inherited during upbuilding and preserved in the reducing conditions have acted as sinks for mobile Al and now resemble podzolic illuvial Bh horizons. Upbuilding through addition of loess to soils promotes a pedogenic pathway distinct from topdown pedogenesis. Consequently, soil chronosequence studies that include soils on old, loess-mantled surfaces do not strictly satisfy the assumptions of soil chronosequences. The nature and rate of soil processes inferred from these studies need revisiting. The findings of this study are transferable to other environments where the rate of soil formation and sediment accumulation are comparable.

CHANGES IN QUANTITY AND COMPOSITION OF CRYSTALLINE CLAY ACROSS E-BH BOUNDARIES OF ALAQUODS

Theories of Spodosol formation emphasize chemical rather than particle translocation. However, some studies have presented evidence for particle as well as chemical migration in the formation of Bh horizons. In addition, abundant data for Florida Alaquods show that Bh horizons have significantly higher clay content than do eluvial and common subjacent horizons. This bulge in clay content has genetic implications if it is partially attributable to crystalline clay because it would be evidence suggesting that colloidal migration (lessivage) has occurred. This study was conducted to compare the amount and composition of crystalline clay contained in Bh and adjoining horizons of Alaquods. Data for more than 200 Alaquod profiles available from the Florida Cooperative Soil Survey database and complementary data generated for six of these profiles selected randomly from the pool were statistically analyzed. Pre-existing data included organic C; pyrophosphate-extractable C, Fe, and Al; citrate-dithionite extractable Fe and Al; and particle size distribution (pipette). Complementary data included particle size (centrifugal separation) and clay mineralogy (by X-ray diffraction and differential scanning colorimetry), each following H2O2 and ammonium oxalate pretreatment. Particle size data in conjunction with mineralogy confirmed a significant increase in resistant secondary phyllosilicates from the E to the Bh horizon, consistent with a physical redistribution of clay particles from the E to the Bh horizon. A possible source of these particles is sand grain coatings, which are absent from Alaquod E horizons but present in E horizons of most other sandy soils on better drained adjacent land-forms. Noncrystalline Al in grain coatings may be the source of Al accumulated in the Bh horizons of these soils, rather than weatherable minerals, which are nearly absent in the upper 2 m.

Mineralogy of poorly crystalline aluminium phases in the B horizon of Podzols in southern Sweden

Poorly crystalline Al components of the clay fraction are often neglected in soil mineralogical studies. In this study 7 B horizons from podzolised soils in Sweden were analysed using a combination of infrared (IR) spectroscopy, transmission electron microscopy (TEM), X-ray diffraction (XRD) and selective extractions. It was found that most Bhs and Bs horizons contained allophane, imogolite and more or less hydroxy-interlayered vermiculite. Some Bhs and Bs horizons also contained small amounts of kaolinite and/or gibbsite. In one acid Bh horizon organically complexed Al was the only reactive Al fraction of importance. The vertical patterns of vermiculite and allophane/imogolite suggested that both had formed during the podzolisation process, but due to different mechanisms. The pattern of kaolinite and gibbsite occurrences indicated that these minerals were mostly inherited from the parent material. Oxalate and pyrophosphate extractions suggested that allophane and imogolite constituted the most important reactive inorganic Al fraction in the soils. This shows that allophane and imogolite seem to be the typical, rather than the occasional, reactive inorganic Al phases that form in the B horizon as a result of podzolisation.

Phosphorus Retention Capacity of the Spodic Horizon under Varying Environmental Conditions

AbstractThe spodic (Bh) horizon of Spodosols with Al, Fe, and C accumulations usually has a high P sorption capacity. However, the Bh horizon of prevalent Spodosols in the Lake Okeechobee basin of Florida is subject to a fluctuating watertable that could change the dynamics of P in these soils under alternating aerobic and anaerobic conditions. Further, the Bh horizon of this basin is often impacted by P moving vertically following heavy surface application of dairy manure. Our objectives were to relate the P retention capacity of the Bh horizons of the Lake Okeechobee basin to other soil parameters, and to evaluate P retention of manure‐impacted Bh horizons under aerobic and anaerobic conditions. High watertable decreased the P retention capacity for the majority of the soils in this study. High manure‐impacted areas have Bh horizons with high P concentrations as a result of P movement from the surface A horizon through the eluted E horizon. The P appeared to be temporarily retained and could be released upon prolonged contact with water. This P is likely to move horizontally above the Bh horizon to drainage ditches and eventually into the lake, causing eutrophication. The equilibrium P concentrations and water soluble P concentrations of Bh horizon soils that did not receive high rates of manure application (native soils and pasture soils) are low and it is unlikely that P would move laterally out of such systems, above the Bh horizon.

Changes in soil sulfur constituents in a forested watershed 8 years after whole-tree harvesting

Soil S constituents were evaluated before and after the whole-tree harvesting of Watershed 5 (W5) at the Hubbard Brook Experimental Forest, New Hampshire. Soil solution and stream water concentrations of SO42-, NO3-, and H+ were compared between W5 and W6 (reference watershed). Whole-tree harvesting increased phosphate-extractable SO42- (PSO4) in the E horizon, from 2 mg S·kg-1 soil in pre-harvest to 9 and 10 mg S·kg-1 soil 3 and 8 years post-harvest, respectively. Harvesting increased PSO4 in the Bh horizon from 11 mg S·kg-1 soil prior to harvesting to 20 and 25 mg S·kg-1 soil 3 and 8 years after harvesting, respectively. Temporal patterns in soil chemistry were also reflected in stream SO42-, NO3-, and H+ concentrations. Eight years after harvesting, PSO4 concentrations in the mineral soil increased with elevation. This elevational pattern was likely due to the higher concentrations of SO42- and H+ in soil solutions that enhanced SO42- adsorption at the higher elevations. The high H+ concentrations were attributed to enhanced nitrification and differences in vegetation at upper elevations. The importance of these factors were discussed with respect to the effects of forest harvesting and changes in atmospheric S deposition.

Inorganic phosphorus and manure effects on bahiagrass production on a Spodosol

Bahiagrass (Paspalum notatum Flugge) pasture fertilization recommendations have traditionally been based upon clipping studies. Inclusion of P from manure, not originally considered when P recommendations were developed for pastures, may minimize the need for P fertilization without reducing bahiagrass production or P uptake. The objective of this research was to determine if manure contributes greatly to the P crop nutrient requirement. A 2-year field study utilized a factorial arrangement of 0 and 6.9 Mg air-dried manure ha-1 with 0, 17, 34, 51, and 68 kg inorganic P ha-1 from triple superphosphate to evaluate bahiagrass yield, root distribution, and P uptake response on a Myakka fine sand (sandy, siliceous, hyperthermic Aeric Alaquod). Because air-dried manure was used in the field study, a greenhouse study was employed to confirm that there were no differences in bahiagrass yield or P uptake from either air-dried or fresh cattle (Bos spp.) manure sources. There were no manure or manure by P interaction effects on yield or P uptake of bahiagrass indicating that manure source did not effect grass production in the greenhouse. In the field study, bahiagrass roots were distributed into the Bh horizon, and the Bh horizon had at least four times more Mehlich-1 extractable P than that of the Ap horizon. This horizon was most likely acting as a main source for P-uptake by the grass. This observation was further confirmed by no yield response to levels of inorganic P application in 1989. A linear-response-and-plateau (R2=0.196) relationship with a critical point of 15.4 kg P ha-1 was found in 1990. Bahiagrass yield and P uptake were not dependent on P fertilization, either from manure or inorganic P, due to the availability of P from the Bh horizon.

Transport of Phosphorus and Fractionation of Residual Phosphorus in Various Horizons of a Spodosol

The retention and transport of P by three horizon samples (A, E, and Bh) of a Spososol (Oldsmar sand: sandy, silicious, hyperthermic Alfic Arenic Haplaquods) were evaluated using a batch-equilibration and leaching column techniques with application of P in rates equivalent to 25 and 100 kg P ha-1. Adsorption coefficient (K) values followed the order: Bh > A > E. Adsorption of P by the E horizon soil sample was negligible (M = 4 μg g-1 soil) as compared to that of either A or Bh horizon samples, e.g., 303 and 479 μg g-1, respectively. The leaching column study with application of P equivalent to 100 kg ha-1 showed 39, 68, and 98% of applied P were leached from the Bh, A, and E horizons, respectively, with eight pore volumes of leachate. Elution curves showed the peak P elution at the second pore volume (equivalent to 3.7 cm of water addition). After leaching with eight pore volumes, the residual P in the soil was present primarily in non-occluded Fe and Al-P forms in the A and Bh horizons.

Changes in soil sulfur constituents in a forested watershed 8 years after whole-tree harvesting

Soil S constituents were evaluated before and after the whole-tree harvesting of Watershed 5 (W5) at the Hubbard Brook Experimental Forest, New Hampshire. Soil solution and stream water concentrations of SO42-, NO3-, and H+ were compared between W5 and W6 (reference watershed). Whole-tree harvesting increased phosphate-extractable SO42- (PSO4) in the E horizon, from 2 mg S·kg-1 soil in pre-harvest to 9 and 10 mg S·kg-1 soil 3 and 8 years post-harvest, respectively. Harvesting increased PSO4 in the Bh horizon from 11 mg S·kg-1 soil prior to harvesting to 20 and 25 mg S·kg-1 soil 3 and 8 years after harvesting, respectively. Temporal patterns in soil chemistry were also reflected in stream SO42-, NO3-, and H+ concentrations. Eight years after harvesting, PSO4 concentrations in the mineral soil increased with elevation. This elevational pattern was likely due to the higher concentrations of SO42- and H+ in soil solutions that enhanced SO42- adsorption at the higher elevations. The high H+ concentrations were attributed to enhanced nitrification and differences in vegetation at upper elevations. The importance of these factors were discussed with respect to the effects of forest harvesting and changes in atmospheric S deposition.

Effects of Soil on Trace Metal Leachability from Papermill Ashes and Sludge

AbstractUnderstanding trace metal leachability is important for successful land application of papermill residues. Trace metal leachability from papermill ashes (Ash 1 and Ash 2) and papermill sludge (Sludge), and the effects of a soil on their leachability were determined by leaching the three papermill residues packed on top of a soil in a column. The leachates were analyzed for pH, electrical conductivity (EC), dissolved organic carbon (DOC), and concentrations of six metals (Cd, Cr, Cu, Pb, Se, and Zn). Ash 1 behaved significantly differently from Ash 2 during the leaching experiment, primarily due to its high pH and Na contents. Application of papermill residues significantly increased the pH, EC, and DOC concentrations in leachates, with Ash 1 having significantly greater impacts than Ash 2 and sludge. Soil columns under alkaline leaching of Ash 1 appeared bleached due to the dissolution of solid‐phase organic matter. Significant amounts of Zn were leached from all papermill residues, whereas significant amounts of Cr, Se, and Cu were leached only in the Ash 1 treatments. The presence of a soil (especially a Bh horizon) generally enhanced metal leachability in the Ash 1 treatments due to the extremely high pH of Ash 1, whereas it decreased metal leachability in the Ash 2 and sludge treatments. Thus, organic matter enhances metal sorption when present as a solid phase, but it increases metal leachability when present in dissolved form under alkaline conditions.

The solubility of aluminium in two swedish acidified forest soils : An evaluation of lysimeter measurements using batch titration data

This paper presents aluminium (Al)-solubility data for two acid forest soils (Inceptisol and Spodosol), obtained in connection with lysimeter measurements (tension-cup and zero-tension lysimeters) and batch equilibrium experiments. The solubility of Al obtained in the batch experiments was used as a reference to test whether Al3+in soil solutions collected by the lysimeters was in equilibrium with secondary forms of solid-phase Al (Al(OH)3or organically bound Al). The relation between pH and Al3+activity found for the zero-tension lysimeter solutions collected from the Inceptisol agreed well with that obtained in the batch experiment. This suggests that Al3+in the lysimeter solutions were in, or close to, equilibrium with the solid phase, whether this was organically bound Al (A horizon) or an Al(OH)3phase (B horizon). For the tension-cup lysimeters, solutions obtained from the Inceptisol B and Spodosol Bs1 horizons were generally close to equilibrium with respect to secondary solid-phase Al (apparently Al(OH)3; average ion activity product was 109.3and 108.8, respectively), whereas the Inceptisol A and Spodosol Bh solutions were not. The Al solubility in Inceptisol A and Spodosol Bh horizons was consistently higher than that obtained in the batch equilibrium experiment, indicating that the sampled solution partly originated from the underlying horizons. Thus, tension-cup lysimeters should be used with care in soils (or in parts of soil profiles) having steep solute concentration gradients because the soil volume from which the sample is drawn with this lysimeter type seems to be poorly defined.

WATER TABLE DYNAMICS ACROSS AN AQUOD-UDULT TRANSITION IN FLORIDA FLATWOODS

Spodosol formation in the coastal plain of the southeastern United States is largely restricted to areas where there are fluctuating water table conditions within the zone of podzolization. The purpose of this study was to document specific hydrologic conditions associated with podzolization, and to address the idea that frequency and duration of saturation are critical threshold factors triggering and driving the process regionally. The study was conducted along an abrupt Aquod-to-Udult transition, which showed the commonly observed trend of an upward curving spodic horizon (Bh) that merges with the A horizon of the Udult. Objectives were to (i) compare the Aquod and the Udult with respect to depth and duration of saturation and (ii) determine hydraulic responses of horizons to rainfall events along the Aquod-Udult transition. Water table fluctuations within a rectangular area (15 × 25 m) encompassing the soils were monitored, using piezometers, over a 1-year period. Hydraulic and horizon surfaces were interpolated by Kriging. Results confirmed that the water table sloped sharply downward across the Aquod-to-Udult transition during most of the sampling period but was nearly level for brief periods after heavy rains. The hydraulic response of the Udult argillic horizon to rain events was much slower than that of the Aquod argillic horizon, such that the Udult periodically experienced epiaquic conditions. The hydraulic head of the Aquod argillic horizon was consistently higher than that of the Udult argillic horizon; discharge from the Aquod argillic compensated for evapotranspiration and maintained wetter conditions in the upper sandy horizons. Depth and color development of the Aquod Bh horizon were inversely related to water table depth along the transition. Hence, these factors are not simple functions of central tendencies in water table dynamics but relate to duration of saturated conditions in the near-surface sandy zone.

Dairy Manure Influences on Phosphorus Retention Capacity of Spodosols

AbstractLand areas used for dairy farming can result in accumulation of manure on soils that could produce nutrient‐rich surface and subsurface runoff and cause accelerated lake eutrophication. This research was conducted on Spodosols that were differentially impacted by manure; the study included sites with different levels of total P (TP), from 2300 mg kg−1 in the soil highly impacted by intensive dairy farming to 18 mg kg−1 in an unimpacted area. The P retention characteristics of these soils were determined by using both single‐point (1000 mg P kg−1 or 100 mg P L1) and traditional Langmuir isotherms. Phosphorus sorption values using a single high P solution had approximately a 1:1 relationship with values obtained for the maximum retention capacity, Smax, obtained from Langmuir isotherms (r2 = 0.98). The surface A and E horizons of manure‐impacted soils had essentially no sorbing capacity while the Bh (spodic) and Bw horizons had mean Smax values 430 and 385 mg kg−1, respectively. The P sorbing capacity of the Bh and Bw horizons were attributed to high Al concentrations in these horizons. Higher P concentrations in the surface A horizon resulted in greater P concentrations in solutions equilibrated with the Bh‐ and Bw‐ horizon materials, which suggests a potential for vertical P movement through the soil profile. The spodic horizon of the less‐impacted soils may not have been exposed to sufficiently high solution P concentrations to accumulate significant P in the soluble fraction.

Sources of Organic Halogens in Spruce Forest Soil

It is known that large amounts of organic halogens are present in soil, but the relative contribution from different sources is unclear. The aim of the present study was to determine the storage of organic halogens in a spruce forest soil and the deposition by needle litterfall and to elucidate the relative contribution from needle litterfall in relation to other sources and sinks. Sampling was conducted in a small spruce forest area in Denmark. Soil samples were collected at six locations to a depth of 60 cm. Litterfall was collected in 15 sample collectors every third month during 1 year. Soil leachate was collected below the Bh horizon over two periods of 5 days at five locations distributed over the study site. Throughfall data was compiled from a previous study conducted at the same site and during the same period as the present study, and data concerning net formation in soil was estimated from previous studies at similar sites. The pool was 630 kg of Clorg ha-1, contribution from litterfall was 0.3...

Stable sulfur isotopic biogeochemistry of the Hubbard Brook Experimental Forest, New Hampshire

In natural ecosystems, differences often exist in the relative abundanceof stable S isotopes (°34S) that can provide clues as tothe source, nature, and cycling of S. Values of °34S inprecipitation, throughfall, soils, soil solution, and stream waters weremeasured at the Hubbard Brook Experimental Forest (HBEF), New Hampshire.Values of °34S in precipitation and throughfall weresimilar to each other but differed seasonally. Precipitation°34S values were higher in the dormant season[°34S = 5.9±0.6‰ (17)][Mean + SE(N)]than in the growing season [°34S = 5.0±0.6‰(40)] but throughfall growing-season values were higher[°34S = 5.6±0.6‰(68)] than for the dormantseason [°34S = 4.9±0.7‰ (9)]. Different treespecies did not affect throughfall °34S values. In soilsolution, °34S values were higher in the growing season(°34S = 8.9±2.8‰; 8.8±1.7‰;and 4.0±0.6‰ for Oa, Bh, and Bs horizons, respectively) thanin the dormant season (°34S = 5.6±1.5‰;3.7±2.4‰; and 3.4±1.2‰ for Oa, Bh, and Bshorizons, respectively). These seasonal differences in°34S were probably caused by biological isotopicfractionation. The °34S values in streams were generally2‰ lower and more variable than those in precipitation andthroughfall, suggesting fractionation and/or different isotopic sources inthe soil.

Three-dimensional representation of tubular horizons in sandy soils

Soil horizons are three-dimensional bodies and this is widely recognised. However, many soil descriptions are still based on the soil profile and the move to three-dimensional diagrams to represent horizons or other soil phenomena is just starting. In the present study computer reconstruction and visualization techniques were used to illustrate the geometry of the illuvial Bh horizon in a buried podzol. The 3D computer representation revealed a complex of tubular forms with diameters varying from 10 to 25 cm and length around 100 cm. Similar tubular shapes are found in Australian podzols.

Mineralogical properties of sandy podzols on the Swan Coastal Plain, south-west Australia, and the effects of drying on their phosphate sorption characteristics

Very sandy and sometimes seasonally inundated humus podzols of the Bassendean soil association in southwest Australia experience severe leaching of fertiliser P with consequent eutrophication of waterways. P sorption by these soils is mostly minimal and is primarily due to the podzol Bh horizon. The consequence of seasonal drying of profiles under the prevailing Mediterranean climate on the P sorption capacity of these B horizon materials is not known. The effects of air-drying on P sorption were studied for 3 sandy podzols using samples from entire soil profiles collected in winter (wet) and summer (dry). Results confirm that the surface and near surface horizons (i.e. A and E horizons) of these soils have very low P sorption capacities. Only some B horizon materials exhibit substantial P sorption and this is mostly due to allophane, with minor contributions from extractable Fe forms, organic carbon, and clay. Air-drying during summer and in the laboratory increased P sorption of B horizon materials by up to 120% compared with field-moist samples. The difference in P sorption between air-dried samples and the field-moist samples decreased for long reaction times.

Phosphorus Sorption Characteristics of Bh and Bt Horizons from Sandy Coastal Plain Soils

AbstractRetention of land‐applied P is an environmental concern in sandy Coastal Plain regions. Compositional differences between Spodosol Bh and Ultisol Bt horizons are likely to have major consequences for P retention. The purpose of this study was to compare P sorption‐desorption characteristics of Bh and Bt horizons using selective chelation to evaluate the effects of organically complexed Fe and Al in Bh samples. The Bh and Bt samples sorbed comparable amounts of P but Bh samples desorbed a higher proportion of their adsorbed P. After alkaline acetylacetone extraction of metal‐organic complexes, Bh samples lost most of their P adsorption capacity, but their desorption behavior was more like that of samples whose clay fractions were dominated by inorganic metal oxides. Aluminum‐organic matter complexes appear to be responsible for the high P adsorption capacity of Bh horizons as well as for the tendency of these horizons to release P more readily at low solution P concentrations.

Concentrations and Distributions of Eleven Metals in Florida Soils

Concentrations and distributions of 11 elements—Hg, Cd, As, Cu, Cr, Pb, Ni, Zn, Mn, Al, and Fe—in 40 Florida soil profiles (94 soil samples) were investigated. The soils were classified as Spodosols, Entisols, and Ultisols, representing major mineral soils in Florida. The geometric mean concentrations of Hg, Cd, As, Cu, Cr, Pb, Ni, Zn, Mn, Al, and Fe in surface soils (A horizons) were 0.0042, 0.21, 1.1, 3.7, 3.9, 4.1, 6.5, 12, 25, 730, and 820 mg kg−1, respectively. Metal concentrations in these soils were lower than those of published values of Florida agricultural soils and U.S. soils. Metal contents, excluding Cd and Mn, were strongly correlated with clay content (r = 0.35–0.77), and some metals (Cr, Ni, Pb, and Al) were correlated with cation exchange capacity (r = 0.23–0.35). Metal distributions in soils, therefore, reflected parent-material and pedogenic factors determining clay content variations between and within soil profiles. Generally, metal contents in soils decreased in the order of Ultisols > Entisols ≥ Spodosols and Bt > Bh > A ≥ E horizons. All metals except Cd, Hg, and Mn were concentrated in Bt horizons; As, Cu, Cr, Fe, and Al were enriched in Bh horizons, where clay and organic matter had accumulated.

Response of Aluminum Solubility to Elevated Nitrification in Soil of a Red Spruce Stand in Eastern Maine

Elevated concentrations of soluble Al can impair tree growth and be toxic to aquatic biota, but effects of acidic deposition on Al solubility in forest soils are only partially understood because of complex interactions with H + and organic matter. We therefore evaluated Al solubility in two red spruce stands in eastern Maine, one of which received dry (NH 4 ) 2 SO 4 at a rate of 1800 equiv ha -1 yr -1 during 1989-1995. Samples of soil (Spodosol Oa and Bh horizons) and soil solution were collected on five dates from 1992 to 1995. The treatment elevated nitrification, causing an increase in acid input that led to inorganic Al concentrations of greater than 60 μmol L -1 in both the Oa and Bh horizons. Solubility of Al was also lower in the Bh horizon of the treated stand than in the reference stand, a response related to higher DOC concentrations in the treated stand. Concentrations of CuCl 2 and pyrophosphate-extractable Al were higher in the Oa horizon of the treated watershed than the reference stand, a result of accelerated weathering of mineral particles caused by lower solution pH in the treated stand (3.47) than in the reference stand (3.69). Dissolved Al concentrations in these soils are the result of complex mechanisms through which mineral matter, organic matter, and pH interactto control Al solubility; mechanisms that are not incorporated in current Al solubility models.

Sandy Wet Spodosols: Water Tables, Chemistry, and Pedon Partitioning

AbstractSpodosols are notably difficult to classify in terms of moisture regime, presumably because redox colors are masked by spodic colors, or perhaps because the absence of structure in sandy Spodosols is a hindrance to detection of redox features. Some views of Spodosol pedons as a series of compartments raise the possibility that some portions of the spodic pedon are simply more responsive than others to saturation parameters. This study attempts to determine whether compartmentalization within Spodosol pedons results in differentiation of soil response to saturation and water table fluctuation. Water table and chemical data were compiled from 16 Aquod pedons. Pyrophosphate‐extractable Fe and Al, oxalate‐extractable Fe and Al, and dithionite‐extractable Fe and Al were determined for all soils; organic C was also determined for at least Bh, Bhs, and Bs horizons, and oxalate‐extractable Si and the optical density of the oxalate extract (ODOE) were also determined for eight of the pedons. Comparisons of chemical data to saturation and water table fluctuation indicated that spodic horizon chemistry was unresponsive to both saturation duration and water table fluctuation. Chemistry of E horizons was most responsive to water table fluctuation, while Al and Si levels of C horizons were more sensitive to saturation and water table fluctuations. Thus, due to compartmentalization of Spodosol pedons, interpretations of saturation and water table fluctuation can be most effectively made from the chemistry of C and E horizons, respectively. The B horizon chemistry was not a good indicator of saturation duration or of water table fluctuation patterns.