Oxalate-extractable Iron Research Articles

Phosphorus retention and sorption by constructed wetland soils in Southeast Ireland

It may be necessary to use constructed wetlands as a land use practice to mitigate phosphorus (P) loss from agriculture in Ireland. The objectives of this study were to determine the ability of two constructed wetland site soils to retain and sorb P. Intact soil/water column studies were used to determine P release/retention rates during a 30-day incubation period. Soil columns flooded with distilled water released P during the first 2 days; however, soluble reactive P (SRP) concentrations in overlying floodwaters decreased thereafter. Soils with overlying floodwaters spiked at 5 and 15 mg SRP L −1 retained highest amounts of P ( p < 0.05 ) with retention at these concentrations controlled by SRP in overlying waters. Retention rates by soils ranged between 0.3 and 60.9 mg P m −2 d −1. Maximum P sorption capacity ( S max) was higher for wetland soils at Dunhill, Waterford (1464 mg P kg −1) in comparison to soils at Johnstown Castle, Wexford (618 mg P kg −1). Equilibrium P concentrations (EPC 0) were low (in the μg SRP L −1 range), indicating a high capacity of these soils to sorb P. Phosphorus sorption parameters were significantly related to ammonium oxalate extractable aluminium (Al) and iron (Fe) content of soils.

Air Drying Affects Extractable Sulfate in Soils of Variable Charge: Test of Two Extraction and Two Quantification Methods

Fertilizer recommendations need to be based on reliable soil sulfate determinations. Airdrying samples changes irreversibly many properties of soils with variable charge and might affect the extractable sulfate. In this study, sulfate extracted from air‐dry and field‐moist samples was compared. Two extracting solutions [water and 00.1 M Ca(H2PO4) 2] and two quantification methods (turbidimetry and ion chromatography) were assayed on A and B horizon samples of five Humic Acrisols from southeast Mexico. Air drying increased water‐extractable sulfate in Ah horizons, whereas in Bt horizons, it increased the 00.1 M Ca(H2PO4)2‐extractable sulfate. Airdrying increased dissolved organic carbon contents in all samples and increased soil acidity and oxalate extractable iron in 70 and 60% of the samples, respectively. Results showed larger coefficients of variation in air‐dried samples. Turbidimetry resulted less sensible than ion chromatography. To enhance sensitivity and reproducibility, particularly organic soil samples should be analyzed field‐moist and by ion chromatography.

Cadmium Solubility and Sorption in a Long‐Term Sludge‐Amended Arable Soil

Cadmium solubility and sorption in an arable clay loam soil that had received sewage sludge for 41 years were compared to an unsludged control in batch studies. Soil pH dominated Cd sorption, explaining >92% of the variation in Kd values in both treatments. At any pH, Cd sorption was apparently slightly but significantly (p < 0.05) smaller in the sludge-amended soil compared to the control, even though the organic carbon content was 70% larger and the ammonium oxalate-extractable iron content was roughly doubled. Correction for dissolved organic carbon (DOC) complexation with the speciation model WHAM reduced the difference in sorption between treatments, but the sludged soil still had significantly smaller Kd values (p < 0.01). Batch equilibrations without addition of Cd showed that there was no significant difference in the solubility of "native" cadmium (defined as EDTA-extractable Cd) in sludged and control soils. The reason for the lack of increase in Cd sorption in the sludge-amended soil has not been established, but it may be due to competition for sorption sites on humic compounds with sludge-derived Fe and trace metals such as zinc. The fact that the pyrophosphate-extractable (i.e., organically associated) iron content was seven times larger in the sludged soil provides some supporting evidence for this hypothesis.

Plant and Soil Responses to Biosolids–Phosphorus in Two Florida Soils with High Phosphorus Content

Greenhouse studies were conducted to evaluate the effects of biosolids amendments on phosphorus (P) availability in two Florida pasture soils with medium to very high native P content. Three granular, anaerobically digested, heat-treated, exceptional quality biosolids (from Baltimore, MD, Tampa, FL, and Largo, FL), and a commercial fertilizer, concentrated super phosphate (CSP) were applied to A horizons of the two soils: the Millhopper sand [very high native P and oxalate extractable iron + aluminum (Fe + Al)] and the Candler sand (medium to high native P and oxalate extractable Fe + Al). After a four-month cropping season, bahiagrass (Paspalum notatum Flugge) yields did not vary with P-sources and application rates primarily because of the natively high soil-P. The effect of added P on P uptake by bahiagrass was minimal in the Millhopper soil, but significant in the Candler soil. The excessive native P and high P retention capacity of Millhopper soil masked the effect of P addition by the amendments. In the Candler soil, P uptake was much larger in treatments involving CSP and Largo biosolids, which have greater KCl-extractable (hence, readily available) P contents than Tampa and Baltimore materials. Biosolids-P availability varied in the order: Largo ≫ Tampa > Baltimore. The Mehlich I-P was better correlated with P uptake by bahiagrass in Candler soil than the Millhopper soil. Two factors appeared to control the availability of P in treated soils: the chemical forms of P in P-sources, and the chemical properties of soils. Native P contents and P fixing capacities of soils need to be considered while interpreting soil test results. This study demonstrated the presence of a soil P threshold beyond which there is virtually no effect of P addition on plant P uptake.

Arsenate sorption by reduced and reoxidised rice soils under the influence of organic matter amendments

Arsenic (As) sorptivity and acetate (pH 4.8) and oxalate (pH 3.0) extractable iron levels were monitored for 180 d, during and after flooding of two As contaminated soils. The effects of three different organic matter supplements/amendments, for example farm yard manure (FYM), municipal solid waste compost (MSWC) and sewage-sludge (SS) on the above parameter were also examined. In nonflooded soils, As sorptivity was mainly influenced by clay content. On flooding, there were large increases in acetate, oxalate extractable iron and As sorptivity. Organic matter addition increased the same parameters. Among the organic matters, SS showed greater effect on As sorption followed by MSWC and FYM. During flooding, As sorption is mainly dependent upon poorly crystalline iron oxide. During oxidation of previously flooded soils, levels of As sorptivity, acetate and oxalate extractable iron decreased rapidly, but did not return to the levels occurring before reduction. SS and MSWC served as binding agents for native and irrigation water As, thereby moderating the rapid As mobilization to the crop rizosphere.

Vertisol genesis in a humid climate of the coastal plain of Texas, U.S.A.

Numerous genetic studies of Vertisols have been conducted using qualitative and semi-quantitative methods across a broad range of climates. However, no detailed investigations exist on Vertisols formed in humid climates using multiple pedogenic techniques on both a microlow (ML) and microhigh (MH). Hence, we sampled and characterized a ML and MH from a Lake Charles pedon (mean annual rainfall=1090 mm, mean annual temperature=20 °C) in the late Pleistocene coastal plain Beaumont Formation of east Texas. According to the official series description the Lake Charles classifies as a fine, smectitic, hyperthermic Typic Hapludert with mollic and calcic diagnostic horizons. Coupled with field morphology and characterization data, micromorphology and constituent mass balance interpretations were used to reconstruct the major pathway of pedogenesis. In response to greater water recharge, the ML contains darker colors, more organic carbon, greater depth of carbonate leaching, and lower pH. The proportion of oxalate-extractable iron increases toward the surface and is in greater abundance in the ML than MH. In contrast, dithionite-extractable iron increases with depth and has similar quantities in both the ML and MH. The parent material and lower profiles contain asepic microfabric dominated by micaceous-rich coarse clay and silt. The asepic zone deep contains an abundance of soft carbonate masses and iron manganese segregations that appear to be forming contemporaneously, with the presence of argillans substantiating clay translocation during the early history of soil formation. Sepic microfabric dominates the upper profiles of both the ML and MH in part from the transformation of biotite to smectite, which is more pronounced in the microlow because of more intense weathering. Hard carbonate nodules and iron manganese concretions are abundant in the upper sepic zone and contain skelsepic microfabric, suggesting that they are no longer growing. Dilation was the dominant strain force during pedogenesis from volume expansion in response to crack infills and shrink–swell processes. Mass flux calculations indicate that total clay gains occurred in both the ML and MH during pedogenesis. Late Pleistocene Vertisols appear to approach steady state when forming in humid climates. The soil mechanics model best explains the observed depth distribution of properties, including slickensides, with pedoturbation playing a secondary role in the genesis of these humid-climate Vertisols.

Phosphorus Sorption Capacity of the Surface Sediment in the Lake Taihu and Risk Assessment of Phosphorus Release

Phosphorus sorption capacity of the surface sediments are estimated by the phosphorus sorption index (PSI) and the degree of phosphorus saturation (DPS) of the sediments in the Lake Taihu, China. In addition, the spatial variability of phosphorus sorption capacity of the sediments is discussed by the geostatistical methods of Kriging griding. There are higher concentrations of ox- alate extractable phosphorus, iron and aluminum in the sediments of northeastern Meiliang Bay and Wuli Lake, while they are lower in the sediments of southern Lake Taihu. The spatial variability of oxalate extractable phosphorus, iron and aluminum may be largely attributed to the inputs of wastewaters. The distribution of phosphorus sorption indices of the Taihu sediments are charac- terized by higher in the north, lower in the south, higher in the west, and lower in the east, etc., while the very reverse is the distribution of degree of phosphorus satufation. DPS are less than 20% in most lake areas except that it is more than 30% in the northwestern Meiliang Bay. The phosphorus sorption capacity may be mainly controlled by the amorphous iron and aluminum ox- ides/hydroxides, and also be affected by organic matter contents in the sediments. The P--induced lake eutrophication risk index (ERI) is developed as the percentage of DPS divided by PSI, and is applied on the assessment of eutrophication risk of the Lake Taihu.

Pools of selenium in some Indian soils at field capacity and submerged moisture regimes

Pools of soil selenium (Se) as influenced by moisture regimes were investigated in some normal and seleniferous (which produce vegetation containing &gt;5 mg Se/kg—the maximum permissible level for animal consumption) soils of India. Soil samples were equilibrated with 75Se by subjecting to alternate wetting and drying cycles and incubated at field capacity and submerged moisture regimes. Each soil sample was subjected to either single extraction with 0.25 M KCl, 0.1 M KH2PO4, and 4 M HCl in a sequence or 7 extractions with KCl followed by 7 extractions with KH2PO4 and 2 with HCl. Amount of 75Se extracted from different soils incubated at field capacity through single extraction with 0.25 M KCl varied from 8.4 to 30.5% of applied 75Se for alkaline and 2.6 to 10.4% for acidic soils. Among alkaline soils, a greater amount of 75Se was extracted from highly calcareous non-seleniferous soils than seleniferous soils. The amount of selenium extracted through 7 sequential extractions with 0.25 M KCl was 1.5–7.0 times greater than that extracted through single extraction. A significant coefficient of correlation between 75Se extracted through repeated extractions with 0.25 M KCl and pH of the soils (r = 0.93, P�≤ 0.01) suggested greater availability of Se in alkaline than acidic soils. Specifically sorbed soil Se extracted with 0.1 M KH2PO4 through 7 sequential extractions ranged from 15.3 to 24.6% for alkaline and 24.4 to 40.1% for acidic soils. The amount of 75Se desorbed through multiple extractions with 4 M HCl was negatively correlated with pH (r�= –0.95, P ≤ 0.01) and electrical conductivity (r = –0.85, P ≤ 0.05) of the soils. After subjecting to single extraction, residual 75Se left in soils incubated at field capacity moisture varied from 11.7 to 59.7%. It was negatively correlated with pH (r = –0.85, P ≤ 0.05) and CaCO3 (r = –0.79, P ≤ 0.10) and positively correlated with ammonium oxalate extractable iron content (r = 0.76, P ≤ 0.10) of soils. Compared with the single extraction procedure, only a small amount (9–36%) of 75Se was left as residual 75Se after multiple extractions. Relatively less 75Se was released when the alkaline or acidic soils incubated under submergence were subjected to single or multiple extraction procedures. The multiple extraction procedure could better assess different soil Se pools than the single extraction procedure. At field capacity moisture, large amounts of Se occur in easily available forms. Under submerged conditions, substantial amounts of Se are maintained in the soil solution when Se is removed from the solution through plant uptake or leaching.

An Andosol–Cambisol toposequence on granite in the Austrian Bohemian Massif

In Europe, non-allophanic Andosols are linked with Hercynian basic and metabasic rocks in smoothed highlands with a cool and humid climate. We describe an Andosol–Cambisol toposequence derived from Variscan coarse-grained granite in Northern Austria (Bohemian Massif), where Andosols have formed on plateaus and Cambisols on steep slopes. The climate is continental, cool and humid (mean annual temperature and rainfall: 5.4 °C and 914 mm), with a 100-day mean annual period of snow cover. The forest is dominated by beech and spruce trees. Both soils are rich in organic matter and strongly acidic, but the Andosol is more strongly weathered than the Cambisol. Below the 15-cm-thick litter in the Andosol, the 38-cm-thick AB-Bw solum is dark reddish brown to strong brown, has a large C content (9.0–4.4%), and meets all the requirements of an andic horizon. In these horizons, oxalate extractable iron content (1.6–2.8% Fe o) represents 76–84% of free iron, and is much larger than Al o (0.8–1.5%). Both biotite and plagioclase are sources of Fe and Al. The formation of non-allophanic Andosol from granite was likely due to the combination of the following factors: cool and humid climate, large accumulation of organic matter, high infiltration rate, intense water percolation during spring thawing and significant content of weatherable minerals. As such conditions are not rare in European highlands, andic soils are probably more widespread in Europe than is currently thought.

Refractory organic carbon in particle-size fractions of arable soils II: organic carbon in relation to mineral surface area and iron oxides in fractions

The interaction of organic compounds with the mineral phase is considered as one stabilization mechanism for organic carbon (OC) in soils. The objective of this study is to assess the role of mineral surfaces for the long-term stabilization of OC in arable soils, with special emphasis on iron oxides. Soil samples were taken from two contrasting treatment types, i.e. fertilized plots and C-depleted plots, in long-term agroecosystem experiments. The soil organic carbon pool of the C-depleted plots is considered to show a lower contribution of labile compounds and consequently to be relatively enriched in refractory compounds compared with the fertilized counterparts. In fractions <6 μm, OC was studied in relation to total mineral surface area, surface area contributed by oxides and silicates, and the content and type of iron oxides (dithionite and oxalate extractable iron, Fed and Feo). In two sandy soils, OC contents were linearly related to total mineral surface area and the content of the two iron oxide fractions (Fed and Feo). The surface area developed by the silicates was low and thus the surface area contribution from oxides was dominant in fractions <6 μm. In contrast to the sandy soils, in a loamy soil OC was not correlated with surface area or the iron oxide content. However, the different soils agreed with respect to the behavior of C in density fractions: losses of OC occurred mainly from the light fraction (⩽2 g cm−3), whereas C in the heavy fraction (>2 g cm−3) proved to be stable. For the sandy soils, mineral surface area appears to control the storage of OC in fine fractions. Given the dominant surface area contribution from oxides, OC storage here primarily depends on the oxides. The C-depleted plots in particular show that surface area controls the accumulation of refractory C. The interaction of organic compounds with the mineral phase, mainly with the surface of oxides, seems to be a major mechanism for the long-term stabilization of OC in these sandy soils. An interaction with minerals seems to be important for stabilizing OC also in the loamy soil, although this is not reflected by a proportional relation between OC and surface area across the fractions.

A simple phosphorus buffering index for Australian soils

Soil phosphorus (P) buffering capacity (PBC) is an important soil property that influences the amount of P fertiliser available for plant uptake. However, current methods of determining PBC are time-consuming and uneconomic in most commercial soil testing programs. The current study examined simpler methods of measuring the PBC of a wide range of Australian soils. Phosphorus sorption and extractable P data from 290 soils (initial data set) were collated to define the range of PBC values of Australian agricultural soils. Independently, detailed chemical and physical analyses were undertaken on a second set of 90 agricultural soils (principal data set), which were selected to represent the range of soil properties measured on the initial data set. Relationships between PBCO&amp;S (Ozanne and Shaw 1968) values (P sorbed between solution P concentrations of 0.25 and 0.35 mg P/L) and 11 different single-point P sorption indices and selected soil properties were examined for the principal data set. Whilst relationships between PBCO&amp;S values and selected soil properties such as oxalate-extractable iron and aluminium, and clay content, were generally poor, strong relationships existed between all of the single-point P sorption indices and PBCO&amp;S. Results suggest that PBCO&amp;S values were most closely related to the P buffering indices (PBI+ColP and PBI+OlsP) when a single addition of 1000 mg P/kg was added to soil and either the Colwell or 4.59 Olsen extractable P were added to the amount of P sorbed: PBI+ColP = (Ps + Colwell P)/c0.41 PBI+OlsP = (Ps + 4.59 Olsen P)/c0.41 where Ps is the amount of P sorbed (mg P/kg) from a single addition of 1000 mg P/kg, and c is the resulting solution P concentration (mg P/L). This index provides a simple and accurate method for estimating PBC, a fundamental soil property that influences the P fertiliser requirements of different soil types. phosphorus sorption capacity, single-point phosphorus sorption index, phosphorus retention index, soil properties, Colwell phosphorus, Olsen phosphorus.

SPATIAL VARIABILITY OF SULFATE ISOTHERMS IN FOREST SOILS AT DIFFERENT SCALES AND ITS IMPLICATIONS FOR THE MODELING OF SOIL SULFATE FLUXES

To predict reversibility of soil and water acidification under conditions of decreasing S-input into forested ecosystems, the amount of reversibly bound SO2−4 in the soil as well as its desorption behavior must be considered. This study investigated variability of sulfate isotherms and their spatial scaling. The Langmuir isotherm parameters in two forested catchments (one deciduous, one coniferous stand) and their spatial distribution at two different scales (site and catchment scale) were investigated. The soil samples (250 cm3) were taken in a systematic grid with spatial distances ranging from 20 × 20 m to 300 × 300 m. Isotherm parameters, soil pH, dithionite- and oxalate-extractable iron and aluminum, crystalline iron oxide, and Corg content were determined. Significant relationships were found between sulfate sorption isotherm parameters and soil chemical properties for each site. It would be useful to be able to replace the experimental determination of isotherm parameters with the less costly measurements of soil chemical properties such as pH, Al- and Fe-oxides, and Corg content of the soils. Regression analysis, however, resulted in different parameters for each site. Thus, at sites where this relation is unknown, isotherms have to be determined via soil extraction procedures and cannot be predicted by soil chemical properties. To determine the average isotherms with an accuracy of ± 0.2 μmol g−1 SO2−4 sorb, a sample size of 55 for the site scale and up to 106 for the catchment scale is required. The semivariance of the isotherm parameters revealed no spatial patterns. The influence of isotherm variability on the prediction of SO2−4 - fluxes with seepage was investigated using the chemical equilibrium model MAGIC. Forecast accuracy depends on proper consideration of the variability of sulfate sorption in a catchment.

Pesticide Sorption by Low Organic Carbon Sediments: A Screening for Seven Herbicides

AbstractThe sorption of seven pesticides in 10 Danish aquifer sediments has been studied. These sediments all have a total organic carbon (TOC) content below 1 g kg−1, and include carbonate‐bearing and carbonate‐free Quatenary sand deposits and a Cretaceous chalk aquifer. Batch experiments were carried out with metamitron, atrazine, isoproturon, mecoprop, 2,4‐D, bentazone, and metsulfuron‐methyl at an initial pesticide concentration of 0.25 mg L−1 in ground water. Generally, the sorption decreases in the order: metamitron, atrazine, isoproturon, mecoprop, 2,4‐D, metsulfuron‐methyl. The bentazone sorption was found to be insignificant. For a specific pesticide the sorption covers a range of Kd values (L kg−1) reflecting the different sediment characteristics. Multivariate regression analyses demonstrate that: (i) metamitron sorption is enhanced by increasing content of iron silicates; by contrast the oxalate extractable iron oxides have no influence on the metamitron sorption; (ii) sorption of atrazine, mecoprop, and 2,4‐D depends primarily on pH; the sorption is high at low pH (&lt;6.7) compared with sorption at higher pH (&gt;7.4); (iii) metsulfuron‐methyl only sorbs at pH below 5; and (iv) isoproturon sorption is primarily influenced by the specific surface area (SSA) and TOC. The present results illustrate the importance of choosing sediments of different geological origin in order to describe the influence of sediment properties on pesticide sorption.

Relating Sulfate Adsorption to Soil Properties in Japanese Forest Soils

The relationship of sulfate adsorption capacity to the presence of aluminum, iron oxides, and organic carbon in four Japanese forest soils was investigated. Sulfate adsorption capacities were higher in subsoils than in surface soils, and their profiles were the inverse of those of organic carbon content. The black soil derived from volcanic ash had high sulfate adsorption capacity and showed no release of sulfate, while some of the surface horizons of the other soils desorbed sulfate. Oxalate extractable aluminum (Al0) and iron (Fe0) and ditionite-citrate-bicarbonate (DCB) extractable iron (Fed) were positively correlated with the sulfate adsorption capacity, and their correlation coefficients were almost identical (0.58–0.61). The lack of significant correlation between Ald and the adsorption capacity suggests that DCB is unsuitable for extracting aluminum compounds which have the ability to adsorb sulfate. In contrast with oxides, organic carbon correlated with sulfate adsorption capacity negatively, and had a negative coefficient in a multiple regression equation, insignificantly. Furthermore, H2O2-treated samples containing decomposed organic matter adsorbed more sulfate than untreated samples. These results clearly indicated that organic matter hinders sulfate adsorption. A comparison of the β value (standard regression coefficient) of organic carbon with that of Al0 showed that the negative contribution of organic matter to sulfate adsorption capacity was slightly less than the positive contribution of oxides.

Iron oxides in plinthic soils on sedimentary deposits in northeastern Brazil

This study was conducted to examine the distribution and nature of Fe oxides in plinthic soils on the sediments of Barreiras Group (in the state of Piauí) and Itapecuru Formation (in the state of Maranhão) in Northeastern Brazil. Four pedons were selected: a "plinthic, dystrophic, epieutrophic Gray Podzolic with low activity clay" and a "dystrophic Plinthosol with low activity clay" (both Plinthic Kandiustalfs) on the Barreiras sediments, as well as an "eutrophic Plinthosol with low activity clay" and an "allic Plinthosol with low activity clay" (both Plinthustalfs) on the Itapecuru sediments. Soil samples were fractionated into &gt; 2 mm (pisoliths), water-stable aggregates (plinthite) and matrices; the aggregates and matrices were further fractionated into sand, silt and clay sizes. Dithionite extractable iron (Fe d) and aluminum (Al d), as well as oxalate extractable iron (Fe o), were determined for all fractions, and X-ray diffraction analyses were performed on the pisoliths. It was observed that the Plinthustalfs contain more iron oxides, exhibit more extensive plinthite development and have a greater potential for further plinthite development than the Kandiustalfs. The distribution of values for the Fe d indicates that plinthite formation and induration in all soils were accompanied by an enrichment of Fe oxides in all particle size fractions. This Fe segregation was accompanied by aggregation of particles leading to a greater degree of crystallinity, as indicated by analysis of the ratios of Al d:Fe d. Larger ratios of goethite to hematite, and relatively smaller amounts of silicates in the more mature pisoliths were revealed by X-ray diffraction analysis. Ratios of Al d:Fe d were larger in the Kandiustalfs than in the Plinthustalfs, and also larger than expected for Al-substituted Fe oxides. According to ratios of Al d:Fe d, Fe mobilization in all soils has likely occurred under reducing conditions, facilitated by organic matter on the soil surface.

Contents and profile distribution of three forms of free iron oxides in three ultisois and an alfisol in Nigeria

The contents and pedogenetic distribution of pyrophosphate, oxalate, and dithionite extractable iron oxides were examined in three Ultisois and an Alfisol developed on older granites. The soils represented a bio‐climatic sequence in Nigeria, the Sudan, Northern Guinea, and Southern Guinea savannas and the Rainforest zones. Pyrophosphate extractable iron (Fe) in the soils rangfid from 0.14 to 0.69%, oxalate extractable iron (Feox) ranged from 0.03 to 0.36%, whereas the dithionite extractable form (total free iron oxides) varied from 0.50 to 8.00%. The contents of pyrophosphate and oxalate extractable Fe, i.e., the amorphous forms were low and represented only 0.9 to 28% and 5 to 6%, respectively, of total free iron oxides. The soil in the more humid rainforest contained the highest amounts of all forms of free Fe oxides. In the savanna soils the contents of free iron oxides decreased in the order Northern Guinea > Sudan > Southern Guinea. Pyrophosphate and oxalate extractable Fe increased slightly with depth but dithionite extractable Fe gave large bulges in the argillic horizons.

Mineralogical properties of andisols of the Kitakami mountain range, Northeastern Japan

We studied the mineralogical properties of Andisols of the Kitakami mountain range. Soils of the northern and central parts of the mountain range contained higher levels of acid oxalate extractable silicon (Sio), aluminum (A1o), and iron (Feo) but smaller amounts of sodium pyrophosphate-extractable aluminum (Alp), iron (Fep), and carbon (Cp) than those of the southern part. Consequently, the soils of the northern and central parts of the mountain range contained large amounts of allophane and ferrihydrite whereas in the soils of the southern part A1 (Fe)-humus complexes and 2:1 and 2:1:1 clays predominated. The amount of sand (20-2,000 μm) in the soils tended to decrease sharply from the north to the south of the mountain range. The soils of the northern and central parts of the mountain range contained larger amounts of heavy minerals in their fine sand fraction (20-200 μm). The soils of the southern part, on the other hand, contained larger amounts of fine-grained quartz (2-20 μm). All the soils of the mountain range contained substantial amounts of volcanic glass in their sand fraction. However, on a total soil basis, the amount of volcanic glass in the soils decreased from the north to the south of the mountain range and the trend was parallel to that of the sand content of the soils. From these results, we concluded that (i) the soils of the northern and central parts of the mountain range were derived mainly from tephras and (ii) the soils of the southern part were strongly influenced by long-range eolian dust.

Sistemas de cultivo e características do solo afetando a estabilidade de agregados

Em um Latossolo Roxo de Santo Ângelo (RS), e em um Podzólico Vermelho-Escuro de Eldorado do Sul (RS), ambos com textura argilosa, submetidos o primeiro à exploração com cultivo convencional de trigo (Triticum aestivum L.) e soja (Glycine max L.) e sob setária (Setaria anceps L.), e o segundo à exploração com capim-pangola (Digitaria decumbens L.), siratro (Macroptilium atropurpureum L.), plantio direto com aveia (Avena bizantina L.)/milho (Zea mays L.) e área sem vegetação, foi realizado o presente trabalho durante a safra de verão (1990/1991), com o objetivo de avaliar a estabilidade e a agregação do solo sob diferentes sistemas de cultivo. Constatou-se, nessa avaliação, que as gramíneas perenes por meio do seu sistema radicular tiveram grande efeito na agregação e estabilidade dos agregados do solo e que os teores de carbono orgânico, de ferro e alumínio-oxalato, argila e grau de dispersão tiveram também efeitos na agregação do solo, porém insuficientes para explicar as variações entre o diâmetro médio ponderado dos agregados sob os diferentes sistemas de cultivo.

Phosphate adsorption characteristics of soils, slags and zeolite to be used as substrates in constructed wetland systems

Constructed wetlands are used to remove pollutants from wastewater. The performance of such wetlands to remove pollutants from wastewater can be improved by using suitable substrates. In this study the phosphorus (P) adsorption capacities of soils, two industrial by-products and a clinoptilolite material (zeolite) were examined for their potential use as substrates to remove P in constructed wetlands. Both Freundlich and Langmuir adsorption isotherms were used to describe the adsorption characteristics of these substrates. The Langmuir adsorption isotherm was used to calculate the maximum P adsorption capacity of these substrates. One of the industrial by-products, namely blast furnace slag, showed the highest P adsorption capacity (44.2 g P kg −1 slag) followed by soil samples collected from an operating (Byron Bay) constructed wetland system in Northern NSW (4.2 to 5.2 g P kg −1 soil). The surface soils collected from two regional constructed wetland systems were found to have the least P adsorption capacity (1153 and 934 mg P kg −1 soil, respectively for Richmond and Carcoar wetlands). The clinoptilolite material (zeolite), which is used to remove ammonium ion from wastewater, was found to have a P adsorption capacity of 2.15 g kg −1. The relationship between P adsorption and oxalate extractable iron (Fe) and aluminium (Al) showed that P adsorption related more closely to extractable Al (r 2 = 0.890) than Fe (r 2 = 0.736). Multiple regression analysis showed that P adsorption is more closely related to a combination of both oxalate extractable Fe and Al (r 2 = 0.901) than extractable Fe or Al alone. The P saturation capacity of wetland systems incorporating these substrates is described. The results suggest that selected industrial by-products and adsorptive materials may be used alone or in combination with soils to improve the performance of constructed wetland systems subject to other properties such as pH, permeability and structural stability of these materials.

Spatial variation of soil test phosphorus and potassium, oxalate‐extractable iron and aluminum, phosphorus‐retention index, and organic carbon content in soils of Western Australia

Spatial variation of bicarbonate soil test phosphorus (P) and bicarbonate soil test potassium (K) was studied by measuring soil test values for 40 individual soil samples collected from random locations within eight uniform 100 m by 100 m field sites in south‐western Australia. In addition, for five of the sites, spatial variation of the three P sorption indices (ammonium oxalate extractable iron, ammonium oxalate extractable aluminum, and the P retention index) and of organic carbon (C) was measured for 20 individual soils samples. Spatial variation was found to be large, with coefficient of variation (CV) exceeding 20% in most cases, and 50% in some cases. It is therefore essential to collect an adequate number of soil samples from uniform areas in paddocks in order to provide a representative composite sample to measure the soil properties.