Calcium Carbonate Equivalent Research Articles

Analytical methods and quality assurance

Soil acidification under tropical and sub‐tropical conditions is a well known phenomenon. Because of cost implications in practice it is important that the best available liming materials be used. Various methods have been employed to distinguish between the effectiveness of such materials, most based on the principle of calcium carbonate equivalent. Many of these use relatively strong acids for dissolution of lime, at concentrations far greater than ever actually occur in even the most acid soils. Because contact exchange between the acidified sites and the liming material is considered to be vital, a method in which a slightly acidified cation exchange resin is used was developed (the resin exchange method). This method has been used by several laboratories in South Africa that take part in the quality control scheme run by ALASA. Several problems were experienced in achieving reproducibility between laboratories, that were diagnosed as being due to variations in applications of the method and especially lack of discipline in using a standardized resin. This resulted in a number of independent investigations into reasons for this apparent lack of reproducibility. Reasons for this included inherent particle size distribution in the sub‐samples of liming material, resin properties, water quality and electrode maintenance and calibration. Under standardized and controlled conditions the method proved to be eminently satisfactory. An alternative possibility that is being investigated is the use of an unbuffered acid topsoil to replace the resin. A bulk sample could be homogenized and subdivided to provide an adequate supply.

Response of Overseeded Alfalfa and Bermudagrass to Alfalfa Row Spacing and Nitrogen Rate

Alfalfa (Medicago sativa L.) is a rare forage crop on Coastal Plain soils. Acid soils, wet conditions, and the prevalence of perennial, warm‐season grasses limit alfalfa production. Development of grazing‐tolerant varieties raised interest in growing alfalfa on the Coastal Plain. This three‐year dryland field study was conducted to evaluate coincident production of ‘Alfagraze’ alfalfa and ‘Coastal’ bermudagrass [Cynodon dactylon (L.) Pers.] as a sustainable forage system. Limestone (effective calcium carbonate equivalence ECCE 72%) at a rate of 6.1 t ha−1 was incorporated by roto‐tilling 15 cm deep in an established sod of Coastal bermudagrass on a Darco loamy fine sand (loamy, siliceous, thermic Grossarenic Paleudults) in late winter 1990, with an additional 3 t ha−1 surface‐applied in June 1991. Alfalfa was seeded in October 1990 at 23, 46, 69, and 92 cm between rows in main plots of a split‐plot design. Nitrogen rates from 0 to 112 kg ha−1 in increments of 28 kg ha−1 were applied to subplots for every bermudagrass regrowth cycle. Other plant nutrients (including P, K, Mg, S, B, Zn, and Cu) were applied at rates considered adequate for alfalfa on a low‐fertility soil. Yield of alfalfa at the 23‐cm row spacing in 1991 was 8.8 t ha−1 and declined to 6.7 t ha−1 at , while yield of bermudagrass increased from 3.2 to 5.7 t ha−1, respectively, at these row spacings. In 1992, alfalfa yield increased an additional 2.2 t ha−1 at each row spacing, with a compensating decline in bermudagrass production. Alfalfa yielded 11 t ha−1 at all row spacings in 1993, despite a midseason drought, while bermudagrass yield was <450 kg ha−1. Row spacing had no effect on total forage production in any year. Higher N rates increased bermudagrass yield the first two years. Applied N increased alfalfa yield at certain harvests, but had no effect on total annual production. Crude protein in alfalfa declined or remained similar as row spacing was widened. Soil pH was lowered by increasing N rates and by narrower alfalfa row spacings. Results indicate that alfalfa competes well with Coastal bermudagrass, even in drought conditions.

Ameliorating acid soils with organic materials: effects of amendments derived from coal on yield and composition of young wheat plants grown on an acid red podzol

Acidity in surface and subsurface soil horizons limits crop and pasture production over considerable areas of the world, and lime is the traditional amendment used to neutralize surface soil acidity. Earlier reports have indicated that calcium (Ca)‐saturated organic materials, produced by the oxidation of coal, may be of value as ameliorants for subsurface acidity. Two of them (OXPR and OXFU) were evaluated and compared with lime in pot studies with wheat (Triticum aestivum). In the first experiment, lime, OXPR and OXFU, each at four rates, were applied to an acid red podzolic soil, high in extractable aluminum (Al) and were compared for their ability to improve seedling root growth. In the second experiment, the three amendments were applied to the same soil and shoot yields and mineral content were measured after five weeks growth. The three amendments raised soil pH, lowered extractable Al and increased root elongation. OXFU at the highest rate (251 ha‐1) inhibited root growth possibly due to the high concentration of solutes as indicated by high electrical conductivity of the soil solution. In the second experiment the three amendments improved shoot yields, with significant increases up to 0.81 Ca ha‐1 application. Yields were in general higher with lime than with OXPR and OXFU at equivalent rates of added Ca. However, a significant asymptotic relationship was observed between yield and calcium carbonate (CaCO3) equivalence of each of the applied amendments. Yield was highly correlated with measures of soil Al {r2 for [Al] in 0.01M calcium chloride (CaCl2), 0.915; [Al] in 0.1M barium chloride (BaCl2)/ammonium chloride (NH4C1), 0.873; [Al] in water, 0.779; [Al] in water/EC, 0.904}. Plant manganese (Mn) concentrations were decreased by lime and OXPR and there were linear correlations between plant Mn concentration and soil Mn extractable in 0.01 M CaCl2 With OXFU, which has a high concentration of water soluble Mn, plant Mn was decreased below the unamended controls only at the higher rates of application. .Leaf tissue zinc (Zn) concentrations were high in treatments receiving the two coal‐derived amendments. In an effort to determine the role of ion complexation in the remediation process, a third study evaluating the Al complexing ability of the two coal derived products was compared to that of a water‐soluble fraction extracted from chestnut (Castanea saliva) litter which is known to have a high affinity for Al. The two coal derived materials had considerably lower affinities for Al than the chestnut extract supporting the thesis that complexing reactions were of minor importance in the observed responses. The results indicate that field testing of these products is warranted particularly at sites where plant growth is constrained by subsurface soil acidity.

Manganese retention by selected calcareous soils as related to soil properties1

Calcareous soils often need supplemental manganese (Mn) to support optimum plant growth, but some reports show that the apparent recovery of applied Mn is very low in such soils, i.e., nearly all of the applied Mn is retained in the soil. This experiment was conducted to find the relationship between the retained Mn and selected properties of calcareous soils. Eleven surface (0–20 cm) soil samples with pH ranging from 7.7 to 8.1 and calcium carbonate equivalent (CCE) ranging from 20 to 50% were used in the Mn adsorption study. Two‐gram subsamples of each soil were equilibrated with 20 mL of 0.01M CaCl2 solutions initially containing 10 to 200 mg Mn L‐1. The Mn that disappeared from solution (after 6 h shaking at 25°C) was considered as adsorbed (retained) Mn. The adsorption data showed a highly significant fit to Freundlich and also to the two‐surface Langmuir adsorption isotherms. The coefficients of both isotherms showed significant positive correlations with cation exchange capacity (CEC), organic matter (OM), and CCE of the soils indicating that OM and calcium carbonate are the sites of Mn retention in calcareous soils. Comparison of the adsorption data of this experiment with those of plant Mn uptake of the same soils (published earlier) shows that as the Langmuir second surface adsorption maxima (maximum retention capacity) of the soils increase the plant Mn concentration and uptake decrease.

DEEP WEATHERING OF CALCAREOUS SEDIMENTARY ROCK AND THE REDISTRIBUTION OF IRON AND MANGANESE IN SOIL AND SAPROLITE

Iron and Mn redistribute in soil and saprolite during weathering. The geological weathering fronts ofcalcareous sedimentary rock were investigated by examining the bulk density, porosity, and distribution ofCa, Fe, and Mn. Core samples were taken ofsoil, saprolite, and bedrock material from both summit (HHMS-4B) and sideslope (HHMS-5A) positions on an interbedded Nolichucky shale and Maryville limestone landform in Solid Waste Storage Area 6 (SWSA-6). This is a low-level radioactive solids waste disposal site on the Dept. ofEnergy (DOE) Oak Ridge Reservation in Roane County Tennessee. This work was initiated because data about the properties of highly weathered sedimentary rock on this site were limited. The core samples were analyzed for pH, calcium carbonate equivalence (CCE), hydroxylamine-extractable (HA) Mn, and dithionite-citrate (CBD)-extractable Fe and Mn. Low pH values occurred from the soil surface down to the depth of the oxidized and leached saprolite in both cores. The CCE and HA-extractable Mn results were also influenced by the weathering that has occurred in these zones. Extractable Mn oxide was higher at a lower depth in the oxidized and leached saprolite compared with the Fe oxide, which was higher in the overlying soil solum. Amounts of Mn oxides were higher in the sideslope core (HHMS-5A) than in the summit core (HHMS-4B). Iron was more abundant in the deeper weathered summit core, but the highest value, 39.4 g kg -1 , was found at 1.8 to 2.4 m in the sideslope core. The zone encompassing the oxidized and partially leached saprolite down to the unoxidized and unleached bedrock had higher densities and larger quantities of CaCO 3 than the soil solum and oxidized and leached saprolite. The overlying soil and oxidized and leached saprolite had lower pH and CCE values and were higher in Fe and Mn oxides than the oxidized and unleached saprolite. The distribution of Fe and Mn is important when evaluating soil and saprolite for hazardous waste disposal site assessment.

Extractability of previously‐applied zinc as influenced by properties of calcareous soils1

The recovery of applied zinc (Zn) by plants is relatively small. Coupled with lack of leaching, this leads to accumulation of Zn in topsoil which may result in unfavorable growth conditions for the subsequent plants. Different extractants may be used for assessing the Zn status of soils previously treated with Zn sources. The extractability of retained Zn is influenced by soil properties. This experiment was conducted to study the influence of selected properties of calcareous soils on extractability of Zn by three popular Zn soil tests. Twenty samples from surface horizons (0–20 cm) of highly calcareous soils of southern Iran (pH 7.9 to 8.5; calcium carbonate equivalent 16 to 58%) previously treated with three levels of Zn (0, 10, and 20 mg Zn kg‐1 soil as ZnSO4#lb7H2O) in triplicate and under one crop of corn (Zea mays L.) were extracted with DTPA, EDTA‐(NH4)2CO3 and Na2‐EDTA. Extractability (EXT) in a particular extractant was defined as the slope of the regression line, relating extractable Zn of each soil to the rate of applied Zn, multiplied by 100. The EXT values of soils ranged from 24.9 to 73.0% for DTPA, 47.2 to 84.4% for EDTA‐(NH4)2CO3, and 28.2 to 56.7% for Na2‐EDTA. Stepwise regression equations showed that cation exchange capacity (CEC) and calcium carbonate equivalent (CCE) followed by clay content were the most influential soil properties in EXT of retained Zn of highly calcareous soils. The EXT values decreased with increase in CEC, and CCE but increased with increase in clay.

Interpretation of Soil Phosphorus Tests for Corn in Soils with Varying pH and Calcium Carbonate Content

There is uncertainty about appropriate soil-test extractants and interpretations in regions with soils varying in pH and calcium carbonate content. The objective of this research was to compare extractable P using the Bray-P 1 (B1), Olsen, and Mehlich-3 (M3) extractants and to obtain soil-test interpretations for corn (Zea mays L.) in soils varying in pH and calcium carbonate equivalent (CCE). The extractants were compared by correlating the amounts of P extracted from 350 soil samples and by calibrations based on 61 field response trials. Correlations between P extracted by the B1 extractant and the Olsen or M3 extractants improved markedly when calcareous soils were excluded from the analyses. The correlation between the Olsen and M3 extractants was high and independent of soil pH. Neither soil pH, CCE, soil type, nor organic matter content completely explained the low correlations between P extracted by the B1 and the Olsen or M3 methods in high pH soils. Critical concentrations across all soils defined by the Cate-Nelson and linear-plateau models were 7 and 9 ppm for the Olsen extractant and 14 and 24 ppm for the M3 extractant. When highly calcareous soils were excluded, the critical concentrations for the B1 extractant were 11 and 20 ppm, respectively. The Olsen and M3 extractants are more reliable than the B1 for estimating plant-available P of Iowa soils over a broad range of soil pH and CCE.

Evaluation of Beneficial Use of Wood‐Fired Boiler Ash on Oat and Bean Growth

AbstractAn evaluation on the effects of pulp and paper mill combined boiler ashes on growth and nutrient uptake by oat (Avena sativa L., var. 501) and bean (Phaseolus vulgaris L., var. blue pole) was conducted in a greenhouse. Ash with a calcium carbonate equivalent of 29.1% and a pH of 12.1 was applied at the rates 30, 40, and 50 dry Mg ha−1 to Chehalis silty clay loam (fine‐silty, mixed, mesic Cumulic Ultic Haploxerolls), with pH 5.4. An agricultural dolomitic lime treatment of 7.4 Mg ha−1 and a nonamended control were also included. Plants grown on ash‐amended soil had higher biomass compared to plants grown on lime and control treatments. Ash treatments 30, 40, and 50 dry Mg ha−1 increased the bean (stems and leaves) dry matter (DM) yield over the control by 49, 57, and 64%, respectively. The lime treatment increased the bean DM yield by 31% compared with the control. The ash rate 30 dry Mg ha−1, equivalent to the recommended agronomic lime rate 7.4 Mg ha−1, increased oat (shoots) DM yields over the control by 45%, while the lime treatment increased biomass by 8% over control. The highest ash treatment, 50 Mg ha−1, produced the lowest oat biomass. The ash was as effective as dolomitic lime in raising soil pH. Ash‐amended soils contained higher concentrations of P, S, and B for plant growth compared to lime and nonamended soils. Soil Zn, Fe, Mn, and Cu concentrations decreased as ash application rates increased. Oat and bean plants grown in the ash‐amended soil had increased concentrations of K, S, and B and decreased concentrations of Mn and Cu compared with plants grown in the nonamended control soil. Overall, oat and bean benefited from the increased nutrient availability and soil pH caused by the application of boiler ash.

O EQUIVALENTE EM CARBONATO DE CÁLCIO DOS CORRETIVOS DA ACIDEZ DOS SOLOS

Os corretivos da acidez dos solos podem ter dois equivalentes em carbonato de cálcio: um, calculado pelos teores de cálcio e magnésio utilizando a expressão: % CaO x 1,79 + % MgO x 2,48 = %ECaCO3; outro, determinado analiticamente pelo poder ou valor de neutralização. Para uma mesma amostra ambos os valores deveriam coincidir, o que raramente acontece. Diversas hipóteses foram levantadas para justificar essa diferença. Os resultados deste trabalho permitiram inferir que nem todo o cálcio e magnésio dos corretivos devem estar associados às bases quimicamente efetivas mas também a fosfato, sulfato ou outras bases de forças inexpressivas; também os constituintes neutralizantes podem estar aprisionados em cristais de outros componentes dos corretivos, como sílica por exemplo, que só são atingidos por um ataque mais enérgico da amostra. Como conclusão, a avaliação química atual dos corretivos da acidez dos solos pode não estar se compatibilizando com o comportamento agrícola desses produtos.

Leaf litter ash alkalinity and neutralisation of soil acidity

Soil acidification is a major factor limiting the sustainability of agricultural production systems throughout the world. Liming may not always be economically possible and therefore alternative methods or complementary methods of amelioration are required. Leaf litter collected from several tree species was examined for ash alkalinity (as an estimate of organic anion content) and ability to ameliorate an acid soil. Ash alkalinity measured by titration of the ash and excess cation values obtained by calculation as the difference between cation and anion content were correlated. Values obtained by the latter method ranged from 247 cmolc kg-1 for Melia azedarach (white cedar) to 36 cmolc kg-1 for Eucalyptus globoidea (white stringybark). There was a significant linear correlation between ash alkalinity and the Ca concentration in the litter. When added to an acid soil (pH 4.04 measured in 0.01 M calcium chloride) and incubated for 8 weeks, leaf litter raised the pH. Species differed markedly with Melia azedarach having the greatest effect. The increase in pH was proportional to the quantity of ash alkalinity (organic anions) added, expressed as calcium carbonate equivalents. Aluminium levels on the exchange complex were lowered by treatment with leaf litter through direct precipitation of a solid phase and again Melia azedarach litter was most effective. There was also indirect evidence of organo-Al complexes affecting the concentration of monomeric Al in soil treated with litter from Liquidambar styraciflua (liquidambar), Quercus robur (English oak) and Pinus radiata (radiata pine).

Paper Mill Boiler Ash and Lime By‐Products as Soil Liming Materials

AbstractThe pulp and paper industry in the southeastern USA produces ≈ 6500 t of boiler ash and lime by‐products (waste lime, grit, and dregs) daily. A survey of 88 pulp and paper mills indicated that most of these by‐products are placed in landfills, with only 10% being land‐applied. Seventeen boiler ash samples and 14 lime by‐products from 12 Alabama pulp and paper mills were analyzed and evaluated for their potential as soil liming materials. Most boiler ash resulted from the burning of wood or wood in combination with other materials and averaged 37% calcium carbonate equivalent (CCE), while 14 lime by‐products averaged 99% CCE. In an 84‐d incubation study, boiler ash and lime by‐products applied to an acid (pH = 5.2) Marvyn loamy sand (fine‐loamy, siliceous, thermic, Typic Kanhapludults) at equivalent rates based on CCE resulted in mean pH values significantly higher than values achieved with agricultural lime. All materials increased Mehlich‐1 extractable P, K, and Mg. In a field study conducted on an acid (pH = 5.1) Vaiden clay (very‐fine, montmorillonitic, thermic Vertic Hapludalfs), dallisgrass‐fescue (Paspalum dilatatum Poir.‐Festuca arundinacea Schreb.) herbage yield increased 62% the second year and 49% the third year after surface application of boiler ash, lime by‐products, and agricultural lime.

Growth and manganese uptake by soybean in highly calcareous soils as affected by native and applied manganese and predicted by nine different extractants

Abstract Manganese (Mn) becomes a limiting factor of plant growth under some soil conditions. High pH and abundance of free calcium carbonate in calcareous soils are conducive to Mn‐deficient plants. The Mn status of highly calcareous soils in Iran has not been studied in detail. This experiment was conducted to obtain such information. Twenty‐three surface (0–20 cm) soil samples with pHs from 7.7 to 8.2 and calcium carbonate equivalent (CCE) from 19 to 46% were used in a 7‐week greenhouse study with soybean [Glycine max (L.) Merr.]. The experiment was a 23 × 3 factorial with three replicates, i.e., 23 soils and 3 Mn levels (0, 15, and 30 mg/kg soil as manganese sulfate). Extractable Mn of the untreated soils were determined before planting by nine different procedures. Dry matter yield, Mn concentration of soybean tops, and Mn uptake were used as the measure of plant response. Multiple regression equations showed that the most influencial soil properties in extractability of Mn in highly calcareous soils...

Phosphate availability in calcareous Vertisols and Inceptisols in relation to fertilizer type and soil properties

The availability to plants of fertilizer phosphorus (P) applied to soil, as measured by chemical extraction, is used to estimate P fertilizer needs. We studied the availability of P, applied as monocalcium phosphate (MCP) powder, ordinary superphosphate (OSP) granules and diammonium phosphate (DAP) granules in 24 calcareous Vertisols and Inceptisols of Andalusia, Spain, by using laboratory incubation techniques. The soils differed widely in their P adsorption- and Ca-phosphate precipitation-related properties. For MCP, availability (defined as the proportion of added P that is recovered by extraction with NaHCO3 or is isotopically exchangeable) decreased markedly with incubation time and increasing addition rate. The mean recoveries after 180 d of incubation at field capacity at a rate of 246 mg P kg−1 soil were 17% for Olsen P, 38% for Colwell P, and 16% for isotopically exchangeable P (IEP). Increasing the application rate to 2460 mg kg−1 resulted in recoveries of 6% for Olsen P, 25% for Colwell P, and 4% for IEP. While IEP-based recovery was not significantly correlated to any soil property, that based on Olsen P (and, to a lesser extent, Colwell P) decreased sharply with increase in the ratio of clay (or Fe oxides) to total (or active) calcium carbonate equivalent. Accordingly, Olsen P might overestimate P availability in those soils relatively rich in carbonate and poor in clay and Fe oxides. On the other hand, recovery of applied P from soils containing more clay and Fe oxides, by a sequential extraction (with H2O, two 0.5M NaHCO3 treatments, 0.5M HCl), was lower than 100%, thereby suggesting phosphate occlusion by Fe oxides or clay.

Use of Spent Mushroom Substrate in Stabilizing Disturbed and Commercial Sites

Severely disturbed sites such as abandoned mine sites, pipeline construction sites and commercial/industrial sites have been successfully stabilized utilizing Spent Mushroom Substrate (SMS). Depending on the application rate, SMS can provide some or all of the nitrogen, phosphate, potash and calcium carbonate equivalence to allow for permanent stabilization by vegetation. SMS also has been substituted as a mulch to protect seeds during germination. The use of SMS as a substitute for lime, fertilizer and mulch requires a properly engineered and installed surface water control system as an integral part of the planning process.

Levels of 137Cs and 40K in wood ash-amended soils

Wood ash is a residual material produced at an annual rate of 1.5–3.0 million tons by wood burning power plants in the USA. Up to 80% of the wood ash generated in northeastern USA is landspread on agricultural soils. Recently, concern has arisen regarding the 137Cs content of wood ash and levels of 137Cs of wood ash-amended soils. The 137Cs originated primarily from above ground nuclear weapons testing in the 1950s and 1960s. This study examined the total and pH 3, NH 4OAc extractable levels of 137Cs and 40K in three soils incubated in the laboratory with 0, 3 and 9 g of wood ash on a calcium carbonate equivalence basis kg −1 soil. The wood ash contained 137Cs and 40K at 3920 and 21700 pCi kg −1, respectively. At the regulated wood ash application rate limit, 3 g wood ash (calcium carbonate equivalent basis) kg −1 of soil, there was no statistical difference from the control treatment in both total and soluble 137Cs and 40K levels. For one soil, there was an increase in the 137Cs level when wood ash was amended at 9 g wood ash (calcium carbonate equivalent basis) kg −1 soil. The 137Cs was strongly bound to the cation exchange sites of the soils with the average fraction soluble in pH 3, NH 4OAc solution at 4.8% in the mineral soils and 0.9% in the organic soil. Considering the current limits on permitted wood ash application rates to soils, there was no statistically significant effect on the levels of 137Cs or 40K found in wood ash-amended soils.

Incubation-derived calcium carbonate equivalence of papermill boiler ashes derived from sludge and wood sources

The burning of a papermill sludge and wood mixture and landspreading the resulting ash is a potential means of disposal of papermill sludge without the use of valuable landfill space. This study evaluated the effectiveness of ashes derived from a mixture of papermill sludge and wood sources to act as an alternative liming agent. The calcium carbonate equivalence of the material was determined using a 91-day laboratory incubation test with three mineral soils and one organic horizon soil. Application rates of soil-incorporated sludge-ash ranged from 2·30 to 32·2 g per kg soil. Soil pH increased linearly with increasing sludge-ash application rate. The calcium carbonate equivalence of the material varied temporally and the average value ranged from 19% to 28%. The fraction of total P, K and Mg added with the sludge-ash and extracted from the ash-amended soils using an NH 4OAc based soil test method were 2·6, 3·8 and 17·6%, respectively. The low soil test extractability of ash-derived plant nutrients suggests that this material would provide only a modest increase in plant available nutrient levels in landspread fields.

Titrimetric determination of calcium carbonate equivalence of wood ash

Wood ash is a residual material produced during the process of biomass burning for energy. Spreading this material on the land is used as a means of its disposal. Wood ash contains carbonates which react to raise soil pH, and its regulation is based on ash calcium carbonate equivalence (CCE). The procedure suggested by the Association of Official Analytical Chemists (AOAC) for the determination of the CCE of agricultural limestone is routinely used for the determination of the CCE of wood ash samples. This procedure involves heating a weighed amount of sample with HCI and then back-titration of the remaining acid with NaOH. Unlike agricultural limestones, which are largely carbonates, some wood ash samples contain significant amounts of contaminants such as alumino-silicate clays which may consume acidity when heated with HCl. Significant consumption of acidity by alumino-silicates during CCE analysis would cause the determination of artificially high CCE values, as these alumino-silicates would not be expected to neutralize acidity under field conditions. This study investigated whether the AOAC method of CCE determination resulted in reproducible, accurate CCE values when applied to wood ash samples with various amounts of alumino-silicate contaminants. The accuracy of the method was calculated by comparing the CCE values with those obtained from a soil incubation method. Time of heating had little effect on the CCE value obtained. The back-titration step was reproducible from operator-to-operator despite the formation of a white precipitate before the end-point. The CCE values obtained from the titrimetric method were similar to those obtained from a soil incubation method.

The reactivity of carbonates in selected soils of southern Spain

The properties of many soils of arid and semiarid areas are influenced by the presence of carbonates. This study was conducted to characterize the reactivity of carbonates in the surface horizons of 25 soils (Entisols, Inceptisols, Vertisols and Alfisols) of southern Spain. The samples were analyzed for calcium carbonate equivalent (CCE), “active” calcium carbonate equivalent (ACCE), predominant carbonate mineralogy, Mg content, particle-size distribution (PSD) of carbonates (by sedimentation and by a pH-stat acid-dissolution method), and surface area (SA) of carbonates (by N 2 adsorption and by 45Ca exchange, from the differences between intact and decalcified soil samples, as well as by estimates from the PSD described above). The CCEs ranged from 70 to 778 g kg −1 of soil, and the ACCEs ranged from 48 to 285 g kg −1. Dolomite was present in only eight samples, and in the dolomite-free samples, calcite generally had Mg / (Ca + Mg) ratio < 0.03. The carbonate PSD as determined by sedimentation differed from the PSD calculated from the pH-stat data, with the latter method giving a much higher proportion of claysize carbonates. The average SAs of carbonates as estimated from the PSD data were 0.49 m 2 g −1 soil for the sedimentation method and 3.2 m 2 g −1 for the pH-state method. The average SAs determined by the N 2 and the 45Ca methods were 6.0 and 2.3 m 2 g −1, respectively. The average specific surface areas (SSAs) of soil carbonate (m 2 g −1 CCE) were 1.5, 7.5, 8.8 and 22 for the sedimentation, 45Ca exchange, pH-stat and N 2 methods, respectively. The low SA and SSA values from the sedimentation method were a consequence of the occurrence of porous aggregates which have considerably higher equivalent spherical diameters than the particles of which these aggregates are composed. The pH-stat and 45Ca methods gave SA values of similar magnitude to each other, probably because both methods are dependent on actual reactive surface area instead of aggregate size of the carbonate mass. The higher values obtained by the N 2 method might indicate that N 2 is physisorbed on carbonate surfaces that are slowly reactive to acid attack or 45Ca exchange. The pH-stat SA was highly correlated with ACCE, which measures the reactivity of carbonates to oxalate. To obtain a rapid estimate of the reactivity of soil carbonate, the ACCE method, because of its simplicity, may be preferred.

Wood ash as a soil additive and liming agent for wheat: Field studies

Abstract An industrial wood ash with a calcium carbonate equivalent (CCE) of 36 and a pH of 12.9 was applied to two field sites at 0, 0.56, 1.12, 1.68, 2.24, 4.48, and 8.96 Mg/ha and at 0, 0.56, 1.12, 2.24, 4.48, 8.96, 17.9, and 35.8 Mg/ha. Soil pH and available K increased with application rate, while growth of wheat and protein content on ash‐amended plots was unaffected. Cadmium, lead and zinc content in the wheat was comparable at 0 and 17.9 Mg/ha, which indicated no net accumulation of heavy metals. Based on this field study and other greenhouse studies described in the literature, wood ash can be recycled as a liming agent and soil amendment when applied at agronomic rates based on soil fertility needs and the chemical composition of the ash.

A Rapid Acid‐Oxalate Extraction Procedure for the Determination of Active Fe‐oxide Forms in Calcareous Soils

AbstractExtraction with acid NH4‐oxalate is widely used to estimate the content of “active” forms of Fe oxides in soil. In calcareous soils, this extraction presents some problems (pH change, production of CO2), which have been circumvented by decalcifying the soil before extraction. However, because of its tediousness, this procedure cannot be applied for routine purposes. In this paper, we describe a rapid procedure in which the soil is treated with oxalic acid before oxalate extraction to neutralize the active calcium carbonate equivalent. The method is simple and provides a useful estimation of the content of active Fe forms that are not occluded in the coarse particles and aggregates of carbonate.