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

Abstract

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.     

Ameliorating subsoil acidity by surface application of calcium fulvates derived from common organic materials

Subsoil acidity is a serious constraint to crop production, and is difficult to correct by conventional liming practices. Thus, a different approach to ameliorating acid subsoils was evaluated. Subsoil material of an acid Ultisol (pH 4.4) was packed into 50-cm long columns, then leached with solutions of CaCl₂, CaCO₃ (suspension) or Ca fulvates prepared from chicken manure, cowpea green manure, or sewage sludge. The total water applied was 30.26 cm (or 800 ml) in 2 days. Thereafter, the columns were dismantled and cut into 5-cm segments for chemical analysis. The results indicated that only 2% of the added Ca from CaCO₃ moved past the 15-cm depth, compared to 68% from CaCl₂ and 35–75% from Ca fulvates. Correspondingly, CaCO₃ precipitated all KCl-extractable Al in the top 5 cm, but had no effect beyond the 10-cm depth. The CaCl₂ displaced a small but significant portion of extractable Al from the top 15 cm and redeposited some of that Al in lower depths. Similar to CaCO₃, Ca fulvates from chicken manure and green mamure only decreased extractable Al significantly in the top 10-cm layers, but had little effect beyond that depth. By contrast, the Ca fulvate from sewage sludge decreased Al down to the 45-cm depth. In terms of reducing Al saturation as a percentage of total extractable cations (effective cation exchange capacity), the Ca fulvates were as effective as CaCO₃ in the 0-to 5-cm layer, and more effective than CaCl₂ in any soil layer because of the increased exchangeable Ca and/or decreased Al. In general, surface application of common organic material-derived Ca fulvates can increase subsoil Ca and decrease the Al saturation percentage. However, Mg depletion and enrichment of unwanted metals (e.g., Na or heavy metals) may be a problem when leaching with these organic sources.     

Organic matter availability for denitrification in soils of different textures and drainage classes

Abstract

Soils from the A, B, and C horizons representing three natural drainage classes and differing textures were chosen to study relationships between denitrification rate and estimates of available carbon. The highest correlation with denitrification rate was obtained with total organic C. Water‐extractable C, mineralizable C and 0.1 N Ba(OH)2‐extractable C produced less satisfactory correlations. When soils of the B and C horizons only were included in the regression analysis, 0.1 N Ba(OH)₂‐extractable C was found to be unsatisfactory as a predictor of available C for soil denitrifiers. None of the four methods for estimating available C were found adequate for B and C horizon soils which were relatively low in available C. Coarser‐textured soils with relatively low C levels had correspondingly low denitrification rates. Regressions of denitrification rate on mineralizable C or water‐extractable C were nonsignificant with poorly drained soils whereas they were highly significant with well or imperfectly drained soils.     

The profile distribution of total and extractable copper in selected Nigerian soils

Abstract

The profile distribution of total, DTPA‐ and 0.1N HCl‐extractable Cu was determined in 11 Nigerian soil profiles formed from various parent materials including the coastal plain sands, shales, basalt, granite and banded gneiss.

Total Cu ranged from 7 to 72 ppm with a mean of 35 ppm₀ The soils formed from basalt had the highest values while those on coastal plains had the least content. Generally, there was a higher content in the subsoils than in the surface horizons. The total Cu significantly correlated with percent clay and the free oxide contents of Fe and Mn.

DTPA ‐ and 0.1N HCl‐extractable Cu ranged from 0.08 to 2.81 ppm and 0.10 to 7.78 ppm, respectively. Soils on metamorphic rocks gave the highest values of DTPA‐extractable Cu. The DTPA‐extractable Cu ‐was only related to pH but the acid extractable Cu was associated with total Cu, clay, free Fe₂O₃ and MnO₂ contents.     

Effect of extractable zinc,phosphorus, and soil ph on zinc concentrations in leaves of field‐grown corn

Abstract

The variability in corn yield responses to applications of Zn fertilizer appears to be associated with several complex soil and climatic factors that affect the availability of endogenous soil Zn to the crop under specific conditions. Among the soil chemical properties that influence availability of endogenous Zn are soil pH, organic matter content, and extractable P. Over a period of several years, soil and plant analysis data were collected from 54 field experiments, field trials, and diagnostic visits to producer's fields. These data were subjected to multiple regression analysis, resulting in an equation: Zn_leaf = 37.14 + 1.513 Zn_st ‐4.04 pH_st ‐ 1.791 ln(P_st/100) where Zn_st, pH_st, and P_st were 0.1N HC1 extractable soil Zn (kg/ha), 1:1 soil‐water pH, and Bray's 1 extractable soil P (kg/ha), respectively. These factors accounted for 67% of variation in leaf Zn, which was a large portion of the variability in Zn_leaf considering that climatic conditions, management levels, and varietal differences were uncontrolled in most instances. Using the previously published critical level in the leaf opposite and below the ear as 17 μg Zn/g, these data can be used to set required soil test levels of Zn at different levels of extractable P and soil pH. Inadequate levels of extractable Zn would range from 2.5 (at pH 6.0, P = 70 kg/ha) to, 9.5 kg/ha (at pH 7.5, P = 420 kg/ha).     

Isotopic fractionation of dissolved organic carbon in shallow forest soils as affected by sorption

Isotopic fractionation of dissolved organic carbon percolating through the soil is often interpreted as due to microbial transformation. We investigated the potential effects of sorption on the δ¹³C of dissolved organic C in field and laboratory experiments. We sampled the organic C in soil water at two forested sites and measured sorption with intact mineral soil and individual minerals (dolomite, ferrihydrite, goethite, and quartz). The dissolved organic C was separated into hydrophilic and hydrophobic fractions using a resin approach. The δ¹³C values of bulk soils, alkaline‐extractable organic C, and dissolved organic C and its fractions were measured. Hydrophilic and hydrophobic fractions in forest floor seepage water were characterized by ¹³C‐NMR spectroscopy. At both sites, δ¹³C of dissolved organic C increased with increasing depth, suggesting that decomposition contributes to the loss of the dissolved organic C. However, there was an enrichment of hydrophilic organic C in the soil solution as the water moved down the soil. The δ¹³C values of hydrophilic fractions were less negative than those of hydrophobic fractions. The smaller δ¹³C in the hydrophobic fraction was due to the large contribution of compounds derived from lignin that are depleted in ¹³C. As the isotope composition of both fractions of dissolved organic C did not change throughout the profile, changes in δ¹³C of total organic C reflected changes in the relative proportions of its hydrophilic and hydrophobic fractions. The sorption experiments with minerals and soil cores gave similar results. When dissolved organic C came into contact with mineral material, the δ¹³C of that remaining in solution increased due to preferential sorption of the ¹³C‐depleted hydrophobic fractions. Moreover, the soils released hydrophilic organic C with large δ¹³C values, increasing the δ¹³C of organic C in effluents from soil compared with that in the inflow. Thus, selective sorption of organic C fractions changes δ¹³C in a way that mimics metabolic transformation and decomposition.     

Effect of some soil properties on extractable boron content in argentine pampas soils

Abstract

The influence of some soil properties on hot 0.02 M calcium chloride (CaCl₂) extractable boron in the Argentine Pampas was studied. The selected soils represent an extensive area in the middle west of the country where most of the grain crops are produced. Soils have all developed on loess and cover a wide range of organic matter, pH, and exchangeable calcium. The most representative soils are Typic Argiudolls and Typic Haplustolls. Two hundred soil samples were taken in order to characterize their 0.02 M CaCl₂ extractable boron content and study the boron behavior with regard to other soils properties and environmental conditions. The amounts of extracted boron on all samples had a significant correlation with soil organic carbon (positive), and soil pH (negative). The regression equation between extractable boron and organic carbon content was y=0.1021+0.3722 OC R²: 0.51. Since solubility in hot CaCl₂, 0,02 M is considered an availability index, these results support the hypothesis that organic carbon content is the main boron reserve for plants. When a multiple regression was calculated, both variables organic carbon and pH explained 57% of variation in extractable boron. The studied area can be subdivided into regions with different boron content, within each region the relationship between boron content and organic carbon and pH were also different. The exchangeable calcium content had a light influence especially in the subsuperficial layer. The influence of environmental conditions on boron content and its relationship with soil properties were discussed.     

An evaluation of chemical methods for extracting copper from rice soils

Abstract

Rice (Oryza sativaL. CV. Lemont) was grown on 19 soils, and eight extractants were evaluated for determining the availability of Cu to rice plants. Correlation analyses were employed as criteria for evaluating methods that would provide the best index of Cu availability. The order of removal of Cu from soils was: 0.5NHC1 + 0.05NA1C1₃> 0.5NHNO₃> 0.5 N HC1 > EDTA + NH₄OAc > 0.1NHC1 > EDTA + (NH₄)₂CO₃? DTPA‐TEA, pH 7.3 >>> 1 N NH₄0Ac, pH 4.8.

Uptake of Cu by rice plants was significantly correlated with soil Cu. Among the eight extractants evaluated, Cu extracted with DTPA‐TEA, pH 7.3 was better related to the concentration (r = 0.563 ) and uptake (r = 0.673 ) of Cu by rice plants grown on the soils with different chemical and physical properties.

A significant negative correlation was found between the concentration of Cu in rice plants and the organic matter content of the soils. Each one percent increase in the organic matter of the soils resulted in a corresponding decrease of approximately one mg/kg in the concentration of Cu in the rice‐plant tissue. Multiple regressions of extractable Cu by eight methods with soil organic matter content accounted for from 53.4 to 70.0% of the variations in the prediction of the concentration of Cu in the rice plants. Combinations of other soil chemical properties measured with extractable Cu did not significantly improve the predictability     

Effects of heavy metal accumulation in apple orchard soils on microbial biomass and microbial activities

Abstract

The effects of heavy metals (Cu, Pb, and As) accumulated in apple orchard surface soils on the microbial biomass, dehydrogenase activity, and soil respiration were investigated. The largest concentrations of total Cu, Pb, and As found in the soils used were 1,010, 926, and 166 mg kg^?1 soil, respectively. The amounts of microbial biomass C and N, expressed on a soil organic C and soil total N basis, respectively, were each negatively correlated with the amounts of total, 0.1 M HCI-extractable, and 0.1 M CaCl₂-extractable Cu as logarithmic functions, the correlation coefficient being lowest for the 0.1 M CaCl₂extractable Cu. Nevertheless, they were not correlated with the soil pH which was controlling the solubility of Cu in 0.1 M CaCl₂. The dehydrogenase activity expressed per unit of soil organic C was also negatively correlated with the amounts of total, 0.1 M HCI-extractable Cu, and 0.1 M CaCl₂-extractable Cu as logarithmic functions. However, the correlation coefficient was highest for the 0.1 M CaCl₂-extractable Cu. Although the soil respiration per unit of soil total organic C did not show any significant correlations with the total concentrations of heavy metals, it showed negative significant correlations with the amount of 0.1 M HCI-extractable Cu, and to a greater extent, with the amount of 0.1 M CaCl₂-extractable Cu. Both the dehydrogenase activity and respiration per unit of soil total organic C increased significantly with increasing soil pH. These results suggested that in apple orchard soils with heavy metal accumulation the microbial biomass was adversely affected by the slightly soluble Cu, whereas the microbial activities by the readily soluble Cu whose amount depended on the soil pH. The respiration per unit of microbial biomass C showed a positive significant correlation with the logarithmic concentration of total Cu. Furthermore, the contribution of fungi to substrate-induced respiration increased with increasing total Cu content in the soils.     

Fractionation of extractable aluminum in acid soils: A review and a proposed procedure

Abstract

Different forms of soil aluminum (Al) are involved in the retention of anions and cations, phytotoxicity of Al in acid soils, CEC reduction and soil physical properties such as aggregate stability and water infiltration. Therefore it is desirable to quantify the different forms of Al in soil especially acidic soils. A rationale was developed from a literature survey to identify the following fractions of Al: (a) exchangeable quantified by 1M KC1 extraction; (b) organic bound quantified by 0.1M CuCl₂ + 0.5M KCl extraction; (c) sorhed Al extractable with 1M NE₄OAc at pH 4.0; (d) amorphous Al oxide and hydroxide and amorphous aluminosilicates (if present) extractable with 0.2M ammonium oxalate at pH 3.0; and (e) interlayered Al extractable with 0. 33M sodium citrate at pH 7.3. Pools (a), (b), and (c) are extracted sequentially. Amorphous Al oxide and hydroxide (pool d) is calculated from ammonium oxalate extractable Al minus (a + b + c). Interlayered Al is calculated from sodium citrate extractable Al minus ammonium oxalate extractable Al. The latter two extractions are done on separate subsamples of soils. From preliminary studies and data for 13 soil samples it is suggested that this fractionation of soil Al is more meaningful than that obtained by the KCl ‐> K₄P₂O₇ ‐> ammonium oxalate > citrate‐bicarbonate‐dithionite extraction sequence.     

Use of routine soil tests in predicting corn leaf zinc

Abstract

Zinc of index corn leaves samples from 91 Minnesota sites on numerous soil types was correlated with soil Zn extracted by four routine procedures. The EDTA?(NH₄)₂CO₃ ‐ extractable soil Zn was more closely correlated with leaf Zn than soil zinc extracted by 0.1N HCl, EDTA‐NH₄OAc, or by NH₄OAc ‐ dithizone. Soil pH, CaCO₃ equivalent, extractable P, and organic matter of both acid and calcareous soils were negatively correlated with leaf Zn. When EDTA ? (NH₄)₂CO₃ ‐ extractable Zn was included with routine soil tests, a prediction equation for corn leaf Zn was formulated and compared with analytical values. However, the use of 1.4 ppm EDTA ? (NH₃)₂CO₃, ‐ extractable soil Zn alone as a critical value was equally effective in predicting leaf Zn.     

Predicting Liming Needs of Soybean Using Soil pH,Aluminum, and Manganese Soil Tests

Abstract

Whether a tropical soil should be limed or not for a particular crop is strongly dependent on the levels of soil aluminum (Al) which can be determined with soil tests. Soil pH is used to predict whether lime is needed in less‐weathered soils, although some evidence indicates a soil Al test would be more accurate. The objectives of this study were to determine and to compare the accuracies of four soil tests to separate soils requiring lime from those that do not, and to determine the cause of acid‐soil injury to soybean [Glycine max (L.) Merr.]. Soybean was grown in the greenhouse on four surface soils representing the major land resource areas of Louisiana and were amended with eight rates of lime, yields determined, and soils analyzed for soil pH, extractable Al, CaCl₂‐extractable Al, CaCl₂‐extractable manganese (Mn), and Al saturation. Acid‐soil injury in soybean grown on the Litro clay and Stough fsl was probably caused by soil‐Al effects while low soil calcium (Ca) and high soil Mn was likely responsible for lower yields from the Mahan fsl. Leaf Ca from the limed Mahan‐soil treatment was 5‐fold greater and leaf‐Mn 7‐fold less than control levels. Regression analyses’ R² values were similar for all soil tests except for CaCl₂‐extractable Mn, which was lower. Soil tests were compared across soil type by selecting treatments that had the same 85% relative yield. Using this data subset, there was no difference in the soil pH among the four soils, while there were significant differences among soils for all other soil test measurements indicating the superiority of soil pH for identifying acid‐soil injury. Critical test values were 5.1 soil pH, 30 mg kg^‐1 extractable Al, 7% Al saturation, 0.7 mg‐kg^‐1 CaCl₂‐extractable Al, and 9 mg‐kg^‐1 CaCl₂‐extractable Mn.     

IMOGOLITE AND PROTO-IMOGOLITE ALLOPHANE IN SPODIC HORIZONS: EVIDENCE FOR A MOBILE ALUMINIUM SILICATE COMPLEX IN PODZOL FORMATION

Examination by infrared spectroscopy and electron microscopy of the fine clays (<0.5 μm) dispersed at pH 3.5 from H₂O₂-treated soil indicates that imogolite and proto-imogolite allophanes are concentrated in podzolic B₂ and B₃ horizons, and make up at least 6 percent of one B₂ horizon soil, which contains virtually no layer silicate clays. It is argued here that imogolite-type components are the principal source of extractable aluminium and silicon in such horizons, that they may act as cementing agents in indurated horizons, and that proto-imogolite, a soluble aluminium-silicate complex, is the predominant mobile form in which aluminium is transported to B₂ and lower horizons of podzols. Comparison of the amounts of aluminium extracted by acetic acid with those extracted by EDTA indicates that extractable aluminium in Bhg, Bh, and organic-rich A₂ horizons is present principally in organic complexes. It is proposed that the aluminium fulvates concentrated in these horizons are formed in situ.     

The influence of tillage systems on soil organic matter and soil hydrophobicity

Management practices including various tillage systems influence quantity and composition of soil organic matter (SOM). Parameters for evaluating both the SOM quantity (organic C [C_ox], total N [N_t]) and quality (microbial biomass C, hydrophobic and hydrophilic organic components) were determined in soil samples, taken from two soil depths (0–0.1 m and 0.1–0.3 m) in a field experiment in the period 2001–2007, with different tillage systems. The experiment, founded in 1995 in Prague-Ruzyně, includes conventional soil tillage (CT) plus some selected methods of conservation tillage: (a) no tillage (NT), (b) no tillage + mulch (NTM), and (c) minimum tillage with pre-crop residues incorporated (MTS). C_ox and microbial biomass C contents increased significantly with conservation tillage as compared to CT in 0–0.1 m layer, non-significant increase was found in 0.1–0.3 m layer. N_t increased non-significantly in both layers. Along with the depth of sampling, the content of the characterized parameters decreased in all variants; but the decrease in the conventionally tilled variant was, for the most part, lower than in the conservation tillage. The functional hydrophobic and hydrophilic groups of soil organic matter were identified by Fourier transform infrared (FTIR) spectroscopy, and the hydrophobic/hydrophilic group intensities ratio was calculated as the parameter of soil hydrophobicity. A higher soil hydrophobicity existed in all three conservation tillage treatments compared to CT due to the significantly higher content of hydrophobic organic components. C_ox correlated significantly with microbial biomass C, N_t, hydrophobic components, and soil hydrophobicity (R = 0.552–0.654; P < 0.05). Hydrophilic components did not correlate with other soil characteristics, with the exception of hydrophobic components. These data show that shifting from CT to the conservation tillage systems increased the content of SOM in top soil layer in relatively short time, improved the SOM quality and increased soil hydrophobicity in the condition of experiment.     

Extractability and plant uptake of heavy metals in alum shale soils

Abstract

Fifty soil samples (0–20 cm) with corresponding numbers of grain, potatoes, cabbage, and cauliflower crops were collected from soils developed on alum shale materials in Southeastern Norway to investigate the availability of [cadmium (Cd), copper (Cu), zinc (Zn), lead (Pb), nickel (Ni), and manganese (Mn)] in the soil and the uptake of the metals by these crops. Both total (aqua regia soluble) and extractable [ammonium nitrate (NH₄NO₃) and DTPA] concentrations of metals in the soils were studied. The total concentration of all the heavy metals in the soils were higher compared to other soils found in this region. Forty‐four percent of the soil samples had higher Cd concentration than the limit for application of sewage sludge, whereas the corresponding values for Ni, Cu, and Zn were 60%, 38%, and 16%, respectively. About 70% the soil samples had a too high concentration of one or more of the heavy metals in relation to the limit for application of sewage sludge. Cadmium was the most soluble of the heavy metals, implying that it is more bioavailable than the other non‐essential metals, Pb and Ni. The total (aqua regia soluble) concentrations of Cd, Cu, Zn, and Ni and the concentrations of DTPA‐extractable Cd and Ni were significantly higher in the loam soils than in the sandy loam soils. The amount of NH₄NCyextractable metals did not differ between the texture classes. The concentrations of DTPA‐extractable metals were positively and significantly correlated with the total concentrations of the same metals. Ammonium nitrate‐extractable metals, on the other hand, were not related to their total concentrations, but they were negatively and significantly correlated to soil pH. The average concentration of Cd (0.1 mg kg^‐1 d.w.) in the plants was relatively high compared to the concentration previously found in plants grown on the other soils. The concentrations of the other heavy metals Cu, Zn, Mn, Ni, and Pb in the plants were considered to be within the normal range, except for some samples with relatively high concentrations of Ni and Mn (0–11.1 and 3.5 to 167 mg kg‘¹ d.w., respectively). The concentrations of Cd, Cu, Zn, Ni, and Mn in grain were positively correlated to the concentrations of these respective metals in the soil extracted by NH₄NO₃. The plant concentrations were negatively correlated to pH. The DTPA‐extractable levels were not correlated with plant concentration and hence DTPA would not be a good extractant for determining plant availability in these soils.     

Development of a New Soil Extractant for Simultaneous Phosphorus,Ammonium, and Nitrate Analysis

Abstract

A new soil extractant (H³A) with the ability to extract NH₄, NO₃, and P from soil was developed and tested against 32 soils, which varied greatly in clay content, organic carbon (C), and soil pH. The extractant (H³A) eliminates the need for separate phosphorus (P) extractants for acid and calcareous soils and maintains the extract pH, on average, within one unit of the soil pH. The extractant is composed of organic root exudates, lithium citrate, and two synthetic chelators (DTPA, EDTA). The new soil extractant was tested against Mehlich 3, Olsen, and water for extractable P, and 1 M KCl and water‐extractable NH₄ and NO₂/NO₃. The pH of the extractant after adding soil, shaking, and filtration was measured for each soil sample (5 extractants×2 reps×32 soils=320 samples) and was shown to be highly influential on extractable P but has no effect on extractable NH₄ or NO₂/NO₃. H³A was highly correlated with soil‐extractable inorganic N (NH₄, NO₂/NO₃) from both water (r=0.98) and 1 M KCl (r=0.97), as well as being significantly correlated with water (r=0.71), Mehlich 3 (r=0.83), and Olsen (r=0.84) for extractable P.     

The effect of site characteristics and farming practices on soil organic matter in long-term field experiments in the Czech Republic

Parameters for evaluating both the soil organic matter quantity (total organic C [TOC]) and quality (hot water extractable C [HWC], hydrophobic and hydrophilic components, soil hydrophobicity) were determined in soil samples taken from selected plots of 13 field experiments under different soil and climatic conditions in the period 2004–2008. Four variants were selected in each experiment: non-fertilized control (Nil), mineral fertilized variant (NPK), farmyard manured variants (FYM) and organic and mineral fertilized variants (FYM + NPK). The TOC and HWC content of topsoil differed mainly as a result of the site conditions. Both organic and mineral fertilization increased the TOC content of soil; the percentage increase in the HWC content was greater than that for the TOC content. Mineral and organic fertilization increased the hydrophobic organic component content but not the hydrophilic organic component content. A significant positive correlation was found between hydrophobic organic components and HWC content (R = 0.746, P < 0.01). Hydrophilic organic component content was highly significantly correlated with the TOC content (R = 0.728, P < 0.01). Soil hydrophobicity was affected by soil texture and clay content, and a positive effect of long-term organic fertilization on soil hydrophobicity, and thereby soil stability, was determined.     

Sorption of dissolved organic nitrogen by acid subsoil horizons and individual mineral phases

Dissolved organic matter is important in translocation and export of nutrients from forest ecosystems. Its mobility in soil is restricted by sorption to mineral surfaces which depends on its chemical properties. Carboxyl and hydroxyl groups form strong bondings to mineral surfaces, whereas the role of N‐containing functional groups in the sorption process is less well understood. We examined in laboratory experiments the binding of dissolved organic matter from the forest floor to amorphous Al(OH)₃, goethite, kaolinite, and illite and to subsoils in order to compare the sorption and desorption of dissolved organic C with that of dissolved organic N. The mineral samples were equilibrated with acidic solutions of organic matter at pH 4. In the equilibrium solutions organic C and N and their contribution to two operationally defined fractions, namely the so‐called hydrophilic and hydrophobic fractions, were determined. We measured neutral and acidic amino sugars to discover the nature of the binding of organic N. Within the hydrophilic and hydrophobic fractions, the sorption and desorption of organic C and N did not differ, indicating that there was no preferential binding of N‐containing compounds. The hydrophilic fraction contained more N and sorbed less than the hydrophobic fraction, and so the overall retention of organic N by the mineral phases and subsoils was smaller than that of organic C. Among the amino sugar compounds, muramic acid was preferentially removed from the solution, whereas the neutral amino sugars were sorbed similar to organic C. The results suggest that the sorption of N‐containing compounds is favoured by acidic groups and not by amino groups.     

Soil pH,extractable aluminum and tree growth on acid minesoils

Abstract

Paper birch and hybrid poplar were grown in acid minesoils amended with different rates and types of lime. Growth of the trees was correlated with soil pH, Ca, Mg, K, P and three measures of extractable Al ‐ 1 N KCl, 0.01 M CaCl₂ and H₂O extractable Al. Correlations between soil pH and extractable Al and between the three measures of extractable Al were also determined. Soil pH accounted for the largest share of the total variation in root and shoot growth of both species over all soils. Correlations between tree growth and extractable Al for all soils combined were low and generally non‐significant. Significant correlations were obtained between soil pH and extractable Al and between the three measures of extractable Al, however, the relationships varied among soils.     

Crop uptake and extractability of cadmium in soils naturally high in metals at different pH levels

Abstract

A greenhouse experiment was conducted for three years to study the effect of different pH levels on metal concentrations in plants and the cadmium (Cd) extractability by DTPA and NH₄NO₃. The soils used were an alum shale (clay loam) and a moraine (loam), which were adjusted to pH levels of 5.5, 6.5, 7.0, and 7.5. Wheat (Triticum aestivum), carrot (Daucus carota L.), and lettuce (Lactuca sativa) were grown as test crops. Crop yields were not consistently affected at increasing soil pH levels. The concentration of Cd in plant species decreased with increasing soil pH in both soils and in all three years. Significant concentration differences between soil pH levels were only seen in wheat and carrot crops. Increasing soil pH also decreased the nickel (Ni) and zinc (Zn) concentrations in plants in the first year crop but the copper (Cu) concentration was not consistently affected by soil pH. The effect of pH was more pronounced in the moraine then the alum shale soil. The DTPA‐and NH₄NO₃‐extractable Cd was decreased with the increasing soil pH and the pH effect was more pronounced with NH₄NO₃ extractable Cd. Both extractants were found equally effective in relation to the Cd concentration in plants in this study.