A comparison of wet oxidation methods for determination of total phosphorus in soils

For 15 soils with widely different extractability of phosphorus (P) two newly introduced digestion techniques for determining total P (P_t) were compared with the standard perchloric acid digestion procedure. The two digestion techniques were: (1) concentrated H₂SO₄ plus 30 % H₂O₂ at 360 °C, (2) concentrated HCl plus concentrated HNO₃ in the ratio 3:1 (aqua regia) at 140 °C. Almost equal amounts of P_t were extracted by the two methods (mean = 188.7 mg kg^—1 for H₂SO₄/H₂O₂ and 188.4 mg kg^—1 for aqua regia) which were slightly higher than the standard method (mean = 183.8 mg kg^—1). However, there is no statistical difference among the three digestion methods, suggesting that the tested methods should be useful for estimating P_t in soils with high content of organic C, eliminating the danger of explosion when hot concentrated HClO₄ is used.     

On the determination of total heavy metal content in saline soils and soils rich in organic matter

Abstract

Methods of soil decomposition for determination of heavy metal total content were considered. Two saline soils (chloride and sulphate solonchak solonetz) and one rich in organic matter were uzed for investigation. It has been established that decomposition by using HF‐HCl with a preliminary ignition at 500°C is a very suitable method. The type of the studied soils and the results obtained allow for this method to be recommended for decomposition of various soils.

On the basis of experiments with modelled soils it has been proved that possibilities for heavy metal losses on ignition are created when NaCl content and the percentage of weakly bound heavy metals (water‐soluble, exchangeable, etc.) are high. Under the conditions of the experiment (acid soils ‐ pH 4.3 and 5.0) losses of Zn and Pb but not of Cu have been incurred. Although these cases are not typical, this requires the applicability of the method for such particular occasions to be checked.     

An acid dichromate digestion procedure for total nitrogen determination in soils

Abstract

Modified version of a dichromate digestion procedure, earlier found suitable for simultaneous determination of organic carbon (C) and potentially mineralizable nitrogen (N) in soils, was evaluated for total N determination in 44 diverse soil samples from the semi‐arid region of India. The soils belonged to Vertisols and Alfisols and had a wide range in total N contents. The method involves digestion of the soil sample with an acidified dichromate solution for 30 minutes in a digestion tube in a block digester preheated to 165°C followed by determination of N in the digest by steam distillation procedure. The efficacy of the dichromate procedure for determining total N differed for the two soil types. Excellent correlations were observed between the values of total N obtained by the dichromate procedure (Dichro‐N) and by Kjeldahl method (Kjeldahl‐N) for Vertisols (R²=0.995; n=21) and Alfisols (R²=0.952; n=23). The regression equations describing the relationships between the two soil types can be used to estimate Kjeldahl‐N from Dichro‐N. Both Kjeldahl and the proposed acid dichromate methods were found to be more precise in determining total N in Vertisols than Alfisols. The proposed procedure is rapid and simple and can be used for routine total N determination especially, in soils such as Vertisols. Based on our results the acid digestion procedure certainly deserves a wider evaluation with a range of soil types.     

A comparison of three methods of organic carbon determination in some New Zealand soils

A dry combustion (Dumas) reference method for measuring total organic C (T), is compared with two other methods: the wet acidified dichromate oxidation, Walkley-Black procedure (an estimator of organic C) and loss on ignition (L) (an estimator of organic matter) for 40 samples from various depths from five New Zealand mineral soils, spanning a range of textures and cultivation treatments. Regression analyses reveal the following: (1) an excellent linear relation exists for all samples between Walkley-Black procedure and reference method results, with a mean conversion factor 1.25, which compares with the original value 1.32 recommended by Walkley & Black (1934). (2) L and T are less well-related by an equation of the form L=a+bT. In contrast to the traditional assumption that b? 1.72 and a? 0, a strong ‘intercept effect’ (a > 0) is revealed, reflecting removal on ignition of non-organic soil constituents. An improved regression of the form L=a+bT+cC, where C= percentage of clay, obtained by inclusion of the clay as an independent variable, points to the role of clay in releasing these constituents, chiefly adsorbed water.     

Heavy solution methord for determination of volcanic glass content in tephras and tephra-derived soils

Abstract

Volcanic glass is the most important primary mineral for the tephra-derived soils because it is the most abundant and the most weatherable among the primary minerals. The chemical properties of volcanic glass in tephras are closely related to the rock types of tephras (Kobayashi et al. 1976; Yamada and Shoji 1983; Shoji 1986; Yamada 1988) and influence on the chemical and clay mineralogical properties of tephra-derived soils (Saigusa and Shoji 1986).     

A simplified procedure for the determination of total mercury in soils

Abstract

A saraimplified procedure for the measurement of total mercury in soils and some preliminary results for Saskatchewan are presented. Soil samoles were digested in aqua regia at low temperatures, followed by determination of Hg with a simplified flameless atomic absorption technique. Hg levels in soils analyzed ranged from 0.003 to 0.071 ug/g.     

Pore-size distribution in loamy soils: A comparison between microtomographic and capillarimetric determination methods

Pore-size distribution in a soddy-podzolic silt loamy soil developing from mantle loesslike loam (Eutric Albic Retisol (Loamic, Cutanic)) was calculated from the water retention curve according to Jurin’s equation and directly determined in microtomographic experiments. Rounded macropores with the diameter of their sections from 75 to 1000 μm predominate in horizontal sections if the studied soil samples. A larger part of the soil pores (>30–35%) belongs to micro- and nanopores, and they cannot be quantitatively determined by the tomographic method, because their sizes are smaller than the detection limit of the applied X-ray microtomography (8.75 μm per pixel). This leads to a significantly larger pore volume determined from the water retention curve in comparison with the “tomographic” pore volume. A comparative analysis of pore-size distribution curves obtained by these methods shows that the major regularities of the pore-size distribution in the range from 30 to 5000 μm are similar in both cases. Fine macropores and, partly, mesopores predominate. Common characteristics of the pore-size distribution curves obtained by these methods, including the coincidence of the peaks, attest to the validity of classical approaches, according to which the hydrology of soil pore space can be perceived as a physical model of cylindrical capillaries of different sizes with capillary-sorbed water.     

Quantitative determination of minerals in acid forest soils of granite

A procedure for quantifying minerals in particle size fractions of fine earth (< 2 mm) is presented. Mineral fractions of the acid forest soils are characterised by various transition products. Transitional minerals between illite and vermiculite or smectite, polyhydroxy-Al polymers interlayered in smectite and vermiculite, as well as poorly crystalline compounds are present. Normative calculations with standard minerals, generally applied to rocks, cannot be used to quantify precisely minerals of these soil samples. Conventional qualitative and quantitative chemical analyses are therefore completed by microanalyses of well-identifiable minerals. The calculation procedure is based mainly on a system of simultaneous linear equations. These are set up from the chemical contents of a particle size fraction on the one hand and from the corresponding element contents of single minerals on the other hand. The contribution of single minerals to overall parameters can be calculated by programmed algorithms. The methodology was adjusted to different particle size fractions.     

Gas-liquid chromatographic determination of 3,6-dichloropicolinic acid in soils.

A gas-liquid chromatographic (GLC) method has been developed for the determination of the experimental herbicide 3,6-dichloropicolinic acid (Dowco 290) in soils. The method involves extraction of 1 g soil samples with 1N NaCl at approximately pH 7, methylation with diazomethane utilizing a microgenerator, and detection by electron capture GLC. Interferences are small, so that a cleanup step is not necessary even at the 6 ppb level. The procedure is rapid, requiring only 45 min/sample. Recoveries range from 84 to 94% at the 6-1000 ppb level with a minimum detectable limit of 6 ppb. Standard deviations for the percentage recovery values vary from 10.9 to 2.3 for the tested range of 6.7-670 ppb, respectively.     

Evaluation of a rapid chromic acid method for determination of total nitrogen in soils

Abstract

A chromic acid method proposed for rapid determination of total nitrogen (N) in soils was evaluated by comparing its results with those obtained by a Kjeldahl method commonly used for total N analysis of soils. Analyses of 12 surface soils selected so that they differed markedly in texture and organic carbon content showed that the chromic acid method recovered only 87.5% to 94.1% (average, 90.5%) of the soil N recovered by the Kjeldahl method. The recovery of N from ammonium sulfate and soils by the chromic acid method decreased with increase in time of digestion with chromic acid from 1 minute to 15 minutes (the recommended digestion time). This indicates that the low recovery of soil N by the chromic acid method was at least partly due to oxidation of ammonium to nitrate and/or nitrite by chromic acid and subsequent gaseous loss of these forms of N. Support for this conclusion was provided by analyses showing that about half of the N that could not be recovered as ammonium after digestion of ammonium sulfate with chromic acid for 15 minutes was in the form of nitrate.     

Influence of the addition of organic residues on carbohydrate content and structural stability of some highland soils in Ethiopia

Abstract. When over exploited and coupled with climatic conditions, tropical soils are subject to increased erosion and a loss of soil organic matter. Countermeasures include the incorporation of organic materials such as crop and animal residues. We studied the effect of adding crop residues and manure to soil, at five sites in Ethiopia, on carbohydrate properties, aggregate stability and the C and N distribution within water-stable aggregates. The effects of organic amendments varied between sites. The largest content of carbohydrates was obtained in the control treatment at Holeta, Ginchi (90 kg ha^–1 mustard meal), Jimma (5 t ha^–1 cow dung + 9 t ha^–1 coffee husk), Awassa (forested soil), and Sirinka (soil alley-cropped with Leuceanae ). The aggregate stability of these soils was highly correlated with the OM content but not with carbohydrates. The smaller aggregates (<1.00 mm) accumulated more carbohydrates than the larger (>1.00 mm), thereby suggesting a protecting effect within the finer soil fractions. A protecting role played by humified OM components was also indicated by the C and N distribution as well as the C:N ratios which showed preferential accumulation in small rather than in large aggregates. The isotopic ¹³C-OC values of carbohydrate extracts were generally low, suggesting that OM was from plants with C3 photosynthetic pathways. Soil treatments with maize alone or combined with coffee husks at Jimma decreased the δ¹³C‰ values slightly, revealing that maize contributed a share of the labile OM. Despite the improvement in the soil OM content, neither the carbohydrate content nor the aggregate stability were increased to the level of the forested sites, suggesting that the additions of crop residues and manure were not alone sufficient to restore the soil physical quality.     

Elimination of chloride interference in the phenoldisulphonic acid method of nitrate determination in soils

Abstract

A technique was developed to eliminate chloride interference using antimony (III) in the determination of nitrates in soils by phenoldisulphonic acid method. This method was found effective upto nearly 300 ppm Cl^‐ in soils ranging in pH from 5.6 to 8.3. By avoiding repeated filtrations of chloride precipitates, this method allowas quick analysis of soils for nitrates in single soil extracts containing other mineral nitrogen fractions.     

A new rapid and accurate method for the determination of carbon in soils

The most reliable method for determining carbon in soils is the dry combustion method, the technique of which was established for the first time by JUSTUS von LIEBIG in 1831 and for nearly a century his combustion technique, essentially unmodified save for improvements in materials, constituted the standard method for determination of carbon and hydrogen. PREGL (1), in his publication on organic microanalyses in 1916, reported an excellent method in which a carbon determination could be carried out in an hour with a sample of only a few milligrams. After that, his method was improved in many respects by many investigators (2,3). Since these methods require, however, both complicated and expensive apparatus as well as trained personnel and are time-consuming, they are not considered to be suitable for practical use in soil research laboratories at all.     

A comparison of water soluble organic substances in acid soils under beech and spruce in NE-Bavaria

Water soluble organic substances extracted from the L, O_f, O_h, A, and B horizons of acid soils under Beech (Fagus sylvatica) and Spruce (Picea abies) were fractionated on Sephadex G-25 (medium). Infrared, ¹H NMR and ¹³C NMR spectra of the fractionated components were obtained and comparisons were made among fractions, among horizons, and between forest types. Usually, the spectra indicated that carbohydrates dominated the water soluble fractions. Substances originated from spruce exhibited more undissociated carboxylic acid character than the beech derived material. Despite many similarities, principal differences in the carbohydrate components were found among fractions, among horizons, and between vegetation types.     

Experimental determination of the active organic matter content in some soils of natural and agricultural ecosystems

In incubation experiments, the soil supply with carbon of mineralizable (C_min), potentially mineralizable (C_pm), and active (C_ac) organic matter, and of microbial mass (C_mb) in natural and agricultural ecosystems of Moscow region (gray forest soil) and Catalonia (Xerochrept) was assessed based on the measurements of the C-CO₂ emission. In the gray forest soil, the C_pm and C_ac contents decreased in the following sequence of ecosystems: forest > meadow > unfertilized agrocenosis; in the Xerochrept, forest > pasture > scrub > agrocenoses with organic fertilizer > unfertilized agrocenosis. A method for measurement of the C_mb according to the C-CO₂ emission during an 11-to 14-day incubation of previously dried soils is proposed.     

Modified method for measuring acid phosphatase activities in forest soils with high organic matter content

Abstract

The acid phosphatase activity (APA) is a key factor in phosphorus (P), mineralization, P nutrition of plants, and P cycling. However, the widely used method of Tabatabai and Bremner for APA determinations is seriously restricted in soils with high organic matter contents, owing to interference in photometric detection by dissolved organic matter. The objectives of this study were: A) to modify the procedure of Tabatabai and Bremner with a view to its application to forest soils rich in organic carbon, b) to determine APA contents in forest soils of the Sierra de Gata mountains, and c) to establish relationships between the APA with different soil parameters. The modified procedure was well adapted to forest soils with high organic matter contents and had good reproducibility, while maintaining the relative simplicity and accuracy of the original Tabatabai and Bremner procedure. APA in the forest soils studied was high but did not correlate with labile P. The APA in the soils studied depended principally on availability of readily degradable energy sources and soil nitrogen (N).     

A comparison of buffered and unbuffered ammonium salts to determine exchangeable base cations in acid soils

Abstract

In soil samples from two study sites in southern Norway, exchangeable cations were determined using two different ammonium (NH₄)‐salts as extractant. As expected, the cation exchange capacity (CEC) determined in 1M ammonium acetate (NH₄OAc), buffered at pH 7.0 was higher than the CEC measured in ammonium nitrate (NH₄NO₃). By contrast, the amount of exchangeable calcium (Ca), magnesium (Mg), and barium (Ba) was lowest in the NH₄OAc extract, in particular in the upper soil horizons high in organic matter (O‐ and E‐horizon). This suggests that NH₄ in 1M NH₄OAc does not compete effectively with multivalent base cations. The relatively high levels of exchangeable base cations in NH₄NO₃ could not be explained by increased weathering. An increase in selectivity of especially divalent cations may explain the relatively low amount of exchangeable base cations extracted by NH₄OAc, as this involves increased deprotonation and thus a higher negative charge.     

A comparison of methods for measuring aluminium in KCl extracts of soils

Abstract

Five colorimetric methods; alzarin red, aluminon, catechol violet, ferron and 8‐hydroxyquinoline, and AAS were compared for measuring aluminium in KCl extracts of soils. An analysis of variance of the results against soils, methods and replicates showed that, apart from the predictably large soil effect, the three two‐way interactions and the method effect gave small but statistically significant differences.

The AAS method showed the most variation, and the catechol violet method gave consistently lower results than the other methods, but provided differences in the order of 10% are not considered critical, any of these methods could be used on a routine basis.     

A comparison of models for characterizing the distribution of radionuclides with depth in soils

It is common practice to fit mathematical models to radionuclide activity–depth profiles in soils in order to quantify rates of vertical migration through the soil profile. We have fitted six such models to 21 different activity–depth profiles of radiocaesium (¹³⁷Cs) derived from Chernobyl and determined relations between the models and the values of their parameters. The advection and dispersion parameters obtained using four solutions to the advection–dispersion equation (each based on different initial and boundary conditions or different simplifications) are in good agreement. We further develop a relation between parameter values obtained using the advection–dispersion models and those determined by a simpler exponential function of the form Aexp(–Bt) where t is the time and A and B are parameters to be estimated. One of the advection–dispersion models proved to be significantly better than the others in terms of goodness-of-fit, versatility and ease of use. A simple model, using calculations based on measured characteristics of the activity–depth profile, was shown to accord well with parameters derived from more complex models based on statistical curve fitting. We have also evaluated the ‘residence time’ or ‘compartmental’ model approach to characterizing radionuclide activity–depth profiles. We relate such models to a numerical solution of a simple advection equation, and we show that apparent dispersion in compartmental models is an artefact of numerical dispersion, which can be quantified by the Courant condition. For activity profiles that have a significant advection component, using solutions to the advection–dispersion equation, we have observed a strong positive correlation between advection and dispersion in the profile.