Predicting total soil lead from an acetic acid‐sodium acetate buffered solution

Abstract

Total soil lead was predicted satisfactorily from the Lead extracted by the Standard Morgan soil testing solution (sodium acetate with acetic acid, pH 4.8). Using 161 soils, 85% of the variance in total lead content was accounted for by:

Total Lead = ‐115 + 106.4 √Sodium Acetate Extracted Lead A modified Morgan solution, utilizing EDTA as a chelating agent, extracted greater than 3 times as much lead as the regular Morgan's solution, but was no better in predicting total lead.     

Effectiveness of three rapid digestion methods to estimate total lead in orchard soils

Abstract

High concentrations of lead in contaminated soils comprise a potential public health hazard. Limits between safe and dangerous levels are often based on total soil lead content. Current chemical procedures to determine total lead are unsuitable for routine soil analysis because they are time‐consuming and require highly trained personnel. This paper describes the effectiveness of three rapid extraction procedures to estimate total lead in a large number of lead arsenate‐contaminated orchard soils. Dissolution of soil lead in Kjeldahl flasks using a nitric acid‐perchloric acid mixture was virtually complete (98%) when compared to values for total lead measured by treatment with a mixture of HF, HNO₃ and KClO₄. Shaking of 5‐g samples in 50 ml of lN HCl or lN HNO₃ for 1½ hours extracted 95 and 93 percent of the total lead, respectively. Regression equations were derived to allow estimation of total lead from values obtained in the HNO₃‐HClO₄, HCl, or HNO₃ extracts. The HNO₃‐HClO₄ digestion procedure is preferred with atomic absorption spectrophotometry, while HCl extraction is suitable for routine soil analysis with inductively coupled argon plasma spectrophotometers or similar instrumentation.

Grinding of the soils to promote sample uniformity appeared unnecessary, at least in the silt loam soils tested.     

The effect of soil lead sorption capacity on the uptake of lead by corn

Abstract

Lead uptake by four‐week‐old corn shoots grown in Fb‐amended soils was found to be dependent upon the level of Pb in the soil relative to the soil's capacity to sorb Pb. At a given level of added Pb, lead uptake by plants was found to decrease with an increase in soil pH, cation exchange capacity, and available phosphorus.     

A rapid steam distillation method of assessing potentially available organic nitrogen in soil

Abstract

A rapid steam distillation of assessing potentially available organic nitrogen in soil is described. It involves determination of the ammonia‐N produced by steam distillation of the soil sample with pH 11.2 phosphate‐borate buffer solution for 8 min. The method is simple and precise, and its results are not significantly affected by air‐drying or air‐dry storage of the soil sample before analysis. It is well suited for use in soil testing laboratories because it does not require extraction, filtration or transfer steps. Studies using 33 Brazilian soils showed that the results obtained by this method were highly correlated with those obtained by aerobic and anaerobic incubation methods of assessing potentially available organic nitrogen in soil.     

Glycerol‐extraction refractometry for determination of gravimetric water content of soil samples

Abstract

We developed a simple and rapid method suitable for on‐site determination of gravimetric water content of soil samples. The proposed procedure was as follows; i) take 10–20 g of a soil sample in a tared mortar and weigh with a portable electronic balance, ii) add glycerol at a soil:glycerol ratio of 1 to 2 and weigh again, iii) mix the soil and glycerol thoroughly to ‘extract’ soil water into the added glycerol, iv) measure the refractive index of the ‘extract’ passed trough a filter placed on a refractometer, and vi) calculate the water content of the soil sample from a calibration curve relating the refractive index to water content of glycerol and the weights of the soil sample and glycerol. We tested the method on four soils at various moisture levels and found that the water contents from the proposed method were close to those from the standard oven‐drying method with slight downward deviations.     

Simple method for estimating 14C in formic acid solutions using liquid scintillation counting

Abstract

The feasibility of using a simple radiochemical method to determine the extent of formylation resulting from interaction of formic acid solutions with soil constituents was investigated. The interaction between formic acid‐^l4C solvents and starch was used as a model reaction. Radioassay of 1 cm³ formic acid solution by liquid scintillation counting in 10 cm³ of the scintillator‐solubilizer Insta‐gel was found to be suitable. The method is simple to use and sample preparation is easy.     

Use of phosphorus vectors to monitor changes in soil phosphorus

Abstract

A study was conducted to evaluate the use of P vectors to predict the amount of P required on a yearly basis to maintain a constant solution‐solid phase P relationship in an irrigated calcareous and a dryland acid soil. Irrigated potato‐spring barley and dryland spring pea spring‐barley crop rotations established at the two locations. Mono‐calcium phosphate (0–45–0) was applied annually at five levels, ranging from 0–4 times estimated crop removal. Phosphorus vectors were determined on soil samples by equilibration with standard P solutions. Yields tended to increase with added P on the calcareous soil; however, significant responses were not recorded at either location. Consequently, critical P vectors were not established. A constant solution‐solid phase P relationship was maintained by addition of P equal to that removed by the crop on the calcareous soil. A constant solution‐solid phase P relationship was not maintained on the acid soil.     

A rapid method of evaluating the zinc status of coastal plain soils

Abstract

A study was made to evaluate Zn removed by extraction with a 0.075 N acid mixture (0.05 N HCl + 0.025 N H₂SO₄). A ratio of soil to extracting solution of 1 to 4 and an extracting time of 15 minutes was selected. Data obtained by the method was significantly correlated with dithizone (0.01%) extraction. The method was found to be acceptable for evaluation of the Zn status of Southern Coastal Plain soils and easily adapted to routine use in soil testing. A significant correlation was obtained between extractable soil Zn and leaf blade content of Zn for Zn‐deficient and non‐deficient corn plants.     

Comparison of chemical methods of assessing potentially available organic nitrogen in soil

Abstract

We recently developed two rapid and precise chemical methods of assessing potentially available organic N in soils. One method involves determination of the ammonia‐N produced by steam distillation of the soil sample with pH 11.2 phosphate‐borate buffer solution for 8 min. The other involves determination of the ammonium‐N produced by treatment of the soil sample with 2M KCl solution at 100°C for 4 hours. Studies using 33 Brazilian soils showed that the results obtained by these methods were highly correlated with those obtained by anaerobic and aerobic incubation methods of assessing potentially available organic N in soil.

The two methods were further evaluated by applying them to 30 Iowa soils and by comparing their results and those obtained by other chemical methods with the results of the incubation methods considered to be the best laboratory methods currently available for assessment of potentially available organic N in soil. The chemical methods used included the acid KMnO₄ method, the alkaline KMnO₄ method, the CaCl₂‐autoclave method, and the NaHCO₃ UV method. The incubation methods used involved determination of the ammonium‐N produced by incubation of the soil sample under anaerobic conditions for 1 week or determination of the (ammonium + nitrate + nitrite)‐N produced by incubation of the sample under aerobic conditions for 2 and 12 weeks. The data obtained showed that the results of the two chemical methods evaluated were highly correlated with those obtained by the incubation techniques used for comparison and that the correlations observed with these two methods were higher than those observed with the previously proposed chemical methods. It is concluded that these two rapid and simple methods are the best chemical methods thus far developed for laboratory assessment of potentially available organic N in soil.     

Boron analysis in soil extracts and plant tissue by plasma emission spectroscopy

Abstract

Nine Colorado soils were treated with sodium borate and were subjected to 3 wetting and drying cycles. These soils were extracted with hot water for boron analysis. Plant samples, including NBS standard reference materials (SRM) 1571, 1570, 1573, were dry ashed and wet digested using nitric acid. All soil extracts and plant digests were analyzed for boron using ICP‐AES and colorimetrically using the Azomethine‐H method.

A high degree of correlation (r² = .99) was found between boron determination by ICP and the Azomethine‐H method for soil extracts and plant digests. The Azomethine‐H method gave B values 9% higher than ICP‐AES on the average.

Boron levels determined by ICP were similar to NBS boron values for both the dry ashed and wet digested SRM plant samples. Boron levels determined colorimetrically were comparable to the NBS values for dry ashed SRM plant samples. Plant samples digested in nitric acid could not be analyzed for boron by the Azomethine‐H colorimetric method due to interferences resulting from nitrate complexes in the wet digest.     

High‐Throughput Microwave‐Assisted Digestion and Extraction Procedures for Agricultural Materials

Abstract

Despite the advances in microwave‐assisted procedures, the sample throughput still remains a critical problem that requires the development of reactor vessels, rotors, and procedures able to deal with a large number of samples simultaneously. In this work, a 36‐vessel rotor was combined with diluted nitric acid solution for digestion of agricultural materials. Accurate results were obtained for aluminum (Al), calcium (Ca), copper (Cu), iron (Fe), potassium (K), magnesium (Mg), manganese (Mn), phosphorus (P), and zinc (Zn) in bovine liver and spinach leaves standard reference materials. The EPA‐3051 method was also evaluated using this system. The procedure led to quantitative recoveries of chromium (Cr), Cu, Mn, nickel (Ni), and Zn in soil. All measurements were carried out using inductively coupled plasma—optical emission spectrometry (ICP‐OES). The main advantages of the proposed procedures are the increase of sample throughput in microwave‐assisted digestions or extractions and the lower dilution required before pneumatic nebulization of digests obtained by using dilute nitric acid.     

The determination of hot‐water‐soluble boron in some acid Oregon soils using a modified azomethine‐H procedure

Abstract

A method is proposed for determination of hot‐water‐soluble boron in acid soils from western Oregon. The soil sample is boiled in 0.02 M CaCl₂, filtered, and B determined using azomethine‐H. Soils extracted in this way yielded extracts with little color in them and the predicted error due to this color was 0.00–0.07 ppm B. The use of charcoal as a decolorizing agent resulted in comparatively high predicted errors.

Inductively‐coupled plasma emission spectroscopic (ICP) analysis of distilled water and 0.02 M CaCl₂ extracts indicated that the extractable B level was not affected by the presence of CaCl₂. Azomethine‐H yielded comparable values to ICP but the curcumin method tended to give high values for hot‐water‐soluble B.     

Role of Different Soil Fractions in Copper Sorption by Soils

Abstract

To evaluate contributions of organic matter, oxides, and clay fraction to copper (Cu) adsorption in six characterized soils, adsorption isotherms and distribution coefficients were obtained by a batch experimental method. Copper adsorption isotherms from untreated soil, organic matter removed from samples, and organic‐matter‐ and oxide‐removed samples were compared with curve patterns and correlated to Langmuir and Freundlich models. Copper sorption data on untreated soils described L or H‐curves, whereas in soils deprived of any component, their curves were S‐type. Distribution coefficients allowed knowing Cu adsorption capacity of untreated soil and of organic matter, oxides, and clay fraction. Soil organic matter is the main component that affects Cu adsorption as long as soil pH is near neutrality. At acid pH, oxides are the main component that affects Cu adsorption, although to a much smaller extent than organic matter near neutral conditions. Soil pH is the main soil factor that determines Cu adsorption.     

Comparison of Root‐System Efficiency and Arsenic Uptake of Two Fern Species

Abstract

This greenhouse study examined the root characteristics (biomass, length, area, and diameter) and root uptake efficiency of Pteris vittata, an arsenic (As) hyperaccumulator and Nephrolepis exaltata, not an As hyperaccumulator, in relation to plant uptake of As and nutrients in an As‐contaminated and a control soil. After 8 weeks of growth, on a per plant basis, P. vittata accumulated 7.3–8.8 g of biomass and removed 2.51 mg of As from the As‐contaminated soil compared to 2.4–2.7 g of biomass and 0.09 mg of As for N. exaltata. This was partially because P. vittata developed a more extensive root system, 2.4–3.8 times greater (biomass, length, and area), and possessed a greater proportion of fine roots than N. exaltata. In addition, the As root‐uptake efficiency (defined as As concentrations in plant tissue per unit root) for fronds of P. vittata was 15–23 times greater than that of N. exaltata in both soils. Whereas N. exaltata removed phosphorus (P) more efficiently from the soils, P. vittata removed As more efficiently. The larger root biomass coupled with more efficient root‐uptake systems for As may have contributed to As hyperaccumulation by P. vittata.     

Estimating soil texture from sample density

Abstract

A number of laboratory methods for determining soil physical fractions have been proposed. The methods being cumbersome and time consuming cannot be adopted for routine analysis in soil testing laboratories. Therefore, a simple method which could provide quantitative estimates of the soil size fractions is required. This study used soil sample density (ratio of mass of soil in a standard scoop to its volume) to estimate soil separates. Regression models were developed for predicting soil separates from sample density. Sand, silt, and silt+clay fractions were best described by second degree polynomials with coefficients of determination ranging from 0.75–0.80. Although the exponential function was statistically equivalent to the second degree polynomial for estimating clay, it was preferable as it yielded a better shape of the fitted curve at sample densities <1.2 g cm^‐3. Validation of the models with independent data showed that model‐predicted values of various size fractions matched well with laboratory measurements with coefficients of correlation ranging between 0.95–0.99. The higher correlation coefficients between the measured and estimated clay, silt, and sand fractions both for model development and their validation on independent data suggest that the models could be used for estimating soil separates from sample density measurements.     

Measurement of available soil phosphorus under conventional and no‐till management

Abstract

The objective of the investigation was to compare the predominant forms of P in fields of an acid Matapeake soil under no‐till and conventional‐till management. The fields, which differed in extent of contact between soil and fertilizer P, also differ in forms of P. Fertilizer P remained in the uppermost layer of no‐till fields and was, therefore, not in as close proximity to the plant (corn) roots as P was in conventional‐till fields. Nevertheless, fertilizer P in the no‐till fields underwent only limited conversion to forms less available to plants and thus, in part, may have accounted for similar plant uptake rates of P in no‐till and conventional‐till fields.

One method used to analyze P in the Matapeake soil was the double‐acid‐extraction method. This method is used by several state soil‐testing laboratories of the eastern and southeastern United States, where acid soils like Matapeake are common. The double‐acid‐extraction method underestimated the soil P available for plant uptake.     

Amino acid interference with ammonium determination in soil extracts using the automated indophenol method

Abstract

The formation of a colored indophenol complex is commonly used as a quantitative measure of the ammonium content of soil extracts. The potential interference with ammonium determination from co‐extracted amino acids was examined. The extent of color development was examined for 22 amino acids by subjecting pure solutions to ammonium determination by both the indophenol method and steam distillation. Apparent detection of amino acid as ammonium ranged from 0 to 94 % of total nitrogen for the indophenol procedure, whereas steam distillation resulted in little apparent ammonium recovery. With the exception of threonine, the extent of color development was inversely related to amino acid molecular weight. The range in recoveries for the indophenol procedure suggests both size and composition of the co‐extracted amino acid pool is important in determining the extent of interference.

Significantly (p=0.001) greater estimates, averaging 0.4 μg mL^‐1, were found in indophenol estimates of mineral‐N content of moist, fresh soil samples. Air drying, oven drying or chloroform fumigation significantly increased the difference (0.3 ‐ 0.7 μg mL^‐1) in estimates of ammonium content. At 10: 1 extract: soil ratios this could cause ? to be overestimated by 3–7 μg g^‐1soil. The increased interference was attributed to a release of amino acid as a result of pretreatment. The difference between distillation and indophenol estimates of ammonium content of 0.5 M K₂SO₄was found to be dependent upon ammonium content. The use of procedures employing a distillation step (manual or automated) is recommended to avoid amino acid interference when precise NH₄+‐N determinations are needed on dried or fumigated samples.     

Automated analysis of 15N and 14C in biological samples

Abstract

An automated method for the simultaneous analysis of total N, total C, ¹⁵N and ¹⁴C in small plant and soil samples is described. A commercial C‐N analyser ‐ continuous flow isotope ratio mass spectrometer (ANCA‐MS) has been extended to also measure CO₂ and collect ¹⁴CO₂ produced by sample combustion. Samples containing 20 ‐ 200 μg N and up to 5 mg C can be analysed directly with no sample preparation other than drying and fine grinding. The precision of total elemental analysis is comparable to that by conventional methods. The average standard deviation of ¹⁵N analyses of plant material at natural abundance was ±1 ‰. This is accurate enough for all ¹⁵N studies except those using natural abundance and possibly long term studies of soil organic matter. Recovery of ¹⁴C in test samples was 100%. The instrument can be operated by graduate students under supervision and operating costs are primarily for sample cups, combustion catalyst and quartz tubes.     

A turbidimetric method for determining phosphate‐extractable sulfates in tropical soils

Abstract

Turbidimetric methods, using Ba ions to precipitate SO₄, are frequently used to determine soil sulfates extracted with phosphate solutions. These methods, as routinely performed, seriously underestimate SO₄ in some soils of the tropics because phosphate is removed from the extractant by soil adsorption and because many extracts fail to yield satisfactory precipitate even if the extracting procedure is adequate. Decolorizing the extracts with carbon black, treating extracts with strong oxidizing agents, adding SO₄ spikes, and seeding the extracts with BaCl₂ seed‐crystals improve precision, but some extracts, especially those from soils derived from volcanic ash, do not yield reliable precipitates even though these procedures are employed. This paper presents a method that consistanlty yielded more SO₄ than other turbidimetric procedures with which it was compared. The proposed method was further validated against an ion‐chromatographic method for SO₄ determination. The two methods yielded virtually identical results.

The proposed method consists of extracting SO₄ with 0.04 M Ca(H₂PO₄)₂ pH 4, at a soil‐to‐solution ratio of 1: 10. Repeated extraction is necessary for phosphate‐retentive soils. (A. single extraction was approximately 40% effective for removing indigenous SO₄ from a Hydric Dystrandept subsoil, approximately 78% effective for an Eutrustox.) Organic materials are removed from the extracts by adsorption on charcoal; SO₄ is concentrated in the extract by volume reduction; a SO₄ spike is added; BaCl₂‐seed crystal is added, after which volume is increased by adding BaCl₂ solution. Optical density is read at 600 nm.     

Reliability of volumetric sampling as compared to weighed samples in quantitative soil test interpretations

Abstract

Weight variability of volumetric soil test samples taken with the standard 4.25 cm³ Urbana Laboratories’ soil scoop was studied as a factor influencing soil test accuracy. Also examined was effect of degree of sample pulverization on volume—weight, differences among technicians, and volume‐weight differences between dry and moist samples.

The results revealed that volumetric sampling of Maine soils can lead to major errors, particularly when quick tests are used to quantify lime requirement, extractable H, exchangeable cations, CEC, and percent base saturation. Good predictions of these properties from quick soil test results, however, are possible when samples are weighed. In the Maine Laboratory poor quantitative results from volumetric samples originated from wide variations in volume‐weight among soils. This variability was traced to degree of aggregation, which in turn was traceable to differences in texture and organic matter among samples. Technician differences were not an important source of volume‐weight variability. Volume‐weights were much lower with moist than with dried soil, but volume‐weight variability among soils was less when sampled moist.