Certification of an air‐dry soil for pH and extractable nutrients using one hundredth molar calcium chloride

Abstract

The preparation of an air‐dry river‐clay soil as reference soil material for pH and extractable nutrients with a 0.01 M calcium chloride (CaCl₂) solution and the homogeneity testing are described. Recommended values for pH and the concentrations of ammonium‐nitrogen (NH₄‐N), total soluble nitrogen (N), phosphorus (P), sodium (Na), potassium (K), and magnesium (Mg) using the unbuffered 0.01M CaCl₂ are given. With respect to nitrate‐nitrogen (NO₃‐N), the sample proved not to be sufficienctly homogeneous. The certified soil sample has also been used as a sample in the International Soil‐Analytical Exchange (ISE), a continuous proficiency testing scheme. The values found by the ISE laboratories compared well with the certified values.     

Certification of B-group vitamins (B1, B2, B6, and B12) in four food reference materials

In 1989, the Community Bureau of Reference started a research program to improve the quality of vitamin analysis in food. To achieve this task, vitamin methodology was evaluated and tested by interlaboratory studies and the preparation of certified reference materials, which will be used for quality control of vitamin measurements. The main improvements in methodology were achieved by testing and standardizing the extraction condition and enzymatic hydrolysis procedures. Results for each individual material are derived from five replicate determinations using at least two independent methods: liquid chromatography (HPLC) and microbiological assay for vitamins B1, B2, and B6; and radioprotein binding and microbiological assays for vitamin B12. The certificate of analysis for four reference materials gives mass fraction values for water-soluble vitamins. These certified values were based on the acceptable statistical agreement of results from collaborating laboratories. Certified values with uncertainties (mg/kg dry matter) for each CRM are as follows: 4.63 (0.20) and 4.10 (0.51) for vitamins B1 and B6, respectively, in CRM 121 (wholemeal flour); 6.51 (0.24), 14.54 (0.3), 6.66 (0.43), and 0.034 (0.003) for vitamins B1, B2, B6, and B12, respectively, in CRM 421 (milk powder); 3.07 (0.17) and 4.80 (0.40) for vitamins B1 and B6, respectively, in CRM 485 (lyophilized mixed vegetables), and 8.58 (0.55), 106.8 (2.8), 19.3 1.5), and 1.12 (0.044) for vitamins B1. B2, B6, and B12, respectively, in CRM 487 (lyophilized pig liver).     

Role of National Metrology Institutes for Comparable Measurements

Abstract

The global economy and fair trade commitment has forced the need to demonstrate equivalence between national measurement standards. That includes a need to meet ever‐increasing demands for accuracy, range, and diversity of measurements. Recent activities of national metrology institutes (NMIs) are among the topics discussed in this article. These include mutual recognition of calibration and measurement certificates of NMIs under mutual recognition arrangements (MRAs), operated among NMIs under an international framework of five regional metrology organizations (RMOs). Particular attention is given to the efforts of Mexico's NMI, Centro Nacional de Metrologia (CENAM), to establish a national traceable measurement system for sectoral testing laboratories for agriculture. Other initiatives include proficiency testing in collaboration with the Colegio de Posgraduados, the intention being to promote development and certification of reference materials and to establish sectoral reference laboratories in the country.     

Assessment of soil and plant analysis laboratories in the West Asia‐North Africa Region

Abstract

Although limited amount of water is the primary constraint to agricultural productivity in the rainfed area of West Asia and North Africa (WANA), yields are also low because of the poor mineral nutrient status of soils. Yields can, therefore, be considerably increased by judicious fertilizer use. Laboratories for soil and plant analysis are essential for identifying nutrient constraints and providing a basis for efficient fertilizer use, through correlation studies to establish suitable soil testing extractants and calibration studies with crop responses. The Soils Laboratory at the International Center for Agricultural Research in the Dry Areas (ICARDA) has initiated a quality control program among the national agricultural research systems (NARS) in the countries of the WANA region. The efforts include linkages with the Wageningen International Soil Analytical Exchange Program, in‐country training courses, and a laboratory analysis manual. Continued improvement in laboratory performance is dependent upon knowledge of the capabilities of such laboratories and identification of their constraints. This presentation reports a fact‐finding survey of laboratories from 16 countries of the WANA region—mainly public, from universities and ministries of agriculture, and some private or commercial ones—based on a questionnaire about analyses, facilities, methodologies, quality assurance, personnel training, and management. Future efforts to improve the quantity and quality output from of these laboratories will address such deficiencies.     

Use of Reference Soils in Determinations of 0.01 M Calcium Chloride Available Metals

There are few readily available standard reference soils for which 0.01 M calcium chloride (CaCl₂) soil extraction available metals data are available. This study assessed the ease with which new available metals data could be generated for reference soils. Data on 0.01 M CaCl₂ available elements for four reference soils from the Wageningen Evaluating Programs for Analytical Laboratories and three reference soils from the Australasian Soil and Plant Analysis Council proficiency testing program are presented. It is difficult to generate new 0.01 M CaCl₂ available metal values for standard reference soils, because trace element concentrations are low and measurements have relatively high variability. We suggest that laboratories can use reference soils as quality control samples in the analysis of 0.01 M CaCl₂ available metals by reporting recoveries for major elements (e.g., potassium [K], magnesium [Mg], and sodium [Na], for which reference values are of high reliability) to provide assurance of acceptable extraction efficiency.     

Total nitrogen in plant material determinated by means of dry combustion: A possible alternative to determination by Kjeldahl digestion

Abstract

The use of dry combustion‐based analyzer (CHN‐600, LECO Corporation, St. Joseph, MI) for nitrogen (N) determination in plant material is described. The method was evalueted in inter‐laboratory proficiency test (International Plant‐Analytical Exchange) and compared with results obtained by the Kjeldahl method. Differences between methods were small and results were in very close agreement. However when differences did occur, correction for nitrates did not fully explain differences between the two methods. A high content of nitrates can lead to serious differences between results obtained by the Dumas and Kjeldahl methods. Accuracy for the dry combustion method was tested with certified reference materials. Long‐term evaluation of repeatability of a determination varied from 1% to 2% with respect to material analyzed or content of nitrogen.     

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.     

Interlaboratory and Intralaboratory Testing of Soil Sulfate Analysis in Mollisols of the Pampas

Sulfur (S) deficiencies in grain and forage crops have been detected in many agricultural regions of the world, but soil tests are not commonly used as the basis for S fertilizer recommendation programs. Errors of measurements of soil sulfate were determined to assess whether the variation among and within soil-testing laboratories could be a factor that prevent the adoption of soil testing to assess soil sulfate availability. Subsamples of 10 selected soils (Mollisols) from the Pampas (Argentina) were sent in two batches to five soil-testing laboratories. Laboratories were unaware of the existence of subsamples and performed routine sulfate analysis as if these soils came from 60 different fields. Soil sulfate ranged from 3.3 to 20.6 mg kg^?1. One laboratory reported sulfate values greater than the other ones, having a mean bias of 4.1 mg kg^?1 S sulfate (SO₄). The other four laboratories reported similar sulfate values when soils had low sulfate availability (less than 10 mg S kg^?1), even when they used different extractants. Considering only these four laboratories, average interlaboratory coefficients of variations ranged from 6 to 24% for the 10 soils. Within-laboratory mean coefficients of variation (CVs) ranged from 12 to 22%. However, mean absolute errors of all laboratories were less than 1.2 mg kg^?1 S-SO₄. Two laboratories reported different sulfate values for the two batches of shipment (an average difference of 4.7 and 3.8 mg kg^?1 of S-SO₄). Laboratories using different extractants obtained similar results, suggesting that using the same extractant is not a prerequisite to standardize laboratory results in these soils. Differences between laboratories in our study were smaller than in other interlaboratory comparisons for soil sulfate. These differences could be easily detected and corrected if laboratories participate in an interlaboratory control system. The observed low mean absolute errors suggested that, in general, all laboratories achieve acceptable precision when evaluating within the same batch of determinations. Differences between batches of shipment (within laboratory error) stressed the importance of using reference material for internal quality control.     

Uniformity,standardization and terminology: Our problems and progress

Abstract

There is increasing interest, particularly among fertilizer company soil testing laboratories, to standardize soil testing laboratory procedures and methods of reporting and interpreting soil test results. A Task Force Committee on Soil Testing was formed in 1969 by the Fertilizer Institute to formulate standard methods of testing soils. In 1971, a new organization called “Council on Soil Testing and Plant Analysis”; will begin soliciting a membership. The Council's primary objective is “to promote uniform soil test and plant analysis methods, use, interpretation and terminology”; with both organizations working toward a common goal. Considerable progress should be made toward standardizing the soil testing and plant analysis techniques.     

Variability of Soil Analysis in Commercial Laboratories: Implications for Lime and Fertilizer Recommendations

Abstract

Data of soil analysis of 20 samples of 84 commercial laboratories were used to estimate discrepancies among results and analyze the implications for fertilizer recommendations. More than 90% of the laboratories had all results of basic routine analysis of individual samples within the confidence interval (CI). Laboratories with the best performance in the proficiency test (grade A) had only 2.9 and 4.0% of the results outside the CI for the basic and the micronutrient set, respectively. However, the corresponding figures for grade C and D laboratories were 26.2% (basic) and 20.7% (micronutrients). Lime recommendation for a soil with 32% of soil base saturation reached the target value of 70±8% in 74% of the cases. In about 90% of the cases, fertilizer recommendations were on or close to the target rates Sizeable deviations of the fertilizer recommendations for P and K that could affect profit occurred in less than 5% of the results reported.     

Using Interlaboratory Proficiency Data to Guide NIR/MIR Calibrations

There is growing interest in the use of near-range and/or midrange infrared (IR) diffuse reflectance spectroscopy (NIR and MIR) as nondestructive alternatives to chemical testing of soils. This trend is supported by research on how best to correlate IR spectral data with results obtained by conventional laboratory measurements. While for soils there is growing interest in developing local and national calibrations using “legacy” data, the proven analytical performance of provider laboratories now and earlier, the moisture status of reported results, and the method of soil preparation warrant greater attention. Examples for soil carbon (C) and total soil nitrogen (N) from Australasian interlaboratory proficiency testing across multiple years from 1993 are provided to demonstrate the magnitude of past and present measurement uncertainties, including the effects of method and different concentrations. The evidence is sufficient to require those commissioned to develop NIR and MIR calibrations to subject their prototype calibrations to external peer review by participating in credible, independent interlaboratory proficiency testing programs for ≥12 months, including checks on soil moisture status and possible effects of sample preparation. To rate as credible for most uses, the prototype results should be within the interquartile range for each sample and ideally there should be no outliers and few stragglers. Across the period of assessment (1993–2008), users of Walkley and Black organic C and Kjeldahl digestion for total soil N (Kjeldahl method does not measure total N, but most of the organic N plus an undetermined proportion of nitrate and nitrate present in the sample; quantitative inclusion of both requires a modification of the Kjeldahl procedure) declined as use of furnace technologies for soil C and N increased linearly. There is a strong case to commission two or three well-performing and experienced laboratories to reanalyze samples in “legacy” soil collections prior to finalizing predictive relationships with NIR/MIR spectra for the same samples.     

Statistical Methods for Evaluating Results from Soil Micronutrient Analyses in Interlaboratory Programs

Interlaboratory comparison programs have been found to be useful to investigate potential error sources and therefore to remove or minimize their effects. A proficiency test was performed for five soil micronutrients [boron (B), iron (Fe), manganese (Mn), copper (Cu), and zinc (Zn)] by forty-nine independent Brazilian laboratories on four duplicated soil samples. Extraction of B was performed by hot water, whereas Fe, Mn, Cu, and Zn were extracted by diethylenetriaminepentaacetic acid (DTPA). The objectives were to compare the performance of different statistical methods for assessing between-laboratory variability (reproducibility) and to quantify the variability within single laboratories (repeatability). The statistical methods employed to compare interlaboratory analytical results were (1) Agronomic Institute method (mean, standard deviation, coefficient of variation), (2) Z₁ score (mean and standard deviation, including outliers), (3) Z₂ score (mean and standard deviation, excluding outliers), (4) robust Z score (median and standardized interquartile amplitude) denoted as Z₃, (5) Cochran test, and (6) Cochran + Grubbs tests. In addition, the robust Z-score method, denoted as Z₄, was used to assess intralaboratory variability. The performance of any laboratory for the analysis of soil micronutrients varied depending on the statistical method applied. The percentage of laboratories providing satisfactory results was 79 percent (Agronomic Institute), 95 percent (Z₁), 92 percent (Z₂), 89 percent (robust Z₃ score), 97 percent (Cochran), and 95 percent (Cochran + Grubbs). The Z-score tests become stronger and more rigorous when outliers were excluded (Z₂) or when the standardized interquartile amplitude was used (Z₃). Cochran and Grubbs tests, which are based on the removal of extreme values, were weaker than the other tests evaluated. In conclusion, the method employed by the proficiency test of the Agronomic Institute for removing outliers has been found to be the strongest and strictest one, yielding a reliable comparison of the results from soil micronutrient analyses.     

Rapid,Wet Oxidation Procedure for the Estimation of Silicon in Plant Tissue

Abstract

The quantification of silicon (Si) in plant samples is being requested more frequently, especially in agricultural laboratories associated with the determination of nutritional requirements of sugarcane (Saccharum officinarum L.) and rice (Oryza sativa L.). The analysis of plant material for Si can be protracted, especially if laboratories do not have access to X‐ray flourescence (XRF) instrumentation and large numbers of samples are involved. A simplified procedure using equipment considered standard in most agricultural laboratories is reported. Dry, ground plant material is subjected to nitric acid/peroxide oxidation in a low‐pressure laboratory microwave digestion system. The hydrated silica liberated from the organic matrix is dissolved in a small volume of sodium hydroxide solution also using the microwave digestion system. Silicon is measured by inductively coupled plasma atomic emission spectrometry (ICP‐AES). This method gives results that are linearly correlated with the much slower conventional techniques and avoids using hazardous chemicals (hydrofluoric acid) sometimes employed in other microwave methods.     

An appraisal of microwave-assisted Tessier and BCR sequential extraction methods for the analysis of metals in sediments and soils

Purpose  

The purpose of this research was to assess the precision and accuracy of a BCR and Tessier microwave-assisted sequential extraction procedure, in comparison to the conventional versions for a range of metals using a soil, lake and estuarine certified reference material (CRM).     

Readily measurable soil properties that affect the phosphorus fertilizer requirement of ultisols

Abstract

Phosphorus fertilizer recommendations could be improved mark‐edly if, in addition to the extractable P concentration, some estimate of the P buffering capacity were considered. Measuring the P buffering capacity or its estimate from clay content or surface area, however, is too time consuming for most soil testing laboratories. Soil samples from the southeastern USA and western Spain were analyzed for several properties that either are or could be measured readily. These properties were cation exchange capacity (CEC), sample density (SD), humic matter (HM), and a color index (CHL). Topsoil samples with HM > 20 g/L were eliminated from the set. The P buffering capacity was estimated with a sorption index. This index correlated well with clay content, so clay content was used for comparison with CEC, SD, and CHL. Of these parameters, clay content was best correlated with CHL (r² = 0.81). Since CHL can be determined very quickly under routine laboratory conditions, it could be utilized for refining the P soil test interpretation and improving subsequent fertilizer P recommendations.     

Quality assurance for plant tissue analysis by ICP‐AES

Abstract

A survey of 12 service laboratories using ICP‐AES for routine plant analysis reveals a variety of sample preparation and instrument calibration procedures in use. With the continued growth of ICP applications in plant analysis laboratories, a need exists for inter‐laboratory quality control.

The assurance of data quality among laboratories cannot be expected unless a standardization of preparation methods and calibration is accomplished. In the selection of a method for multi‐element determination on the same sample solution, the completeness of elemental release and sensitivity for some elements may have to be compromised.

In addition to the above survey, 8 plant samples were sent to 5 ICP laboratories that handle large volumes of plant samples with each using different preparation and calibration methods. The results for 11 elements show that the best precision among laboratories was for P, Mg, Mn, Ca and K, and the poorest precision for Al, Zn, Fe, Na, Cu and B. The imprecision noted for some elements was presumed to be caused by the diversity of preparation and calibration methods. Quality control efforts taken by this laboratory will also be given.     

User-Based Photometer Analysis of Effluent from Advanced Nitrogen-Removal Onsite Wastewater Treatment Systems

Advanced nitrogen-removal onsite wastewater treatment systems (OWTS) are used to reduce total nitrogen (N) levels in domestic wastewater. Maintaining system performance requires regular monitoring and in situ rapid tests can provide an inexpensive option for assessing treatment performance. We used a portable photometer to measure ammonium and nitrate concentrations in final effluent from 46 advanced N-removal OWTS, sampling each site at least three times in 2017. To assess photometer accuracy, we compared measurements made using the photometer with those determined by standard laboratory methods using linear regression analysis and a two-tailed t test to compare regression parameters to those for a perfect linear relationship (slope?=?1, intercept?=?0). Our results show that photometer-based analysis reliably estimates inorganic N (ammonium and nitrate) concentration in field and laboratory settings. Photometer-based analysis of the sum of inorganic N species also consistently approximated the total N concentration in the final effluent from the systems. A cost-benefit analysis indicated that the photometer is a more cost-effective option than having samples analyzed by commercial environmental testing laboratories after analysis of 8 to 33 samples. A portable photometer can be used to provide reliable, cost-effective measurements of ammonium and nitrate concentrations, and estimates of total N levels in advanced N-removal OWTS effluent. This method can be a viable tool for triaging system performance in the field, helping to identify systems that are not functioning properly and may need to be adjusted or repaired by an operation and maintenance service provider in order to meet treatment standards.     

Soil testing in the united states

Abstract

There has been a marked change in the soil testing procedures used in the United States by state soil testing laboratories since the early 1950's. In the Coastal Plain states of the south and east, the Double Acid extraction procedure is used for P, K, Ca, and Mg determinations. Bray P₁ is the most frequently used method for P extraction except for the alkaline soils of the west where the Olsen method is used. Neutral normal ammonium acetate is the most frequently used extractant for K, Ca, and Mg determinations. The Morgan extraction procedures for P, K, Ca, and Mg, commonly used in the 1950's, is used by only a few states in the northeast and west. Although similar extraction reagents are used in many sections of the United States, there is considerable variance among states regarding weighed versus volume sampling, soil to solution ratio, shaking speed and time, and extraction vessel size and shape. For soil water pH, there is little variance in method as most states are using a 1:1 soil to solution ratio. The only exception is in several western states where water pH's are read in a saturated soil paste.

Considerable efforts are underway to standardize the techniques used to test soils primarily for the extractable elements.     

Estimation of soil texture from the sample density

Abstract

Soil texture often plays an important role in the interpretation of soil analytical data for fertilizer advisory purposes. A reliable and inexpensive method of clay content estimation is, therefore, a requirement of most advisory laboratories. This note discusses the use of sample density (i.e. the mass of a scooped volume of soil) as an index of clay content. A strong relationship was found to exist between sample density and clay content, and such estimates of clay content were superior to those obtained by experienced pedologists using the “finger test” procedure. The use of this quick and simple procedure is considered to be ideally suited to soil testing laboratories handling large numbers of samples.     

The variability between different analytical procedures and laboratories for measuring soil microbial biomass C and biomass N by the fumigation extraction method

The interlaboratory variations in the fumigation extraction method and the analytical procedures for measuring C and N in the soil microbial biomass were tested with one soil sample, and two soil extracts (non-fumigated and fumigated) sent to 25 different laboratories. Four groups of analytical procedures for organic C, i.e. (1) oven oxidation/ IR detection, (2) UV-persulfate oxidation/lR detection, (3) UV-persulfate oxidation/colorimetric detection and (4) dichromate oxidation/ titration, and three groups for total N, i.e. (1) Kjedahl reduction to NH₄⁺, (2) UV-persulfate and (3) persulfate-borate oxidation to NO₃^? were used by the different laboratories. The coefficient of variation for C and N measurements between different laboratories and analytical procedures varied between 15 and 34% in non-fumigated samples, between 13 and 20% in fumigated samples, and between 12 and 24% in the differences E_c and E_N. The average coefficients of variation between the replicate measurements within one laboratory were much smaller, i.e. they varied between 3.0 and 9.2% in non-fumigated samples, between 2.4 and 5.5% in fumigated samples, and between 4.5 and 12.8% in the differences E_c and E_n. Extraction and fumigation were not the major source of the variations observed. They were mainly a result of differences in the analytical procedures used to measure the low concentrations of C and N in the extracts. However, all of these analytical procedures should be able to measure correct values if they are properly calibrated and performed.