V. J. G. Houba

A novel digestion technique for multi-element plant analyses

Abstract An expedient digestion method for serial determinations of N‐total, P, Na, K, Ca and Mg in plant material is proposed. All determinations are performed on one digest, the only limitation being that the Ca content should not exceed 1100 mmol Ca per kg dry plant material.

Soil analysis procedures using 0.01 M calcium chloride as extraction reagent

Abstract This publication gives details of laboratory procedures for the determinations of bioavailable (e.g., plants) quantities of nutritional and polluting inorganic elements in 0.01 M CaCl2 extracts of air‐dry soil samples. Air‐day soil samples are extracted for two hours with a 0.01 M CaCl2 solution of 20°C in a 1:10 extraction ratio (W/V). After measuring the pH in the settling suspension, the concentrations of nutritional and polluting elements are measured in the clear centrifugate or filtrate. The procedure is simple, easy to perform, and cheap (labor, chemicals) in daily use in routine soil laboratories. The method receives internationally more and more attention as an alternative for the many extraction procedures for a single nutrient or pollutant that are still in use nowadays. The soil is extracted with a solution what has more or less the same ionic strength as the average salt concentration in many soil solutions. Various nutrients and metals can be measured in a single extract that allows considering relationships between them during interpretation of the data. For most elements, different detection techniques are described in detail in this publication. Detailed laboratory procedures are described for the determination of pH, total dissolved organic carbon, nitrate, ammonium, total dissolved nitrogen, sulphate, total dissolved sulfur, ortho‐phosphate, total dissolved phosphate, sodium, potassium, magnesium, cadmium, copper, nickel, lead, aluminum, iron, arsenic, boron, and phenols. Since only one extract of soil samples is used, profitable use can be made of multi‐element detection techniques like segmented‐flow analysis spectrometry, ICP‐OES, and ICP‐MS.

Plant analysis manual

Introduction. 1. Digestion in tubes with H2SO4 - salicylic acid - H2O2 and selenium: Ca, K, Mg, Mn, N-total, Na, P, Zn. 2. Digestion in flasks with H2SO4 - salicylic acid - H2O2: Ca, Ka, Mg, Mn, N-total, Na, P, Zn. 3. Digestion with HNO3 - HClO4 - H2SO4: Al, Cd, Cu, Fe, Mn, Pb, Zn. 4. Digestion with HNO3: S-total. 5. Extraction with HNO3 - H2O2 - HF: Al, Cd, Cu, Fe, Mn, Pb, Zn, ... 6. Digestion by dry-ashing followed by treatment with HF: Ca, Cd, Cu, Fe, K, Mn, Na, Pb, Zn. 7. Digestion by dry-ashing in the presence of CaO: B. 8. Extraction with water: Cl, NO2, NO3, SO4. 9. Extraction with water in the presence of Ag and Cu: NO3. 10. Extraction with HF - HCl: B, Si. Appendices.

A rapid determination of silicon in plant material

Abstract Silicates in dried plant material can be extracted quantitatively by a mixture of diluted hydrogen fluoride and hydrochloric acid. The silicon in the extract can be determined by either atomic absorption or atomic emission spectrometry. Three methods were compared: (a) the classical method, i.e. dry‐ashing, followed by fusion with sodium carbonate; (b) wet digestion by a mixture of HF and HNO3 in a closed system (“bomb” technique); (c) the proposed extraction at room temperature.

Determination of total sulphur and extractable sulphate in plant materials by inductively-coupled plasma atomic emission spectrometry.

Abstract Total sulphur and extractable sulphate were determined in plant materials by inductively‐coupled plasma emission spectrometry. For total sulphur, plant material was digested in concentrated nitric acid only. For the sulphate determination, the plant material was extracted with water, sulphate was precipitated as barium sulphate, washed, and redissolved in (NH4)4‐EDTA. In the determination of sulphur no spectral interferences were observed, when using the 182.04 nm emission line. The data for total sulphur compared well with a set of certified reference plant samples. For extractable sulphate no such certified plant material is available, but it was established that the proposed procedure did not lead to losses nor interferences.

Solubilization of plant tissue with nitric acid‐hydrofluoric acid‐hydrogen peroxide in a closed‐system microwave digestor

Abstract Application of a microwave dissolution technique for plant tissues using hydrofluoric acid (HF), nitric acid (HNO3), and hydrogen peroxide (H2O2) as reagents was studied. It was found that the use of all reagents in the mixture followed by the microwave heating in many cases does not lead to complete dissolution. The solid, remaining after the reaction, was found to contain fluoride (F), calcium (Ca), magnesium (Mg), aluminum (Al), and silicon (Si) as major components. However, when HF was allowed to react first and evaporated prior to the addition of H2O2+HNO3 with subsequent microwave heating in a closed system, complete dissolution with high degree of mineralization was achieved. The procedure was applied to a number of plant Certified Reference Materials (CRMs) with very good recoveries of Ca, Mg, iron (Fe), lead (Pb), zinc (Zn), copper (Cu), Al, manganese (Mn), cadmium (Cd), potassium (K), sodium (Na), sulfur (S), and phosphorus (P).

One hundredth molar calcium chloride extraction procedure. part I: A review of soil chemical, analytical, and plant nutritional aspects

Abstract The economical and operational aspects of multinutrient extractants make them attractive for soil testing programs. However, the value of a multi element extractant is primarily determined by the relationship between the amount of nutrient extracted and crop response. To determine the perspectives of the 0.01M calcium chloride (CaCl2) extraction procedure as a multinutrient extractant, this paper reviews literature on the soil chemical, analytical and plant nutritional aspects of CaCl2 solutions as a soil extractant. Recent decades, CaCl2 solutions were common single nutrient extractants in plant nutritional and soil chemical research but the amount of nutrient extracted was sensitive for differences in sample treatment and extraction procedure. Therefore, a 0.01M CaCl2 procedure should be standarized to obtain a robust procedure. Calibration studies between conventional soil extraction procedure and the 0.01M CaCl2 procedure show fairly good relationships. A first step to develop a multielement ...

A CONVENIENT WET DIGESTION PROCEDURE FOR MULTI- ELEMENT ANALYSIS OF PLANT MATERIALS

Abstract For the determination of total element contents in plant material by atomic spectrometry after wet digestion, both dissolution and oxidation of the matrix are necessary. This was achieved by a sequential digestion procedure using first hydrogen fluoride (HF) for dissolution of silicate, followed by oxidation with nitric acid (HNO3) and hydrogen peroxide (H2O2). The final solution is 0.2M HNO3, and contains only traces of HF. Application of the method for the determination of aluminium (Al), boron (B), calcium (Ca), cadmium (Cd), copper (Cu), iron (Fe), potassium (K), magnesium (Mg), manganese (Mn), sodium (Na), phosphorus (P), lead (Pb), sulfur (S), and zinc (Zn) in various materials showed good agreement with certified reference materials.

Comparison of a hot water and cold 0.01 M CaCl2 extraction procedures for the determination of boron in soil.

Abstract In 100 different soils, hot (100C) water extractable boron was determined and the results were compared with boron data after extraction of the same soil samples with cold (20C) 0.01 M CaCl2. Since the boron concentrations in cold soil extracts are too low for direct determination, the extracted boron was converted into BF4‐ and subsequently extracted with a liquid anion exchanger, Aliquat 336, into xylene, and measured by ICP‐AES. A linear relation with R2 = 0.74 was found between the two tested procedures. It is, therefore, concluded that with a cold 0.01 M CaCl2 extraction equally valuable soil boron values can be obtained as with the more difficult to standardize hot water extraction procedure.

EFFECT OF DRYING TEMPERATURE ON AMOUNT OF NUTRIENT ELEMENTS EXTRACTED WITH 0.01 M CaCl2 SOIL EXTRACTION PROCEDURE

In the current soil drying protocol of the 0.01 M calcium chloride (CaCl2) procedure, soils are oven dried at 40°C for 24 h. At this drying temperature, as well as at lower drying temperatures, a change of the actual soil nutrient element status cannot be excluded because microbes will be active during part of the drying period. However, a higher drying temperature may affect soil characteristics and soil processes and also lead to a misinterpretation of the soil nutrient element status. An explanatory study was conducted to get more insight into the effect of i) oven drying temperature and ii) the use of forced-air ventilation at low drying temperatures on nutrient elements extracted with the 0.01 M CaCl2 procedure. The goal of the study was to investigate the perspectives of optimization of the soil drying protocol of the 0.01 M CaCl2 procedure. Three moist test soils with different soil characteristics were oven dried at 20 and 40°C with and without forced air ventilation and at 70 and 105°C without forced-air ventilation. The moist test soils and the dried soils were extracted with a 0.01 M CaCl2 solution and pH and total N (N), ammonium-nitrogen (NH4-N), nitrate-nitrogen (NO3-N), ortho-phosphate (ortho-P), potassium (K), magnesium (Mg), sodium (Na), and manganese (Mn) determined in the supernatant after centrifugation. Soluble organic N (org-N) was calculated as the difference between N and the summation of NH4-N and NO3-N. In the temperature range from 40 to 105°C, ortho-P, NH4-N, org-N, and Mn extracted tended to increase two or threefold for each 30–35°C increase in drying temperature. Differences in ortho-P, NH4-N, org-N, and Mn extracted at 20 and 40°C were relatively small. The pH, K, Na, and NO3-N extracted were affected by drying temperature but the effect was variable. Magnesium extracted was not affected by drying temperature. The use of forced air ventilation at 20 and 40°C had no significant effect on the amount of org-N, NH4-N, ortho-P, K, and Mg extracted. There were significant effects of forced-air ventilation on pH and NO3-N, Na, and Mn extracted but the effects were variable. Test values (60–70%) of the moist test soils were significantly different from the respective test values of the test soils dried at 20 and 40°C with and without forced-air ventilation. Based on the differences between moist and dried soils, it is questionable if soil drying should be recommended in the 0.01 M CaCl2 procedure. Therefore, further research should focus on the relationship between soil test values of moist and dried soils with crop response. If soil drying is preferable drying temperature should not exceed 40°C.