A rapid dichromate procedure for routine estimation of total nitrogen in soils

Abstract

A simple procedure for routine estimation of total nitrogen (N) in soils is described. It involves (a) digestion of the soil sample with an acidified dichromate (K₂Cr₂O₇‐H2SO₄) solution for 45 minutes in a Pyrex digestion tube in a 40‐tube block digester preheated to 170°C, (b) titrimetric determination of the ammonia‐N liberated by direct steam distillation of the digest with alkali (NaOH), and (c) calculation of the total‐N value by application of a correction factor (1.1) to the measured NH₃‐N value. Studies using 14 soils selected to obtain a wide range in total N content and other properties showed that the uncorrected recovery of N by the procedure described ranged from 88.5% to 92.3% and averaged 90.5%. When a correction factor of 1.1 was applied to the results, the recovery of N ranged from 97.4% to 101.5% and averaged 99.6%.

The dichromate procedure described is rapid and precise, and it permits at least 80 analyses in a normal working day. The only equipment required for its use is equipment commonly used for total N analysis of soils by the Kjeldahl method (40‐tube block digester and steam distillation unit), and the acidified dichromate solution used for digestion of the soil is, the reagent commonly used for determination of organic carbon in soil by a modified Mebius procedure. Besides being simpler and more rapid than the Kjeldahl method, the procedure described has the advantage that it does not require the expensive fume disposal system needed for Kjeldahl digestion.     

Premixed digestion salts for Kjeldahl determination of total nitrogen in selected forest soils

Abstract

Estimates of total soil nitrogen by a standard Kjeldahl procedure and a modified procedure employing packets of premixed digestion salts were closely correlated (r² = 0.983). The modified procedure appears to be as reliable as the standard method for determining total nitrogen in southern alluvial forest soils.     

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.     

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.     

An automatic procedure for determination of available iron in Indian soils

Abstract

An on‐line automatic procedure for the flow injection analysis (FIA) determination of iron (Fe) in a variety of soil extracts with common laboratory reagents, i.e., thiocyanate, thiocyanate +1,10‐phenanthroline/bipyridine has been tested. The apparent molar absorptivity of the complexes lies in the range of (5.5–7.0)x10³ L mole^‐1 cm^‐1 at an absorption maximum between 470–495 nm. The detection limit of the method is 15 ppb Fe. The sample output is 100 samples/hr. Almost all ions associated with Fe in the soil extract do not interfere in this method. Optimization of FIA variables, composition of the complex, and effect of other ions on the determination of Fe are discussed. The method has been used for determination of Fe status in a variety of agricultural soils in east Madhya Pradesh, India.     

Mixed acid solubilization procedure for determination of total mercury in food samples

A mixed acid solubilization procedure has been developed for the determination of total mercury in food samples. This procedure has eliminated the problem of mercury loss from samples that are high in lipid or carbohydrate content. The solubilization is rapid and quantitative and can be used for a wide range of food items.     

Alternative procedure for total phosphorus determination in plant tissue

Abstract

Surface liming will prevent the formation of an ‘acid roof’ on the surface of soil cropped in no‐till corn (Zea mays L.). A study was begun in 1985 to determine the effectiveness of unincorporated liming in raising pH in no‐till soil which had developed significant acidity throughout the upper 15 cm. Lime was applied at 0, 3.36, 6.72 and 10.08 Mg ha^‐1. All lime was applied on 26 April 1985 and was not incorporated. The pre‐liming pH at 0‐5 cm below the surface was 4.5; after two months the pH was raised to 5.6, 5.8, and 6.0 by 3.36, 6.72 and 10.08 Mg ha^‐1 of lime, respectively. After 19 months soil‐pH was raised to 6.0, 6.4 and 6.6 by liming at 3.36, 6.72 and 10.08 Mg ha^‐1 respectively. Soil‐pH below 5 cm was not affected by any rate of lime during the first 19 months after liming. Tissue analysis of corn ear leaves indicated that calcium uptake was increased significantly by lime in 1985, while manganese uptake was significantly reduced. In 1986, increases in calcium were greater than in 1985 and addtional significant reduction in manganese uptake was accompanied by significantly reduced zinc and copper uptake. In both 1985 and 1986, a trend toward lower average corn grain yield in unlimed plots than in limed plots was noted, but the yield increases due to lime were not statistically significant in either year. This study will be continued as a long term investigation of lime penetration into no‐till soil and response of corn to soil‐pH changes.     

微波消解ICP-OES法同时测定土壤中全磷和全钾

研究和建立了微波消解土壤样品,等离子体发射光谱仪一次进样曝光,同时测定全磷、全钾的分析方法.本方法一次消解土壤样品,2个元素同时测定,方法准确、快速、精密度高,符合分析要求.     

Use of an AutoAnalyzer for total nitrogen determination in plants

Abstract

An AutoAnalyzer was evaluated as a means of determining ammonium concentration in semi‐micro Kjeldahl digests of plant tissue. Results of the AutoAnalyzer determination agree closely with distillation‐titration results. Advantages of the AutoAnalyzer method include speed, precision, and release of labor. Only a small aliquot of each digest is utilized.     

Use of ammonia electrode for total nitrogen determination in plants

Abstract

An ammonia electrode was evaluated as a means of determining ammonium concentration in semi‐micro Kjeldahl digests of plant samples. Results of the ammonia electrode determination agreed closely with distillation and titration results. Advantages of the electrode method include speed, precision, increased safety, simplicity and the fact that only a small aliquot of the digest is used.     

Urea enzymatic dialysis procedure for determination of total dietary fiber

A method that uses urea and enzymes for determination of total dietary fiber (TDF) in foods has been developed and compared with the AOAC enzymatic-gravimetric method (43.A14-43.A20). In the evaluation, results for crude protein and ash contamination were higher by the AOAC method, particularly for samples that form gels during ethanol precipitation. The new urea enzymatic dialysis (UED) method quantitatively recovered, with less variation, more of the purified and semipurified dietary fiber products. TDF recoveries for carboxymethylcellulose and locust bean gum were 98% (SD 3.3) and 95% (SD 6.1) by the AOAC method and 99% (SD 1.0) and 100% (SD 0.6) by the UED method, respectively. The UED method was the more effective in removing starch. For kale samples, starch recovery was 3.5 and 0.2% from TDF residues obtained using the AOAC and UED methods, respectively. Differences were not significant among replicate values for determination of TDF in foods by the UED method (P greater than 0.01). Preliminary studies suggest that the new method can separately determine soluble and insoluble dietary fiber. The data indicate that the UED method is more precise and accurate than the AOAC method.     

快速测定化肥中的总氮方法

应用美国力可公司生产的煤炭碳、氢、氮分析仪测定化肥中总氮的含量 ,通过炉温、样品量、放大器增益的选择 ,积分时间等的对比 ,确定了以CHN— 1 0 0 0分析仪测定化肥总氮的检测方法 ,本方法测定速度快、精密度高、准确度好 .氮的相对标准偏差小于 0 5%     

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.     

A field method for the determination of total nitrogen in plant tissue

Abstract

While studying sward quality in Kenya, East Africa, we established a field laboratory for the determination of total nitrogen. Using Kjeldahl digestion procedures and an indophenol colorimetric method, we successfully analyzed over 900 plant and fecal samples while living in a tent camp. Variation from one digestion to the next was corrected for by using a grass standard with each digestion. Independent tests by other laboratories verified the accuracy of our methods.     

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.     

Evaluation of a rapid microwave digestion method for determination of total organic carbon in soil

Precise measurement of soil organic carbon (SOC) is essential for constructing regional inventories, developing best agricultural management practices, and modeling purposes. Currently, the automated dry combustion method is considered standard, but the method is both costly and time-consuming. There is a need for a simple, easy to use and cost-effective method of organic C determination in soil. A simple method of total organic carbon (TOC) determination in soil that involved wet digestion of K₂Cr₂O₇-H₂SO₄-soil mixture in a commercial microwave oven followed by spectrophotomteric measurement of Cr (III) was evaluated. The method was compared with automated dry combustion and two other wet digestion methods. The method showed close agreement with dry combustion method (R² = 0.90; root mean square error = 0.70) and the TOC measured with the two methods did not differ for a range of soils drawn from lowland and upland land-uses and varying in pH (6.2–9.3), TOC (2.8–14 g kg^?1), and calcium carbonate content (0–6.7%). The recovery of the added organic C by the microwave method was 98.6 ± 4.2%. The results suggested that microwave-spectrophotometric method could be easily adopted in routine soil analysis as it is not only precise, rapid, and cost-effective but also produced small volume of reagent waste.     

Limitations of acid digestion techniques for the determination of fluoride in plant material

Abstract

Procedures for determination of fluoride (F) in plant material employing acid digestion and solution analysis by ion specific electrode (ISE) were compared to alkali fusion using a range of plant materials. The efficiency of the methods were assessed using standard reference plant material (SRM) not previously available for plant F analysis. All acid digestion procedures tested failed to obtain the certified value for F in the SRM. This was due to failure of the acids to liberate F bound strongly within silicate minerals found in the plant materials. Acid digestion is therefore not recommended for determination of total F, but could be used to determine labile F in plant materials. During investigation of the acid digestion procedures, it was also found that F concentrations determined in solution using the ISE are sensitive to solution pH, even at solution pH values where complexation of F with hydrogen ions (H⁺) can be discounted. It is therefore recommended that both ionic strength and pH of sample and standard solutions be matched when determining F concentrations in solution using the F‐ISE.     

自动定氮仪碱解蒸馏法测定土壤中水解性氮含量

介绍了自动定氮仪碱解蒸馏法测定土壤中水解性氮含量的方法,探讨了试验中主要影响因素。与现行林业行业标准碱解扩散法相比,该方法具有操作简便、快捷、干扰小、精度高、准确性好的优点,特别适合大批量样品的分析。值得在土壤分析工作中参考应用。     

Dicyandiamide effects on nitrification and total inorganic soil nitrogen in sandy soils

Abstract

Inhibition of nitrification in soil results in a decreased ratio of nitrate‐nitrogen (NO₃‐N) to ammonium‐nitrogen (NH₄‐N). If the conditions for NO₃‐N loss by leaching or denitrification exist, nitrification inhibitors should increase concentrations of total inorganic soil nitrogen (N) (TISN) (NH₄‐N + NO₃‐N). This can then result in plants taking up more N and developing more crop yield or biomass. This study examined whether inhibition of nitrification by dicyandiamide (DCD) would result in increased concentrations of TISN under field conditions. The effects of DCD on soil N were evaluated in hyperthermic sandy soils planted to potato (Solanum tuberosum L., cv. Atlantic). Treatments were factorial combinations of N as ammonium nitrate (NH₄NO₃) at 67, 134, and 202 kg N ha^‐1 and DCD at 0, 5.6, and 11.2 kg DCD ha^‐1. Soil NH₄‐N, NO₃‐N, and TISN concentrations were determined for up to five potato growth stages at two locations for two years for a total of 16 determinations (cases), i.e., four were not determined. The N form ratio [NO₃‐N/(NH₄‐N + NO₃‐N] x 100 was decreased in 10 of 16 cases, indicating that nitrification was inhibited by DCD. With two of these 10 cases, TISN concentration increased, but with four others, TISN concentration decreased with at least one N rate. With four of these 10 cases, inhibition of nitrification had no effect on TISN concentration. Under the conditions of these field studies, DCD inhibited nitrification more often than not. Inhibition of nitrification was, however, more likely to reduce TISN concentration than to increase it. This may have been due to DCD effects on immobization of applied NH₄‐N.