Evaluation of methods for soil inorganic nitrogen analysis

Abstract

This study determined the effects of soil preservation methods on inorganic nitrogen (N) analysis and evaluated methods of soil inorganic N analysis. Soils were preserved by oven‐drying at 55'C, air‐drying at 27°C, and freezing at ‐ 7°C. Inorganic N results were compared with initial N levels prior to imposing preservation treatments. Soil preservation effects on ammonium‐nitrogen (NH₄ ⁺‐N) were not consistent across soil types. Soil nitrate‐nitrogen (NO₃ ^‐‐N) levels after air‐drying and freezing compared most favorably with initial levels indicating that both are acceptable methods of soil inorganic‐N preservation. Levels of NH₄ ⁺‐N averaged across soils were 3.9 mg/kg for steam distillation, 4.2 mg/kg for sodium salicylate‐hypochlorite, and 3.7 mg/kg for indophenol blue. When compared with steam distillation averaged across soils, NO₃ ^‐‐N for cadmium‐copper (Cd‐Cu) reduction was 4 mg/kg greater, followed by nitrate electrode at 3 mg/kg, and salicylic acid at 2 mg/kg. Recovery of added N ranged from 83.3 to 94.8% for the NH4+‐N methods and from 74.8 to 112.4% for the NO₃ ^‐‐N methods with the nitrate electrode averaging 98.3%.     

Technique of soil sample pretreatment for analysis of 15N:14N isotope ratio

Abstract

The technique of simultaneous quantitative determination of mineral N soil forms (nitrates, exchangeable and non‐exchangeable ammonium, and total amount of these compounds) and sample pretreatment for the analysis of ¹⁵N:¹⁴N ratio is suggested. The technique is based on the selective association of NH₄ ⁺‐ions into indophenol complex and subsequent ethyl‐acetate extraction of this complex from solution. The mineralization of indophenol is carried out in alkaline medium with simultaneous NH₃ distillation into H₂SO₄ titrant. The application of given technique allows us to shorten significantly the time required for analysis and to increase the accuracy of analytical determination.     

Microscale determination of inorganic nitrogen in water and soil extracts

Abstract

Rapid, sensitive analysis of NH₄ ^‐ NO₃ ^‐, and NO₂ ^‐ in 1–150 μL of soil extract or water was achieved using a modified indophenol blue technique adapted to microtiter plate format. The microplate technique was similar to conventional steam distillation in accuracy and precision. By varying aliquot volume, a wide linear dynamic range (0.05 to 1000 mg of NH₄ ⁺‐ or NO₃ ^‐‐NL^‐1) was achieved without the need for sample dilution or concentration. High sample throughput (250–500 NH₄ ⁺ analyses d^‐1) was accomplished manually, but could be significantly increased by automation. Of considerable importance was the very low waste stream produced by the method. All equipment and supplies required are commercially available and need no modifications for this use. The microtiter plate format could be used for other soil colorimetric analyses with little or no down time for equipment setup, a major consideration for commercial soil‐testing laboratories. The method and equipment used are well suited to quality control and quality assurance programs, as required under FIFRA Good Laboratory Practices.     

Use of diffusion for automated nttrogen‐15 analysis of soil extracts

Abstract

Studies to evaluate the use of diffusion for automated ¹⁵N analysis of inorganic N in soil extracts showed that serious error can arise from use of the Devarda's alloy recommended for steam distillations and that the error can be avoided by using a commercial product of higher purity. These studies showed that serious error can also arise when NO₃ ^‐‐N is diffused following NH₄ ⁺‐N and that separate diffusions should be performed for NH₄ ⁺‐N and (NH₄ ⁺ + NO₃‐)‐N. Other work demonstrated that the plastic specimen containers employed for diffusion can be reused if acid‐washed, that diffusions can be performed using either light or heavy MgO without ignition to decompose carbonate, and that labeled NO₂‐is completely removed from soil extracts by treatment with sulfamic acid before diffusion. A comparison of ¹⁵N analyses by steam distillation and diffusion using extracts from two soils revealed better agreement for the soil having a lower content of organic matter. Substantial differences in analyses by the two techniques for the soil having a higher organic‐matter content were attributed to enzymatic conversions of inorganic N during the 6‐d diffusion period.     

Potential of Chemically Labile Fractions to Measure Mineralizable Soil Nitrogen

Nitrogen (N) in the soil is largely organic and is available to crops only after it is mineralized to inorganic N by microbial or enzyme action. To develop a soil test for guiding N applications, a method to predict the relative amount of organic N that will mineralize in a growing season is necessary. Several chemical analysis methods proposed in the literature to measure mineralizable N were examined for chemical interference, measurement precision, response to procedure modifications, and ability to distinguish differences among soils. The chemical analyses examined involved various acid or alkaline hydrolysis, with the resulting inorganic ammonium N measured by steam distillation and manual or automated diffusion. A gelatinous precipitate in the filtered and neutralized 6 M hydrochloric acid (HCl) hydrolysis solution interfered with magnesium oxide (MgO) diffusion traditionally used to measure inorganic ammonium N. Removing the precipitate appeared to circumvent the interference. The precipitate did not appear to interfere with the sodium hydroxide (NaOH) diffusion. The 6 M HCl hydrolysis extracted 34 to 103% of clay‐fixed ammonium in the soils. Steam distillation was shown to be an acceptable alternative to diffusion for measuring NaOH‐labile N. The vigor of NaOH measurement conditions caused differences in results, showing that precise and reproducible conditions are necessary. Several methods were closely correlated (r² > 0.62) with N mineralized during aerobic incubations and could be considered for further evaluation for soil N testing. This study showed that modifications are required to several proposed analytical methods to improve their potential to estimate mineralizable N for fetilizer or other amendment recommendations for crop production     

Arylamidase Activity as an Index of Nitrogen Mineralization in Soils

Abstract

The enzyme arylamidase [EC 3.4.11.2] catalyzes the hydrolysis of N‐terminal amino acids from arylamides. Because it has been proposed that this enzyme may play a major role in nitrogen (N) mineralization in soils, studies were carried out using short‐term laboratory incubations under aerobic and anaerobic conditions and chemical hydrolysis of soil organic N to assess the N mineralization in a range of 51 soils from six agroecological zones of the North Central region of the United States. The enzyme activity was assayed at its optimal pH value. With the exception of the values obtained for field‐moist soils incubated under anaerobic conditions, the amounts of N mineralized by all the biological and chemical methods studied were significantly correlated with arylamidase activity, with r values of 0.54*** for the amounts of inorganic N produced under aerobic incubation, of 0.44** for anaerobic incubation of air‐dried soils, of 0.53*** and 0.55*** for the amounts of ammonium (NH₄ ⁺)‐N released by steam distillation with PO₄‐B₄O₇ for 4 and 8 min, respectively; and of 0.49*** and 0.53*** for the amounts of NH₄ ⁺‐N released by steam distillation with disodium tetraborate (Na₂B₄O₇) for 4 min or 8 min, respectively. The amounts of N extractable with hot potassium chloride (KCl) were most significantly correlated with arylamidase activity (r=0.56***). Arylamidase activity was significantly correlated with organic carbon (C) (r=0.49***), organic N (r=0.55***), and fixed ammonium (NH₄ ⁺)‐N (r =0.42**).     

Reducing interferences by amino acids in the determination of ammonium by an automated indophenol method

Abstract

Positive interference by amino acids in the determination of ammonium in soil extracts by automated indophenol methods can be minimised by using the nitroprusside catalysed reaction. Hydrolysis of amino acids is virtually eliminated because this reaction enables the use of low sample volumes, reagent concentrations and reaction temperatures.     

Interference by amino acids during the determination of N ammonium in soil

In the study of terrestrial N cycling, NH₄⁺ concentration and ¹⁵N enrichment are routinely determined by colorimetric continuous flow analysis and microdiffusion methods. Amino acids can interfere in these determinations; consequently the aim of the present study was to evaluate the significance of the interference. Glycine and glutamine are key amino acids in soil and were therefore used as ‘models’. Both glycine and glutamine interfered during continuous flow analysis, whereas interference during microdiffusion was of little importance. The effects of interference can be significant, e.g. estimates of gross mineralisation rate were reduced up to 33%, where we allowed for amino acid interference during determination of NH₄⁺ concentration. The potential influence of amino acid interference emphasises that development of continuous flow analysis to increase NH₄⁺ specificity is needed.     

Determination of surface charge density of soils

Abstract

A simple and precise method for determination of surface charge density of soils is described. It involves saturating the negative and positive exchange sites with NH⁺ ₄ and NO^‐ ₃ ions, respectively, removing the excess solution by centrifugation, and determining the ions on the exchange sites by a steam distillation method. Results showed that the concentration and type of saturating ions and the extractant used significantly affected the surface negative charge densities. The average value of surface negative charge densities of 10 surface soils from Iowa, Chile, and Costa Rica by the proposed method agreed closely with that obtained by the original method proposed by Schofield in 1949 (14.6 vs. 13.7 cmol(‐) kg^‐1 soil). The advantages of the proposed method are no need for the laborious extraction steps and simplicity of the steam distillation method for determination of NH⁺ ₄ and NO^‐ ₃ in soil samples.     

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.     

Determination of ammonium n and nitrate n in acid permanganate solution used to absorb ammonia,nitric oxide,and nitrogen dioxide evolved from soils

Abstract

Simple steam distillation methods are described for determination of ammonium N and nitrate N in acid KMnO₄ solution used to absorb NH₃, NO and NO₂ evolved from soils. They involve use of MgO for distillation of ammonia and of FeSO₄, Ag₂SO₄, and MgO for reduction of nitrate to ammonia. The methods are rapid and precise, and they permit nitrogen‐15 analysis of NH₃‐N and (NO + NO₂)‐N evolved from soils.     

基于多元回归估算残留P

The remaining phosphorus （Prem）, P concentration that remains in solution after shaking soil with 0.01 mol L-1 CaCl2 containing 60μg mL-1 P, is a very useful index for studies related to the chemistry of variable charge soils. Although the Prem determination is a simple procedure, the possibility of estimating accurate values of this index from easily and/or routinely determined soil properties can be very useful for practical purposes. The present research evaluated the Prem estimation through multiple regression analysis in which routinely determined soil chemical data, soil clay content and soil pH measured in 1 mol L-1 NaF （pHNaF） figured as Prem predictor variables. The Prem can be estimated with acceptable accuracy using the above-mentioned approach, and pHNaF not only substitutes for clay content as a predictor variable but also confers more accuracy to the Prem estimates.     

Soil Ammonium Diffusion Constraints Contribute to Large Differences in Nitrogen Supply to Rice in the Southern United States

This study was to determine if diffusion of soil ammonium may explain why many sandy soils have greater nitrogen (N)–supplying capacity to rice than clay soils. A laboratory procedure using transient-state methods measured the linear movement of soil ammonium (NH₄) in tubes packed with five field soils under aerobic conditions. Ammonium diffusion was measured by sectioning tubes after 48 h of equilibration and then measuring NH₄ by steam distillation. Effective diffusion coefficients, D_e, and NH₄ diffusion distance, d, per day ranged from D_e = 4.6 × 10^?5 cm² d^?1 and 1.5 cm d^?1 for Katy sandy loam to D_e = 2.9 × 10^?7 cm² d^?1 and 0.11 cm d^?1 for League clay. Ammonium diffusion distance d was strongly related to soil clay content and hence was predicted by d = Y × {[100/(% clay)] ? 1}, where Y is set to 0.1. Predicted d and measured d were highly related (R² = 0.99).     

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.     

Availability of extractable boron in some acid soils,west Bengal,India

Abstract

A relatively small range between deficiency and toxic limits of boron (B) necessitates precise evaluation of the availability of extractable boron before applying B in deficient soils. Keeping this in view, laboratory and greenhouse experiments were conducted to assess the availability of native B in soils. For this purpose, 25 acid soils with diverse properties and varying hot water extractable B content, were selected from lateritic and alluvial tracts of Southern West Bengal. A greenhouse pot experiment with four rates of B (0, 0.5, 1.0, and 2.0 mg kg^‐1) was conducted in completely randomized design to study the response of soybean (Glycine max L.) to native and applied B in all 25 soils. The suitability of nine extractants for determining available soil B was assessed by correlating the amount of extractable B in untreated soils with Bray's percent yield, uptake, and tissue B concentration of soybean plants. Optimization of salicylic acid concentration is described and the advantages of this extractant are discussed. The interference of amethyst color (produced by iron and salicylic acid) with the colorimetric estimation of B is studied. Hot CaCl₂ was found to be the most suitable extractant for the determination of available B in these soils, followed by hot water, salicylic acid, and ammonium acetate. However, salicylic acid appeared to be the most efficient extractant for routine soil analysis for available B, where a large number of samples are analyzed. The critical values in respect to sufficiency of extractable B for soybean plants were 0.51 for hot water, 0.61 for hot CaCl₂, 0.27 for ammonium acetate and 0.45 mg kg^‐1 for salicylic acid. The critical B concentration in soybean plants was 18 mg kg^‐1 on dry weight basis. Multiple regression equations relating soil properties to native soil B extracted by various extractante were developed. It was observed that organic carbon and clay contributed positively to B extracted by hot water, hot CaCl₂, and ammonium acetate, while salicylic acid extractable B showed positive relationships with cation exchange capacity (CEC) and clay. The CEC and Fe₂O₃ were found to have positive influence on tartaric acid extractable B. Implications of the influences of soil properties on the extractable B content of soils are discussed.     

Rapid and Inexpensive Steam Distillation Method for Routine Analysis of Inorganic Nitrogen in Alkaline Calcareous Soils

Determination of inorganic nitrogen (N) in soil is important in making N fertilizer recommendations for crops. To find a rapid, reliable, and economical method for the estimation of inorganic N in alkaline calcareous soils of Pakistan, three steam distillation methods were compared using soils varying in ammonium (NH₄) and nitrate (NO₃) N contents and other physicochemical properties. In the standard method, the soil sample is shaken with 2 N potassium chloride (KCl) for 1 h, and the extract is then analyzed by steam distillation. In the other two methods, the soil sample is distilled directly with either 2 N KCl or distilled/deionized water. Based on the results of the present work, a method that involves steam distillation with only distilled/deionized water and that requires half the quantity of magnesium oxide (MgO) of the standard method has been proposed, as all the three methods yielded identical results for NH₄- and NO₃-N contents. Being economical, the proposed method for inorganic N estimation by direct distillation of soil with distilled/deionized water deserves consideration for adoption by soil-testing laboratories.     

Nitrification in soils incubated with pig slurry or ammonium sulphate

The effects of temperature, moisture content and the addition of pig slurry on nitrification in two soils were studed. There was no accumulation of NO₂^?-N under the incubation conditions investigated and the accumulation of NO₃^?-N was linear for additions of 50–250 μg NH₄⁺-N g^? soil, either as ammonium sulphate or as pig slurry. Nitrate formation was treated as a single step, zero order process to enable a rate constant to be calculated. Nitrification rate increased with increasing moisture content up to the highest level tested, soil water potential ?8.0 kPa, corresponding to approximately 60% of water holding capacity in both soils. Measurable nitrification was found in both soils at the lowest moisture content (soil water potential ?1.5 MPa) and temperature (5° C) tested. The nitrification rate constant in soils treated with 50 μg NH₄⁺-N g^? soil was not significantly affected (P = 0.05) by the form of ammonium added. Addition of 250 μg NH₄⁺-N as ammonium sulphate caused a marked inhibition of nitrification at all moisture contents and temperatures. Addition of 250 μg NH₄⁺-N as pig slurry caused a marked increase in nitrification rate, the increase being greater at the higher temperatures and moisture contents.     

Reactions of urea phosphate in calcareous and alkaline soils: I. Ammonia volatilization

Abstract

Nitrogen (N) loss in the form of volatilized ammonia (NH₃) is a considerable problem when ammonium (NH₄ ⁺⁾ forming fertilizers are applied to calcareous or alkaline soils. The volatilization of NH₃ from urea phosphate (UP) and urea (U) was studied on three selected soils (Hayhook SL, Laveen L, and Latene L) with the use of a laboratory aeration system. Urea phosphate and U were each applied at rates of 0, 50, 100, and 200 mg N kg^‐1 soil, either to the surface dry or in solution or mixed with the soil. The volatilized NH₃ was trapped in sulfuric acid, sampled periodically, and analyzed for N with the semi microkjeldahl distillation apparatus.

The highest N loss in the form of NH₃ occurred when U was applied to Hayhook soil (neutral to acidic, coarse textured, and low CaCO₃ content). However, UP applied to Hayhook soil resulted in the lowest NH₃‐N loss. Less NH₃‐N loss was found from U application to Laveen and Latene soils (fine textured with higher CaCO₃ content) than with Hayhook soil. The general trend was higher N loss when a surface application was made, either dry or in solution, than when the fertilizer was mixed with the soil. This trend showed an increase in the amount of volatilized NH₃ with increasing N application rates.

Generally, UP is a potential fertilizer for supplying N and phosphorus (P) as plant nutrients with a low potential for losses due to NH₃ volatilization.     

Centrifugal extraction and determination of free amino acids in soil solutions by TLC using tritiated 1-fluoro-2,4-dinitrobenzene

A method is described to separate and quantitate free amino acids from soil solutions extracted rapidly by centrifugation at 10,000 g for 5 min. Centrifugation of soil samples with forces up to 20,000 g did not affect the content of ammonium and water soluble organic carbon in solution, therefore it was concluded that the integrity of microbial cells was unaffected.The method of amino acid analysis involved treatment of the soil solution with tritiated 1-Fluoro-2,4-dinitrobenzene under alkaline conditions after addition of a known concentration of a standard mixture of amino acids. After extraction, the dinitrophenyl (DNP)-amino acids were separated by two-dimensional thin layer chromatography. Quantification was effected by counting the ³H-activity of each spot and comparing it to that of spots of a standard amino acid mixture of known concentration. The method has been tested and found satisfactory on a variety of cultivated soils, except for an Andept soil with a high content of metallic ions in solution.The total free amino acid content in cultivated and virgin soil samples ranged between 0.32 and 4.72 μg g^?1 soil.Alanine, phenylalanine and threonine were the most abundant followed by valine and the aspartic-glutamic acid complex. Basic amino acids, those containing S (methionine and cystine), and the isoleucine-leucine pair were the least abundant and frequently not detected. With the Chernozemic order the total amino acid content decreased in the following order: Brown > Dark Brown > Black. Virgin soil samples contained more but not always a wider range of free amino acids than did cultivated soils. A Luvisolic soil cropped for 50 yr to a 5-yr rotation contained fewer and a narrower range of free amino acids than did the same soil cropped to a wheat-fallow rotation.     

Survey of molybdenum fertility status in Maryland coastal plain soils for tobacco production

Abstract

Coastal Plain soils in southern Maryland are typically acid (pH = 5.0±0.5) with low organic matter (1.2±0.5%), clay (2.8 to 9.8%), CEC (2.4 to 6.8 meq 100/g), and total Fe contents (4.5 to 34.9 g/kg). The objectives of this investigation were to assess the status of plant available molybdenum (Mo) in these soils by examining the extractable Mo levels in Ap horizon soil samples and tissue Mo contents in cured tobacco collected across a five‐county region. Seventy soil samples representing 11 soil series and 198 composite samples of tobacco served as the basis for the surveys. Plant available Mo in soil, estimated using a solution containing 0.18M ammonium oxalate and 0.1M oxalic acid as the extractant, ranged from 0.02 to 0.53 (ig/g and averaged 0.08 μg/g Mo. Three of the 11 soil series examined and 30% of the total soil samples exhibited extractable Mo levels ≤ 0.03 μg/g therefore may have less than adequate available Mo for tobacco. Cured leaf Mo contents ranged from non‐detectable to 7.95 μg/g and averaged 0.84±0.95 μg/g Mo. Approximately 15% of the leaf samples contained ≤ 0.2 μ/g Mo which approaches borderline deficiency for Mo with 12.2% having Mo contents within the range 0.2 to 0.4 ng/g where growth responses were reported in burley tobacco. The causes for the approximate one fourth of the plant samples having less than optimum Mo concentrations for maximum productivity for tobacco can likely be attributed to: 1) acid soils associated with inadequate liming programs; 2) very low extractable Mo levels in several soil series; and 3) excess input of SO₄ ^‐2 in fertilizers and acid rainfall in the region which have been shown to inhibit MoO₄ ^‐2 ion uptake by tobacco plants.