Determination Of Nitrogen In Soils Research Articles

Effects of sample pretreatment and particle size on the determination of nitrogen in soil by portable LIBS and potential use on robotic-borne remote Martian and agricultural soil analysis systems.

Field determination of nitrogen in soil is of interest for both terrestrial and Martian applications. Improved management of soil nitrogen levels on Earth could benefit global food production, whilst the determination of soil nitrogen on Mars is required to assess the planet's future habitability. In this study, a mobile laser induced breakdown spectroscopy (LIBS) system with a 1064 nm Nd:YAG laser delivering 25 mJ per pulse was used to assess the effects of sample pretreatment on the measurement of nitrogen in soil. Although pelletisation was preferred, simply milling the sample to <100 mm particle size – which may be more feasible on a remote rover-based analytical platform – improved the spectra obtained. Ablation craters formed in targets prepared from different particle size fractions of the same commercially-available topsoil showed a clear trend in morphology, with smaller particles yielding more uniform craters with fewer fractures. The LIBS emission intensity at 746.83 nm followed a similar trend to results obtained for total nitrogen content in the soil particle size fractions by microanalysis (Perkin Elmer CHN Elemental Analyser) and was well-correlated (R2 = 0.94) with soil nitrate determined by ion chromatography (Dionex DX-100). Although correlations were less good when analysing field soil samples collected from central Scotland (R2 = 0.82 for comparison between LIBS and microanalysis) the study nevertheless demonstrates the potential of portable LIBS for measurement of soil nitrogen content.

A comparison of dry combustion and acid digestion for the determination of nitrogen in soil and plant material

Abstract A comparison was made between dry combustion in a Leco NP‐28 nitrogen and protein determinator, and acid digestion by the Kjeldahl procedure in the analyses of soil and plant material for total nitrogen. A statistical functional relationship demonstrated that the methods gave results similar in size and reproducibility. Thus the traditional Kjeldahl procedure can be replaced by a simpler and quicker method.

Rapid determination of nitrate nitrogen in soils

A simple but effective method for pretreatment of soil samples is suggested. The application of an electrodynamic vibrator or ultrasonic device eliminates the necessity for continuous stirring in direct potentiometric determination of nitrate nitrogen. It also makes the extraction process faster, and the apparatus could easily be used in automatic systems for continuous soil control.

The determination of nitrogen in soils by rapid high‐temperature Kjeldahl digestion and autoanalysis

Abstract Kjeldahl digestion tine can be reduced to 10 minutes after clearing by using a phosphoric ‐ sulphuric acid mixture. The digest is analysed for nitrogen by autoanalysis incorporating a distillation step. Agreement with a standard 5‐hour digestion procedure is satisfactory and an acceptable level of precision is obtained. The method may be readily adapted to include nitrite and nitrate and recovery of added nitrate is satisfactory.

Reducing Mercury Pollution from Kjeldahl Determination of Total Nitrogen

AbstractMercury as a digestion catalyst in Kjeldahl determination of nitrogen in soil and plant tissue is a potential pollutant if washed into laboratory drains. In an effort to reduce this pollution hazard, a study was conducted to develop a means of freeing Kjeldahl waste solutions of mercury. By using an inexpensive polyethylene trap, developed in our laboratory, and increasing the quantity of zinc in the distillation phase of the Kjeldahl procedure, more than 90% of the mercury was recovered and retained in the laboratory.

Rapid Procedure for Determination of Nitrogen in Soil by Kjehldahl Method

Rapid Procedure for Determination of Nitrogen in Soil by Kjehldahl Method

Determination of nitrogen in soil by the Kjeldahl method

1. The reliability of the Kjeldahl method for the determination of nitrogen in soils has been investigated using a range of soils containing from 0·03 to 2·7% nitrogen.2. The same result was obtained when soil was analysed by a variety of Kjeldahl procedures which included methods known to recover various forms of nitrogen not determined by Kjeldahl procedures commonly employed for soil analysis. From this and other evidence presented it is concluded that very little, if any, of the nitrogen in the soils examined was in the form of highly refractory nitrogen compounds or of compounds containing N—N or N—O linkages.3. Results by the method of determining nitrogen in soils recommended by the Association of Official Agricultural Chemists were 10–37% lower than those obtained by other methods tested. Satisfactory results were obtained by this method when the period of digestion recommended was increased.4. Ammonium-N fixed by clay minerals is determined by the Kjeldahl method.5. Selenium and mercury are considerably more effective than copper for catalysis of Kjeldahl digestion of soil. Conditions leading to loss of nitrogen using selenium are defined, and difficulties encountered using mercury are discussed.6. The most important factor in Kjeldahl analysis is the temperature of digestion with sulphuric acid, which is controlled largely by the amount of potassium (or sodium) sulphate used for digestion.7. The period of digestion required for Kjeldahl analysis of soil depends on the concentration of potassium sulphate in the digest. When the concentration is low (e.g. 0·3 g./ml. sulphuric acid) it is necessary to digest for several hours; when it is high (e.g. 1·0 g./ml. sulphuric acid) short periods of digestion are adequate. Catalysts greatly affect the rate of digestion when the salt concentration is low, but have little effect when the salt concentration is high.8. Nitrogen is lost during Kjeldahl analysis when the temperature of digestion exceeds about 400° C.9. Determinations of the amounts of sulphuric acid consumed by various mineral and organic soils during Kjeldahl digestion showed that there is little risk of loss of nitrogen under the conditions usually employed for Kjeldahl digestion of soil. Acid consumption values for various soil constituents are given, from which the amounts of sulphuric acid likely to be consumed during Kjeldahl digestion of different types of soil can be calculated.10. Semi-micro Kjeldahl methods of determining soil nitrogen gave the same results as macro-Kjeldahl methods.11. The use of the Hoskins apparatus for the determination of ammonium is described.12. It is concluded that the Kjeldahl method is satisfactory for the determination of nitrogen in soils provided a few simple precautions are observed. The merits and defects of different Kjeldahl procedures are discussed.

Determination of nitrogen in soil and plant materials: Use of boric acid in the micro‐kjeldahl method

AbstractThe use of boric acid for trapping ammonia in the micro‐Kjeldahl determination is examined. A suitable procedure, together with a modified type of micro‐distillation apparatus, is described.The buffer capacity of boric acid solutions was examined in relation to the sensitivity in the titration of ammonia dissolved in them. Two grades of boric acid, ‘pure’ (technical) and AnalaR, were compared; the former showed appreciable buffering on the acid side.The pH values of solutions of both grades decreased with increasing concentration. The sensitivity of the three indicators examined for the titration of ammonia diminished with increasing concentration of boric acid as a result of the increased buffering. With concentrated boric acid, all three indicators showed wide transitional periods at the end‐point, but in solutions of concentration up to 1‐0% of AnalaR grade the end‐points shown by all three indicators were sharp. The methylene blue‐methyl red indicator, however, was generally preferable.The ammonia‐fixing capacity of boric acid was studied in air‐bubbling tests and by recovery of a known amount of ammonia by distillation. A volume of 10 ml. of 1‐0% boric acid fixed 5 mg. of nitrogen as ammonia sufficiently firmly to afford accurate analyses. For macro‐determinations, 100 ml. of 2‐0% boric acid held firmly up to 90 mg. of nitrogen.

Inhibition of Bumping in the Determination of Nitrogen in Soil1

Inhibition of Bumping in the Determination of Nitrogen in Soil¹

A new method for the determination of ammoniacal nitrogen in soils

A method for the determination of ammoniacal nitrogen in soils is described. It is an extension of the Hissink method for exchangeable bases to ammonium present in the soil. The working details are similar to the Hissink method, except that the leaching process is entirely carried out in the cold. The ammonia is distilled off with magnesium oxide.Using normal sodium chloride as a leaching solution and collecting half a litre of leachings for distillation with magnesia, results were obtained which showed excellent agreement with those by the aeration method. Similar results were obtained using 250 c.c. of 15 per cent, sodium chloride solution, but the results are on an average about 1·6 per cent, lower. With high proportions of ammoniacal nitrogen a second half litre of normal sodium chloride leachings should be taken, or half a litre of 15 per cent, solution used.The leaching method is economical of apparatus and water supply. It is therefore suitable for small laboratories with limited resources. It is fairly rapid: six estimations can be completed in a day.The close agreement of the new method with the aeration method suggests that the amount of ammoniacal nitrogen in the soil at any given time is not an arbitrary quantity depending on conditions of estimation, but a definite amount. It is improbable that any ammonium compounds exist in the soil apart from those which take part in base exchange.