Total soil nitrogen

This is distilled into a receiving flask containing boric acid indicator mixture and titrated against 0.001 M HCI. The colorimetric method using the autoanalyser is based on that used for plant materials (see below), but care should be taken that any precipitate formed does not collect in the flowcell, which must be occasionally inverted or cleared by passing a bubble of air through it. Any nitrate (and nitrite, which is usually insignificant) should be reduced 

The original method for the determination of nitrogen by sulphuric acid-digestion was published by Kjeldahl in 1883 and fully described by Burns (1984). Many modifications have since been made with various catalysts and acid mixtures. 

The digestions can be carried out in up to 40-place multiple heating units using specialized glassware which is commercially available some suppliers are listed below  

Gerhardt UK Ltd http //www.gerhardt.de/gb/kb.htm Foss (Digestor 2000 System) http //www.foss.dk/foss.asp Distillation systems  

Foss (Kjeltec 2300 Analyzer Unit) httpy/www.foss.dk/foss.asp Gerhardt UK Ltd http //www.gerhardt.de/gb/vap.htm We have devised a method enabling the digestion of up to 152 samples at a time, and with the wearing of some essential personal protective equipment (PPE), it has proved successful for over 32 years (Faithfull, 1969). 

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Refer to Chapter 4 for a discussion on Total soil nitrogen. Instructions for using the Foss Tecator Kjeltec Auto 1030 Analyzer are given in USDA, 1996, pp. 535-538. 

Purines and pyrimidines are components of nucleic acids and are known to occur in soils. According to Bremner (1967), the nitrogen in purines and pyrimidines accounts for less than 1% of the total soil nitrogen. Much of the earlier information on the presence of these compounds comes from G. Anderson (1957, 1958, 1961) who identified guanine, adenine, cytosine, thymine, and traces of uracil in acid hydrolyzates of humic acids extracted from three Scottish soils. Anderson used paper and ion-exchange chromatography to detect and estimate the concentrations of nucleic acid bases. More... 

Much of the nitrogen not discussed above, amounting to about 50% of the total soil nitrogen, occurs in complexes and mixtures with polysaccharides, lignin degradation products and other substances not yet clearly defined. Some of the nitrogen is present as fixed ammonia and in heterocyclic and aromatic ring compounds. 

Fig.14.1. Nitrate formation in relation to total soil nitrogen. (From Allison and Sterling, 1949.)...

Nucleic acids are polymers of mononucleotides. Each mononucleotide is made up of a base-sugar-phosphate unit. These units are linked to each other by a phosphoric acid ester linkage to form nucleic acids. This form of nitrogen accounts for less than 1% of the total soil nitrogen. 

Nitrogen remaining in soil residue following acid hydrolysis. Usually obtained by difference (total soil nitrogen-hydrolyzable nitrogen) Ammonia recovered from hydrolysate by steam distillation with MgO... 

Fig. 6.2 (a) Niche dimension of a habitat that is co-limited by nitrogen (N), phosphorus (P), and potassium (K), and (b) niche dimension of the same habitat after N addition. The different shapes indicate soil areas that are limited by N, P, or K. If one nutrient is added, e.g., N by N deposition, the total soil area with limiting amounts of one or more nutrients for plant growth becomes smaller. The habitat becomes more uniform and may offer less niches for plants to coexist... 

Calculation. Subtract the blank titre from that of the soil extract, multiply by 700 and divide by y(see Method 5.5b.i) to give the mg kg nitrate-N, potassium chloride extractable, in the air-dry soil. Express results for oven-dry soil as in Method 5.2, Calculation (2). Sum the extractable ammonium-N and nitrate-N to obtain the total mineralizable nitrogen in the soil. 

Mineralization is usually defined as the production of ammonium from soil organic matter. This is sometimes called ammonification, which is a less confusing term. Mineralization usually causes only a small fractionation ( l%o) between soil organic matter and soil ammonium. In general, the 6 N of soil ammonium is usually within a few per mil of the composition of total organic nitrogen in the soil. 

The use of microwaves in the acceleration of digestion and colour development in the determination of total Kjeldahl nitrogen in soil has been examined [1]. Visual method based on the colour development of indothymol blue formed between ammonia and thymol has recently been developed for the determination of ammonia-nitrogen in environmental waters [2]. UV photo-oxidation of reduced forms of nitrogen to nitrate by peroxodisulfate can make a basis for the determination of total nitrogen in urban and industrial waste waters [3]. 

ISO 14255 1998 Soil quality - Determination of nitrate nitrogen, ammonium nitrogen and total soluble nitrogen in air-dry soils using calcium chloride solution as extractant. 

Kowalenko CG (2001) Assessment ofLECO CNS-2000 analyzer for simultaneously measuring total carbon, nitrogen and sulphur in soil. Commun Soil Sci Plant Analysis 32 2065-2078. 

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