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% nitrogen2 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 linkages3 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 increased4 Ammonium-N fixed by clay minerals is determined by the Kjeldahl method5 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 discussed6 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 digestion7 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 (eg 0·3 g/ml sulphuric acid) it is necessary to digest for several hours; when it is high (eg 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 high8 Nitrogen is lost during Kjeldahl analysis when the temperature of digestion exceeds about 400° C9 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 calculated10 Semi-micro Kjeldahl methods of determining soil nitrogen gave the same results as macro-Kjeldahl methods11 The use of the Hoskins apparatus for the determination of ammonium is described12 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

https://www.cambridge.org/core/services/aop-cambridge-core/content/view/S0021859600021572

Determination of nitrogen in soil by the Kjeldahl method

A consideration of a large number of procedures for the collection and analysis of benthic samples, with particular emphasis on stream investigations and the importance of substrate particle size as a common denominator in benthic ecology, reveals that only certain techniques are suitable. Although either systematic or stratified random samplings are appropriate for faunal surveys, the careful selection of sample sites in singlespecies studies can provide maximum information per unit sampling effort. In order to adequately describe the micro-distribution of benthic organisms, investigations must be conducted on a year-round basis. Only bottom samplers, such as the core-type, which retain the entire sediment sample for analysis are desirable. Measurements of current velocity should be made close to the substrate-water interface. The removal of the fauna by elutriation and hand sorting allows for further physical and chemical analyses. Physical analysis of stream sediments can be accomplished through the decantation of silt and clay followed by dry sieving of the coarser material. In addition, a new photographic technique for substrate analysis, described in detail, can provide information on the surface sediments. Indications of the organic content of sediments can be obtained by the dry combustion carbon train method or, when clay content is low, from loss of weight on ignition values. However, new techniques are called for, especially those directed toward the food habits of particular species. The Wentworth classification, modified to include a gravel category, should be followed, and the size classes converted to the phi scale in graphic presentations of sediment data. Since Shelford (1914) became interested in the ecology of benthic macro-invertebrates, Needham (1928) conducted surveys of New York streams, and Shelford and Eddy (1929) formulated some fundamental approaches for the study of stream communities, a great many benthic investigations have appeared in the literature. The facts accumulated to date show that the orientation of aquatic invertebrates to various environmental parameters results in nonuniform distributions in which given animal groups are associated with measurable ranges of environmental conditions. Benithic ecologists have spent considerable effort measuring the most obvious parameters in the aquatic environment to determine their effects on the distribution of various groups of animals. Substrate, current velocity, and food materials have been shown to -be of primary importance, although the way in which these interrelated parameters determine distribution remains to be completely delineated. Undoubtedly, some parameters are more critical than others, but it may be that all physical " Present address, Department of Biological Sciences, Northwestern University.

An Evaluation of Some Techniques for the Collection and Analysis of Benthic Samples with Special Emphasis on Lotic Waters

rate of change, over a short period, of many soil properties, with most of the above difficulties reduced to the minimum. This especially applies to those properties which relate directly to vegetation. At Glacier Bay a fairly detailed knowledge of the history of recent deglaciation has been established (Cooper, 1937; Field, 1947), and along with Cooper's (1923, 1931, 1939) classic vegetation succession studies it affords an exceptionally good basis for this kind of investigation. In the present paper the rate of development of some of the characteristics of the forest floor, and changes in the mineral-soil properties of reaction (pH), organic carbon, total nitrogen, calcium carbonate, and bulk density of the fine earth are reported. These changes are related both to age of the surface and to the

Soil development in relation to vegetation and surface age at glacier bay, alaska*

The effect of long-term irrigation using wastewater on heavy metal contents of soils under vegetables in Harare, Zimbabwe

Nitrate and Exchangeable Ammonium Nitrogen

BOOKS on methods of analysis can be divided into two classes, one of which is the ‘collected methods’ type. Here each chapter or section of the book is devoted to a specific analysis or group of related analyses, and gives the working details of all or nearly all the existing methods. Such books are not only very useful and convenient but also are a necessity for those analysts to whom the original papers in the literature are not easily accessible. It is, however, the other class of book that the analyst most appreciates, namely, the book in which he is not bewildered by an array of methods but is presented with a selection recommended from considerable experience. Dr. Piper has compiled his book along these lines, and all the methods, with a very few exceptions, are those in use at the Waite Agricultural Research Institute. Concise, and more important still, precise working details are given with ample explanation and a wealth of guidance and help.Soil and Plant AnalysisA Laboratory Manual of Methods for the Examination of Soils and the Determination of the Inorganic Constituents of Plants. By Dr. C. S. Piper. (A Monograph from the Waite Agricultural Research Institute.) Pp. xiv + 368. (Adelaide: University of Adelaide, 1942.) 15s.

C. S. Piper

Papers

Soil and plant analysis.

Soil and plant analysis

Soil and Plant Analysis