Humus fractionation

Anderson DW, Schoenau JJ. Soil humus fractions. In Carter M (ed.), Soil Sampling and Methods of Analysis. Boca Raton, FL CRC press 1993, pp. 391-396. 

C N (or carbohydrate protein) ratios are important with respect to the relative requirements of plants and microbes. Straw has a C N value of approximately 80 1, whereas after ploughing under to form a humus-rich soil, the value narrows to about 12 1. Albrecht found that the humus fraction of the experimental Sanborn Field, cultivated over 50 years, had a C N ratio of about from 2 1 to 3.4 1, where the lower ratio is similar to that of the microbes themselves. Therefore, if microbes feed on straw that has been incorporated into the soil, they will require an additional source of nitrogen, and happen to be more successful at competing with plants for the same nutrient. In Missouri clay, Albrecht found 1.5% C and 0.15% N, which represents a favourable ratio of 10 1, and is an average value for well-weathered soils (Walters, 1989). 

C.M. Preston, S.P. Mathur and B.S. Rauthan, The distribution of copper, amino compounds, and humus fractions in organic soils of different copper content, Soil Sci. 131 (1981) 344-352. 

Gjessing, E. T., and Gjerdahl,T. (1972). Electromobility of aquatic humus Fractionation by the use of the isoelectric focusing technique. In Proceedings, International Meeting on Humic Substances, Nieuwersluis, Pudoc, pp. 33-51. 

TABLE 1. Names Suggested for the Common Humus Fractions Obtained on the Basis of Solubility Characteristics"... 

The MRTs of individual humus fractions also vary, as can be seen from Table 8. The MRT of the original soil (Melfort silt loam) was 870 years whereas the MRTs of individual fractions ranged from 25 to 1410 years. For both humic and fulvic acids, the acid hydrolyzable fractions (6A HCl for 18 hours) had lower MRTs than the nonhydrolyzable fractions. This result is in accord with expectations, because the hydrolyzable material would include the carbon of readily decomposable substrates (e.g., carbohydrates and amino acids). Stability of the major humus fractions followed the order humin = humic acid > fulvic acid (Campbell et al., 1967a). 

The distribution of nitrogen and types of amino compounds in peats and mucks, or their humus fractions, have been found to be similar to those in mineral soils (Preston et al., 1981). The unknown nitrogen component of peats has not yet received the attention given to the same in mineral soils (Schnitzer, Chapter 12 of this book). 

Another important consideration in the use of copper to reduce subsidence is a possible effect on the availability of plant nutrients. Studies of a natural cupriferous bog that has contained elevated levels of copper for centuries revealed that the distributions of carbon and nitrogen in the soils and humus fractions were affected quantitatively but not qualitatively... 

Pennanen, V. (1975). Humus fractions and their distribution in some lakes in Finland. Proc. Inti. Meet. Humic Substances, Mieuwersluis., pp. 207-215. 

Explain the phenomenon of bioaccumulation, that is, the gradual buildup over time of certain trace metals in the humus fraction of the soil surface. 

Soil minerals such as feldspars, micas, clay minerals, and calcite contain bases in nonexchangeable form. Weathering causes a release of cations from these minerals, after which the ions accumulate on the negatively charged soil colloids (clay and humus fraction of the soil) in exchangeable form. 

Attempts to recover the saponins immediately following their addition to the soil were unsuccessfiil by using several extraction techniques, but no humic or fiilvic acid was isolated. This was interpreted to mean that the saponins added might become bound to the humus fraction of the soil... 

PASZEWSKI A., TROJANOWSKI J. and LOBARZEWSKA W. 1957. (Influence of the humus fraction on the growth of oat coleoptiles). Annales Universitatis Marie Curie-Sklodowska, 12, 1-13. 

BUKVOVA M. and TICHY V. 1967. The effect of humus fractions on the phosphorylase activity of wheat Tritioum aestivum, L.). Biologia Plantarum, 9, 401-406. 

Lowe LE (1980) Humus fraction ratios as a means of discriminating between horizon types. Can J Soil Sci 60 219-229... 

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