Pyrophosphate-extractable

R. Pinton, S. Cesco, M. De Nobili, S. Santi, and Z. Varanini, Water- and pyrophosphate-extractable humic substances fractions as a source of iron for Fe-dettcient cucumber plants. Biol. Fert. Soils 26 23 (1998). 

Soil minerals play a stabilizing role in organic matter. The Al and Fe that complex and stabilize organic matter against microbial decomposition are released from soil minerals during soil formation. The supply rates apparently control the content of soil organic matter to a great extent. This is demonstrated by the relationship between pyrophosphate-extractable C and pyrophosphate-extractable Al plus Fe (Wada 1995). 

Bascomb, C.L. (1968) Distribution of pyrophosphate-extractable iron and organic carbon in soils of various groups./. Soil Sci., 19, 251-268. 

LaZerte B. D. and Findeis J. (1995) The relative importance of oxalate and pyrophosphate extractable aluminum to the acidic leaching of aluminum in podzol B horizons from the Precambrium Shield, Ontario, Canada. Can. J. Soil. Sci. 75, 43-54. 

Peatlands, or organic soils, are water-logged deposits of partly decomposed plant debris. Ecological variation and diversity in extent of domination by water influence the degree of humification in peatlands. Humification in peatlands does not coincide with decomposition as well as in mineral soils. Measurement and extraction of peatland humus are hampered by the presence of large proportions of unhumified material. Therefore, most studies on the characterization of peatland humus have focused on humic acids, or on pyrophosphate extracts of the organic soils. Pyrophosphate extracts contain less unhumified materials than alkali extracts but are far less effective in extracting the peat humic substances. 

The presence of large proportions of nonhumified material of diverse origins and properties hampers the dissolution, fractionation, and estimation of humic substances in peatlands. No satisfactory methods exist for these purposes. Most studies of peat humus therefore focus on pyrophosphate extracts or humic acids obtained by sodium hydroxide extraction. 

Pyrophosphate Index. An index of the degree of humification of organic matter as measured by the determination of the absorbance of the pyrophosphate extract using a colorimeter. 

Krishnamurti, G. S. R., Huang, P. M., Van Rees, K. C. J., Kozak, L. M., and Rostad, H. P. W. (1997b). Differential FUR study of pyrophosphate extractable material of soils implication in cadmium-bonding sites and availability. In Contaminated Soils, Proc. 3rd International Conference on the Biogeochemistry of Trace Elements, May 15-19, 1995, Paris, ed. Prost, R., INRA, Paris, 012pdf. 1-10. 

Chemical extractions were performed in parallel (non-sequential extraction) on soil subsamples to characterize the speciation of trace metals (1) the exchangeable fraction was determined by a CaCl2 extract (2) the fraction supposedly bound to iron and manganese oxides was determined by a Na-dithionite - Na-citrate extraction (3) the fraction supposedly bound to organic matter was determined by a Na-pyrophosphate extraction and (4) the acid-soluble fraction was determined by a 0.43 M HNO3 extract. 

Mayaudon et al. also showed that the casein-hydrolysing activities of soil extracts were poorly correlated to microbial numbers in soils. Ladd and Paul demonstrated with a glucose-amended soil that the highest activities of proteinases towards casein were achieved during a rapid phase of turnover of microbial cells and of net decline in microbial cell numbers, at which time equivalent to 14% of the net gain in soil caseinase activity was extractable with a dilute bicarbonate solution. Nannipieri et reported that the casein activities of pyrophosphate extracts of tw o soils were equivalent to about 60% of the activities of the respective unextracted soils and, in the case of a third soil, to about 140%, indicative of higher active enzyme concentrations or higher specific activities due perhaps to facilitation of enzyme-substrate reactions in extracts. 

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