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Database of Hedley fractionation for manures


Samples of manure and feces were extracted according to modified Hedley fractionation scheme (Sharpley and Moyer, 2001). Air-dried and finely ground sub-samples (1 g) were first extracted twice with water at a 1:60 (w/v) ratio and then sequentially with each of the following: 0.5 M NaHCO3, 0.1 M NaOH and 1 M HCl. Extraction times were 16 h, except for the first water extraction (4 h). After the extraction, the samples were centrifuged (3000 g, 15 min) and inorganic P (Pi) [supernatants filtered through a 0.2 µm nucleopore membrane (Whatman, Maidstone, UK)] and total P (unfiltered supernatant digested at 120 °C with sulfuric acid and peroxodisulfate) concentrations in the supernatants were analyzed according to Murphy and Riley (1962). The difference between total P and Pi was assumed to represent organic P (Po).


Water-soluble P is the most soluble P fraction and therefore most vulnerable for leaching. Labile P content (water + 0.5 M NaHCO3 –extractable) is considered to be plant available, whereas 0.1 M NaOH and 0.1 M HCl –extractable P fractions probably turn into a plant available form slowly after P concentration decreases in the soil solution. When extracting soil samples, 1 M HCl is considered to extract apatite-type minerals (Hedley et al. 1982), but in manure samples, 1 M HCl –extractable P fraction is probably more plant-available.

References
Hedley, M.J., Stewart, J.W.B., Chauhan, B.S. 1982. Changes in inorganic and organic soil phosphorus fractions induced by cultivation practices and by laboratory incubations. Soil Science Society of America Journal 46: 970-976.
Murphy, J. and Riley, J.P. 1962. A modified single solution method for the determination of phosphate in natural waters. Analytica Chimica Acta 27: 31-36.
Sharpley, A.N. & Moyer, B. 2001. Phosphorus forms in manure and compost and their release during simulated rainfall. Journal of Environmental Quality 29: 1462-1469.

The database was prepared as part of work package 4 on Standardisation of Manure Types with Focus on Phosphorus in the project Baltic Manure.

 

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