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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.

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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