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Determination of phosphatase activities of soils and animal wastes |
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| Authors: | RG Gerritse H van Dijk |
| Institution: | aInstitute for Soil Fertility, Haren (Gr., The Netherlands |
| Abstract: | A method is described to determine acid and alkaline phosphatase activities from the rate of decomposition of p-nitrophenylphosphate in the presence of large amounts of organic matter, such as occur in the surface layers of soils or in animal wastes. The p-nitrophenol formed is separated by high pressure liquid chromatography on a cellulose column from p-nitrophenylphosphate and other organic compounds present in the soil or waste extract. After separation, p-nitrophenol is measured on-line in a spectrophotometric flow cell at a wavelength of 405 nm. In this way p-nitrophenol concentrations down to 0.1 μm can be measured, making it possible to work with substrate concentrations of 1 μm. The necessity of correcting the phosphatase activity measured in this way for adsorption of enzyme, substrate (p-nitrophenylphosphate) and product (p-nitrophenol) is discussed. Acid and alkaline phosphatases are inhibited strongly at phosphate concentrations greater than 0.1 mm, consequently substrate concentrations in the range of 0.01 to 0.1 mm were used. The method was applied to a number of sandy soils and to pig slurry. Air drying or freeze drying of soils was found to decrease the phosphatase activity. Freeze drying did not affect the phosphatase activity of pig slurry. Michaelis-Menten kinetics were found to apply reasonably well. The resulting kinetic parameters are compared with values from the literature. Phosphatase activities are correlated with organic P and organic matter contents of soils and pig slurry. |
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