Effect of storage on soluble phosphorus fractions in water extracts of soils

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Abstract
The effects of storage on soluble phosphorus (P) fractions in water extracts of two soils, and standard solutions of inorganic and organic P compounds have been quantified. The water extracts were obtained from a peaty podzol and an iron humus podzol and contained about 140 and 270 μg P/dm3, respectively. The standard solutions contined 100 μg P/dm3. Storage conditions investigated included different types of containers (glass and polythene), different temperatures (4, 22, and ‐12°C), and times. Hydrolysis of dissolved condensed phosphorus (DCP) and dissolved organic phosphorus (DOP) compounds in the water extract of the soils and standard solutions were observed at 4 and 22°C after one day. Total dissolved phosphorus (TDP) in the standard P solutions was not significantly affected by storage. However, TDP in water extracts of soils decreased significantly when the solutions were stored in polythene at 22°C. The loss of P after 15 days was 56 and 31% in the extracts from the peaty podzol and iron humus podzol, respectively. In relation to the storage of samples frozen at ‐12°C, freeze‐thawing the water extracts of the soils or standard solutions did not affect their P composition. Storage of a water extract of the peaty podzol in polythene at 4°C for 74 days did not affect TDP but MRP increased by 60% at the expense of both DOP and DCP.