Extractability of residual phosphorus from highly manured soils
1999
Indiati, R. (Istituto Sperimentale per la Nutrizione delle Piante, Rome (Italy)) | Rossi, N. (Bologna Univ. (Italy). Istituto di Chimica Agraria)
High applications of manure produced by intensive animal husbandry often result in levels of soil available P above crop requirements. In this research the P status of these kinds of soils is examined and discussed from an environmental point of view. Phosphate was extracted from 8 different soils using 12 different methods, 9 traditional and 3 innovative. The innovative methods were extraction with (i) an anion exchange resin, (ii) a cation/anion exchange resin, and (iii) a Fe-oxide coated paper strip. The anion exchange resin was also used in a sequential extraction experiment (11 extractions) to investigate the release of soil P. In addition, an ammonium oxalate extraction was used to determine the degree of phosphorus saturation (DPS). The best correlation (r = 0.999**] among P extracted using the various methods was found between the P data obtained with the anionic exchange resin membrane and those obtained with the Fe-oxide coated paper strip. The cumulative P removed in the sequential extraction experiment fitted a first-order rate equation, the asymptote of which indicates the overall amount of potentially releasable P. Highly significant correlations were found between the P obtained with the first extraction and both DPS and potentially releasable P. The DPS, initially proposed to characterise the P leaching potential of acid soils, is also suitable for neutral-slightly alkaline/calcareous soils like those used in this investigation. A value of around 100 mg kg*[-1) soil for Olsen-extractable P corresponds to a DPS value of 25%, which represents a critical level to distinguish soils that may be a potential source of surface water eutrophication
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