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Abstract

Abstract:The anion-exchange resin (AER) method for the estimation of bioavailable phosphorus was slightly optimised for soils with high contents of readily soluble organic compounds as well as for those having very different clay and sand contents. The method based on a strong base anion exchanger, the active group of trimethyl benzyl ammonium, the field moist soil, and the enclosure of resin beds in a bag was very different soils under relatively uniform outer conditions where the determination of the absorbance of (blue) phosphate-molybdate complex at 870 nm is used. The motivation of the proposed method comes from distinctive features of forest soils where marked differences are commonly encountered between clay/silt/sand contents, pH-values, and the contents of organic substances. A modestly new methodology was applied for the evaluation of seasonal phosphorus dynamics in a forest environment. The recommended rapid assay for available phosphorus was statistically compared with other procedures. Considerable seasonal effects on the bioavailable P contents were demonstrated.Keywords: soil phosphorus; forest soils; available P determination 118Soil & Water Res., 1, 2006 (4): 117-126 ELRASHIDI et al. 1975SIBBESEN 1978) that AER phosphorus correlates highly with the uptake of phosphates by plants. Methodological development of the bioavailable phosphorus content measurements using AER in bags is useful for forest soils from the viewpoint of their distinctive features such as a greater quantity of humic substances with markedly different qualities, easily soluble organic compounds, conspicuous organic horizons, distinctive biota, frequently a higher degree of rockiness and stoniness, lower soil reaction, and more extreme mobility of elements. In addition, each of the methods for bioavailable P determinations may result in the mobilisation of not only available phosphates (BISSANI et al. 2002) but also of part of the non-mobile phosphorus pool in the soil sample. Alternatively, there exist available methods that eliminate this disadvantage, out of which the use of isotopical solutions of 32 P (OLSEN & SOMMERS 1982), water-extraction methods based on deionised water ( VAN DER PAAUW 1971), and AER methods are the most relevant for the routine use. The use of isotopical solutions of P is negatively influenced by both short-term and long-term phosphate resorptions, the amount of phosphates extracted by deionised water being extremely low and the anion-exchange resin methods before usage of polyester-netting bags being time consuming. With respect to the facts and to the distinctive features of forest soils, resin-extractable phosphates were studied. The particular analytical steps were derived from the facts that the amount of anion resin-extractable phosphorus used depends upon the time required for adsorption, the concentration of the resin, and the concentration of phosphates.The following analytical limitations of particular extractions were tested: (i) the extremely low amount of phosphates extracted by deionise...