How does the Hedley sequential phosphorus fractionation reflect impacts of land use and management on soil phosphorus: A review

The Hedley sequential-phosphorus (P)-fractionation method has been used in many countries to study the effects of land-use and management systems on soil P. Many data sets have been obtained but collectively never have been considered or to goal topic reviewed. Therefore, the objectives of this review were to compile and systematically evaluate these data. The data generated over many years were grouped into temperate, and subtropical and tropical soils of different land use and duration of soil-management studies. In natural ecosystems, vegetation types and composition and percent of vegetation covers substantially affected all P fractions with pronounced impacts on the labile and moderately labile P. In short-term studies (<= 10 y), changes in the labile and moderately labile inorganic P (P) fractions were detected when more P (e.g., by factor 5) was applied than commonly recommended for agricultural crops. However, without P application the changes in all P fractions were subtle in temperate soils, but declines were significant in labile and moderately labile P in subtropical and tropical soils. In both temperate and tropical climates, medium (10-25 y) and long-term (>25 y) cultivation without P application depleted all P fractions, whereas most of P fractions increased with continuous P application, regardless of the amount and source of P. Synthesis of data resulted in multiple-regression functions which described differences in labile and moderately labile P fractions as function of differences in amount of P application and duration of the experiments. Moreover, the correlation analysis also showed strong association among most of the P fractions. Current limitations in data interpretation of Hedley fractionation can be overcome by the application of P-31 nuclear-magnetic resonance (NMR) and X-ray absorption near-edge fine-structure (XANES) spectroscopy.