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<p>Soils of central Chile underpin much of the region´s agricultural production of the country, yet their phosphate sorption behaviour remains poorly characterized. We investigated whether soils from central Chile exhibit distinct phosphate dynamics along a transect spanning four soil orders, from the Andean foothills to the Pacific coast, representing a gradient in the influence of volcanic parent materials.&#xa0;We analysed eight paired sites (fertilized and unfertilized) representing Andisols, Alfisols, Mollisols, and Inceptisols with 50-fold variation in total phosphorus (P) and 22-fold variation in ammonium acetate extractable aluminium (Al<sub>ext</sub>). Phosphate sorption-desorption curves were fitted using Freundlich and Sibbesen equations with nonlinear optimization methods, and we calculated hysteresis ratios and sorption slopes to characterize surface heterogeneity and post-adsorption diffusion.&#xa0;Despite substantial pedological diversity, all soils exhibited remarkably similar sorption curve shapes, enabling description with common index parameters. Exceptionally low Freundlich <i>b</i> values (0.013–0.309) indicated extreme surface heterogeneity, while consistently low hysteresis ratios (1.0-1.8) revealed limited intraparticle diffusion across all soil orders. The convergence of normalized sorption curves into a single linear pattern further demonstrates a common underlying sorption mechanism among these contrasting soils. Sorption correlated strongly with Al<sub>ext</sub> and oxalic acid extractable Al and iron (Fe) (Al<sub>o</sub>+0.5Fe<sub>o</sub>), suggesting that short-range-order phases, from allophane/imogolite in volcanic soils to poorly crystalline Al-Fe compounds in non-volcanic soils, govern phosphate behaviour across the transect.&#xa0;Despite their contrasting pedological origins, the soils assessed exhibited remarkably similar phosphate sorption behaviour. Exceptionally low Freundlich <i>b</i> values and consistently low hysteresis ratios indicate extreme surface heterogeneity and limited intraparticle diffusion across all soil orders.</p>

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Common Phosphate Sorption Behaviour Across Contrasting Soils in Central Chile

  • 期刊论文

  • 发表日期：

    2026年5月29日

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  • Ricardo A. Cabeza,
  • Alejandro del Pozo,
  • Susana Valle,
  • Ben Ingram,
  • N. J. Barrow

摘要

Soils of central Chile underpin much of the region´s agricultural production of the country, yet their phosphate sorption behaviour remains poorly characterized. We investigated whether soils from central Chile exhibit distinct phosphate dynamics along a transect spanning four soil orders, from the Andean foothills to the Pacific coast, representing a gradient in the influence of volcanic parent materials. We analysed eight paired sites (fertilized and unfertilized) representing Andisols, Alfisols, Mollisols, and Inceptisols with 50-fold variation in total phosphorus (P) and 22-fold variation in ammonium acetate extractable aluminium (Alext). Phosphate sorption-desorption curves were fitted using Freundlich and Sibbesen equations with nonlinear optimization methods, and we calculated hysteresis ratios and sorption slopes to characterize surface heterogeneity and post-adsorption diffusion. Despite substantial pedological diversity, all soils exhibited remarkably similar sorption curve shapes, enabling description with common index parameters. Exceptionally low Freundlich b values (0.013–0.309) indicated extreme surface heterogeneity, while consistently low hysteresis ratios (1.0-1.8) revealed limited intraparticle diffusion across all soil orders. The convergence of normalized sorption curves into a single linear pattern further demonstrates a common underlying sorption mechanism among these contrasting soils. Sorption correlated strongly with Alext and oxalic acid extractable Al and iron (Fe) (Alo+0.5Feo), suggesting that short-range-order phases, from allophane/imogolite in volcanic soils to poorly crystalline Al-Fe compounds in non-volcanic soils, govern phosphate behaviour across the transect. Despite their contrasting pedological origins, the soils assessed exhibited remarkably similar phosphate sorption behaviour. Exceptionally low Freundlich b values and consistently low hysteresis ratios indicate extreme surface heterogeneity and limited intraparticle diffusion across all soil orders.