Soil phosphorus fractions after seven decades of fertilizer application in the Rengen Grassland Experiment

Authors

  • Stefan Pätzold,

    1. University of Bonn, Institute of Crop Science and Resource Conservation (INRES), Soil Science, Nussallee 13, 53115 Bonn, Germany
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  • Michal Hejcman,

    1. Department of Ecology, Faculty of Environmental Sciences, Czech University of Life Sciences, Kamýcká 1176, Prague 6, Suchdol, 165 21, Prague, Czech Republic
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  • Julia Barej,

    1. University of Bonn, Institute of Crop Science and Resource Conservation (INRES), Soil Science, Nussallee 13, 53115 Bonn, Germany
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  • Jürgen Schellberg

    Corresponding author
    1. University of Bonn, Institute of Crop Science and Resource Conservation (INRES), Crop Science, Katzenburgweg 5, 53115 Bonn, Germany
    • University of Bonn, Institute of Crop Science and Resource Conservation (INRES), Crop Science, Katzenburgweg 5, 53115 Bonn, Germany

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Abstract

Declining global P reserves require a better understanding of P cycling in soil and related plant uptake. On managed grasslands, application of lime and fertilizer affects not only soil nutrient status, but also plant-species composition of the sward. We examined the P fractionation in the Rengen Grassland Experiment (RGE) on a naturally acid Stagnic Cambisol in the Eifel Mts. (Germany) 69 y after the setup of the experiment. A modified sequential Hedley fractionation was carried out for samples from 30 plots at 0–10 cm depth. Application of inorganic phosphorus fertilizer had diverse effects on inorganic (Pi) and organic P (Po) fractions. Resin-Pi, NaHCO3-Pi, NaHCO3-Po, NaOH-Pi, HCldil-Pi, HClconc-Pi, and HClconc-Po contents increased, while NaOH-Po significantly decreased and residual-P remained unaffected. Strongest enrichment occurred in the HCldil-Pi fraction, probably due to the chemical nature of the basic Thomas slag applied as P fertilizer. Without P fertilization, all fractions except residual-P were more or less depleted. Strong P limitation of the vegetation in the limed treatments without P led to lowered contents also for NaOH-Pi and NaOH-Po. However, NaOH-Po was largest in the Control and even exceeded the respective content in the treatments with P. It remained unclear why species adapted to a low soil P status did not access this P fraction though being P-limited. Published theory on the availability of Hedley P fractions does neither match P exploitation nor P nutritional status of the vegetation in the RGE. Regarding NaOH-Po as stable and HCldil-Pi as moderately labile led to a more realistic evaluation of plant P uptake. Evaluation of P availability on the basis of chemical extractions alone is questionable for conditions like in the RGE. On long-term grassland, plant-species composition has to be taken into account to estimate access of plants to soil P.

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